modeling-app/rust/kcl-lib/src/parsing/parser.rs

// TODO optimise size of CompilationError
#![allow(clippy::result_large_err)]

use std::{cell::RefCell, collections::BTreeMap};

use winnow::{
    combinator::{alt, delimited, opt, peek, preceded, repeat, repeat_till, separated, separated_pair, terminated},
    dispatch,
    error::{ErrMode, StrContext, StrContextValue},
    prelude::*,
    stream::Stream,
    token::{any, none_of, one_of, take_till},
};

use super::{
    ast::types::{Ascription, ImportPath, LabelledExpression},
    token::{NumericSuffix, RESERVED_WORDS},
    DeprecationKind,
};
use crate::{
    errors::{CompilationError, Severity, Tag},
    execution::types::ArrayLen,
    parsing::{
        ast::types::{
            Annotation, ArrayExpression, ArrayRangeExpression, BinaryExpression, BinaryOperator, BinaryPart, BodyItem,
            BoxNode, CallExpression, CallExpressionKw, CommentStyle, DefaultParamVal, ElseIf, Expr,
            ExpressionStatement, FunctionExpression, Identifier, IfExpression, ImportItem, ImportSelector,
            ImportStatement, ItemVisibility, LabeledArg, Literal, LiteralIdentifier, LiteralValue, MemberExpression,
            MemberObject, Name, Node, NodeList, NonCodeMeta, NonCodeNode, NonCodeValue, ObjectExpression,
            ObjectProperty, Parameter, PipeExpression, PipeSubstitution, PrimitiveType, Program, ReturnStatement,
            Shebang, TagDeclarator, Type, TypeDeclaration, UnaryExpression, UnaryOperator, VariableDeclaration,
            VariableDeclarator, VariableKind,
        },
        math::BinaryExpressionToken,
        token::{Token, TokenSlice, TokenType},
        PIPE_OPERATOR, PIPE_SUBSTITUTION_OPERATOR,
    },
    SourceRange,
};

thread_local! {
    /// The current `ParseContext`. `None` if parsing is not currently happening on this thread.
    static CTXT: RefCell<Option<ParseContext>> = const { RefCell::new(None) };
}

pub fn run_parser(i: TokenSlice) -> super::ParseResult {
    let _stats = crate::log::LogPerfStats::new("Parsing");
    ParseContext::init();

    let result = match program.parse(i) {
        Ok(result) => Some(result),
        Err(e) => {
            ParseContext::err(e.into());
            None
        }
    };
    let ctxt = ParseContext::take();
    (result, ctxt.errors).into()
}

/// Context built up while parsing a program.
///
/// When returned from parsing contains the errors and warnings from the current parse.
#[derive(Debug, Clone, Default)]
struct ParseContext {
    pub errors: Vec<CompilationError>,
}

impl ParseContext {
    fn new() -> Self {
        ParseContext { errors: Vec::new() }
    }

    /// Set a new `ParseContext` in thread-local storage. Panics if one already exists.
    fn init() {
        assert!(CTXT.with_borrow(|ctxt| ctxt.is_none()));
        CTXT.with_borrow_mut(|ctxt| *ctxt = Some(ParseContext::new()));
    }

    /// Take the current `ParseContext` from thread-local storage, leaving `None`. Panics if a `ParseContext`
    /// is not present.
    fn take() -> ParseContext {
        CTXT.with_borrow_mut(|ctxt| ctxt.take()).unwrap()
    }

    /// Add an error to the current `ParseContext`, panics if there is none.
    fn err(err: CompilationError) {
        CTXT.with_borrow_mut(|ctxt| {
            // Avoid duplicating errors. This is possible since the parser can try one path, find
            // a warning, then backtrack and decide not to take that path and try another. This can
            // happen 'high up the stack', so it's impossible to fix where the errors are generated.
            // Ideally we would pass errors up the call stack rather than use a context object or
            // have some way to mark errors as speculative or committed, but I don't think Winnow
            // is flexible enough for that (or at least, not without significant changes to the
            // parser).
            let errors = &mut ctxt.as_mut().unwrap().errors;
            for e in errors.iter_mut().rev() {
                if e.source_range == err.source_range {
                    *e = err;
                    return;
                }
            }
            errors.push(err);
        });
    }

    /// Add a warning to the current `ParseContext`, panics if there is none.
    fn warn(mut e: CompilationError) {
        e.severity = Severity::Warning;
        Self::err(e);
    }
}

/// Accumulate context while backtracking errors
/// Very similar to [`winnow::error::ContextError`] type,
/// but the 'cause' field is always a [`CompilationError`],
/// instead of a dynamic [`std::error::Error`] trait object.
#[derive(Debug, Clone)]
pub(crate) struct ContextError<C = StrContext> {
    pub context: Vec<C>,
    pub cause: Option<CompilationError>,
}

impl From<winnow::error::ParseError<TokenSlice<'_>, ContextError>> for CompilationError {
    fn from(err: winnow::error::ParseError<TokenSlice<'_>, ContextError>) -> Self {
        let Some(last_token) = err.input().last() else {
            return CompilationError::fatal(Default::default(), "file is empty");
        };

        let (input, offset, err) = (err.input(), err.offset(), err.clone().into_inner());

        if let Some(e) = err.cause {
            return e;
        }

        // See docs on `offset`.
        if offset >= input.len() {
            let context = err.context.first();
            return CompilationError::fatal(
                last_token.as_source_range(),
                match context {
                    Some(what) => format!("Unexpected end of file. The compiler {what}"),
                    None => "Unexpected end of file while still parsing".to_owned(),
                },
            );
        }

        let bad_token = input.token(offset);
        // TODO: Add the Winnow parser context to the error.
        // See https://github.com/KittyCAD/modeling-app/issues/784
        CompilationError::fatal(
            bad_token.as_source_range(),
            format!("Unexpected token: {}", bad_token.value),
        )
    }
}

impl<C> From<CompilationError> for ContextError<C> {
    fn from(e: CompilationError) -> Self {
        Self {
            context: Default::default(),
            cause: Some(e),
        }
    }
}

impl<C> std::default::Default for ContextError<C> {
    fn default() -> Self {
        Self {
            context: Default::default(),
            cause: None,
        }
    }
}

impl<I, C> winnow::error::ParserError<I> for ContextError<C>
where
    I: Stream,
{
    #[inline]
    fn from_error_kind(_input: &I, _kind: winnow::error::ErrorKind) -> Self {
        Self::default()
    }

    #[inline]
    fn append(
        self,
        _input: &I,
        _input_checkpoint: &<I as Stream>::Checkpoint,
        _kind: winnow::error::ErrorKind,
    ) -> Self {
        self
    }

    #[inline]
    fn or(self, other: Self) -> Self {
        other
    }
}

impl<C, I> winnow::error::AddContext<I, C> for ContextError<C>
where
    I: Stream,
{
    #[inline]
    fn add_context(mut self, _input: &I, _input_checkpoint: &<I as Stream>::Checkpoint, ctx: C) -> Self {
        self.context.push(ctx);
        self
    }
}

impl<C, I> winnow::error::FromExternalError<I, CompilationError> for ContextError<C> {
    #[inline]
    fn from_external_error(_input: &I, _kind: winnow::error::ErrorKind, e: CompilationError) -> Self {
        let mut err = Self::default();
        {
            err.cause = Some(e);
        }
        err
    }
}

type PResult<O, E = ContextError> = winnow::prelude::PResult<O, E>;

fn expected(what: &'static str) -> StrContext {
    StrContext::Expected(StrContextValue::Description(what))
}

fn program(i: &mut TokenSlice) -> PResult<Node<Program>> {
    let shebang = opt(shebang).parse_next(i)?;
    let mut out: Node<Program> = function_body.parse_next(i)?;
    out.shebang = shebang;

    // Match original parser behaviour, for now.
    // Once this is merged and stable, consider changing this as I think it's more accurate
    // without the -1.
    out.end -= 1;
    Ok(out)
}

fn pipe_surrounded_by_whitespace(i: &mut TokenSlice) -> PResult<()> {
    (
        repeat(0.., whitespace).map(|_: Vec<_>| ()),
        pipe_operator,
        repeat(0.., whitespace).map(|_: Vec<_>| ()),
    )
        .parse_next(i)?;
    Ok(())
}

/// Note this is O(n).
fn count_in(target: char, s: &str) -> usize {
    s.chars().filter(|&c| c == target).count()
}

/// Matches all four cases of NonCodeValue
fn non_code_node(i: &mut TokenSlice) -> PResult<Node<NonCodeNode>> {
    /// Matches one case of NonCodeValue
    /// See docstring on [NonCodeValue::NewLineBlockComment] for why that case is different to the others.
    fn non_code_node_leading_whitespace(i: &mut TokenSlice) -> PResult<Node<NonCodeNode>> {
        let leading_whitespace = one_of(TokenType::Whitespace)
            .context(expected("whitespace, with a newline"))
            .parse_next(i)?;
        let has_empty_line = count_in('\n', &leading_whitespace.value) >= 2;
        non_code_node_no_leading_whitespace
            .verify_map(|node: Node<NonCodeNode>| match node.inner.value {
                NonCodeValue::BlockComment { value, style } => Some(Node::new(
                    NonCodeNode {
                        value: if has_empty_line {
                            NonCodeValue::NewLineBlockComment { value, style }
                        } else {
                            NonCodeValue::BlockComment { value, style }
                        },
                        digest: None,
                    },
                    leading_whitespace.start,
                    node.end + 1,
                    node.module_id,
                )),
                _ => None,
            })
            .context(expected("a comment or whitespace"))
            .parse_next(i)
    }

    alt((non_code_node_leading_whitespace, non_code_node_no_leading_whitespace)).parse_next(i)
}

fn annotation(i: &mut TokenSlice) -> PResult<Node<Annotation>> {
    let at = at_sign.parse_next(i)?;
    let name = opt(binding_name).parse_next(i)?;
    let mut end = name.as_ref().map(|n| n.end).unwrap_or(at.end);

    let properties = if peek(open_paren).parse_next(i).is_ok() {
        open_paren(i)?;
        ignore_whitespace(i);
        let properties: Vec<_> = separated(
            0..,
            separated_pair(
                terminated(identifier, opt(whitespace)),
                terminated(one_of((TokenType::Operator, "=")), opt(whitespace)),
                expression,
            )
            .map(|(key, value)| {
                Node::new_node(
                    key.start,
                    value.end(),
                    key.module_id,
                    ObjectProperty {
                        key,
                        value,
                        digest: None,
                    },
                )
            }),
            comma_sep,
        )
        .parse_next(i)?;
        ignore_trailing_comma(i);
        ignore_whitespace(i);
        end = close_paren(i)?.end;
        Some(properties)
    } else {
        None
    };

    if name.is_none() && properties.is_none() {
        return Err(ErrMode::Cut(
            CompilationError::fatal(at.as_source_range(), format!("Unexpected token: {}", at.value)).into(),
        ));
    }

    let value = Annotation {
        name,
        properties,
        digest: None,
    };
    Ok(Node::new(value, at.start, end, at.module_id))
}

// Matches remaining three cases of NonCodeValue
fn non_code_node_no_leading_whitespace(i: &mut TokenSlice) -> PResult<Node<NonCodeNode>> {
    any.verify_map(|token: Token| {
        if token.is_code_token() {
            None
        } else {
            let value = match token.token_type {
                TokenType::Whitespace if token.value.contains("\n\n") || token.value.contains("\n\r\n") => {
                    NonCodeValue::NewLine
                }
                TokenType::LineComment => NonCodeValue::BlockComment {
                    value: token.value.trim_start_matches("//").trim().to_owned(),
                    style: CommentStyle::Line,
                },
                TokenType::BlockComment => NonCodeValue::BlockComment {
                    style: CommentStyle::Block,
                    value: token
                        .value
                        .trim_start_matches("/*")
                        .trim_end_matches("*/")
                        .trim()
                        .to_owned(),
                },
                _ => return None,
            };
            Some(Node::new(
                NonCodeNode { value, digest: None },
                token.start,
                token.end,
                token.module_id,
            ))
        }
    })
    .context(expected("Non-code token (comments or whitespace)"))
    .parse_next(i)
}

fn pipe_expression(i: &mut TokenSlice) -> PResult<Node<PipeExpression>> {
    let mut non_code_meta = NonCodeMeta::default();
    let (head, noncode): (_, Vec<_>) = terminated(
        (
            expression_but_not_pipe,
            repeat(0.., preceded(whitespace, non_code_node)),
        ),
        peek(pipe_surrounded_by_whitespace),
    )
    .context(expected("an expression, followed by the |> (pipe) operator"))
    .parse_next(i)?;
    for nc in noncode {
        non_code_meta.insert(0, nc);
    }
    let mut values = vec![head];
    let value_surrounded_by_comments = (
        repeat(0.., preceded(opt(whitespace), non_code_node)), // Before the expression.
        preceded(opt(whitespace), labelled_fn_call),           // The expression.
        repeat(0.., noncode_just_after_code),                  // After the expression.
    );
    let tail: Vec<(Vec<_>, _, Vec<_>)> = repeat(
        1..,
        preceded(pipe_surrounded_by_whitespace, value_surrounded_by_comments),
    )
    .context(expected(
        "a sequence of at least one |> (pipe) operator, followed by an expression",
    ))
    .parse_next(i)?;

    // Time to structure the return value.
    let mut code_count = 0;
    let mut max_noncode_end = 0;
    for (noncode_before, code, noncode_after) in tail {
        for nc in noncode_before {
            max_noncode_end = nc.end.max(max_noncode_end);
            non_code_meta.insert(code_count, nc);
        }
        values.push(code);
        code_count += 1;
        for nc in noncode_after {
            max_noncode_end = nc.end.max(max_noncode_end);
            non_code_meta.insert(code_count, nc);
        }
    }
    Ok(Node::new_node(
        values.first().unwrap().start(),
        values.last().unwrap().end().max(max_noncode_end),
        values.first().unwrap().module_id(),
        PipeExpression {
            body: values,
            non_code_meta,
            digest: None,
        },
    ))
}

fn bool_value(i: &mut TokenSlice) -> PResult<BoxNode<Literal>> {
    let (value, token) = any
        .try_map(|token: Token| match token.token_type {
            TokenType::Keyword if token.value == "true" => Ok((true, token)),
            TokenType::Keyword if token.value == "false" => Ok((false, token)),
            _ => Err(CompilationError::fatal(
                token.as_source_range(),
                "invalid boolean literal",
            )),
        })
        .context(expected("a boolean literal (either true or false)"))
        .parse_next(i)?;
    Ok(Box::new(Node::new(
        Literal {
            value: LiteralValue::Bool(value),
            raw: value.to_string(),
            digest: None,
        },
        token.start,
        token.end,
        token.module_id,
    )))
}

fn literal(i: &mut TokenSlice) -> PResult<BoxNode<Literal>> {
    alt((string_literal, unsigned_number_literal))
        .map(Box::new)
        .context(expected("a KCL literal, like 'myPart' or 3"))
        .parse_next(i)
}

/// Parse a KCL string literal
fn string_literal(i: &mut TokenSlice) -> PResult<Node<Literal>> {
    let (value, token) = any
        .try_map(|token: Token| match token.token_type {
            TokenType::String => {
                let s = token.value[1..token.value.len() - 1].to_string();
                Ok((LiteralValue::from(s), token))
            }
            _ => Err(CompilationError::fatal(
                token.as_source_range(),
                "invalid string literal",
            )),
        })
        .context(expected("string literal (like \"myPart\""))
        .parse_next(i)?;

    let result = Node::new(
        Literal {
            value,
            raw: token.value.clone(),
            digest: None,
        },
        token.start,
        token.end,
        token.module_id,
    );

    if let Some(suggestion) = super::deprecation(result.value.string_value().unwrap(), DeprecationKind::String) {
        ParseContext::warn(
            CompilationError::err(
                result.as_source_range(),
                format!(
                    "Using `\"{}\"` is deprecated, prefer using `{}`.",
                    result.value.string_value().unwrap(),
                    suggestion
                ),
            )
            .with_suggestion(
                format!(
                    "Replace `\"{}\"` with `{}`",
                    result.value.string_value().unwrap(),
                    suggestion
                ),
                suggestion,
                None,
                Tag::Deprecated,
            ),
        );
    }

    Ok(result)
}

/// Parse a KCL literal number, with no - sign.
pub(crate) fn unsigned_number_literal(i: &mut TokenSlice) -> PResult<Node<Literal>> {
    let (value, token) = any
        .try_map(|token: Token| match token.token_type {
            TokenType::Number => {
                let value: f64 = token.numeric_value().ok_or_else(|| {
                    CompilationError::fatal(token.as_source_range(), format!("Invalid float: {}", token.value))
                })?;

                if token.numeric_suffix().is_some() {
                    ParseContext::warn(CompilationError::err(
                        (&token).into(),
                        "Unit of Measure suffixes are experimental and currently do nothing.",
                    ));
                }

                Ok((
                    LiteralValue::Number {
                        value,
                        suffix: token.numeric_suffix(),
                    },
                    token,
                ))
            }
            _ => Err(CompilationError::fatal(token.as_source_range(), "invalid literal")),
        })
        .context(expected("an unsigned number literal (e.g. 3 or 12.5)"))
        .parse_next(i)?;
    Ok(Node::new(
        Literal {
            value,
            raw: token.value.clone(),
            digest: None,
        },
        token.start,
        token.end,
        token.module_id,
    ))
}

/// Parse a KCL operator that takes a left- and right-hand side argument.
fn binary_operator(i: &mut TokenSlice) -> PResult<BinaryOperator> {
    any.try_map(|token: Token| {
        if !matches!(token.token_type, TokenType::Operator) {
            return Err(CompilationError::fatal(
                token.as_source_range(),
                format!("unexpected token, should be an operator but was {}", token.token_type),
            ));
        }
        let op = match token.value.as_str() {
            "+" => BinaryOperator::Add,
            "-" => BinaryOperator::Sub,
            "/" => BinaryOperator::Div,
            "*" => BinaryOperator::Mul,
            "%" => BinaryOperator::Mod,
            "^" => BinaryOperator::Pow,
            "==" => BinaryOperator::Eq,
            "!=" => BinaryOperator::Neq,
            ">" => BinaryOperator::Gt,
            ">=" => BinaryOperator::Gte,
            "<" => BinaryOperator::Lt,
            "<=" => BinaryOperator::Lte,
            "|" => BinaryOperator::Or,
            "&" => BinaryOperator::And,
            _ => {
                return Err(CompilationError::fatal(
                    token.as_source_range(),
                    format!("{} is not a binary operator", token.value.as_str()),
                ))
            }
        };
        Ok(op)
    })
    .context(expected("a binary operator (like + or *)"))
    .parse_next(i)
}

/// Parse a KCL operand that can be used with an operator.
fn operand(i: &mut TokenSlice) -> PResult<BinaryPart> {
    const TODO_783: &str = "found a value, but this kind of value cannot be used as the operand to an operator yet (see https://github.com/KittyCAD/modeling-app/issues/783)";
    let op = possible_operands
        .try_map(|part| {
            let source_range = SourceRange::from(&part);
            let expr = match part {
                // TODO: these should be valid operands eventually,
                // users should be able to run "let x = f() + g()"
                // see https://github.com/KittyCAD/modeling-app/issues/783
                Expr::FunctionExpression(_)
                | Expr::PipeExpression(_)
                | Expr::PipeSubstitution(_)
                | Expr::ArrayExpression(_)
                | Expr::ArrayRangeExpression(_)
                | Expr::ObjectExpression(_)
                | Expr::LabelledExpression(..)
                | Expr::AscribedExpression(..) => return Err(CompilationError::fatal(source_range, TODO_783)),
                Expr::None(_) => {
                    return Err(CompilationError::fatal(
                        source_range,
                        // TODO: Better error message here.
                        // Once we have ways to use None values (e.g. by replacing with a default value)
                        // we should suggest one of them here.
                        "cannot use a KCL None value as an operand",
                    ));
                }
                Expr::TagDeclarator(_) => {
                    return Err(CompilationError::fatal(
                        source_range,
                        // TODO: Better error message here.
                        // Once we have ways to use None values (e.g. by replacing with a default value)
                        // we should suggest one of them here.
                        "cannot use a KCL tag declaration as an operand",
                    ));
                }
                Expr::UnaryExpression(x) => BinaryPart::UnaryExpression(x),
                Expr::Literal(x) => BinaryPart::Literal(x),
                Expr::Name(x) => BinaryPart::Name(x),
                Expr::BinaryExpression(x) => BinaryPart::BinaryExpression(x),
                Expr::CallExpression(x) => BinaryPart::CallExpression(x),
                Expr::CallExpressionKw(x) => BinaryPart::CallExpressionKw(x),
                Expr::MemberExpression(x) => BinaryPart::MemberExpression(x),
                Expr::IfExpression(x) => BinaryPart::IfExpression(x),
            };
            Ok(expr)
        })
        .context(expected("an operand (a value which can be used with an operator)"))
        .parse_next(i)?;
    Ok(op)
}

impl TokenType {
    fn parse_from(self, i: &mut TokenSlice) -> PResult<Token> {
        any.try_map(|token: Token| {
            if token.token_type == self {
                Ok(token)
            } else {
                Err(CompilationError::fatal(
                    token.as_source_range(),
                    format!(
                        "expected {self} but found {} which is a {}",
                        token.value.as_str(),
                        token.token_type
                    ),
                ))
            }
        })
        .parse_next(i)
    }
}

/// Parse some whitespace (i.e. at least one whitespace token)
fn whitespace(i: &mut TokenSlice) -> PResult<Vec<Token>> {
    repeat(
        1..,
        any.try_map(|token: Token| {
            if token.token_type == TokenType::Whitespace {
                Ok(token)
            } else {
                Err(CompilationError::fatal(
                    token.as_source_range(),
                    format!(
                        "expected whitespace, found '{}' which is {}",
                        token.value.as_str(),
                        token.token_type
                    ),
                ))
            }
        }),
    )
    .context(expected("some whitespace (e.g. spaces, tabs, new lines)"))
    .parse_next(i)
}

/// A shebang is a line at the start of a file that starts with `#!`.
/// If the shebang is present it takes up the whole line.
fn shebang(i: &mut TokenSlice) -> PResult<Node<Shebang>> {
    // Parse the hash and the bang.
    hash.parse_next(i)?;
    let tok = bang.parse_next(i)?;
    // Get the rest of the line.
    // Parse everything until the next newline.
    let tokens = take_till(0.., |token: Token| token.value.contains('\n')).parse_next(i)?;
    let value = tokens.iter().map(|t| t.value.as_str()).collect::<String>();

    if tokens.is_empty() {
        return Err(ErrMode::Cut(
            CompilationError::fatal(tok.as_source_range(), "expected a shebang value after #!").into(),
        ));
    }

    // Strip all the whitespace after the shebang.
    opt(whitespace).parse_next(i)?;

    Ok(Node::new(
        Shebang::new(format!("#!{}", value)),
        0,
        tokens.last().unwrap().end,
        tokens.first().unwrap().module_id,
    ))
}

#[allow(clippy::large_enum_variant)]
pub enum NonCodeOr<T> {
    NonCode(Node<NonCodeNode>),
    Code(T),
}

/// Parse a KCL array of elements.
fn array(i: &mut TokenSlice) -> PResult<Expr> {
    alt((
        array_empty.map(Box::new).map(Expr::ArrayExpression),
        array_end_start.map(Box::new).map(Expr::ArrayRangeExpression),
        array_elem_by_elem.map(Box::new).map(Expr::ArrayExpression),
    ))
    .parse_next(i)
}

/// Match an empty array.
fn array_empty(i: &mut TokenSlice) -> PResult<Node<ArrayExpression>> {
    let open = open_bracket(i)?;
    let start = open.start;
    ignore_whitespace(i);
    let end = close_bracket(i)?.end;
    Ok(Node::new(
        ArrayExpression {
            elements: Default::default(),
            non_code_meta: Default::default(),
            digest: None,
        },
        start,
        end,
        open.module_id,
    ))
}

/// Match something that separates elements of an array.
fn array_separator(i: &mut TokenSlice) -> PResult<()> {
    alt((
        // Normally you need a comma.
        comma_sep,
        // But, if the array is ending, no need for a comma.
        peek(preceded(opt(whitespace), close_bracket)).void(),
    ))
    .parse_next(i)
}

pub(crate) fn array_elem_by_elem(i: &mut TokenSlice) -> PResult<Node<ArrayExpression>> {
    let open = open_bracket(i)?;
    let start = open.start;
    ignore_whitespace(i);
    let elements: Vec<_> = repeat(
        0..,
        alt((
            terminated(expression.map(NonCodeOr::Code), array_separator),
            terminated(non_code_node.map(NonCodeOr::NonCode), whitespace),
        )),
    )
    .context(expected("array contents, a list of elements (like [1, 2, 3])"))
    .parse_next(i)?;
    ignore_trailing_comma(i);
    ignore_whitespace(i);

    let maybe_end = close_bracket(i).map_err(|e| {
        if let Some(mut err) = e.clone().into_inner() {
            let start_range = open.as_source_range();
            let end_range = i.as_source_range();
            err.cause = Some(CompilationError::fatal(
                SourceRange::from([start_range.start(), end_range.start(), end_range.module_id().as_usize()]),
                "Encountered an unexpected character(s) before finding a closing bracket(`]`) for the array",
            ));
            ErrMode::Cut(err)
        } else {
            // ErrMode::Incomplete, not sure if it's actually possible to end up with this here
            e
        }
    });

    if maybe_end.is_err() {
        // if there is a closing bracket at some point, but it wasn't the next token, it's likely that they forgot a comma between some
        // of the elements
        let maybe_closing_bracket: PResult<((), Token)> = peek(repeat_till(
            0..,
            none_of(|token: Token| {
                // bail out early if we encounter something that is for sure not allowed in an
                // array, otherwise we could seek to find a closing bracket until the end of the
                // file
                RESERVED_WORDS
                    .keys()
                    .chain([",,", "{", "}", "["].iter())
                    .any(|word| *word == token.value)
            })
            .void(),
            one_of(|term: Token| term.value == "]"),
        ))
        .parse_next(i);
        let has_closing_bracket = maybe_closing_bracket.is_ok();
        if has_closing_bracket {
            let start_range = i.as_source_range();
            // safe to unwrap here because we checked it was Ok above
            let end_range = maybe_closing_bracket.unwrap().1.as_source_range();
            let e = ContextError {
                context: vec![],
                cause: Some(CompilationError::fatal(
                    SourceRange::from([start_range.start(), end_range.end(), end_range.module_id().as_usize()]),
                    "Unexpected character encountered. You might be missing a comma in between elements.",
                )),
            };
            return Err(ErrMode::Cut(e));
        }
    }
    let end = maybe_end?.end;

    // Sort the array's elements (i.e. expression nodes) from the noncode nodes.
    let (elements, non_code_nodes): (Vec<_>, BTreeMap<usize, _>) = elements.into_iter().enumerate().fold(
        (Vec::new(), BTreeMap::new()),
        |(mut elements, mut non_code_nodes), (i, e)| {
            match e {
                NonCodeOr::NonCode(x) => {
                    non_code_nodes.insert(i, vec![x]);
                }
                NonCodeOr::Code(x) => {
                    elements.push(x);
                }
            }
            (elements, non_code_nodes)
        },
    );
    let non_code_meta = NonCodeMeta {
        non_code_nodes,
        start_nodes: Vec::new(),
        digest: None,
    };
    Ok(Node::new(
        ArrayExpression {
            elements,
            non_code_meta,
            digest: None,
        },
        start,
        end,
        open.module_id,
    ))
}

fn array_end_start(i: &mut TokenSlice) -> PResult<Node<ArrayRangeExpression>> {
    let open = open_bracket(i)?;
    let start = open.start;
    ignore_whitespace(i);
    let start_element = expression.parse_next(i)?;
    ignore_whitespace(i);
    double_period.parse_next(i)?;
    ignore_whitespace(i);
    let end_element = expression.parse_next(i)?;
    ignore_whitespace(i);
    let end = close_bracket(i)?.end;
    Ok(Node::new(
        ArrayRangeExpression {
            start_element,
            end_element,
            end_inclusive: true,
            digest: None,
        },
        start,
        end,
        open.module_id,
    ))
}

fn object_property_same_key_and_val(i: &mut TokenSlice) -> PResult<Node<ObjectProperty>> {
    let key = nameable_identifier.context(expected("the property's key (the name or identifier of the property), e.g. in 'height = 4', 'height' is the property key")).parse_next(i)?;
    ignore_whitespace(i);
    Ok(Node::new_node(
        key.start,
        key.end,
        key.module_id,
        ObjectProperty {
            value: Expr::Name(Box::new(key.clone().into())),
            key,
            digest: None,
        },
    ))
}

fn object_property(i: &mut TokenSlice) -> PResult<Node<ObjectProperty>> {
    let key = identifier.context(expected("the property's key (the name or identifier of the property), e.g. in 'height = 4', 'height' is the property key")).parse_next(i)?;
    ignore_whitespace(i);
    // Temporarily accept both `:` and `=` for compatibility.
    let sep = alt((colon, equals))
        .context(expected(
            "`=`, which separates the property's key from the value you're setting it to, e.g. 'height = 4'",
        ))
        .parse_next(i)?;
    ignore_whitespace(i);
    let expr = match expression
        .context(expected(
            "the value which you're setting the property to, e.g. in 'height = 4', the value is 4",
        ))
        .parse_next(i)
    {
        Ok(expr) => expr,
        Err(_) => {
            return Err(ErrMode::Cut(
                CompilationError::fatal(
                    SourceRange::from(sep),
                    "This property has a label, but no value. Put some value after the equals sign",
                )
                .into(),
            ));
        }
    };

    let result = Node::new_node(
        key.start,
        expr.end(),
        key.module_id,
        ObjectProperty {
            key,
            value: expr,
            digest: None,
        },
    );

    if sep.token_type == TokenType::Colon {
        ParseContext::warn(
            CompilationError::err(
                sep.into(),
                "Using `:` to initialize objects is deprecated, prefer using `=`.",
            )
            .with_suggestion("Replace `:` with `=`", " =", None, Tag::Deprecated),
        );
    }

    Ok(result)
}

/// Match something that separates properties of an object.
fn property_separator(i: &mut TokenSlice) -> PResult<()> {
    alt((
        // Normally you need a comma.
        comma_sep,
        // But, if the object is ending, no need for a comma.
        peek(preceded(opt(whitespace), close_brace)).void(),
    ))
    .parse_next(i)
}

/// Match something that separates the labeled arguments of a fn call.
fn labeled_arg_separator(i: &mut TokenSlice) -> PResult<()> {
    alt((
        // Normally you need a comma.
        comma_sep,
        // But, if the argument list is ending, no need for a comma.
        peek(preceded(opt(whitespace), close_paren)).void(),
    ))
    .parse_next(i)
}

/// Parse a KCL object value.
pub(crate) fn object(i: &mut TokenSlice) -> PResult<Node<ObjectExpression>> {
    let open = open_brace(i)?;
    let start = open.start;
    ignore_whitespace(i);
    let properties: Vec<_> = repeat(
        0..,
        alt((
            terminated(non_code_node.map(NonCodeOr::NonCode), whitespace),
            terminated(
                alt((object_property, object_property_same_key_and_val)),
                property_separator,
            )
            .map(NonCodeOr::Code),
        )),
    )
    .context(expected(
        "a comma-separated list of key-value pairs, e.g. 'height = 4, width = 3'",
    ))
    .parse_next(i)?;
    ignore_trailing_comma(i);
    ignore_whitespace(i);

    let maybe_end = close_brace(i).map_err(|e| {
        if let Some(mut err) = e.clone().into_inner() {
            let start_range = open.as_source_range();
            let end_range = i.as_source_range();
            err.cause = Some(CompilationError::fatal(
                SourceRange::from([start_range.start(), end_range.start(), end_range.module_id().as_usize()]),
                "Encountered an unexpected character(s) before finding a closing brace(`}`) for the object",
            ));
            ErrMode::Cut(err)
        } else {
            // ErrMode::Incomplete, not sure if it's actually possible to end up with this here
            e
        }
    });
    if maybe_end.is_err() {
        // if there is a closing brace at some point, but it wasn't the next token, it's likely that they forgot a comma between some
        // of the properties
        let maybe_closing_brace: PResult<((), Token)> = peek(repeat_till(
            0..,
            none_of(|token: Token| {
                // bail out early if we encounter something that is for sure not allowed in an
                // object, otherwise we could seek to find a closing brace until the end of the
                // file
                RESERVED_WORDS
                    .keys()
                    .chain([",,", "[", "]", "{"].iter())
                    .any(|word| *word == token.value)
            })
            .void(),
            one_of(|c: Token| c.value == "}"),
        ))
        .parse_next(i);
        let has_closing_brace = maybe_closing_brace.is_ok();
        if has_closing_brace {
            let start_range = i.as_source_range();
            // okay to unwrap here because we checked it was Ok above
            let end_range = maybe_closing_brace.unwrap().1.as_source_range();

            let e = ContextError {
                context: vec![],
                cause: Some(CompilationError::fatal(
                    SourceRange::from([start_range.start(), end_range.end(), end_range.module_id().as_usize()]),
                    "Unexpected character encountered. You might be missing a comma in between properties.",
                )),
            };
            return Err(ErrMode::Cut(e));
        }
    }

    let end = maybe_end?.end;
    // Sort the object's properties from the noncode nodes.
    let (properties, non_code_nodes): (Vec<_>, BTreeMap<usize, _>) = properties.into_iter().enumerate().fold(
        (Vec::new(), BTreeMap::new()),
        |(mut properties, mut non_code_nodes), (i, e)| {
            match e {
                NonCodeOr::NonCode(x) => {
                    non_code_nodes.insert(i, vec![x]);
                }
                NonCodeOr::Code(x) => {
                    properties.push(x);
                }
            }
            (properties, non_code_nodes)
        },
    );

    let non_code_meta = NonCodeMeta {
        non_code_nodes,
        ..Default::default()
    };
    Ok(Node::new(
        ObjectExpression {
            properties,
            non_code_meta,
            digest: None,
        },
        start,
        end,
        open.module_id,
    ))
}

/// Parse the % symbol, used to substitute a curried argument from a |> (pipe).
fn pipe_sub(i: &mut TokenSlice) -> PResult<Node<PipeSubstitution>> {
    any.try_map(|token: Token| {
        if matches!(token.token_type, TokenType::Operator) && token.value == PIPE_SUBSTITUTION_OPERATOR {
            Ok(Node::new(
                PipeSubstitution { digest: None },
                token.start,
                token.end,
                token.module_id,
            ))
        } else {
            Err(CompilationError::fatal(
                token.as_source_range(),
                format!(
                    "expected a pipe substitution symbol (%) but found {}",
                    token.value.as_str()
                ),
            ))
        }
    })
    .context(expected("the substitution symbol, %"))
    .parse_next(i)
}

fn else_if(i: &mut TokenSlice) -> PResult<Node<ElseIf>> {
    let else_ = any
        .try_map(|token: Token| {
            if matches!(token.token_type, TokenType::Keyword) && token.value == "else" {
                Ok(token)
            } else {
                Err(CompilationError::fatal(
                    token.as_source_range(),
                    format!("{} is not 'else'", token.value.as_str()),
                ))
            }
        })
        .context(expected("the 'else' keyword"))
        .parse_next(i)?;
    ignore_whitespace(i);
    let _if = any
        .try_map(|token: Token| {
            if matches!(token.token_type, TokenType::Keyword) && token.value == "if" {
                Ok(token.start)
            } else {
                Err(CompilationError::fatal(
                    token.as_source_range(),
                    format!("{} is not 'if'", token.value.as_str()),
                ))
            }
        })
        .context(expected("the 'if' keyword"))
        .parse_next(i)?;
    ignore_whitespace(i);
    let cond = expression(i)?;
    ignore_whitespace(i);
    let _ = open_brace(i)?;
    let then_val = program
        .verify(|block| block.ends_with_expr())
        .parse_next(i)
        .map(Box::new)?;
    ignore_whitespace(i);
    let end = close_brace(i)?.end;
    ignore_whitespace(i);
    Ok(Node::new(
        ElseIf {
            cond,
            then_val,
            digest: Default::default(),
        },
        else_.start,
        end,
        else_.module_id,
    ))
}

fn if_expr(i: &mut TokenSlice) -> PResult<BoxNode<IfExpression>> {
    let if_ = any
        .try_map(|token: Token| {
            if matches!(token.token_type, TokenType::Keyword) && token.value == "if" {
                Ok(token)
            } else {
                Err(CompilationError::fatal(
                    token.as_source_range(),
                    format!("{} is not 'if'", token.value.as_str()),
                ))
            }
        })
        .context(expected("the 'if' keyword"))
        .parse_next(i)?;
    let _ = whitespace(i)?;
    let cond = expression(i).map(Box::new)?;
    let _ = whitespace(i)?;
    let _ = open_brace(i)?;
    ignore_whitespace(i);
    let then_val = program
        .verify(|block| block.ends_with_expr())
        .parse_next(i)
        .map_err(|e| e.cut())
        .map(Box::new)?;
    ignore_whitespace(i);
    let _ = close_brace(i)?;
    ignore_whitespace(i);
    let else_ifs = repeat(0.., else_if).parse_next(i)?;

    ignore_whitespace(i);
    let _ = any
        .try_map(|token: Token| {
            if matches!(token.token_type, TokenType::Keyword) && token.value == "else" {
                Ok(token.start)
            } else {
                Err(CompilationError::fatal(
                    token.as_source_range(),
                    format!("{} is not 'else'", token.value.as_str()),
                ))
            }
        })
        .context(expected("the 'else' keyword"))
        .parse_next(i)?;
    ignore_whitespace(i);
    let _ = open_brace(i)?;
    ignore_whitespace(i);

    let final_else = program
        .verify(|block| block.ends_with_expr())
        .parse_next(i)
        .map_err(|e| e.cut())
        .map(Box::new)?;
    ignore_whitespace(i);
    let end = close_brace(i)?.end;
    Ok(Node::boxed(
        IfExpression {
            cond,
            then_val,
            else_ifs,
            final_else,
            digest: Default::default(),
        },
        if_.start,
        end,
        if_.module_id,
    ))
}

fn function_expr(i: &mut TokenSlice) -> PResult<Expr> {
    let fn_tok = opt(fun).parse_next(i)?;
    ignore_whitespace(i);
    let (result, has_arrow) = function_decl.parse_next(i)?;
    if fn_tok.is_none() {
        if has_arrow {
            ParseContext::warn(
                CompilationError::err(
                    result.as_source_range().start_as_range(),
                    "Missing `fn` in function declaration",
                )
                .with_suggestion("Add `fn`", "fn", None, Tag::None),
            );
        } else {
            let err = CompilationError::fatal(result.as_source_range(), "Anonymous function requires `fn` before `(`");
            return Err(ErrMode::Cut(err.into()));
        }
    }
    Ok(Expr::FunctionExpression(Box::new(result)))
}

// Looks like
// (arg0, arg1) {
//     const x = arg0 + arg1;
//     return x
// }
fn function_decl(i: &mut TokenSlice) -> PResult<(Node<FunctionExpression>, bool)> {
    fn return_type(i: &mut TokenSlice) -> PResult<Node<Type>> {
        colon(i)?;
        ignore_whitespace(i);
        argument_type(i)
    }

    let open = open_paren(i)?;
    let start = open.start;
    let params = parameters(i)?;
    close_paren(i)?;
    ignore_whitespace(i);
    let arrow = opt(big_arrow).parse_next(i)?;
    ignore_whitespace(i);
    // Optional return type.
    let return_type = opt(return_type).parse_next(i)?;
    ignore_whitespace(i);
    let brace = open_brace(i)?;
    let close: Option<(Vec<Vec<Token>>, Token)> = opt((repeat(0.., whitespace), close_brace)).parse_next(i)?;
    let (body, end) = match close {
        Some((_, end)) => (
            Node::new(Program::default(), brace.end, brace.end, brace.module_id),
            end.end,
        ),
        None => (function_body(i)?, close_brace(i)?.end),
    };
    let result = Node::new(
        FunctionExpression {
            params,
            body,
            return_type,
            digest: None,
        },
        start,
        end,
        open.module_id,
    );

    let has_arrow =
        if let Some(arrow) = arrow {
            ParseContext::warn(
                CompilationError::err(arrow.as_source_range(), "Unnecessary `=>` in function declaration")
                    .with_suggestion("Remove `=>`", "", None, Tag::Unnecessary),
            );
            true
        } else {
            false
        };

    Ok((result, has_arrow))
}

/// E.g. `person.name`
fn member_expression_dot(i: &mut TokenSlice) -> PResult<(LiteralIdentifier, usize, bool)> {
    period.parse_next(i)?;
    let property = nameable_identifier
        .map(Box::new)
        .map(LiteralIdentifier::Identifier)
        .parse_next(i)?;
    let end = property.end();
    Ok((property, end, false))
}

/// E.g. `people[0]` or `people[i]` or `people['adam']`
fn member_expression_subscript(i: &mut TokenSlice) -> PResult<(LiteralIdentifier, usize, bool)> {
    let _ = open_bracket.parse_next(i)?;
    let property = alt((
        literal.map(LiteralIdentifier::Literal),
        nameable_identifier.map(Box::new).map(LiteralIdentifier::Identifier),
    ))
    .parse_next(i)?;

    let end = close_bracket.parse_next(i)?.end;
    let computed = matches!(property, LiteralIdentifier::Identifier(_));
    Ok((property, end, computed))
}

/// Get a property of an object, or an index of an array, or a member of a collection.
/// Can be arbitrarily nested, e.g. `people[i]['adam'].age`.
fn member_expression(i: &mut TokenSlice) -> PResult<Node<MemberExpression>> {
    // This is an identifier, followed by a sequence of members (aka properties)
    // First, the identifier.
    let id = nameable_identifier.context(expected("the identifier of the object whose property you're trying to access, e.g. in 'shape.size.width', 'shape' is the identifier")).parse_next(i)?;
    // Now a sequence of members.
    let member = alt((member_expression_dot, member_expression_subscript)).context(expected("a member/property, e.g. size.x and size['height'] and size[0] are all different ways to access a member/property of 'size'"));
    let mut members: Vec<_> = repeat(1.., member)
        .context(expected("a sequence of at least one members/properties"))
        .parse_next(i)?;

    // Process the first member.
    // It's safe to call remove(0), because the vec is created from repeat(1..),
    // which is guaranteed to have >=1 elements.
    let (property, end, computed) = members.remove(0);
    let start = id.start;
    let module_id = id.module_id;
    let initial_member_expression = Node::new(
        MemberExpression {
            object: MemberObject::Identifier(Box::new(id)),
            computed,
            property,
            digest: None,
        },
        start,
        end,
        module_id,
    );

    // Each remaining member wraps the current member expression inside another member expression.
    Ok(members
        .into_iter()
        // Take the accumulated member expression from the previous iteration,
        // and use it as the `object` of a new, bigger member expression.
        .fold(initial_member_expression, |accumulated, (property, end, computed)| {
            Node::new(
                MemberExpression {
                    object: MemberObject::MemberExpression(Box::new(accumulated)),
                    computed,
                    property,
                    digest: None,
                },
                start,
                end,
                module_id,
            )
        }))
}

/// Find a noncode node which occurs just after a body item,
/// such that if the noncode item is a comment, it might be an inline comment.
fn noncode_just_after_code(i: &mut TokenSlice) -> PResult<Node<NonCodeNode>> {
    let ws = opt(whitespace).parse_next(i)?;

    // What is the preceding whitespace like?
    let (has_newline, has_empty_line) = if let Some(ref ws) = ws {
        (
            ws.iter().any(|token| token.value.contains('\n')),
            ws.iter().any(|token| count_in('\n', &token.value) >= 2),
        )
    } else {
        (false, false)
    };

    // Look for a non-code node (e.g. comment)
    let nc = non_code_node_no_leading_whitespace
        .map(|nc| {
            if has_empty_line {
                // There's an empty line between the body item and the comment,
                // This means the comment is a NewLineBlockComment!
                let value = match nc.inner.value {
                    // Change block comments to inline, as discussed above
                    NonCodeValue::BlockComment { value, style } => NonCodeValue::NewLineBlockComment { value, style },
                    // Other variants don't need to change.
                    x @ NonCodeValue::InlineComment { .. } => x,
                    x @ NonCodeValue::NewLineBlockComment { .. } => x,
                    x @ NonCodeValue::NewLine => x,
                };
                Node::new(
                    NonCodeNode { value, ..nc.inner },
                    nc.start.saturating_sub(1),
                    nc.end,
                    nc.module_id,
                )
            } else if has_newline {
                // Nothing has to change, a single newline does not need preserving.
                nc
            } else {
                // There's no newline between the body item and comment,
                // so if this is a comment, it must be inline with code.
                let value = match nc.inner.value {
                    // Change block comments to inline, as discussed above
                    NonCodeValue::BlockComment { value, style } => NonCodeValue::InlineComment { value, style },
                    // Other variants don't need to change.
                    x @ NonCodeValue::InlineComment { .. } => x,
                    x @ NonCodeValue::NewLineBlockComment { .. } => x,
                    x @ NonCodeValue::NewLine => x,
                };
                Node::new(NonCodeNode { value, ..nc.inner }, nc.start, nc.end, nc.module_id)
            }
        })
        .map(|nc| Node::new(nc.inner, nc.start.saturating_sub(1), nc.end, nc.module_id))
        .parse_next(i)?;
    Ok(nc)
}

// the large_enum_variant lint below introduces a LOT of code complexity in a
// match!() that's super clean that isn't worth it for the marginal space
// savings. revisit if that's a lie.
#[derive(Debug)]
#[allow(clippy::large_enum_variant)]
enum WithinFunction {
    Annotation(Node<Annotation>),
    BodyItem((BodyItem, Option<Node<NonCodeNode>>)),
    NonCode(Node<NonCodeNode>),
}

impl WithinFunction {
    fn is_newline(&self) -> bool {
        match self {
            WithinFunction::NonCode(nc) => nc.value == NonCodeValue::NewLine,
            _ => false,
        }
    }
}

fn body_items_within_function(i: &mut TokenSlice) -> PResult<WithinFunction> {
    // Any of the body item variants, each of which can optionally be followed by a comment.
    // If there is a comment, it may be preceded by whitespace.
    let item = dispatch! {peek(any);
        token if token.visibility_keyword().is_some() => (alt((import_stmt.map(BodyItem::ImportStatement), ty_decl.map(BodyItem::TypeDeclaration), declaration.map(BodyItem::VariableDeclaration))), opt(noncode_just_after_code)).map(WithinFunction::BodyItem),
        token if token.value == "type" && matches!(token.token_type, TokenType::Keyword) =>
            (ty_decl.map(BodyItem::TypeDeclaration), opt(noncode_just_after_code)).map(WithinFunction::BodyItem),
        token if token.declaration_keyword().is_some() =>
            (declaration.map(BodyItem::VariableDeclaration), opt(noncode_just_after_code)).map(WithinFunction::BodyItem),
        token if token.value == "import" && matches!(token.token_type, TokenType::Keyword) =>
            (import_stmt.map(BodyItem::ImportStatement), opt(noncode_just_after_code)).map(WithinFunction::BodyItem),
        Token { ref value, .. } if value == "return" =>
            (return_stmt.map(BodyItem::ReturnStatement), opt(noncode_just_after_code)).map(WithinFunction::BodyItem),
        token if !token.is_code_token() => {
            non_code_node.map(WithinFunction::NonCode)
        },
        token if token.token_type == TokenType::At => {
            annotation.map(WithinFunction::Annotation)
        },
        _ =>
            alt((
                (
                    declaration.map(BodyItem::VariableDeclaration),
                    opt(noncode_just_after_code)
                ).map(WithinFunction::BodyItem),
                (
                    expression_stmt.map(BodyItem::ExpressionStatement),
                    opt(noncode_just_after_code)
                ).map(WithinFunction::BodyItem),
            ))
    }
    .context(expected("a function body items (functions are made up of variable declarations, expressions, and return statements, each of those is a possible body item"))
    .parse_next(i)?;
    Ok(item)
}

/// Parse the body of a user-defined function.
fn function_body(i: &mut TokenSlice) -> PResult<Node<Program>> {
    let leading_whitespace_start = alt((
        peek(non_code_node).map(|_| None),
        // Subtract 1 from `t.start` to match behaviour of the old parser.
        // Consider removing the -1 in the future because I think it's inaccurate, but for now,
        // I prefer to match the old parser exactly when I can.
        opt(whitespace).map(|tok| tok.and_then(|t| t.first().map(|t| (t.start.saturating_sub(1), t.module_id)))),
    ))
    .parse_next(i)?;

    let mut things_within_body = Vec::new();
    // Parse the first item
    things_within_body.push(body_items_within_function.parse_next(i)?);

    // This loop is complicated! I'm sorry!
    // It's almost identical to the loop in `winnow::combinator::separated1`,
    // see <https://docs.rs/winnow/latest/winnow/combinator/fn.separated1.html>,
    // where the "main" parser is body_items_within_function and the `sep` (separator) parser is
    // ws_with_newline.
    //
    // Except for one thing.
    //
    // In this case, one of the body items being matched could be a whitespace with a newline,
    // and that could _also_ be the separator.
    //
    // So, if both the main parser and the `sep` parser within `separated1` try to match the same
    // token, the main parser will consume it and then the `sep` parser will fail.
    //
    // The solution is that this parser should check if the last matched body item was an empty line,
    // and if so, then ignore the separator parser for the current iteration.
    loop {
        let last_match_was_empty_line = things_within_body.last().map(|wf| wf.is_newline()).unwrap_or(false);

        use winnow::stream::Stream;

        let start = i.checkpoint();
        let len = i.eof_offset();

        let found_ws = ws_with_newline.parse_next(i);

        // The separator whitespace might be important:
        // if it has an empty line, it should be considered a noncode token, because the user
        // deliberately put an empty line there. We should track this and preserve it.
        if let Ok(ref ws_token) = found_ws {
            if ws_token.value.contains("\n\n") || ws_token.value.contains("\n\r\n") {
                things_within_body.push(WithinFunction::NonCode(Node::new(
                    NonCodeNode {
                        value: NonCodeValue::NewLine,
                        digest: None,
                    },
                    ws_token.start,
                    ws_token.end,
                    ws_token.module_id,
                )));
            }
        }

        match (found_ws, last_match_was_empty_line) {
            (Ok(_), _) | (_, true) => {
                // Infinite loop check: this loop must always consume tokens from the input.
                // That can either happen through the `sep` parser (i.e. ws_with_newline) or through
                // the main parser (body_items_within_function).
                // LHS of this checks fht
                if i.eof_offset() == len && !last_match_was_empty_line {
                    use winnow::error::ParserError;
                    return Err(ErrMode::assert(i, "sep parsers must always consume"));
                }

                match body_items_within_function.parse_next(i) {
                    Err(ErrMode::Backtrack(_)) => {
                        i.reset(&start);
                        break;
                    }
                    Err(e) => return Err(e),
                    Ok(o) => {
                        things_within_body.push(o);
                    }
                }
            }
            (Err(ErrMode::Backtrack(_)), _) => {
                i.reset(&start);
                break;
            }
            (Err(e), _) => return Err(e),
        }
    }

    let mut body = Vec::new();
    let mut inner_attrs = Vec::new();
    let mut pending_attrs = Vec::new();
    let mut non_code_meta = NonCodeMeta::default();
    let mut pending_non_code: Vec<Node<NonCodeNode>> = Vec::new();
    let mut end = 0;
    let mut start = leading_whitespace_start;

    macro_rules! handle_pending_non_code {
        ($node: ident) => {
            if !pending_non_code.is_empty() {
                let start = pending_non_code[0].start;
                let force_disoc = matches!(
                    &pending_non_code.last().unwrap().inner.value,
                    NonCodeValue::NewLine
                );
                let mut comments = Vec::new();
                for nc in pending_non_code {
                    match nc.inner.value {
                        NonCodeValue::BlockComment { value, style } if !force_disoc => {
                            comments.push(style.render_comment(&value));
                        }
                        NonCodeValue::NewLineBlockComment { value, style } if !force_disoc => {
                            if comments.is_empty() && nc.start != 0 {
                                comments.push(String::new());
                                comments.push(String::new());
                            }
                            comments.push(style.render_comment(&value));
                        }
                        NonCodeValue::NewLine if !force_disoc && !comments.is_empty() => {
                            comments.push(String::new());
                            comments.push(String::new());
                        }
                        _ => {
                            if body.is_empty() {
                                non_code_meta.start_nodes.push(nc);
                            } else {
                                non_code_meta.insert(body.len() - 1, nc);
                            }
                        }
                    }
                }
                $node.set_comments(comments, start);
                pending_non_code = Vec::new();
            }
        };
    }

    for thing_in_body in things_within_body {
        match thing_in_body {
            WithinFunction::Annotation(mut attr) => {
                if start.is_none() {
                    start = Some((attr.start, attr.module_id))
                }
                handle_pending_non_code!(attr);
                if attr.is_inner() {
                    inner_attrs.push(attr);
                } else {
                    pending_attrs.push(attr);
                }
            }
            WithinFunction::BodyItem((mut b, maybe_noncode)) => {
                if start.is_none() {
                    start = Some((b.start(), b.module_id()));
                }
                end = b.end();
                if !pending_attrs.is_empty() {
                    b.set_attrs(pending_attrs);
                    pending_attrs = Vec::new();
                }
                handle_pending_non_code!(b);
                body.push(b);
                if let Some(nc) = maybe_noncode {
                    end = nc.end;
                    pending_non_code.push(nc);
                }
            }
            WithinFunction::NonCode(nc) => {
                if start.is_none() {
                    start = Some((nc.start, nc.module_id));
                }
                end = nc.end;
                pending_non_code.push(nc);
            }
        }
    }

    let start = start.expect(
        "the `things_within_body` vec should have looped at least once, and each loop overwrites `start` if it is None",
    );

    if !pending_attrs.is_empty() {
        for a in pending_attrs {
            ParseContext::err(CompilationError::err(
                a.as_source_range(),
                "Attribute is not attached to any item",
            ));
        }
        return Err(ErrMode::Cut(
            CompilationError::fatal(
                SourceRange::new(start.0, end, start.1),
                "Block contains un-attached attributes",
            )
            .into(),
        ));
    }

    for nc in pending_non_code {
        if body.is_empty() {
            non_code_meta.start_nodes.push(nc);
        } else {
            non_code_meta.insert(body.len() - 1, nc);
        }
    }

    // Safe to unwrap `body.first()` because `body` is `separated1` therefore guaranteed
    // to have len >= 1.
    let end_ws = opt(whitespace)
        .parse_next(i)?
        .and_then(|ws| ws.first().map(|tok| tok.end));
    if let Some(end_ws) = end_ws {
        end = end.max(end_ws);
    }
    end += 1;
    Ok(Node::new(
        Program {
            body,
            non_code_meta,
            inner_attrs,
            shebang: None,
            digest: None,
        },
        start.0,
        end,
        start.1,
    ))
}

fn import_items(i: &mut TokenSlice) -> PResult<NodeList<ImportItem>> {
    separated(1.., import_item, comma_sep)
        .parse_next(i)
        .map_err(|e| e.cut())
}

fn glob(i: &mut TokenSlice) -> PResult<Token> {
    one_of((TokenType::Operator, "*"))
        .context(expected("the multiple import operator, *"))
        .parse_next(i)
}

fn import_stmt(i: &mut TokenSlice) -> PResult<BoxNode<ImportStatement>> {
    let (visibility, visibility_token) = opt(terminated(item_visibility, whitespace))
        .parse_next(i)?
        .map_or((ItemVisibility::Default, None), |pair| (pair.0, Some(pair.1)));
    let import_token = any
        .try_map(|token: Token| {
            if matches!(token.token_type, TokenType::Keyword) && token.value == "import" {
                Ok(token)
            } else {
                Err(CompilationError::fatal(
                    token.as_source_range(),
                    format!("{} is not the 'import' keyword", token.value.as_str()),
                ))
            }
        })
        .context(expected("the 'import' keyword"))
        .parse_next(i)?;

    let module_id = import_token.module_id;
    let start = visibility_token.unwrap_or(import_token).start;

    require_whitespace(i)?;

    let (mut selector, path) = alt((
        string_literal.map(|s| (ImportSelector::None { alias: None }, Some(s))),
        glob.map(|t| {
            let s = t.as_source_range();
            (
                ImportSelector::Glob(Node::new((), s.start(), s.end(), s.module_id())),
                None,
            )
        }),
        import_items.map(|items| (ImportSelector::List { items }, None)),
    ))
    .parse_next(i)?;

    let path = match path {
        Some(path) => path,
        None => {
            require_whitespace(i)?;
            any.try_map(|token: Token| {
                if matches!(token.token_type, TokenType::Keyword | TokenType::Word) && token.value == "from" {
                    Ok(())
                } else {
                    Err(CompilationError::fatal(
                        token.as_source_range(),
                        format!("{} is not the 'from' keyword", token.value.as_str()),
                    ))
                }
            })
            .context(expected("the 'from' keyword"))
            .parse_next(i)
            .map_err(|e| e.cut())?;

            require_whitespace(i)?;

            string_literal(i)?
        }
    };

    let mut end: usize = path.end;

    if let ImportSelector::None {
        alias: ref mut selector_alias,
    } = selector
    {
        if let Some(alias) = opt(preceded(
            (whitespace, import_as_keyword, whitespace),
            identifier.context(expected("an identifier to alias the import")),
        ))
        .parse_next(i)?
        {
            end = alias.end;
            *selector_alias = Some(alias);
        }

        ParseContext::warn(CompilationError::err(
            SourceRange::new(start, path.end, path.module_id),
            "Importing a whole module is experimental, likely to be buggy, and likely to change",
        ));
    }

    let path_string = match path.inner.value {
        LiteralValue::String(s) => s,
        _ => unreachable!(),
    };
    let path = validate_path_string(
        path_string,
        selector.exposes_imported_name(),
        SourceRange::new(path.start, path.end, path.module_id),
    )?;

    if matches!(path, ImportPath::Foreign { .. }) && selector.imports_items() {
        return Err(ErrMode::Cut(
            CompilationError::fatal(
                SourceRange::new(start, end, module_id),
                "individual items can only be imported from KCL files",
            )
            .into(),
        ));
    } else if matches!(path, ImportPath::Std { .. }) && matches!(selector, ImportSelector::None { .. }) {
        return Err(ErrMode::Cut(
            CompilationError::fatal(
                SourceRange::new(start, end, module_id),
                "the standard library cannot be imported as a part",
            )
            .into(),
        ));
    }

    Ok(Node::boxed(
        ImportStatement {
            selector,
            visibility,
            path,
            digest: None,
        },
        start,
        end,
        module_id,
    ))
}

const FOREIGN_IMPORT_EXTENSIONS: [&str; 8] = ["fbx", "gltf", "glb", "obj", "ply", "sldprt", "step", "stl"];

/// Validates the path string in an `import` statement.
///
/// `var_name` is `true` if the path will be used as a variable name.
fn validate_path_string(path_string: String, var_name: bool, path_range: SourceRange) -> PResult<ImportPath> {
    if path_string.is_empty() {
        return Err(ErrMode::Cut(
            CompilationError::fatal(path_range, "import path cannot be empty").into(),
        ));
    }

    if var_name
        && (path_string.starts_with("_")
            || path_string.contains('-')
            || path_string.chars().filter(|c| *c == '.').count() > 1)
    {
        return Err(ErrMode::Cut(
            CompilationError::fatal(path_range, "import path is not a valid identifier and must be aliased.").into(),
        ));
    }

    let path = if path_string.ends_with(".kcl") {
        if path_string
            .chars()
            .any(|c| !c.is_ascii_alphanumeric() && c != '_' && c != '-' && c != '.')
        {
            return Err(ErrMode::Cut(
                CompilationError::fatal(
                    path_range,
                    "import path may only contain alphanumeric characters, underscore, hyphen, and period. KCL files in other directories are not yet supported.",
                )
                .into(),
            ));
        }

        ImportPath::Kcl { filename: path_string }
    } else if path_string.starts_with("std::") {
        ParseContext::warn(CompilationError::err(
            path_range,
            "explicit imports from the standard library are experimental, likely to be buggy, and likely to change.",
        ));

        let segments: Vec<String> = path_string.split("::").map(str::to_owned).collect();

        for s in &segments {
            if s.chars().any(|c| !c.is_ascii_alphanumeric() && c != '_') || s.starts_with('_') {
                return Err(ErrMode::Cut(
                    CompilationError::fatal(path_range, "invalid path in import statement.").into(),
                ));
            }
        }

        // For now we only support importing from singly-nested modules inside std.
        if segments.len() != 2 {
            return Err(ErrMode::Cut(
                CompilationError::fatal(
                    path_range,
                    format!("Invalid import path for import from std: {}.", path_string),
                )
                .into(),
            ));
        }

        ImportPath::Std { path: segments }
    } else if path_string.contains('.') {
        // TODO should allow other extensions if there is a format attribute.
        let extn = &path_string[path_string.rfind('.').unwrap() + 1..];
        if !FOREIGN_IMPORT_EXTENSIONS.contains(&extn) {
            ParseContext::warn(CompilationError::err(
                path_range,
                format!("unsupported import path format. KCL files can be imported from the current project, CAD files with the following formats are supported: {}", FOREIGN_IMPORT_EXTENSIONS.join(", ")),
            ))
        }
        ImportPath::Foreign { path: path_string }
    } else {
        return Err(ErrMode::Cut(
            CompilationError::fatal(
                path_range,
                format!("unsupported import path format. KCL files can be imported from the current project, CAD files with the following formats are supported: {}", FOREIGN_IMPORT_EXTENSIONS.join(", ")),
            )
            .into(),
        ));
    };

    Ok(path)
}

fn import_item(i: &mut TokenSlice) -> PResult<Node<ImportItem>> {
    let name = nameable_identifier
        .context(expected("an identifier to import"))
        .parse_next(i)?;
    let start = name.start;
    let module_id = name.module_id;
    let alias = opt(preceded(
        (whitespace, import_as_keyword, whitespace),
        identifier.context(expected("an identifier to alias the import")),
    ))
    .parse_next(i)?;
    let end = if let Some(ref alias) = alias {
        alias.end
    } else {
        name.end
    };
    Ok(Node::new(
        ImportItem {
            name,
            alias,
            digest: None,
        },
        start,
        end,
        module_id,
    ))
}

fn import_as_keyword(i: &mut TokenSlice) -> PResult<Token> {
    any.try_map(|token: Token| {
        if matches!(token.token_type, TokenType::Keyword | TokenType::Word) && token.value == "as" {
            Ok(token)
        } else {
            Err(CompilationError::fatal(
                token.as_source_range(),
                format!("{} is not the 'as' keyword", token.value.as_str()),
            ))
        }
    })
    .context(expected("the 'as' keyword"))
    .parse_next(i)
}

/// Parse a return statement of a user-defined function, e.g. `return x`.
fn return_stmt(i: &mut TokenSlice) -> PResult<Node<ReturnStatement>> {
    let ret = any
        .try_map(|token: Token| {
            if matches!(token.token_type, TokenType::Keyword) && token.value == "return" {
                Ok(token)
            } else {
                Err(CompilationError::fatal(
                    token.as_source_range(),
                    format!("{} is not a return keyword", token.value.as_str()),
                ))
            }
        })
        .context(expected(
            "the 'return' keyword, which ends your function (and becomes this function's value when it's called)",
        ))
        .parse_next(i)?;
    require_whitespace(i)?;
    let argument = expression(i)?;
    Ok(Node::new_node(
        ret.start,
        argument.end(),
        ret.module_id,
        ReturnStatement { argument, digest: None },
    ))
}

/// Parse a KCL expression.
fn expression(i: &mut TokenSlice) -> PResult<Expr> {
    alt((
        pipe_expression.map(Box::new).map(Expr::PipeExpression),
        expression_but_not_pipe,
    ))
    .context(expected("a KCL value"))
    .parse_next(i)
}

fn expression_but_not_pipe(i: &mut TokenSlice) -> PResult<Expr> {
    let mut expr = alt((
        binary_expression.map(Box::new).map(Expr::BinaryExpression),
        unary_expression.map(Box::new).map(Expr::UnaryExpression),
        expr_allowed_in_pipe_expr,
    ))
    .context(expected("a KCL value"))
    .parse_next(i)?;

    let ty = opt((colon, opt(whitespace), argument_type)).parse_next(i)?;
    if let Some((_, _, ty)) = ty {
        ParseContext::warn(CompilationError::err((&ty).into(), "Type ascription is experimental."));

        expr = Expr::AscribedExpression(Box::new(Ascription::new(expr, ty)))
    }
    let label = opt(label).parse_next(i)?;
    match label {
        Some(label) => Ok(Expr::LabelledExpression(Box::new(LabelledExpression::new(expr, label)))),
        None => Ok(expr),
    }
}

fn label(i: &mut TokenSlice) -> PResult<Node<Identifier>> {
    let result = preceded(
        (whitespace, import_as_keyword, whitespace),
        identifier.context(expected("an identifier")),
    )
    .parse_next(i)?;

    ParseContext::warn(CompilationError::err(
        SourceRange::new(result.start, result.end, result.module_id),
        "Using `as` for tagging expressions is experimental, likely to be buggy, and likely to change",
    ));

    Ok(result)
}

fn unnecessarily_bracketed(i: &mut TokenSlice) -> PResult<Expr> {
    delimited(
        terminated(open_paren, opt(whitespace)),
        expression,
        preceded(opt(whitespace), close_paren),
    )
    .parse_next(i)
}

fn expr_allowed_in_pipe_expr(i: &mut TokenSlice) -> PResult<Expr> {
    alt((
        member_expression.map(Box::new).map(Expr::MemberExpression),
        bool_value.map(Expr::Literal),
        tag.map(Box::new).map(Expr::TagDeclarator),
        literal.map(Expr::Literal),
        fn_call.map(Box::new).map(Expr::CallExpression),
        fn_call_kw.map(Box::new).map(Expr::CallExpressionKw),
        name.map(Box::new).map(Expr::Name),
        array,
        object.map(Box::new).map(Expr::ObjectExpression),
        pipe_sub.map(Box::new).map(Expr::PipeSubstitution),
        function_expr,
        if_expr.map(Expr::IfExpression),
        unnecessarily_bracketed,
    ))
    .context(expected("a KCL expression (but not a pipe expression)"))
    .parse_next(i)
}

fn possible_operands(i: &mut TokenSlice) -> PResult<Expr> {
    alt((
        unary_expression.map(Box::new).map(Expr::UnaryExpression),
        bool_value.map(Expr::Literal),
        member_expression.map(Box::new).map(Expr::MemberExpression),
        literal.map(Expr::Literal),
        fn_call.map(Box::new).map(Expr::CallExpression),
        name.map(Box::new).map(Expr::Name),
        binary_expr_in_parens.map(Box::new).map(Expr::BinaryExpression),
        unnecessarily_bracketed,
    ))
    .context(expected(
        "a KCL value which can be used as an argument/operand to an operator",
    ))
    .parse_next(i)
}

/// Parse an item visibility specifier, e.g. export.
fn item_visibility(i: &mut TokenSlice) -> PResult<(ItemVisibility, Token)> {
    any.verify_map(|token: Token| {
        if token.token_type == TokenType::Keyword && token.value == "export" {
            Some((ItemVisibility::Export, token))
        } else {
            None
        }
    })
    .context(expected("item visibility, e.g. 'export'"))
    .parse_next(i)
}

fn declaration_keyword(i: &mut TokenSlice) -> PResult<(VariableKind, Token)> {
    let res = any
        .verify_map(|token: Token| token.declaration_keyword().map(|kw| (kw, token)))
        .parse_next(i)?;
    Ok(res)
}

/// Parse a variable/constant declaration.
fn declaration(i: &mut TokenSlice) -> PResult<BoxNode<VariableDeclaration>> {
    let (visibility, visibility_token) = opt(terminated(item_visibility, whitespace))
        .parse_next(i)?
        .map_or((ItemVisibility::Default, None), |pair| (pair.0, Some(pair.1)));
    let decl_token = opt(declaration_keyword).parse_next(i)?;
    if decl_token.is_some() {
        // If there was a declaration keyword like `fn`, then it must be followed by some spaces.
        // `fnx = ...` is not valid!
        require_whitespace(i)?;
    }

    let id = binding_name
        .context(expected(
            "an identifier, which becomes name you're binding the value to",
        ))
        .parse_next(i)?;
    let (kind, mut start, dec_end) = if let Some((kind, token)) = &decl_token {
        (*kind, token.start, token.end)
    } else {
        (VariableKind::Const, id.start, id.end)
    };
    if let Some(token) = visibility_token {
        start = token.start;
    }

    ignore_whitespace(i);

    let val =
        if kind == VariableKind::Fn {
            let eq = opt(equals).parse_next(i)?;
            ignore_whitespace(i);

            let val = function_decl
                .map(|t| Box::new(t.0))
                .map(Expr::FunctionExpression)
                .context(expected("a KCL function expression, like () { return 1 }"))
                .parse_next(i);

            if let Some(t) = eq {
                ParseContext::warn(
                    CompilationError::err(t.as_source_range(), "Unnecessary `=` in function declaration")
                        .with_suggestion("Remove `=`", "", None, Tag::Unnecessary),
                );
            }

            val
        } else {
            equals(i)?;
            ignore_whitespace(i);

            let val = expression
                .try_map(|val| {
                    // Function bodies can be used if and only if declaring a function.
                    // Check the 'if' direction:
                    if matches!(val, Expr::FunctionExpression(_)) {
                        return Err(CompilationError::fatal(
                            SourceRange::new(start, dec_end, id.module_id),
                            format!("Expected a `fn` variable kind, found: `{}`", kind),
                        ));
                    }
                    Ok(val)
                })
                .context(expected("a KCL value, which is being bound to a variable"))
                .parse_next(i);

            if let Some((_, tok)) = decl_token {
                let range_to_remove = SourceRange::new(tok.start, id.start, id.module_id);
                ParseContext::warn(
                    CompilationError::err(
                        tok.as_source_range(),
                        format!(
                            "Using `{}` to declare constants is deprecated; no keyword is required",
                            tok.value
                        ),
                    )
                    .with_suggestion(
                        format!("Remove `{}`", tok.value),
                        "",
                        Some(range_to_remove),
                        Tag::Deprecated,
                    ),
                );
            }

            val
        }
        .map_err(|e| e.cut())?;

    let end = val.end();
    let module_id = id.module_id;
    Ok(Node::boxed(
        VariableDeclaration {
            declaration: Node::new_node(
                id.start,
                end,
                module_id,
                VariableDeclarator {
                    id,
                    init: val,
                    digest: None,
                },
            ),
            visibility,
            kind,
            digest: None,
        },
        start,
        end,
        module_id,
    ))
}

fn ty_decl(i: &mut TokenSlice) -> PResult<BoxNode<TypeDeclaration>> {
    let (visibility, visibility_token) = opt(terminated(item_visibility, whitespace))
        .parse_next(i)?
        .map_or((ItemVisibility::Default, None), |pair| (pair.0, Some(pair.1)));

    let decl_token = ty(i)?;
    let start = visibility_token.map(|t| t.start).unwrap_or_else(|| decl_token.start);
    whitespace(i)?;

    let name = identifier(i)?;
    let mut end = name.end;

    let args = if peek((opt(whitespace), open_paren)).parse_next(i).is_ok() {
        ignore_whitespace(i);
        open_paren(i)?;
        ignore_whitespace(i);
        let args: Vec<_> = separated(0.., identifier, comma_sep).parse_next(i)?;
        ignore_trailing_comma(i);
        ignore_whitespace(i);
        end = close_paren(i)?.end;
        Some(args)
    } else {
        None
    };

    let alias = if peek((opt(whitespace), equals)).parse_next(i).is_ok() {
        ignore_whitespace(i);
        equals(i)?;
        ignore_whitespace(i);
        let ty = argument_type(i)?;

        ParseContext::warn(CompilationError::err(
            ty.as_source_range(),
            "Type aliases are experimental, likely to change in the future, and likely to not work properly.",
        ));

        Some(ty)
    } else {
        None
    };

    let module_id = name.module_id;
    let result = Node::boxed(
        TypeDeclaration {
            name,
            args,
            alias,
            visibility,
            digest: None,
        },
        start,
        end,
        module_id,
    );

    ParseContext::warn(CompilationError::err(
        result.as_source_range(),
        "Type declarations are experimental, likely to change, and may or may not do anything useful.",
    ));

    Ok(result)
}

impl TryFrom<Token> for Node<Identifier> {
    type Error = CompilationError;

    fn try_from(token: Token) -> Result<Self, Self::Error> {
        if token.token_type == TokenType::Word {
            Ok(Node::new(
                Identifier {
                    name: token.value,
                    digest: None,
                },
                token.start,
                token.end,
                token.module_id,
            ))
        } else {
            Err(CompilationError::fatal(
                token.as_source_range(),
                format!(
                    "Cannot assign a variable to a reserved keyword: {}",
                    token.value.as_str()
                ),
            ))
        }
    }
}

/// Parse a KCL identifier (name of a constant/variable/function)
fn identifier(i: &mut TokenSlice) -> PResult<Node<Identifier>> {
    any.try_map(Node::<Identifier>::try_from)
        .context(expected("an identifier, e.g. 'width' or 'myPart'"))
        .parse_next(i)
}

fn nameable_identifier(i: &mut TokenSlice) -> PResult<Node<Identifier>> {
    let result = identifier.parse_next(i)?;

    if !result.is_nameable() {
        let desc = if result.name == "_" {
            "Underscores"
        } else {
            "Names with a leading underscore"
        };
        ParseContext::err(CompilationError::err(
            SourceRange::new(result.start, result.end, result.module_id),
            format!("{desc} cannot be referred to, only declared."),
        ));
    }

    if let Some(suggestion) = super::deprecation(&result.name, DeprecationKind::Const) {
        ParseContext::warn(
            CompilationError::err(
                result.as_source_range(),
                format!("Using `{}` is deprecated, prefer using `{}`.", result.name, suggestion),
            )
            .with_suggestion(
                format!("Replace `{}` with `{}`", result.name, suggestion),
                suggestion,
                None,
                Tag::Deprecated,
            ),
        );
    }

    Ok(result)
}

fn name(i: &mut TokenSlice) -> PResult<Node<Name>> {
    let abs_path = opt(double_colon).parse_next(i)?;
    let mut idents: NodeList<Identifier> = separated(1.., nameable_identifier, double_colon)
        .parse_next(i)
        .map_err(|e| e.backtrack())?;

    let mut start = idents[0].start;
    if let Some(abs_path) = &abs_path {
        start = abs_path.start;
    }
    let abs_path = abs_path.is_some();

    let name = idents.pop().unwrap();
    let end = name.end;
    let module_id = name.module_id;

    Ok(Node::new(
        Name {
            name,
            path: idents,
            abs_path,
            digest: None,
        },
        start,
        end,
        module_id,
    ))
}

impl TryFrom<Token> for Node<TagDeclarator> {
    type Error = CompilationError;

    fn try_from(token: Token) -> Result<Self, Self::Error> {
        match token.token_type {
            TokenType::Word => {
                Ok(Node::new(
                    TagDeclarator {
                        // We subtract 1 from the start because the tag starts with a `$`.
                        name: token.value,
                        digest: None,
                    },
                    token.start - 1,
                    token.end,
                    token.module_id,
                ))
            }
            TokenType::Number => Err(CompilationError::fatal(
                token.as_source_range(),
                format!(
                    "Tag names must not start with a number. Tag starts with `{}`",
                    token.value.as_str()
                ),
            )),

            // e.g. `line(%, $)` or `line(%, $ , 5)`
            TokenType::Brace | TokenType::Whitespace | TokenType::Comma => Err(CompilationError::fatal(
                token.as_source_range(),
                "Tag names must not be empty".to_string(),
            )),

            TokenType::Type => Err(CompilationError::fatal(
                token.as_source_range(),
                format!("Cannot assign a tag to a reserved keyword: {}", token.value.as_str()),
            )),

            _ => Err(CompilationError::fatal(
                token.as_source_range(),
                // this is `start with` because if most of these cases are in the middle, it ends
                // up hitting a different error path(e.g. including a bang) or being valid(e.g. including a comment) since it will get broken up into
                // multiple tokens
                format!("Tag names must not start with a {}", token.token_type),
            )),
        }
    }
}

impl Node<TagDeclarator> {
    fn into_valid_binding_name(self) -> Result<Self, CompilationError> {
        // Make sure they are not assigning a variable to a stdlib function.
        if crate::std::name_in_stdlib(&self.name) {
            return Err(CompilationError::fatal(
                SourceRange::from(&self),
                format!("Cannot assign a tag to a reserved keyword: {}", self.name),
            ));
        }
        Ok(self)
    }
}

/// Parse a Kcl tag that starts with a `$`.
fn tag(i: &mut TokenSlice) -> PResult<Node<TagDeclarator>> {
    dollar.parse_next(i)?;
    let tag_declarator = any
        .try_map(Node::<TagDeclarator>::try_from)
        .context(expected("a tag, e.g. '$seg01' or '$line01'"))
        .parse_next(i)
        .map_err(|e| e.cut())?;
    // Now that we've parsed a tag declarator, verify that it's not a stdlib
    // name.  If it is, stop backtracking.
    tag_declarator
        .into_valid_binding_name()
        .map_err(|e| ErrMode::Cut(ContextError::from(e)))
}

/// Helper function. Matches any number of whitespace tokens and ignores them.
fn ignore_whitespace(i: &mut TokenSlice) {
    let _: PResult<()> = repeat(0.., whitespace).parse_next(i);
}

// A helper function to ignore a trailing comma.
fn ignore_trailing_comma(i: &mut TokenSlice) {
    let _ = opt(comma).parse_next(i);
}

/// Matches at least 1 whitespace.
fn require_whitespace(i: &mut TokenSlice) -> PResult<()> {
    repeat(1.., whitespace).parse_next(i)
}

fn unary_expression(i: &mut TokenSlice) -> PResult<Node<UnaryExpression>> {
    const EXPECTED: &str = "expected a unary operator (like '-', the negative-numeric operator),";
    let (operator, op_token) = any
        .try_map(|token: Token| match token.token_type {
            TokenType::Operator if token.value == "-" => Ok((UnaryOperator::Neg, token)),
            TokenType::Operator => Err(CompilationError::fatal(
                 token.as_source_range(),
                 format!("{EXPECTED} but found {} which is an operator, but not a unary one (unary operators apply to just a single operand, your operator applies to two or more operands)", token.value.as_str(),),
            )),
            TokenType::Bang => Ok((UnaryOperator::Not, token)),
            other => Err(CompilationError::fatal(  token.as_source_range(), format!("{EXPECTED} but found {} which is {}", token.value.as_str(), other,) )),
        })
        .context(expected("a unary expression, e.g. -x or -3"))
        .parse_next(i)?;
    let argument = operand.parse_next(i)?;
    Ok(Node::new_node(
        op_token.start,
        argument.end(),
        op_token.module_id,
        UnaryExpression {
            operator,
            argument,
            digest: None,
        },
    ))
}

/// Consume tokens that make up a binary expression, but don't actually return them.
/// Why not?
/// Because this is designed to be used with .take() within the `binary_expression` parser.
fn binary_expression_tokens(i: &mut TokenSlice) -> PResult<Vec<BinaryExpressionToken>> {
    let first = operand.parse_next(i).map(BinaryExpressionToken::from)?;
    let remaining: Vec<_> = repeat(
        1..,
        (
            preceded(opt(whitespace), binary_operator).map(BinaryExpressionToken::from),
            preceded(opt(whitespace), operand).map(BinaryExpressionToken::from),
        ),
    )
    .context(expected(
        "one or more binary operators (like + or -) and operands for them, e.g. 1 + 2 - 3",
    ))
    .parse_next(i)?;
    let mut out = Vec::with_capacity(1 + 2 * remaining.len());
    out.push(first);
    out.extend(remaining.into_iter().flat_map(|(a, b)| [a, b]));
    Ok(out)
}

/// Parse an infix binary expression.
fn binary_expression(i: &mut TokenSlice) -> PResult<Node<BinaryExpression>> {
    // Find the slice of tokens which makes up the binary expression
    let tokens = binary_expression_tokens.parse_next(i)?;

    // Pass the token slice into the specialized math parser, for things like
    // precedence and converting infix operations to an AST.
    let expr = super::math::parse(tokens).map_err(|e| ErrMode::Backtrack(e.into()))?;
    Ok(expr)
}

fn binary_expr_in_parens(i: &mut TokenSlice) -> PResult<Node<BinaryExpression>> {
    let span_with_brackets = bracketed_section.take().parse_next(i)?;
    let mut span_no_brackets = span_with_brackets.without_ends();
    let expr = binary_expression.parse_next(&mut span_no_brackets)?;
    Ok(expr)
}

/// Match a starting bracket, then match to the corresponding end bracket.
/// Return the count of how many tokens are in that span
/// (not including the bracket tokens).
fn bracketed_section(i: &mut TokenSlice) -> PResult<usize> {
    // Find the start of this bracketed expression.
    let _ = open_paren.parse_next(i)?;
    let mut opened_braces = 1usize;
    let mut tokens_examined = 0;
    while opened_braces > 0 {
        let tok = any.parse_next(i)?;
        tokens_examined += 1;
        if matches!(tok.token_type, TokenType::Brace) {
            if tok.value == "(" {
                opened_braces += 1;
            } else if tok.value == ")" {
                opened_braces -= 1;
            }
        }
    }
    Ok(tokens_examined)
}

/// Parse a KCL expression statement.
fn expression_stmt(i: &mut TokenSlice) -> PResult<Node<ExpressionStatement>> {
    let val = expression
        .context(expected(
            "an expression (i.e. a value, or an algorithm for calculating one), e.g. 'x + y' or '3' or 'width * 2'",
        ))
        .parse_next(i)?;
    Ok(Node::new_node(
        val.start(),
        val.end(),
        val.module_id(),
        ExpressionStatement {
            expression: val,
            digest: None,
        },
    ))
}

/// Parse the given brace symbol.
fn some_brace(symbol: &'static str, i: &mut TokenSlice) -> PResult<Token> {
    one_of((TokenType::Brace, symbol))
        .context(expected(symbol))
        .parse_next(i)
}

/// Parse a => operator.
fn big_arrow(i: &mut TokenSlice) -> PResult<Token> {
    one_of((TokenType::Operator, "=>"))
        .context(expected("the => symbol, used for declaring functions"))
        .parse_next(i)
}
/// Parse a |> operator.
fn pipe_operator(i: &mut TokenSlice) -> PResult<Token> {
    one_of((TokenType::Operator, PIPE_OPERATOR))
        .context(expected(
            "the |> operator, used for 'piping' one function's output into another function's input",
        ))
        .parse_next(i)
}

fn ws_with_newline(i: &mut TokenSlice) -> PResult<Token> {
    one_of(TokenType::Whitespace)
        .verify(|token: &Token| token.value.contains('\n'))
        .context(expected("a newline, possibly with whitespace"))
        .parse_next(i)
}

/// (
fn open_paren(i: &mut TokenSlice) -> PResult<Token> {
    some_brace("(", i)
}

/// )
fn close_paren(i: &mut TokenSlice) -> PResult<Token> {
    some_brace(")", i)
}

/// [
fn open_bracket(i: &mut TokenSlice) -> PResult<Token> {
    some_brace("[", i)
}

/// ]
fn close_bracket(i: &mut TokenSlice) -> PResult<Token> {
    some_brace("]", i)
}

/// {
fn open_brace(i: &mut TokenSlice) -> PResult<Token> {
    some_brace("{", i)
}

/// }
fn close_brace(i: &mut TokenSlice) -> PResult<Token> {
    some_brace("}", i)
}

fn comma(i: &mut TokenSlice) -> PResult<()> {
    TokenType::Comma.parse_from(i)?;
    Ok(())
}

fn hash(i: &mut TokenSlice) -> PResult<()> {
    TokenType::Hash.parse_from(i)?;
    Ok(())
}

fn bang(i: &mut TokenSlice) -> PResult<Token> {
    TokenType::Bang.parse_from(i)
}

fn dollar(i: &mut TokenSlice) -> PResult<()> {
    TokenType::Dollar.parse_from(i)?;
    Ok(())
}

fn period(i: &mut TokenSlice) -> PResult<()> {
    TokenType::Period.parse_from(i)?;
    Ok(())
}

fn double_period(i: &mut TokenSlice) -> PResult<Token> {
    any.try_map(|token: Token| {
        if matches!(token.token_type, TokenType::DoublePeriod) {
            Ok(token)
        } else {
            Err(CompilationError::fatal(
                token.as_source_range(),
                format!(
                    "expected a '..' (double period) found {} which is {}",
                    token.value.as_str(),
                    token.token_type
                ),
            ))
        }
    })
    .context(expected("the .. operator, used for array ranges like [0..10]"))
    .parse_next(i)
}

fn colon(i: &mut TokenSlice) -> PResult<Token> {
    TokenType::Colon.parse_from(i)
}

fn semi_colon(i: &mut TokenSlice) -> PResult<Token> {
    TokenType::SemiColon.parse_from(i)
}

fn plus(i: &mut TokenSlice) -> PResult<Token> {
    one_of((TokenType::Operator, "+")).parse_next(i)
}

fn double_colon(i: &mut TokenSlice) -> PResult<Token> {
    TokenType::DoubleColon.parse_from(i)
}

fn equals(i: &mut TokenSlice) -> PResult<Token> {
    one_of((TokenType::Operator, "="))
        .context(expected("the equals operator, ="))
        .parse_next(i)
}

fn question_mark(i: &mut TokenSlice) -> PResult<()> {
    TokenType::QuestionMark.parse_from(i)?;
    Ok(())
}

fn at_sign(i: &mut TokenSlice) -> PResult<Token> {
    TokenType::At.parse_from(i)
}

fn fun(i: &mut TokenSlice) -> PResult<Token> {
    keyword(i, "fn")
}

fn ty(i: &mut TokenSlice) -> PResult<Token> {
    keyword(i, "type")
}

fn keyword(i: &mut TokenSlice, expected: &str) -> PResult<Token> {
    any.try_map(|token: Token| match token.token_type {
        TokenType::Keyword if token.value == expected => Ok(token),
        _ => Err(CompilationError::fatal(
            token.as_source_range(),
            format!("expected '{expected}', found {}", token.value.as_str(),),
        )),
    })
    .parse_next(i)
}

/// Parse a comma, optionally followed by some whitespace.
fn comma_sep(i: &mut TokenSlice) -> PResult<()> {
    (opt(whitespace), comma, opt(whitespace))
        .context(expected("a comma, optionally followed by whitespace"))
        .parse_next(i)?;
    Ok(())
}

/// Parse a `|`, optionally followed by some whitespace.
fn pipe_sep(i: &mut TokenSlice) -> PResult<()> {
    (opt(whitespace), one_of((TokenType::Operator, "|")), opt(whitespace)).parse_next(i)?;
    Ok(())
}

/// Arguments are passed into a function.
fn arguments(i: &mut TokenSlice) -> PResult<Vec<Expr>> {
    separated(0.., expression, comma_sep)
        .context(expected("function arguments"))
        .parse_next(i)
}

fn labeled_argument(i: &mut TokenSlice) -> PResult<LabeledArg> {
    separated_pair(
        terminated(nameable_identifier, opt(whitespace)),
        terminated(one_of((TokenType::Operator, "=")), opt(whitespace)),
        expression,
    )
    .map(|(label, arg)| LabeledArg { label, arg })
    .parse_next(i)
}

/// A type of a function argument.
/// This can be:
/// - a primitive type, e.g. 'number' or 'string' or 'bool'
/// - an array type, e.g. 'number[]' or 'string[]' or 'bool[]'
/// - an object type, e.g. '{x: number, y: number}' or '{name: string, age: number}'
fn argument_type(i: &mut TokenSlice) -> PResult<Node<Type>> {
    let type_ = alt((
        // Object types
        // TODO it is buggy to treat object fields like parameters since the parameters parser assumes a terminating `)`.
        (open_brace, parameters, close_brace).try_map(|(open, params, close)| {
            for p in &params {
                if p.type_.is_none() {
                    return Err(CompilationError::fatal(
                        p.identifier.as_source_range(),
                        "Missing type for field in record type",
                    ));
                }
            }
            Ok(Node::new(
                Type::Object { properties: params },
                open.start,
                close.end,
                open.module_id,
            ))
        }),
        // Array types
        array_type,
        // Primitive or union types
        separated(1.., primitive_type, pipe_sep).map(|mut tys: Vec<_>| {
            if tys.len() == 1 {
                tys.pop().unwrap().map(Type::Primitive)
            } else {
                let start = tys[0].start;
                let module_id = tys[0].module_id;
                let end = tys.last().unwrap().end;
                Node::new(Type::Union { tys }, start, end, module_id)
            }
        }),
    ))
    .parse_next(i)?;

    Ok(type_)
}

fn primitive_type(i: &mut TokenSlice) -> PResult<Node<PrimitiveType>> {
    let ident = identifier(i)?;

    let suffix = opt(delimited(open_paren, uom_for_type, close_paren)).parse_next(i)?;

    let mut result = Node::new(PrimitiveType::Boolean, ident.start, ident.end, ident.module_id);
    result.inner = PrimitiveType::primitive_from_str(&ident.name, suffix).unwrap_or(PrimitiveType::Named(ident));

    if suffix.is_some() {
        ParseContext::warn(CompilationError::err(
            result.as_source_range(),
            "Unit of Measure types are experimental and currently do nothing.",
        ));
    }

    Ok(result)
}

fn array_type(i: &mut TokenSlice) -> PResult<Node<Type>> {
    fn opt_whitespace(i: &mut TokenSlice) -> PResult<()> {
        ignore_whitespace(i);
        Ok(())
    }

    open_bracket(i)?;
    let ty = primitive_type(i)?;
    let len = opt((
        semi_colon,
        opt_whitespace,
        any.try_map(|token: Token| match token.token_type {
            TokenType::Number => {
                let value = token.uint_value().ok_or_else(|| {
                    CompilationError::fatal(
                        token.as_source_range(),
                        format!("Expected unsigned integer literal, found: {}", token.value),
                    )
                })?;

                Ok(value as usize)
            }
            _ => Err(CompilationError::fatal(token.as_source_range(), "invalid array length")),
        }),
        opt(plus),
    ))
    .parse_next(i)?;
    close_bracket(i)?;

    let len = if let Some((tok, _, n, plus)) = len {
        if plus.is_some() {
            if n != 1 {
                return Err(ErrMode::Cut(ContextError::from(CompilationError::fatal(
                    tok.as_source_range(),
                    "Non-empty arrays are specified using `1+`, for a fixed-size array use just an integer",
                ))));
            } else {
                ArrayLen::NonEmpty
            }
        } else {
            ArrayLen::Known(n)
        }
    } else {
        ArrayLen::None
    };

    Ok(ty.map(|ty| Type::Array { ty, len }))
}

fn uom_for_type(i: &mut TokenSlice) -> PResult<NumericSuffix> {
    any.try_map(|t: Token| t.value.parse()).parse_next(i)
}

fn comment(i: &mut TokenSlice) -> PResult<Node<String>> {
    any.verify_map(|token: Token| {
        let value = match token.token_type {
            TokenType::LineComment => token.value,
            TokenType::BlockComment => token.value,
            _ => return None,
        };
        Some(Node::new(value, token.start, token.end, token.module_id))
    })
    .context(expected("Comment"))
    .parse_next(i)
}

fn comments(i: &mut TokenSlice) -> PResult<Node<Vec<String>>> {
    let comments: Vec<Node<String>> = repeat(1.., (comment, opt(whitespace)).map(|(c, _)| c)).parse_next(i)?;
    let start = comments[0].start;
    let module_id = comments[0].module_id;
    let end = comments.last().unwrap().end;
    let inner = comments.into_iter().map(|n| n.inner).collect();
    Ok(Node::new(inner, start, end, module_id))
}

struct ParamDescription {
    labeled: bool,
    arg_name: Token,
    type_: std::option::Option<Node<Type>>,
    default_value: Option<DefaultParamVal>,
    comments: Option<Node<Vec<String>>>,
}

fn parameter(i: &mut TokenSlice) -> PResult<ParamDescription> {
    let (_, comments, found_at_sign, arg_name, question_mark, _, type_, _ws, default_literal) = (
        opt(whitespace),
        opt(comments),
        opt(at_sign),
        any.verify(|token: &Token| !matches!(token.token_type, TokenType::Brace) || token.value != ")"),
        opt(question_mark),
        opt(whitespace),
        opt((colon, opt(whitespace), argument_type).map(|tup| tup.2)),
        opt(whitespace),
        opt((equals, opt(whitespace), literal).map(|(_, _, literal)| literal)),
    )
        .parse_next(i)?;

    Ok(ParamDescription {
        labeled: found_at_sign.is_none(),
        arg_name,
        type_,
        default_value: match (question_mark.is_some(), default_literal) {
            (true, Some(lit)) => Some(DefaultParamVal::Literal(*lit)),
            (true, None) => Some(DefaultParamVal::none()),
            (false, None) => None,
            (false, Some(lit)) => {
                let msg = "You're trying to set a default value for an argument, but only optional arguments can have default values, and this argument is mandatory. Try putting a ? after the argument name, to make the argument optional.";
                let e = CompilationError::fatal((&lit).into(), msg);
                return Err(ErrMode::Backtrack(ContextError::from(e)));
            }
        },
        comments,
    })
}

/// Parameters are declared in a function signature, and used within a function.
fn parameters(i: &mut TokenSlice) -> PResult<Vec<Parameter>> {
    // Get all tokens until the next ), because that ends the parameter list.
    let candidates: Vec<_> = separated(0.., parameter, comma_sep)
        .context(expected("function parameters"))
        .parse_next(i)?;
    opt(comma_sep).parse_next(i)?;

    // Make sure all those tokens are valid parameters.
    let params: Vec<Parameter> = candidates
        .into_iter()
        .map(
            |ParamDescription {
                 labeled,
                 arg_name,
                 type_,
                 default_value,
                 comments,
             }| {
                let mut identifier = Node::<Identifier>::try_from(arg_name)?;
                if let Some(comments) = comments {
                    identifier.comment_start = comments.start;
                    identifier.pre_comments = comments.inner;
                }

                Ok(Parameter {
                    identifier,
                    type_,
                    default_value,
                    labeled,
                    digest: None,
                })
            },
        )
        .collect::<Result<_, _>>()
        .map_err(|e: CompilationError| ErrMode::Backtrack(ContextError::from(e)))?;

    // Make sure the only unlabeled parameter is the first one.
    if let Some(param) = params.iter().skip(1).find(|param| !param.labeled) {
        let source_range = SourceRange::from(param);
        return Err(ErrMode::Cut(ContextError::from(CompilationError::fatal(
            source_range,
            "Only the first parameter can be declared unlabeled",
        ))));
    }

    // Make sure optional parameters are last.
    if let Err(e) = optional_after_required(&params) {
        return Err(ErrMode::Cut(ContextError::from(e)));
    }
    Ok(params)
}

fn optional_after_required(params: &[Parameter]) -> Result<(), CompilationError> {
    let mut found_optional = false;
    for p in params {
        if p.optional() {
            found_optional = true;
        }
        if !p.optional() && found_optional {
            let e = CompilationError::fatal(
                (&p.identifier).into(),
                "mandatory parameters must be declared before optional parameters",
            );
            return Err(e);
        }
    }
    Ok(())
}

/// Introduce a new name, which binds some value.
fn binding_name(i: &mut TokenSlice) -> PResult<Node<Identifier>> {
    identifier
        .context(expected("an identifier, which will be the name of some value"))
        .parse_next(i)
}

/// Either a positional or keyword function call.
fn fn_call_pos_or_kw(i: &mut TokenSlice) -> PResult<Expr> {
    alt((
        fn_call.map(Box::new).map(Expr::CallExpression),
        fn_call_kw.map(Box::new).map(Expr::CallExpressionKw),
    ))
    .parse_next(i)
}

fn labelled_fn_call(i: &mut TokenSlice) -> PResult<Expr> {
    let expr = fn_call_pos_or_kw.parse_next(i)?;

    let label = opt(label).parse_next(i)?;
    match label {
        Some(label) => Ok(Expr::LabelledExpression(Box::new(LabelledExpression::new(expr, label)))),
        None => Ok(expr),
    }
}

fn fn_call(i: &mut TokenSlice) -> PResult<Node<CallExpression>> {
    let fn_name = name(i)?;
    opt(whitespace).parse_next(i)?;
    let _ = terminated(open_paren, opt(whitespace)).parse_next(i)?;
    let args = arguments(i)?;
    let end = preceded(opt(whitespace), close_paren).parse_next(i)?.end;

    let result = Node::new_node(
        fn_name.start,
        end,
        fn_name.module_id,
        CallExpression {
            callee: fn_name,
            arguments: args,
            digest: None,
        },
    );

    let callee_str = result.callee.name.name.to_string();
    if let Some(suggestion) = super::deprecation(&callee_str, DeprecationKind::Function) {
        ParseContext::warn(
            CompilationError::err(
                result.as_source_range(),
                format!("Calling `{}` is deprecated, prefer using `{}`.", callee_str, suggestion),
            )
            .with_suggestion(
                format!("Replace `{}` with `{}`", callee_str, suggestion),
                suggestion,
                None,
                Tag::Deprecated,
            ),
        );
    }

    Ok(result)
}

fn fn_call_kw(i: &mut TokenSlice) -> PResult<Node<CallExpressionKw>> {
    let fn_name = name(i)?;
    opt(whitespace).parse_next(i)?;
    let _ = open_paren.parse_next(i)?;
    ignore_whitespace(i);

    #[allow(clippy::large_enum_variant)]
    enum ArgPlace {
        NonCode(Node<NonCodeNode>),
        LabeledArg(LabeledArg),
        UnlabeledArg(Expr),
    }
    let initial_unlabeled_arg = opt((expression, comma, opt(whitespace)).map(|(arg, _, _)| arg)).parse_next(i)?;
    let args: Vec<_> = repeat(
        0..,
        alt((
            terminated(non_code_node.map(ArgPlace::NonCode), whitespace),
            terminated(labeled_argument, labeled_arg_separator).map(ArgPlace::LabeledArg),
            expression.map(ArgPlace::UnlabeledArg),
        )),
    )
    .parse_next(i)?;
    let (args, non_code_nodes): (Vec<_>, BTreeMap<usize, _>) = args.into_iter().enumerate().try_fold(
        (Vec::new(), BTreeMap::new()),
        |(mut args, mut non_code_nodes), (index, e)| {
            match e {
                ArgPlace::NonCode(x) => {
                    non_code_nodes.insert(index, vec![x]);
                }
                ArgPlace::LabeledArg(x) => {
                    args.push(x);
                }
                ArgPlace::UnlabeledArg(arg) => {
                    let followed_by_equals = peek((opt(whitespace), equals)).parse_next(i).is_ok();
                    let err = if followed_by_equals {
                        ErrMode::Cut(
                            CompilationError::fatal(
                                SourceRange::from(arg),
                                "This argument has a label, but no value. Put some value after the equals sign",
                            )
                            .into(),
                        )
                    } else {
                        ErrMode::Cut(
                            CompilationError::fatal(
                                SourceRange::from(arg),
                                "This argument needs a label, but it doesn't have one",
                            )
                            .into(),
                        )
                    };
                    return Err(err);
                }
            }
            Ok((args, non_code_nodes))
        },
    )?;
    ignore_whitespace(i);
    opt(comma_sep).parse_next(i)?;
    let end = close_paren.parse_next(i)?.end;

    let non_code_meta = NonCodeMeta {
        non_code_nodes,
        ..Default::default()
    };
    let result = Node::new_node(
        fn_name.start,
        end,
        fn_name.module_id,
        CallExpressionKw {
            callee: fn_name,
            unlabeled: initial_unlabeled_arg,
            arguments: args,
            digest: None,
            non_code_meta,
        },
    );

    let callee_str = result.callee.name.name.to_string();
    if let Some(suggestion) = super::deprecation(&callee_str, DeprecationKind::Function) {
        ParseContext::warn(
            CompilationError::err(
                result.as_source_range(),
                format!("Calling `{}` is deprecated, prefer using `{}`.", callee_str, suggestion),
            )
            .with_suggestion(
                format!("Replace `{}` with `{}`", callee_str, suggestion),
                suggestion,
                None,
                Tag::Deprecated,
            ),
        );
    }

    Ok(result)
}

#[cfg(test)]
mod tests {
    use itertools::Itertools;
    use pretty_assertions::assert_eq;

    use super::*;
    use crate::{
        parsing::ast::types::{BodyItem, Expr, VariableKind},
        KclError, ModuleId,
    };

    fn assert_reserved(word: &str) {
        // Try to use it as a variable name.
        let code = format!(r#"{} = 0"#, word);
        let result = crate::parsing::top_level_parse(code.as_str());
        let err = &result.unwrap_errs().next().unwrap();
        // Which token causes the error may change.  In "return = 0", for
        // example, "return" is the problem.
        assert!(
            err.message.starts_with("Unexpected token: ")
                || err.message.starts_with("= is not")
                || err
                    .message
                    .starts_with("Cannot assign a variable to a reserved keyword: "),
            "Error message is: `{}`",
            err.message,
        );
    }

    #[test]
    fn reserved_words() {
        // Since these are stored in a set, we sort to make the tests
        // deterministic.
        for word in crate::parsing::token::RESERVED_WORDS.keys().sorted() {
            assert_reserved(word);
        }
        assert_reserved("import");
    }

    #[test]
    fn parse_args() {
        for (i, (test, expected_len)) in [("someVar", 1), ("5, 3", 2), (r#""a""#, 1)].into_iter().enumerate() {
            let tokens = crate::parsing::token::lex(test, ModuleId::default()).unwrap();
            let actual = match arguments.parse(tokens.as_slice()) {
                Ok(x) => x,
                Err(e) => panic!("Failed test {i}, could not parse function arguments from \"{test}\": {e:?}"),
            };
            assert_eq!(actual.len(), expected_len, "failed test {i}");
        }
    }

    #[test]
    fn parse_names() {
        for (test, expected_len) in [("someVar", 0), ("::foo", 0), ("foo::bar::baz", 2)] {
            let tokens = crate::parsing::token::lex(test, ModuleId::default()).unwrap();
            match name.parse(tokens.as_slice()) {
                Ok(n) => assert_eq!(n.path.len(), expected_len, "Could not parse name from `{test}`: {n:?}"),
                Err(e) => panic!("Could not parse name from `{test}`: {e:?}"),
            }
        }
    }

    #[test]
    fn weird_program_unclosed_paren() {
        let tokens = crate::parsing::token::lex("fn firstPrime(", ModuleId::default()).unwrap();
        let tokens = tokens.as_slice();
        let last = tokens.last().unwrap().as_source_range();
        let err: CompilationError = program.parse(tokens).unwrap_err().into();
        assert_eq!(err.source_range, last);
        // TODO: Better comment. This should explain the compiler expected ) because the user had started declaring the function's parameters.
        // Part of https://github.com/KittyCAD/modeling-app/issues/784
        assert_eq!(err.message, "Unexpected end of file. The compiler expected )");
    }

    #[test]
    fn weird_program_just_a_pipe() {
        let tokens = crate::parsing::token::lex("|", ModuleId::default()).unwrap();
        let err: CompilationError = program.parse(tokens.as_slice()).unwrap_err().into();
        assert_eq!(err.source_range, SourceRange::new(0, 1, ModuleId::default()));
        assert_eq!(err.message, "Unexpected token: |");
    }

    #[test]
    fn parse_binary_expressions() {
        for (i, test_program) in ["1 + 2 + 3"].into_iter().enumerate() {
            let tokens = crate::parsing::token::lex(test_program, ModuleId::default()).unwrap();
            let _actual = match binary_expression.parse_next(&mut tokens.as_slice()) {
                Ok(x) => x,
                Err(e) => panic!("Failed test {i}, could not parse binary expressions from \"{test_program}\": {e:?}"),
            };
        }
    }

    #[test]
    fn test_vardec_no_keyword() {
        let tokens = crate::parsing::token::lex("x = 4", ModuleId::default()).unwrap();
        let vardec = declaration(&mut tokens.as_slice()).unwrap();
        assert_eq!(vardec.inner.kind, VariableKind::Const);
        let vardec = &vardec.declaration;
        assert_eq!(vardec.id.name, "x");
        let Expr::Literal(init_val) = &vardec.init else {
            panic!("weird init value")
        };
        assert_eq!(init_val.raw, "4");
    }

    #[test]
    fn test_negative_operands() {
        let tokens = crate::parsing::token::lex("-leg2", ModuleId::default()).unwrap();
        let _s = operand.parse_next(&mut tokens.as_slice()).unwrap();
    }

    #[test]
    fn test_comments_in_function1() {
        let test_program = r#"() {
            // comment 0
            a = 1
            // comment 1
            b = 2
            /// comment 2
            return 1
        }"#;
        let tokens = crate::parsing::token::lex(test_program, ModuleId::default()).unwrap();
        let expr = function_decl.map(|t| t.0).parse_next(&mut tokens.as_slice()).unwrap();
        assert_eq!(expr.params, vec![]);
        let comment_start = expr.body.body[0].get_comments();
        let comment0 = expr.body.body[1].get_comments();
        let comment1 = expr.body.body[2].get_comments();
        assert_eq!(comment_start, vec!["// comment 0".to_owned()]);
        assert_eq!(comment0, vec!["// comment 1".to_owned()]);
        assert_eq!(comment1, vec!["/// comment 2".to_owned()]);
    }

    #[test]
    fn test_comments_in_function2() {
        let test_program = r#"() {
  yo = { a = { b = { c = '123' } } } /* block
comment */
}"#;
        let tokens = crate::parsing::token::lex(test_program, ModuleId::default()).unwrap();
        let expr = function_decl.map(|t| t.0).parse_next(&mut tokens.as_slice()).unwrap();
        let comment0 = &expr.body.non_code_meta.non_code_nodes.get(&0).unwrap()[0];
        assert_eq!(comment0.value(), "block\ncomment");
    }

    #[test]
    fn test_comment_at_start_of_program() {
        let test_program = r#"
/* comment at start */

mySk1 = startSketchOn(XY)
  |> startProfileAt([0, 0], %)"#;
        let tokens = crate::parsing::token::lex(test_program, ModuleId::default()).unwrap();
        let program = program.parse(tokens.as_slice()).unwrap();
        let mut starting_comments = program.inner.non_code_meta.start_nodes;
        assert_eq!(starting_comments.len(), 2);
        let start0 = starting_comments.remove(0);
        let start1 = starting_comments.remove(0);
        assert_eq!(
            start0.value,
            NonCodeValue::BlockComment {
                value: "comment at start".to_owned(),
                style: CommentStyle::Block
            }
        );
        assert_eq!(start1.value, NonCodeValue::NewLine);
    }

    #[test]
    fn test_comment_in_pipe() {
        let tokens = crate::parsing::token::lex(r#"x = y() |> /*hi*/ z(%)"#, ModuleId::default()).unwrap();
        let mut body = program.parse(tokens.as_slice()).unwrap().inner.body;
        let BodyItem::VariableDeclaration(item) = body.remove(0) else {
            panic!("expected vardec");
        };
        let val = item.inner.declaration.inner.init;
        let Expr::PipeExpression(pipe) = val else {
            panic!("expected pipe");
        };
        let mut noncode = pipe.inner.non_code_meta;
        assert_eq!(noncode.non_code_nodes.len(), 1);
        let comment = noncode.non_code_nodes.remove(&0).unwrap().pop().unwrap();
        assert_eq!(
            comment.value,
            NonCodeValue::BlockComment {
                value: "hi".to_owned(),
                style: CommentStyle::Block
            }
        );
    }

    #[test]
    fn test_whitespace_in_function() {
        let test_program = r#"() {
            return sg
            return sg
          }"#;
        let tokens = crate::parsing::token::lex(test_program, ModuleId::default()).unwrap();
        let _expr = function_decl.parse_next(&mut tokens.as_slice()).unwrap();
    }

    #[test]
    fn test_empty_lines_in_function() {
        let test_program = "() {

                return 2
            }";
        let module_id = ModuleId::from_usize(1);
        let tokens = crate::parsing::token::lex(test_program, module_id).unwrap();
        let expr = function_decl.map(|t| t.0).parse_next(&mut tokens.as_slice()).unwrap();
        assert_eq!(
            expr.body.non_code_meta.start_nodes,
            vec![Node::new(
                NonCodeNode {
                    value: NonCodeValue::NewLine,
                    digest: None
                },
                4,
                22,
                module_id,
            )]
        );
    }

    #[test]
    fn inline_comment_pipe_expression() {
        let test_input = r#"a(XY)
        |> b(%)
        |> c(%) // inline-comment
        |> d(%)"#;

        let tokens = crate::parsing::token::lex(test_input, ModuleId::default()).unwrap();
        let Node {
            inner: PipeExpression {
                body, non_code_meta, ..
            },
            ..
        } = pipe_expression.parse_next(&mut tokens.as_slice()).unwrap();
        assert_eq!(non_code_meta.non_code_nodes.len(), 1);
        assert_eq!(
            non_code_meta.non_code_nodes.get(&2).unwrap()[0].value,
            NonCodeValue::InlineComment {
                value: "inline-comment".to_owned(),
                style: CommentStyle::Line
            }
        );
        assert_eq!(body.len(), 4);
    }

    #[test]
    fn many_comments() {
        let test_program = r#"// this is a comment
  yo = { a = { b = { c = '123' } } } /* block
  comment */

  key = 'c'
  // this is also a comment
  return things
"#;

        let module_id = ModuleId::default();
        let tokens = crate::parsing::token::lex(test_program, module_id).unwrap();
        let Program {
            body, non_code_meta, ..
        } = function_body.parse(tokens.as_slice()).unwrap().inner;
        assert_eq!(body[0].get_comments(), vec!["// this is a comment".to_owned()],);

        assert_eq!(
            Some(&vec![
                Node::new(
                    NonCodeNode {
                        value: NonCodeValue::InlineComment {
                            value: "block\n  comment".to_owned(),
                            style: CommentStyle::Block
                        },
                        digest: None,
                    },
                    57,
                    79,
                    module_id,
                ),
                Node::new(
                    NonCodeNode {
                        value: NonCodeValue::NewLine,
                        digest: None,
                    },
                    79,
                    83,
                    module_id,
                )
            ]),
            non_code_meta.non_code_nodes.get(&0),
        );

        assert_eq!(body[2].get_comments(), vec!["// this is also a comment".to_owned()],);
    }

    #[test]
    fn inline_block_comments() {
        let test_program = r#"yo = 3 /* block
  comment */
  return 1"#;

        let tokens = crate::parsing::token::lex(test_program, ModuleId::default()).unwrap();
        let actual = program.parse(tokens.as_slice()).unwrap();
        assert_eq!(actual.non_code_meta.non_code_nodes.len(), 1);
        assert_eq!(
            actual.non_code_meta.non_code_nodes.get(&0).unwrap()[0].value,
            NonCodeValue::InlineComment {
                value: "block\n  comment".to_owned(),
                style: CommentStyle::Block
            }
        );
    }

    #[test]
    fn test_bracketed_binary_expression() {
        let input = "(2 - 3)";
        let tokens = crate::parsing::token::lex(input, ModuleId::default()).unwrap();
        let actual = match binary_expr_in_parens.parse(tokens.as_slice()) {
            Ok(x) => x,
            Err(e) => panic!("{e:?}"),
        };
        assert_eq!(actual.operator, BinaryOperator::Sub);
    }

    #[test]
    fn test_arg() {
        for input in [
            "( sigmaAllow * width )",
            "6 / ( sigmaAllow * width )",
            "sqrt(distance * p * FOS * 6 / ( sigmaAllow * width ))",
        ] {
            let tokens = crate::parsing::token::lex(input, ModuleId::default()).unwrap();
            let _actual = match expression.parse(tokens.as_slice()) {
                Ok(x) => x,
                Err(e) => panic!("{e:?}"),
            };
        }
    }

    #[test]
    fn test_arithmetic() {
        let input = "1 * (2 - 3)";
        let tokens = crate::parsing::token::lex(input, ModuleId::default()).unwrap();
        // The RHS should be a binary expression.
        let actual = binary_expression.parse(tokens.as_slice()).unwrap();
        assert_eq!(actual.operator, BinaryOperator::Mul);
        let BinaryPart::BinaryExpression(rhs) = actual.inner.right else {
            panic!("Expected RHS to be another binary expression");
        };
        assert_eq!(rhs.operator, BinaryOperator::Sub);
        match &rhs.right {
            BinaryPart::Literal(lit) => {
                assert!(lit.start == 9 && lit.end == 10);
                assert!(
                    lit.value
                        == LiteralValue::Number {
                            value: 3.0,
                            suffix: NumericSuffix::None
                        }
                        && &lit.raw == "3"
                        && lit.digest.is_none()
                );
            }
            _ => panic!(),
        }
    }

    #[test]
    fn assign_brackets() {
        for (i, test_input) in [
            "thickness_squared = (1 + 1)",
            "thickness_squared = ( 1 + 1)",
            "thickness_squared = (1 + 1 )",
            "thickness_squared = ( 1 + 1 )",
        ]
        .into_iter()
        .enumerate()
        {
            let tokens = crate::parsing::token::lex(test_input, ModuleId::default()).unwrap();
            let actual = match declaration.parse(tokens.as_slice()) {
                Err(e) => panic!("Could not parse test {i}: {e:#?}"),
                Ok(a) => a,
            };
            let Expr::BinaryExpression(_expr) = &actual.declaration.inner.init else {
                panic!(
                    "Expected test {i} to be a binary expression but it wasn't, it was {:?}",
                    actual.declaration
                );
            };
            // TODO: check both sides are 1... probably not necessary but should do.
        }
    }

    #[test]
    fn test_function_call() {
        for (i, test_input) in ["x = f(1)", "x = f( 1 )"].into_iter().enumerate() {
            let tokens = crate::parsing::token::lex(test_input, ModuleId::default()).unwrap();
            let _actual = match declaration.parse(tokens.as_slice()) {
                Err(e) => panic!("Could not parse test {i}: {e:#?}"),
                Ok(a) => a,
            };
        }
    }

    #[test]
    fn test_nested_arithmetic() {
        let input = "1 * ((2 - 3) / 4)";
        let tokens = crate::parsing::token::lex(input, ModuleId::default()).unwrap();
        // The RHS should be a binary expression.
        let outer = binary_expression.parse(tokens.as_slice()).unwrap();
        assert_eq!(outer.operator, BinaryOperator::Mul);
        let BinaryPart::BinaryExpression(middle) = outer.inner.right else {
            panic!("Expected RHS to be another binary expression");
        };

        assert_eq!(middle.operator, BinaryOperator::Div);
        let BinaryPart::BinaryExpression(inner) = middle.inner.left else {
            panic!("expected nested binary expression");
        };
        assert_eq!(inner.operator, BinaryOperator::Sub);
    }

    #[test]
    fn binary_expression_ignores_whitespace() {
        let tests = ["1 - 2", "1- 2", "1 -2", "1-2"];
        for test in tests {
            let tokens = crate::parsing::token::lex(test, ModuleId::default()).unwrap();
            let actual = binary_expression.parse(tokens.as_slice()).unwrap();
            assert_eq!(actual.operator, BinaryOperator::Sub);
            let BinaryPart::Literal(left) = actual.inner.left else {
                panic!("should be expression");
            };
            assert_eq!(
                left.value,
                LiteralValue::Number {
                    value: 1.0,
                    suffix: NumericSuffix::None
                }
            );
            let BinaryPart::Literal(right) = actual.inner.right else {
                panic!("should be expression");
            };
            assert_eq!(
                right.value,
                LiteralValue::Number {
                    value: 2.0,
                    suffix: NumericSuffix::None
                }
            );
        }
    }

    #[test]
    fn some_pipe_expr() {
        let test_program = r#"x()
        |> y(%) /* this is
        a comment
        spanning a few lines */
        |> z(%)"#;
        let tokens = crate::parsing::token::lex(test_program, ModuleId::default()).unwrap();
        let actual = pipe_expression.parse(tokens.as_slice()).unwrap();
        let n = actual.non_code_meta.non_code_nodes.len();
        assert_eq!(n, 1, "expected one comment in pipe expression but found {n}");
        let nc = &actual.non_code_meta.non_code_nodes.get(&1).unwrap()[0];
        assert!(nc.value().starts_with("this"));
        assert!(nc.value().ends_with("lines"));
    }

    #[test]
    fn comments_in_pipe_expr() {
        for (i, test_program) in [
            r#"y() |> /*hi*/ z(%)"#,
            "1 |>/*hi*/ f(%)",
            r#"y() |> /*hi*/ z(%)"#,
            "1 /*hi*/ |> f(%)",
            "1
        // Hi
        |> f(%)",
            "1
        /* Hi 
        there
        */
        |> f(%)",
        ]
        .into_iter()
        .enumerate()
        {
            let tokens = crate::parsing::token::lex(test_program, ModuleId::default()).unwrap();
            let actual = pipe_expression.parse(tokens.as_slice());
            assert!(actual.is_ok(), "could not parse test {i}, '{test_program}'");
            let actual = actual.unwrap();
            let n = actual.non_code_meta.non_code_nodes.len();
            assert_eq!(n, 1, "expected one comment in pipe expression but found {n}",)
        }
    }

    #[test]
    fn comments() {
        let module_id = ModuleId::from_usize(1);
        for (i, (test_program, expected)) in [
            (
                "//hi",
                Node::new(
                    NonCodeNode {
                        value: NonCodeValue::BlockComment {
                            value: "hi".to_owned(),
                            style: CommentStyle::Line,
                        },
                        digest: None,
                    },
                    0,
                    4,
                    module_id,
                ),
            ),
            (
                "/*hello*/",
                Node::new(
                    NonCodeNode {
                        value: NonCodeValue::BlockComment {
                            value: "hello".to_owned(),
                            style: CommentStyle::Block,
                        },
                        digest: None,
                    },
                    0,
                    9,
                    module_id,
                ),
            ),
            (
                "/* hello */",
                Node::new(
                    NonCodeNode {
                        value: NonCodeValue::BlockComment {
                            value: "hello".to_owned(),
                            style: CommentStyle::Block,
                        },
                        digest: None,
                    },
                    0,
                    11,
                    module_id,
                ),
            ),
            (
                "/* \nhello */",
                Node::new(
                    NonCodeNode {
                        value: NonCodeValue::BlockComment {
                            value: "hello".to_owned(),
                            style: CommentStyle::Block,
                        },
                        digest: None,
                    },
                    0,
                    12,
                    module_id,
                ),
            ),
            (
                "
                /* hello */",
                Node::new(
                    NonCodeNode {
                        value: NonCodeValue::BlockComment {
                            value: "hello".to_owned(),
                            style: CommentStyle::Block,
                        },
                        digest: None,
                    },
                    0,
                    29,
                    module_id,
                ),
            ),
            (
                // Empty line with trailing whitespace
                "
  
                /* hello */",
                Node::new(
                    NonCodeNode {
                        value: NonCodeValue::NewLineBlockComment {
                            value: "hello".to_owned(),
                            style: CommentStyle::Block,
                        },
                        digest: None,
                    },
                    0,
                    32,
                    module_id,
                ),
            ),
            (
                // Empty line, no trailing whitespace
                "

                /* hello */",
                Node::new(
                    NonCodeNode {
                        value: NonCodeValue::NewLineBlockComment {
                            value: "hello".to_owned(),
                            style: CommentStyle::Block,
                        },
                        digest: None,
                    },
                    0,
                    30,
                    module_id,
                ),
            ),
            (
                r#"/* block
                    comment */"#,
                Node::new(
                    NonCodeNode {
                        value: NonCodeValue::BlockComment {
                            value: "block\n                    comment".to_owned(),
                            style: CommentStyle::Block,
                        },
                        digest: None,
                    },
                    0,
                    39,
                    module_id,
                ),
            ),
        ]
        .into_iter()
        .enumerate()
        {
            let tokens = crate::parsing::token::lex(test_program, module_id).unwrap();
            let actual = non_code_node.parse(tokens.as_slice());
            assert!(actual.is_ok(), "could not parse test {i}: {actual:#?}");
            let actual = actual.unwrap();
            assert_eq!(actual, expected, "failed test {i}");
        }
    }

    #[test]
    fn recognize_invalid_params() {
        let test_fn = "(let) => { return 1 }";
        let module_id = ModuleId::from_usize(2);
        let tokens = crate::parsing::token::lex(test_fn, module_id).unwrap();
        let err = function_decl.parse(tokens.as_slice()).unwrap_err().into_inner();
        let cause = err.cause.unwrap();
        // This is the token `let`
        assert_eq!(cause.source_range, SourceRange::new(1, 4, ModuleId::from_usize(2)));
        assert_eq!(cause.message, "Cannot assign a variable to a reserved keyword: let");
    }

    #[test]
    fn comment_in_string() {
        let string_literal = r#""
           // a comment
             ""#;
        let tokens = crate::parsing::token::lex(string_literal, ModuleId::default()).unwrap();
        let parsed_literal = literal.parse(tokens.as_slice()).unwrap();
        assert_eq!(
            parsed_literal.value,
            "
           // a comment
             "
            .into()
        );
    }

    #[test]
    fn pipes_on_pipes_minimal() {
        let test_program = r#"startSketchOn(XY)
        |> startProfileAt([0, 0], %)
        |> line(endAbsolute = [0, -0]) // MoveRelative

        "#;
        let tokens = crate::parsing::token::lex(test_program, ModuleId::default()).unwrap();
        let tokens = &mut tokens.as_slice();
        let _actual = pipe_expression.parse_next(tokens).unwrap();
        assert_eq!(tokens.first().unwrap().token_type, TokenType::Whitespace);
    }

    #[test]
    fn test_pipes_on_pipes() {
        let test_program = include_str!("../../e2e/executor/inputs/pipes_on_pipes.kcl");
        let tokens = crate::parsing::token::lex(test_program, ModuleId::default()).unwrap();
        let _ = run_parser(tokens.as_slice()).unwrap();
    }

    #[test]
    fn test_cube() {
        let test_program = include_str!("../../e2e/executor/inputs/cube.kcl");
        let tokens = crate::parsing::token::lex(test_program, ModuleId::default()).unwrap();
        match program.parse(tokens.as_slice()) {
            Ok(_) => {}
            Err(e) => {
                panic!("{e:#?}");
            }
        }
    }

    #[test]
    fn test_parameter_list() {
        let tests = [
            ("", vec![]),
            ("a", vec!["a"]),
            ("a, b", vec!["a", "b"]),
            ("a,b", vec!["a", "b"]),
        ];
        for (i, (input, expected)) in tests.into_iter().enumerate() {
            let tokens = crate::parsing::token::lex(input, ModuleId::default()).unwrap();
            let actual = parameters.parse(tokens.as_slice());
            assert!(actual.is_ok(), "could not parse test {i}");
            let actual_ids: Vec<_> = actual.unwrap().into_iter().map(|p| p.identifier.inner.name).collect();
            assert_eq!(actual_ids, expected);
        }
    }

    #[test]
    fn test_user_function() {
        let input = "() {
            return 2
        }";

        let tokens = crate::parsing::token::lex(input, ModuleId::default()).unwrap();
        let actual = function_decl.parse(tokens.as_slice());
        assert!(actual.is_ok(), "could not parse test function");
    }

    #[test]
    fn test_declaration() {
        let tests = ["myVar = 5", "myVar=5", "myVar =5", "myVar= 5"];
        for test in tests {
            // Run the original parser
            let tokens = crate::parsing::token::lex(test, ModuleId::default()).unwrap();
            let mut expected_body = crate::parsing::parse_tokens(tokens.clone()).unwrap().inner.body;
            assert_eq!(expected_body.len(), 1);
            let BodyItem::VariableDeclaration(expected) = expected_body.pop().unwrap() else {
                panic!("Expected variable declaration");
            };

            // Run the second parser, check it matches the first parser.
            let actual = declaration.parse(tokens.as_slice()).unwrap();
            assert_eq!(expected, actual);

            // Inspect its output in more detail.
            assert_eq!(actual.inner.kind, VariableKind::Const);
            assert_eq!(actual.start, 0);
            let decl = &actual.declaration;
            assert_eq!(decl.id.name, "myVar");
            let Expr::Literal(value) = &decl.inner.init else {
                panic!("value should be a literal")
            };
            assert_eq!(value.end, test.len());
            assert_eq!(value.raw, "5");
        }
    }

    #[test]
    fn test_math_parse() {
        let module_id = ModuleId::default();
        let actual = crate::parsing::parse_str(r#"5 + "a""#, module_id).unwrap().inner.body;
        let expr = Node::boxed(
            BinaryExpression {
                operator: BinaryOperator::Add,
                left: BinaryPart::Literal(Box::new(Node::new(
                    Literal {
                        value: LiteralValue::Number {
                            value: 5.0,
                            suffix: NumericSuffix::None,
                        },
                        raw: "5".to_owned(),
                        digest: None,
                    },
                    0,
                    1,
                    module_id,
                ))),
                right: BinaryPart::Literal(Box::new(Node::new(
                    Literal {
                        value: "a".into(),
                        raw: r#""a""#.to_owned(),
                        digest: None,
                    },
                    4,
                    7,
                    module_id,
                ))),
                digest: None,
            },
            0,
            7,
            module_id,
        );
        let expected = vec![BodyItem::ExpressionStatement(Node::new(
            ExpressionStatement {
                expression: Expr::BinaryExpression(expr),
                digest: None,
            },
            0,
            7,
            module_id,
        ))];
        assert_eq!(expected, actual);
    }

    #[test]
    fn test_abstract_syntax_tree() {
        let code = "5 +6";
        let module_id = ModuleId::default();
        let result = crate::parsing::parse_str(code, module_id).unwrap();
        let expected_result = Node::new(
            Program {
                body: vec![BodyItem::ExpressionStatement(Node::new(
                    ExpressionStatement {
                        expression: Expr::BinaryExpression(Node::boxed(
                            BinaryExpression {
                                left: BinaryPart::Literal(Box::new(Node::new(
                                    Literal {
                                        value: LiteralValue::Number {
                                            value: 5.0,
                                            suffix: NumericSuffix::None,
                                        },
                                        raw: "5".to_string(),
                                        digest: None,
                                    },
                                    0,
                                    1,
                                    module_id,
                                ))),
                                operator: BinaryOperator::Add,
                                right: BinaryPart::Literal(Box::new(Node::new(
                                    Literal {
                                        value: LiteralValue::Number {
                                            value: 6.0,
                                            suffix: NumericSuffix::None,
                                        },
                                        raw: "6".to_string(),
                                        digest: None,
                                    },
                                    3,
                                    4,
                                    module_id,
                                ))),
                                digest: None,
                            },
                            0,
                            4,
                            module_id,
                        )),
                        digest: None,
                    },
                    0,
                    4,
                    module_id,
                ))],
                shebang: None,
                non_code_meta: NonCodeMeta::default(),
                inner_attrs: Vec::new(),
                digest: None,
            },
            0,
            4,
            module_id,
        );

        assert_eq!(result, expected_result);
    }

    #[test]
    fn test_empty_file() {
        let some_program_string = r#""#;
        let result = crate::parsing::top_level_parse(some_program_string);
        assert!(result.is_ok());
    }

    #[track_caller]
    fn assert_no_err(p: &str) -> (Node<Program>, Vec<CompilationError>) {
        let result = crate::parsing::top_level_parse(p);
        let result = result.0.unwrap();
        assert!(result.1.iter().all(|e| !e.severity.is_err()), "found: {:#?}", result.1);
        (result.0.unwrap(), result.1)
    }

    #[track_caller]
    fn assert_no_fatal(p: &str) -> (Node<Program>, Vec<CompilationError>) {
        let result = crate::parsing::top_level_parse(p);
        let result = result.0.unwrap();
        assert!(
            result.1.iter().all(|e| e.severity != Severity::Fatal),
            "found: {:#?}",
            result.1
        );
        (result.0.unwrap(), result.1)
    }

    #[track_caller]
    fn assert_err(p: &str, msg: &str, src_expected: [usize; 2]) {
        let result = crate::parsing::top_level_parse(p);
        let err = result.unwrap_errs().next().unwrap();
        assert!(
            err.message.starts_with(msg),
            "Found `{}`, expected `{msg}`",
            err.message
        );
        let src_actual = [err.source_range.start(), err.source_range.end()];
        assert_eq!(
            src_expected,
            src_actual,
            "expected error would highlight `{}` but it actually highlighted `{}`",
            &p[src_expected[0]..src_expected[1]],
            &p[src_actual[0]..src_actual[1]],
        );
    }

    #[track_caller]
    fn assert_err_contains(p: &str, expected: &str) {
        let result = crate::parsing::top_level_parse(p);
        let err = &result.unwrap_errs().next().unwrap().message;
        assert!(err.contains(expected), "actual='{err}'");
    }

    #[test]
    fn test_parse_half_pipe_small() {
        assert_err_contains(
            "secondExtrude = startSketchOn('XY')
  |> startProfileAt([0,0], %)
  |",
            "Unexpected token: |",
        );
    }

    #[test]
    fn test_parse_member_expression_double_nested_braces() {
        let code = r#"prop = yo["one"][two]"#;
        crate::parsing::top_level_parse(code).unwrap();
    }

    #[test]
    fn test_parse_member_expression_binary_expression_period_number_first() {
        let code = r#"obj = { a: 1, b: 2 }
height = 1 - obj.a"#;
        crate::parsing::top_level_parse(code).unwrap();
    }

    #[test]
    fn test_parse_member_expression_allowed_type_in_expression() {
        let code = r#"obj = { thing: 1 }
startSketchOn(obj.sketch)"#;

        crate::parsing::top_level_parse(code).unwrap();
    }

    #[test]
    fn test_parse_member_expression_binary_expression_brace_number_first() {
        let code = r#"obj = { a: 1, b: 2 }
height = 1 - obj["a"]"#;
        crate::parsing::top_level_parse(code).unwrap();
    }

    #[test]
    fn test_parse_member_expression_binary_expression_brace_number_second() {
        let code = r#"obj = { a: 1, b: 2 }
height = obj["a"] - 1"#;
        crate::parsing::top_level_parse(code).unwrap();
    }

    #[test]
    fn test_parse_member_expression_binary_expression_in_array_number_first() {
        let code = r#"obj = { a: 1, b: 2 }
height = [1 - obj["a"], 0]"#;
        crate::parsing::top_level_parse(code).unwrap();
    }

    #[test]
    fn test_parse_member_expression_binary_expression_in_array_number_second() {
        let code = r#"obj = { a: 1, b: 2 }
height = [obj["a"] - 1, 0]"#;
        crate::parsing::top_level_parse(code).unwrap();
    }

    #[test]
    fn test_parse_member_expression_binary_expression_in_array_number_second_missing_space() {
        let code = r#"obj = { a: 1, b: 2 }
height = [obj["a"] -1, 0]"#;
        crate::parsing::top_level_parse(code).unwrap();
    }

    #[test]
    fn test_anon_fn() {
        crate::parsing::top_level_parse("foo(42, fn(x) { return x + 1 })").unwrap();
    }

    #[test]
    fn test_annotation_fn() {
        crate::parsing::top_level_parse(
            r#"fn foo() {
  @annotated
  return 1
}"#,
        )
        .unwrap();
    }

    #[test]
    fn test_annotation_settings() {
        crate::parsing::top_level_parse("@settings(units = mm)").unwrap();
    }

    #[test]
    fn test_anon_fn_no_fn() {
        assert_err_contains("foo(42, (x) { return x + 1 })", "Anonymous function requires `fn`");
    }

    #[test]
    fn test_parse_half_pipe() {
        let code = "height = 10

firstExtrude = startSketchOn('XY')
  |> startProfileAt([0,0], %)
  |> line([0, 8], %)
  |> line([20, 0], %)
  |> line([0, -8], %)
  |> close()
  |> extrude(length=2)

secondExtrude = startSketchOn('XY')
  |> startProfileAt([0,0], %)
  |";
        assert_err_contains(code, "Unexpected token: |");
    }

    #[test]
    fn test_parse_greater_bang() {
        assert_err(">!", "Unexpected token: >", [0, 1]);
    }

    #[test]
    fn test_parse_unlabeled_param_not_allowed() {
        assert_err(
            "fn f(@x, @y) { return 1 }",
            "Only the first parameter can be declared unlabeled",
            [9, 11],
        );
        assert_err(
            "fn f(x, @y) { return 1 }",
            "Only the first parameter can be declared unlabeled",
            [8, 10],
        );
    }

    #[test]
    fn test_parse_z_percent_parens() {
        assert_err("z%)", "Unexpected token: %", [1, 2]);
    }

    #[test]
    fn test_parse_parens_unicode() {
        let result = crate::parsing::top_level_parse("(ޜ");
        let KclError::Lexical(details) = result.0.unwrap_err() else {
            panic!();
        };
        // TODO: Better errors when program cannot tokenize.
        // https://github.com/KittyCAD/modeling-app/issues/696
        assert_eq!(details.message, "found unknown token 'ޜ'");
        assert_eq!(details.source_ranges[0].start(), 1);
        assert_eq!(details.source_ranges[0].end(), 2);
    }

    #[test]
    fn test_parse_negative_in_array_binary_expression() {
        let code = r#"leg1 = 5
thickness = 0.56

bracket = [-leg2 + thickness, 0]
"#;
        crate::parsing::top_level_parse(code).unwrap();
    }

    #[test]
    fn test_parse_nested_open_brackets() {
        let _ = crate::parsing::top_level_parse(
            r#"
z(-[["#,
        )
        .unwrap_errs();
    }

    #[test]
    fn test_parse_weird_new_line_function() {
        assert_err(
            r#"z
(--#"#,
            "Unexpected token: (",
            [2, 3],
        );
    }

    #[test]
    fn test_parse_weird_lots_of_fancy_brackets() {
        assert_err(
            r#"zz({{{{{{{{)iegAng{{{{{{{##"#,
            "Encountered an unexpected character(s) before finding a closing brace(`}`) for the object",
            [3, 4],
        );
    }

    #[test]
    fn test_parse_weird_close_before_open() {
        assert_err_contains(
            r#"fn)n
e
["#,
            "expected whitespace, found ')' which is brace",
        );
    }

    #[test]
    fn test_parse_weird_close_before_nada() {
        assert_err_contains(r#"fn)n-"#, "expected whitespace, found ')' which is brace");
    }

    #[test]
    fn test_parse_weird_lots_of_slashes() {
        assert_err_contains(
            r#"J///////////o//+///////////P++++*++++++P///////˟
++4"#,
            "Unexpected token: +",
        );
    }

    #[test]
    fn test_optional_param_order() {
        for (i, (params, expect_ok)) in [
            (
                vec![Parameter {
                    identifier: Node::no_src(Identifier {
                        name: "a".to_owned(),
                        digest: None,
                    }),
                    type_: None,
                    default_value: Some(DefaultParamVal::none()),
                    labeled: true,
                    digest: None,
                }],
                true,
            ),
            (
                vec![Parameter {
                    identifier: Node::no_src(Identifier {
                        name: "a".to_owned(),
                        digest: None,
                    }),
                    type_: None,
                    default_value: None,
                    labeled: true,
                    digest: None,
                }],
                true,
            ),
            (
                vec![
                    Parameter {
                        identifier: Node::no_src(Identifier {
                            name: "a".to_owned(),
                            digest: None,
                        }),
                        type_: None,
                        default_value: None,
                        labeled: true,
                        digest: None,
                    },
                    Parameter {
                        identifier: Node::no_src(Identifier {
                            name: "b".to_owned(),
                            digest: None,
                        }),
                        type_: None,
                        default_value: Some(DefaultParamVal::none()),
                        labeled: true,
                        digest: None,
                    },
                ],
                true,
            ),
            (
                vec![
                    Parameter {
                        identifier: Node::no_src(Identifier {
                            name: "a".to_owned(),
                            digest: None,
                        }),
                        type_: None,
                        default_value: Some(DefaultParamVal::none()),
                        labeled: true,
                        digest: None,
                    },
                    Parameter {
                        identifier: Node::no_src(Identifier {
                            name: "b".to_owned(),
                            digest: None,
                        }),
                        type_: None,
                        default_value: None,
                        labeled: true,
                        digest: None,
                    },
                ],
                false,
            ),
        ]
        .into_iter()
        .enumerate()
        {
            let actual = optional_after_required(&params);
            assert_eq!(actual.is_ok(), expect_ok, "failed test {i}");
        }
    }

    #[test]
    fn test_error_keyword_in_variable() {
        assert_err(
            r#"const let = "thing""#,
            "Cannot assign a variable to a reserved keyword: let",
            [6, 9],
        );
    }

    #[test]
    fn test_error_keyword_in_fn_name() {
        assert_err(
            r#"fn let = () {}"#,
            "Cannot assign a variable to a reserved keyword: let",
            [3, 6],
        );
    }

    #[test]
    fn test_error_keyword_in_fn_args() {
        assert_err(
            r#"fn thing = (let) => {
    return 1
}"#,
            "Cannot assign a variable to a reserved keyword: let",
            [12, 15],
        )
    }

    #[test]
    fn bad_imports() {
        assert_err(
            r#"import cube from "../cube.kcl""#,
            "import path may only contain alphanumeric characters, underscore, hyphen, and period. KCL files in other directories are not yet supported.",
            [17, 30],
        );
        assert_err(
            r#"import * as foo from "dsfs""#,
            "as is not the 'from' keyword",
            [9, 11],
        );
        assert_err(
            r#"import a from "dsfs" as b"#,
            "unsupported import path format",
            [14, 20],
        );
        assert_err(
            r#"import * from "dsfs" as b"#,
            "unsupported import path format",
            [14, 20],
        );
        assert_err(r#"import a from b"#, "invalid string literal", [14, 15]);
        assert_err(r#"import * "dsfs""#, "\"dsfs\" is not the 'from' keyword", [9, 15]);
        assert_err(r#"import from "dsfs""#, "\"dsfs\" is not the 'from' keyword", [12, 18]);
        assert_err(r#"import "dsfs.kcl" as *"#, "Unexpected token: as", [18, 20]);
        assert_err(r#"import "dsfs""#, "unsupported import path format", [7, 13]);
        assert_err(
            r#"import "foo.bar.kcl""#,
            "import path is not a valid identifier and must be aliased.",
            [7, 20],
        );
        assert_err(
            r#"import "_foo.kcl""#,
            "import path is not a valid identifier and must be aliased.",
            [7, 17],
        );
        assert_err(
            r#"import "foo-bar.kcl""#,
            "import path is not a valid identifier and must be aliased.",
            [7, 20],
        );
    }

    #[test]
    fn std_fn_decl() {
        let code = r#"/// Compute the cosine of a number (in radians).
///
/// ```
/// exampleSketch = startSketchOn("XZ")
///   |> startProfileAt([0, 0], %)
///   |> angledLine({
///     angle = 30,
///     length = 3 / cos(toRadians(30)),
///   }, %)
///   |> yLine(endAbsolute = 0)
///   |> close(%)
///  
/// example = extrude(5, exampleSketch)
/// ```
@(impl = std_rust)
export fn cos(num: number(rad)): number(_) {}"#;
        let _ast = crate::parsing::top_level_parse(code).unwrap();
    }

    #[test]
    fn warn_import() {
        let some_program_string = r#"import "foo.kcl""#;
        let (_, errs) = assert_no_err(some_program_string);
        assert_eq!(errs.len(), 1, "{errs:#?}");

        let some_program_string = r#"import "foo.obj""#;
        let (_, errs) = assert_no_err(some_program_string);
        assert_eq!(errs.len(), 1, "{errs:#?}");

        let some_program_string = r#"import "foo.sldprt""#;
        let (_, errs) = assert_no_err(some_program_string);
        assert_eq!(errs.len(), 1, "{errs:#?}");

        let some_program_string = r#"import "foo.bad""#;
        let (_, errs) = assert_no_err(some_program_string);
        assert_eq!(errs.len(), 2, "{errs:#?}");
    }

    #[test]
    fn fn_decl_uom_ty() {
        let some_program_string = r#"fn foo(x: number(mm)): number(_) { return 1 }"#;
        let (_, errs) = assert_no_fatal(some_program_string);
        assert_eq!(errs.len(), 2);
    }

    #[test]
    fn error_underscore() {
        let (_, errs) = assert_no_fatal("_foo(_blah, _)");
        assert_eq!(errs.len(), 3, "found: {:#?}", errs);
    }

    #[test]
    fn error_type_ascription() {
        let (_, errs) = assert_no_fatal("a + b: number");
        assert_eq!(errs.len(), 1, "found: {:#?}", errs);
    }

    #[test]
    fn zero_param_function() {
        let code = r#"
        fn firstPrimeNumber = () => {
            return 2
        }
        firstPrimeNumber()
        "#;
        let _ast = crate::parsing::top_level_parse(code).unwrap();
    }

    #[test]
    fn array() {
        let program = r#"[1, 2, 3]"#;
        let module_id = ModuleId::default();
        let tokens = crate::parsing::token::lex(program, module_id).unwrap();
        let _arr = array_elem_by_elem(&mut tokens.as_slice()).unwrap();
    }

    #[test]
    fn array_linesep_trailing_comma() {
        let program = r#"[
            1,
            2,
            3,
        ]"#;
        let module_id = ModuleId::default();
        let tokens = crate::parsing::token::lex(program, module_id).unwrap();
        let _arr = array_elem_by_elem(&mut tokens.as_slice()).unwrap();
    }

    #[allow(unused)]
    #[test]
    fn array_linesep_no_trailing_comma() {
        let program = r#"[
            1,
            2,
            3
        ]"#;
        let module_id = ModuleId::default();
        let tokens = crate::parsing::token::lex(program, module_id).unwrap();
        let _arr = array_elem_by_elem(&mut tokens.as_slice()).unwrap();
    }

    #[test]
    fn basic_if_else() {
        let some_program_string = "if true {
            3
        } else {
            4
        }";
        let module_id = ModuleId::default();
        let tokens = crate::parsing::token::lex(some_program_string, module_id).unwrap();
        let _res = if_expr(&mut tokens.as_slice()).unwrap();
    }

    #[test]
    fn basic_else_if() {
        let some_program_string = "else if true {
            4
        }";
        let module_id = ModuleId::default();
        let tokens = crate::parsing::token::lex(some_program_string, module_id).unwrap();
        let _res = else_if(&mut tokens.as_slice()).unwrap();
    }

    #[test]
    fn basic_if_else_if() {
        let some_program_string = "if true {
            3  
        } else if true {
            4
        } else {
            5
        }";
        let module_id = ModuleId::default();
        let tokens = crate::parsing::token::lex(some_program_string, module_id).unwrap();
        let _res = if_expr(&mut tokens.as_slice()).unwrap();
    }

    #[test]
    fn test_keyword_ok_in_fn_args_return() {
        let some_program_string = r#"fn thing(param) {
    return true
}

thing(false)
"#;
        crate::parsing::top_level_parse(some_program_string).unwrap();
    }

    #[test]
    fn test_error_define_function_as_var() {
        for name in ["var", "let", "const"] {
            let some_program_string = format!(
                r#"{} thing = (param) => {{
    return true
}}

thing(false)
"#,
                name
            );
            assert_err(
                &some_program_string,
                "Expected a `fn` variable kind, found: `const`",
                [0, name.len()],
            );
        }
    }

    #[test]
    fn test_error_define_var_as_function() {
        // TODO: https://github.com/KittyCAD/modeling-app/issues/784
        // Improve this error message.
        // It should say that the compiler is expecting a function expression on the RHS.
        assert_err(r#"fn thing = "thing""#, "Unexpected token: \"thing\"", [11, 18]);
    }

    #[test]
    fn random_words_fail() {
        let test_program = r#"part001 = startSketchOn('-XZ')
    |> startProfileAt([8.53, 11.8], %)
    asdasd asdasd
    |> line([11.12, -14.82], %)
    |> line([-13.27, -6.98], %)
    |> line([-5.09, 12.33], %)
    asdasd
"#;
        let _ = crate::parsing::top_level_parse(test_program).unwrap_errs();
    }

    #[test]
    fn test_member_expression_sketch() {
        let some_program_string = r#"fn cube = (pos, scale) => {
  sg = startSketchOn('XY')
  |> startProfileAt(pos, %)
    |> line([0, scale], %)
    |> line([scale, 0], %)
    |> line([0, -scale], %)

  return sg
}

b1 = cube([0,0], 10)
b2 = cube([3,3], 4)

pt1 = b1[0]
pt2 = b2[0]
"#;
        crate::parsing::top_level_parse(some_program_string).unwrap();
    }

    #[test]
    fn test_math_with_stdlib() {
        let some_program_string = r#"d2r = pi() / 2
let other_thing = 2 * cos(3)"#;
        crate::parsing::top_level_parse(some_program_string).unwrap();
    }

    #[test]
    fn test_negative_arguments() {
        let some_program_string = r#"fn box = (p, h, l, w) => {
 myBox = startSketchOn('XY')
    |> startProfileAt(p, %)
    |> line([0, l], %)
    |> line([w, 0], %)
    |> line([0, -l], %)
    |> close()
    |> extrude(length=h)

  return myBox
}
let myBox = box([0,0], -3, -16, -10)
"#;
        crate::parsing::top_level_parse(some_program_string).unwrap();
    }

    #[test]
    fn kw_fn() {
        for input in ["val = foo(x, y = z)", "val = foo(y = z)"] {
            let module_id = ModuleId::default();
            let tokens = crate::parsing::token::lex(input, module_id).unwrap();
            super::program.parse(tokens.as_slice()).unwrap();
        }
    }

    #[test]
    fn test_parse_tag_named_std_lib() {
        let some_program_string = r#"startSketchOn('XY')
    |> startProfileAt([0, 0], %)
    |> line([5, 5], %, $xLine)
"#;
        assert_err(
            some_program_string,
            "Cannot assign a tag to a reserved keyword: xLine",
            [76, 82],
        );
    }

    #[test]
    fn test_parse_empty_tag_brace() {
        let some_program_string = r#"startSketchOn('XY')
    |> startProfileAt([0, 0], %)
    |> line(%, $)
    "#;
        assert_err(some_program_string, "Tag names must not be empty", [69, 70]);
    }
    #[test]
    fn test_parse_empty_tag_whitespace() {
        let some_program_string = r#"startSketchOn('XY')
    |> startProfileAt([0, 0], %)
    |> line(%, $ ,01)
    "#;
        assert_err(some_program_string, "Tag names must not be empty", [69, 70]);
    }

    #[test]
    fn test_parse_empty_tag_comma() {
        let some_program_string = r#"startSketchOn('XY')
    |> startProfileAt([0, 0], %)
    |> line(%, $,)
    "#;
        assert_err(some_program_string, "Tag names must not be empty", [69, 70]);
    }
    #[test]
    fn test_parse_tag_starting_with_digit() {
        let some_program_string = r#"
    startSketchOn('XY')
    |> startProfileAt([0, 0], %)
    |> line(%, $01)"#;
        assert_err(
            some_program_string,
            "Tag names must not start with a number. Tag starts with `01`",
            [74, 76],
        );
    }
    #[test]
    fn test_parse_tag_including_digit() {
        let some_program_string = r#"
    startSketchOn('XY')
    |> startProfileAt([0, 0], %)
    |> line(%, $var01)"#;
        assert_no_err(some_program_string);
    }
    #[test]
    fn test_parse_tag_starting_with_bang() {
        let some_program_string = r#"startSketchOn('XY')
    |> startProfileAt([0, 0], %)
    |> line(%, $!var,01)
    "#;
        assert_err(some_program_string, "Tag names must not start with a bang", [69, 70]);
    }
    #[test]
    fn test_parse_tag_starting_with_dollar() {
        let some_program_string = r#"startSketchOn('XY')
    |> startProfileAt([0, 0], %)
    |> line(%, $$,01)
    "#;
        assert_err(some_program_string, "Tag names must not start with a dollar", [69, 70]);
    }
    #[test]
    fn test_parse_tag_starting_with_fn() {
        let some_program_string = r#"startSketchOn('XY')
    |> startProfileAt([0, 0], %)
    |> line(%, $fn,01)
    "#;
        assert_err(some_program_string, "Tag names must not start with a keyword", [69, 71]);
    }
    #[test]
    fn test_parse_tag_starting_with_a_comment() {
        let some_program_string = r#"startSketchOn('XY')
    |> startProfileAt([0, 0], %)
    |> line(%, $//
    ,01)
    "#;
        assert_err(
            some_program_string,
            "Tag names must not start with a lineComment",
            [69, 71],
        );
    }

    #[test]
    fn test_parse_tag_with_reserved_in_middle_works() {
        let some_program_string = r#"
    startSketchOn('XY')
    |> startProfileAt([0, 0], %)
    |> line([5, 5], %, $sketching)
    "#;
        assert_no_err(some_program_string);
    }

    #[test]
    fn test_parse_array_missing_closing_bracket() {
        let some_program_string = r#"
sketch001 = startSketchOn('XZ') |> startProfileAt([90.45, 119.09, %)"#;
        assert_err(
            some_program_string,
            "Encountered an unexpected character(s) before finding a closing bracket(`]`) for the array",
            [51, 67],
        );
    }
    #[test]
    fn test_parse_array_missing_comma() {
        let some_program_string = r#"
sketch001 = startSketchOn('XZ') |> startProfileAt([90.45 119.09], %)"#;
        assert_err(
            some_program_string,
            "Unexpected character encountered. You might be missing a comma in between elements.",
            [52, 65],
        );
    }
    #[test]
    fn test_parse_array_reserved_word_early_exit() {
        // since there is an early exit if encountering a reserved word, the error should be about
        // that and not the missing comma
        let some_program_string = r#"
sketch001 = startSketchOn('XZ') |> startProfileAt([90.45 $struct], %)"#;
        assert_err(
            some_program_string,
            "Encountered an unexpected character(s) before finding a closing bracket(`]`) for the array",
            [51, 52],
        );
    }
    #[test]
    fn test_parse_array_random_brace() {
        let some_program_string = r#"
sketch001 = startSketchOn('XZ') |> startProfileAt([}], %)"#;
        assert_err(
            some_program_string,
            "Encountered an unexpected character(s) before finding a closing bracket(`]`) for the array",
            [51, 52],
        );
    }

    #[test]
    fn test_parse_object_missing_closing_brace() {
        let some_program_string = r#"{
            foo = bar,"#;

        assert_err(
            some_program_string,
            "Encountered an unexpected character(s) before finding a closing brace(`}`) for the object",
            [0, 23],
        );
    }
    #[test]
    fn test_parse_object_reserved_word_early_exit() {
        // since there is an early exit if encountering a reserved word, the error should be about
        // that and not the missing comma
        let some_program_string = r#"{bar = foo struct = man}"#;

        assert_err(
            some_program_string,
            "Encountered an unexpected character(s) before finding a closing brace(`}`) for the object",
            [0, 1],
        );
    }
    #[test]
    fn test_parse_object_missing_comma() {
        let some_program_string = r#"{
            foo = bar,
            bar = foo
            bat = man
        }"#;

        assert_err(
            some_program_string,
            "Unexpected character encountered. You might be missing a comma in between properties.",
            [37, 78],
        );
    }

    #[test]
    fn test_parse_object_missing_comma_one_line() {
        let some_program_string = r#"{bar = foo bat = man}"#;

        assert_err(
            some_program_string,
            "Unexpected character encountered. You might be missing a comma in between properties.",
            [1, 21],
        );
    }

    #[test]
    fn test_parse_object_random_bracket() {
        let some_program_string = r#"{]}"#;

        assert_err(
            some_program_string,
            "Encountered an unexpected character(s) before finding a closing brace(`}`) for the object",
            [0, 1],
        );
    }

    #[test]
    fn test_parse_object_shorthand_missing_comma() {
        let some_program_string = r#"
bar = 1
        {
            foo = bar,
            bar
            bat = man
        }"#;

        assert_err(
            some_program_string,
            "Unexpected character encountered. You might be missing a comma in between properties.",
            [54, 89],
        );
    }

    #[test]
    fn warn_object_expr() {
        let some_program_string = "{ foo: bar }";
        let (_, errs) = assert_no_err(some_program_string);
        assert_eq!(errs.len(), 1);
        assert_eq!(errs[0].apply_suggestion(some_program_string).unwrap(), "{ foo = bar }")
    }

    #[test]
    fn warn_fn_decl() {
        let some_program_string = r#"fn foo = () => {
    return 0
}"#;
        let (_, errs) = assert_no_err(some_program_string);
        assert_eq!(errs.len(), 2);
        let replaced = errs[0].apply_suggestion(some_program_string).unwrap();
        let replaced = errs[1].apply_suggestion(&replaced).unwrap();
        // Note the whitespace here is bad, but we're just testing the suggestion spans really. In
        // real life we might reformat after applying suggestions.
        assert_eq!(
            replaced,
            r#"fn foo  ()  {
    return 0
}"#
        );

        let some_program_string = r#"myMap = map([0..5], (n) => {
    return n * 2
})"#;
        let (_, errs) = assert_no_err(some_program_string);
        assert_eq!(errs.len(), 2);
        let replaced = errs[0].apply_suggestion(some_program_string).unwrap();
        let replaced = errs[1].apply_suggestion(&replaced).unwrap();
        assert_eq!(
            replaced,
            r#"myMap = map([0..5], fn(n)  {
    return n * 2
})"#
        );
    }

    #[test]
    fn warn_const() {
        let some_program_string = r#"const foo = 0
let bar = 1
var baz = 2
"#;
        let (_, errs) = assert_no_err(some_program_string);
        assert_eq!(errs.len(), 3);
        let replaced = errs[2].apply_suggestion(some_program_string).unwrap();
        let replaced = errs[1].apply_suggestion(&replaced).unwrap();
        let replaced = errs[0].apply_suggestion(&replaced).unwrap();
        assert_eq!(
            replaced,
            r#"foo = 0
bar = 1
baz = 2
"#
        );
    }

    #[test]
    fn test_unary_not_on_keyword_bool() {
        let some_program_string = r#"!true"#;
        let module_id = ModuleId::default();
        let tokens = crate::parsing::token::lex(some_program_string, module_id).unwrap(); // Updated import path
        let actual = match unary_expression.parse(tokens.as_slice()) {
            // Use tokens.as_slice() for parsing
            Ok(x) => x,
            Err(e) => panic!("{e:?}"),
        };
        assert_eq!(actual.operator, UnaryOperator::Not);
        crate::parsing::top_level_parse(some_program_string).unwrap(); // Updated import path
    }

    #[test]
    fn test_sensible_error_when_missing_equals_in_kwarg() {
        for (i, program) in ["f(x=1,y)", "f(x=1,y,z)", "f(x=1,y,z=1)", "f(x=1, y, z=1)"]
            .into_iter()
            .enumerate()
        {
            let tokens = crate::parsing::token::lex(program, ModuleId::default()).unwrap();
            let err = fn_call_kw.parse(tokens.as_slice()).unwrap_err();
            let cause = err.inner().cause.as_ref().unwrap();
            assert_eq!(
                cause.message, "This argument needs a label, but it doesn't have one",
                "failed test {i}: {program}"
            );
            assert_eq!(
                cause.source_range.start(),
                program.find("y").unwrap(),
                "failed test {i}: {program}"
            );
        }
    }

    #[test]
    fn test_sensible_error_when_missing_rhs_of_kw_arg() {
        for (i, program) in ["f(x, y=)"].into_iter().enumerate() {
            let tokens = crate::parsing::token::lex(program, ModuleId::default()).unwrap();
            let err = fn_call_kw.parse(tokens.as_slice()).unwrap_err();
            let cause = err.inner().cause.as_ref().unwrap();
            assert_eq!(
                cause.message, "This argument has a label, but no value. Put some value after the equals sign",
                "failed test {i}: {program}"
            );
            assert_eq!(
                cause.source_range.start(),
                program.find("y").unwrap(),
                "failed test {i}: {program}"
            );
        }
    }

    #[test]
    fn test_sensible_error_when_missing_rhs_of_obj_property() {
        for (i, program) in ["{x = 1, y =}"].into_iter().enumerate() {
            let tokens = crate::parsing::token::lex(program, ModuleId::default()).unwrap();
            let err = object.parse(tokens.as_slice()).unwrap_err();
            let cause = err.inner().cause.as_ref().unwrap();
            assert_eq!(
                cause.message, "This property has a label, but no value. Put some value after the equals sign",
                "failed test {i}: {program}"
            );
            assert_eq!(
                cause.source_range.start(),
                program.rfind('=').unwrap(),
                "failed test {i}: {program}"
            );
        }
    }
}

#[cfg(test)]
mod snapshot_math_tests {
    use super::*;

    // This macro generates a test function with the given function name.
    // The macro takes a KCL program, ensures it tokenizes and parses, then compares
    // its parsed AST to a snapshot (kept in this repo in a file under snapshots/ dir)
    macro_rules! snapshot_test {
        ($func_name:ident, $test_kcl_program:expr) => {
            #[test]
            fn $func_name() {
                let module_id = crate::ModuleId::default();
                let tokens = crate::parsing::token::lex($test_kcl_program, module_id).unwrap();
                ParseContext::init();

                let actual = match binary_expression.parse(tokens.as_slice()) {
                    Ok(x) => x,
                    Err(_e) => panic!("could not parse test"),
                };
                insta::assert_json_snapshot!(actual);
                let _ = ParseContext::take();
            }
        };
    }

    snapshot_test!(a, "1 + 2");
    snapshot_test!(b, "1+2");
    snapshot_test!(c, "1 -2");
    snapshot_test!(d, "1 + 2 * 3");
    snapshot_test!(e, "1 * ( 2 + 3 )");
    snapshot_test!(f, "1 * ( 2 + 3 ) / 4");
    snapshot_test!(g, "1 + ( 2 + 3 ) / 4");
    snapshot_test!(h, "1 * (( 2 + 3 ) / 4 + 5 )");
    snapshot_test!(i, "1 * ((( 2 + 3 )))");
    snapshot_test!(j, "distance * p * FOS * 6 / (sigmaAllow * width)");
    snapshot_test!(k, "2 + (((3)))");
}

#[cfg(test)]
mod snapshot_tests {
    use super::*;

    // This macro generates a test function with the given function name.
    // The macro takes a KCL program, ensures it tokenizes and parses, then compares
    // its parsed AST to a snapshot (kept in this repo in a file under snapshots/ dir)
    macro_rules! snapshot_test {
        ($func_name:ident, $test_kcl_program:expr) => {
            #[test]
            fn $func_name() {
                let module_id = crate::ModuleId::default();
                println!("{}", $test_kcl_program);
                let tokens = crate::parsing::token::lex($test_kcl_program, module_id).unwrap();
                print_tokens(tokens.as_slice());
                ParseContext::init();
                let actual = match program.parse(tokens.as_slice()) {
                    Ok(x) => x,
                    Err(e) => panic!("could not parse test: {e:?}"),
                };
                let mut settings = insta::Settings::clone_current();
                settings.set_sort_maps(true);
                settings.bind(|| {
                    insta::assert_json_snapshot!(actual);
                });
                let _ = ParseContext::take();
            }
        };
    }

    snapshot_test!(
        a,
        r#"boxSketch = startSketchOn(XY)
    |> startProfileAt([0, 0], %)
    |> line([0, 10], %)
    |> tangentialArc([-5, 5], %)
    |> line([5, -15], %)
    |> extrude(length=10)
"#
    );
    snapshot_test!(b, "myVar = min(5 , -legLen(5, 4))"); // Space before comma

    snapshot_test!(c, "myVar = min(-legLen(5, 4), 5)");
    snapshot_test!(d, "myVar = 5 + 6 |> myFunc(45, %)");
    snapshot_test!(e, "let x = 1 * (3 - 4)");
    snapshot_test!(f, r#"x = 1 // this is an inline comment"#);
    snapshot_test!(
        g,
        r#"fn x = () => {
        return sg
        return sg
      }"#
    );
    snapshot_test!(d2, r#"x = -leg2 + thickness"#);
    snapshot_test!(
        h,
        r#"obj = { a: 1, b: 2 }
    height = 1 - obj.a"#
    );
    snapshot_test!(
        i,
        r#"obj = { a: 1, b: 2 }
     height = 1 - obj["a"]"#
    );
    snapshot_test!(
        j,
        r#"obj = { a: 1, b: 2 }
    height = obj["a"] - 1"#
    );
    snapshot_test!(
        k,
        r#"obj = { a: 1, b: 2 }
    height = [1 - obj["a"], 0]"#
    );
    snapshot_test!(
        l,
        r#"obj = { a: 1, b: 2 }
    height = [obj["a"] - 1, 0]"#
    );
    snapshot_test!(
        m,
        r#"obj = { a: 1, b: 2 }
    height = [obj["a"] -1, 0]"#
    );
    snapshot_test!(n, "height = 1 - obj.a");
    snapshot_test!(o, "six = 1 + 2 + 3");
    snapshot_test!(p, "five = 3 * 1 + 2");
    snapshot_test!(q, r#"height = [ obj["a"], 0 ]"#);
    snapshot_test!(
        r,
        r#"obj = { a: 1, b: 2 }
    height = obj["a"]"#
    );
    snapshot_test!(s, r#"prop = yo["one"][two]"#);
    snapshot_test!(t, r#"pt1 = b1[x]"#);
    snapshot_test!(u, "prop = yo.one.two.three.four");
    snapshot_test!(v, r#"pt1 = b1[0]"#);
    snapshot_test!(w, r#"pt1 = b1['zero']"#);
    snapshot_test!(x, r#"pt1 = b1.zero"#);
    snapshot_test!(y, r#"sg = startSketchOn(XY) |> startProfileAt(pos, %)"#);
    snapshot_test!(
        z,
        "sg = startSketchOn(XY)
    |> startProfileAt(pos) |> line([0, -scale], %)"
    );
    snapshot_test!(aa, r#"sg = -scale"#);
    snapshot_test!(ab, "line(endAbsolute = [0, -1])");
    snapshot_test!(ac, "myArray = [0..10]");
    snapshot_test!(
        ad,
        r#"
    fn firstPrimeNumber = () => {
        return 2
    }
    firstPrimeNumber()"#
    );
    snapshot_test!(
        ae,
        r#"fn thing = (param) => {
        return true
    }
    thing(false)"#
    );
    snapshot_test!(
        af,
        r#"mySketch = startSketchOn(XY)
        |> startProfileAt([0,0], %)
        |> line(endAbsolute = [0, 1], tag = $myPath)
        |> line(endAbsolute = [1, 1])
        |> line(endAbsolute = [1, 0], tag = $rightPath)
        |> close()"#
    );
    snapshot_test!(
        ag,
        "mySketch = startSketchOn(XY) |> startProfileAt([0,0], %) |> line(endAbsolute = [1, 1]) |> close()"
    );
    snapshot_test!(ah, "myBox = startSketchOn(XY) |> startProfileAt(p, %)");
    snapshot_test!(ai, r#"myBox = f(1) |> g(2, %)"#);
    snapshot_test!(
        aj,
        r#"myBox = startSketchOn(XY) |> startProfileAt(p, %) |> line(end = [0, l])"#
    );
    snapshot_test!(ak, "line(endAbsolute = [0, 1])");
    snapshot_test!(ap, "mySketch = startSketchOn(XY) |> startProfileAt([0,0], %)");
    snapshot_test!(aq, "log(5, \"hello\", aIdentifier)");
    snapshot_test!(ar, r#"5 + "a""#);
    snapshot_test!(at, "line([0, l], %)");
    snapshot_test!(au, include_str!("../../e2e/executor/inputs/cylinder.kcl"));
    snapshot_test!(av, "fn f = (angle?) => { return default(angle, 360) }");
    snapshot_test!(
        aw,
        "let numbers = [
            1,
            // A,
            // B,
            3,
        ]"
    );
    snapshot_test!(
        ax,
        "let numbers = [
            1,
            2,
            // A,
            // B,
        ]"
    );
    snapshot_test!(
        ay,
        "let props = {
            a: 1,
            // b: 2,
            c: 3,
        }"
    );
    snapshot_test!(
        az,
        "let props = {
            a: 1,
            // b: 2,
            c: 3
        }"
    );
    snapshot_test!(
        ba,
        r#"
sketch001 = startSketchOn('XY')
  // |> arc({
  //   angleEnd: 270,
  //   angleStart: 450,
  // }, %)
  |> startProfileAt(%)
"#
    );
    snapshot_test!(
        bb,
        r#"
my14 = 4 ^ 2 - 3 ^ 2 * 2
"#
    );
    snapshot_test!(
        bc,
        r#"x = if true {
            3
        } else {
            4
        }"#
    );
    snapshot_test!(
        bd,
        r#"x = if true {
            3
        } else if func(radius) {
            4
        } else {
            5
        }"#
    );
    snapshot_test!(be, "let x = 3 == 3");
    snapshot_test!(bf, "let x = 3 != 3");
    snapshot_test!(bg, r#"x = 4"#);
    snapshot_test!(bh, "obj = {center : [10, 10], radius: 5}");
    snapshot_test!(
        bi,
        r#"x = 3
        obj = { x, y: 4}"#
    );
    snapshot_test!(bj, "true");
    snapshot_test!(bk, "truee");
    snapshot_test!(bl, "x = !true");
    snapshot_test!(bm, "x = true & false");
    snapshot_test!(bn, "x = true | false");
    snapshot_test!(kw_function_unnamed_first, r#"val = foo(x, y = z)"#);
    snapshot_test!(kw_function_all_named, r#"val = foo(x = a, y = b)"#);
    snapshot_test!(kw_function_decl_all_labeled, r#"fn foo(x, y) { return 1 }"#);
    snapshot_test!(kw_function_decl_first_unlabeled, r#"fn foo(@x, y) { return 1 }"#);
    snapshot_test!(kw_function_decl_with_default_no_type, r#"fn foo(x? = 2) { return 1 }"#);
    snapshot_test!(
        kw_function_decl_with_default_and_type,
        r#"fn foo(x?: number = 2) { return 1 }"#
    );
    snapshot_test!(kw_function_call_in_pipe, r#"val = 1 |> f(arg = x)"#);
    snapshot_test!(
        kw_function_call_multiline,
        r#"val = f(
             arg = x,
             foo = x,
             bar = x,
           )"#
    );
    snapshot_test!(
        kw_function_call_multiline_with_comments,
        r#"val = f(
             arg = x,
             // foo = x,
             bar = x,
           )"#
    );
}

#[allow(unused)]
#[cfg(test)]
pub(crate) fn print_tokens(tokens: TokenSlice) {
    for (i, tok) in tokens.iter().enumerate() {
        println!("{i:.2}: ({:?}):) '{}'", tok.token_type, tok.value.replace("\n", "\\n"));
    }
}