Restrict subdirectory imports to main.kcl (#7094)

Signed-off-by: Nick Cameron <nrc@ncameron.org>

docs/kcl-lang/modules.md

@@ -27,9 +27,6 @@ import increment from "util.kcl"
 answer = increment(41)
 ```
 
-Imported files _must_ be in the same project so that units are uniform across
-modules. This means that it must be in the same directory.
-
 Import statements must be at the top-level of a file. It is not allowed to have
 an `import` statement inside a function or in the body of an if‑else.
 
@@ -58,6 +55,9 @@ Imported symbols can be renamed for convenience or to avoid name collisions.
 import increment as inc, decrement as dec from "util.kcl"
 ```
 
+You can import files from the current directory or from subdirectories, but if importing from a
+subdirectory you can only import `main.kcl`.
+
 ---
 
 ## Functions vs `clone`
@@ -229,6 +229,19 @@ The final statement is what's important because it's the return value of the
 entire module. The module is expected to return a single object that can be used
 as a variable by the file that imports it.
 
+The name of the file or subdirectory is used as the name of the variable within the importing program.
+If you want to use a different name, you can do so by using the `as` keyword:
+
+```kcl,norun
+import "cube.kcl"                // Introduces a new variable called `cube`.
+import "cube.kcl" as block       // Introduces a new variable called `block`.
+import "cube/main.kcl"           // Introduces a new variable called `cube`.
+import "cube/main.kcl" as block  // Introduces a new variable called `block`.
+```
+
+If the filename includes hyphens (`-`) or starts with an underscore (`_`), then you must specify a
+variable name.
+
 ---
 
 ## Multiple instances of the same import

rust/kcl-lib/src/parsing/ast/types/mod.rs

@@ -1811,14 +1811,25 @@ impl ImportStatement {
 
         match &self.path {
             ImportPath::Kcl { filename: s } | ImportPath::Foreign { path: s } => {
-                let name = s.file_name().map(|f| f.to_string());
+                let name = s.to_string_lossy();
+                if name.ends_with("/main.kcl") || name.ends_with("\\main.kcl") {
+                    let name = &name[..name.len() - 9];
+                    let start = name.rfind(['/', '\\']).map(|s| s + 1).unwrap_or(0);
+                    return Some(name[start..].to_owned());
+                }
+
+                let name = s.file_name().map(|f| f.to_string())?;
+                if name.contains('\\') || name.contains('/') {
+                    return None;
+                }
+
                 // Remove the extension if it exists.
                 let extension = s.extension();
-                if let Some(extension) = extension {
-                    name.map(|n| n.trim_end_matches(extension).trim_end_matches('.').to_string())
+                Some(if let Some(extension) = extension {
+                    name.trim_end_matches(extension).trim_end_matches('.').to_string()
                 } else {
                     name
-                }
+                })
             }
             ImportPath::Std { path } => path.last().cloned(),
         }
@@ -4330,4 +4341,20 @@ startSketchOn(XY)
 "#
         );
     }
+
+    #[test]
+    fn module_name() {
+        #[track_caller]
+        fn assert_mod_name(stmt: &str, name: &str) {
+            let tokens = crate::parsing::token::lex(stmt, ModuleId::default()).unwrap();
+            let stmt = crate::parsing::parser::import_stmt(&mut tokens.as_slice()).unwrap();
+            assert_eq!(stmt.module_name().unwrap(), name);
+        }
+
+        assert_mod_name("import 'foo.kcl'", "foo");
+        assert_mod_name("import 'foo.kcl' as bar", "bar");
+        assert_mod_name("import 'main.kcl'", "main");
+        assert_mod_name("import 'foo/main.kcl'", "foo");
+        assert_mod_name("import 'foo\\bar\\main.kcl'", "bar");
+    }
 }

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

@@ -1729,7 +1729,7 @@ fn glob(i: &mut TokenSlice) -> PResult<Token> {
         .parse_next(i)
 }
 
-fn import_stmt(i: &mut TokenSlice) -> PResult<BoxNode<ImportStatement>> {
+pub(super) 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)));
@@ -1867,7 +1867,7 @@ fn validate_path_string(path_string: String, var_name: bool, path_range: SourceR
             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.",
+                    "import path may only contain alphanumeric characters, `_`, `-`, `.`, `/`, and `\\`.",
                 )
                 .into(),
             ));
@@ -1894,6 +1894,15 @@ fn validate_path_string(path_string: String, var_name: bool, path_range: SourceR
             ));
         }
 
+        if (path_string.contains('/') || path_string.contains('\\'))
+            && !(path_string.ends_with("/main.kcl") || path_string.ends_with("\\main.kcl"))
+        {
+            return Err(ErrMode::Cut(
+                CompilationError::fatal(path_range, "import path to a subdirectory must only refer to main.kcl.")
+                    .into(),
+            ));
+        }
+
         ImportPath::Kcl {
             filename: TypedPath::new(&path_string),
         }
@@ -4569,9 +4578,14 @@ e
         );
         assert_err(
             r#"import cube from "C:\cube.kcl""#,
-            "import path may only contain alphanumeric characters, underscore, hyphen, and period. KCL files in other directories are not yet supported.",
+            "import path may only contain alphanumeric characters, `_`, `-`, `.`, `/`, and `\\`.",
             [17, 30],
         );
+        assert_err(
+            r#"import cube from "cube/cube.kcl""#,
+            "import path to a subdirectory must only refer to main.kcl.",
+            [17, 32],
+        );
         assert_err(
             r#"import * as foo from "dsfs""#,
             "as is not the 'from' keyword",

rust/kcl-lib/tests/nested_windows_main_kcl/ast.snap

@@ -14,13 +14,7 @@ description: Result of parsing nested_windows_main_kcl.kcl
         },
         "selector": {
           "type": "None",
-          "alias": {
-            "commentStart": 0,
-            "end": 0,
-            "name": "bar",
-            "start": 0,
-            "type": "Identifier"
-          }
+          "alias": null
         },
         "start": 0,
         "type": "ImportStatement",

rust/kcl-lib/tests/nested_windows_main_kcl/input.kcl

@@ -1,3 +1,3 @@
-import "nested\foo\bar\main.kcl" as bar
+import "nested\foo\bar\main.kcl"
 
 bar

rust/kcl-lib/tests/nested_windows_main_kcl/unparsed.snap

@@ -2,6 +2,6 @@
 source: kcl-lib/src/simulation_tests.rs
 description: Result of unparsing nested_windows_main_kcl.kcl
 ---
-import "nested/foo/bar/main.kcl" as bar
+import "nested/foo/bar/main.kcl"
 
 bar