KCL: Better error message when using var in its own definition (#7339)

I thought I did this in https://github.com/KittyCAD/modeling-app/pull/7325, but I forgot to actually set the better message.

Actually fixes, for real this time, https://github.com/KittyCAD/modeling-app/issues/6072 this time.

rust/kcl-lib/src/execution/exec_ast.rs

@@ -304,9 +304,10 @@ impl ExecutorContext {
 
                     let annotations = &variable_declaration.outer_attrs;
 
-                    // During the evaluation of the variable's LHS, set context that this is all happening inside a variable
+                    // During the evaluation of the variable's RHS, set context that this is all happening inside a variable
                     // declaration, for the given name. This helps improve user-facing error messages.
-                    exec_state.mod_local.being_declared = Some(variable_declaration.inner.name().to_owned());
+                    let lhs = variable_declaration.inner.name().to_owned();
+                    exec_state.mod_local.being_declared = Some(lhs);
                     let rhs_result = self
                         .execute_expr(
                             &variable_declaration.declaration.init,
@@ -645,7 +646,12 @@ impl ExecutorContext {
             Expr::Literal(literal) => KclValue::from_literal((**literal).clone(), exec_state),
             Expr::TagDeclarator(tag) => tag.execute(exec_state).await?,
             Expr::Name(name) => {
-                let value = name.get_result(exec_state, self).await?.clone();
+                let being_declared = exec_state.mod_local.being_declared.clone();
+                let value = name
+                    .get_result(exec_state, self)
+                    .await
+                    .map_err(|e| var_in_own_ref_err(e, &being_declared))?
+                    .clone();
                 if let KclValue::Module { value: module_id, meta } = value {
                     self.exec_module_for_result(
                         module_id,
@@ -751,6 +757,24 @@ impl ExecutorContext {
     }
 }
 
+/// If the error is about an undefined name, and that name matches the name being defined,
+/// make the error message more specific.
+fn var_in_own_ref_err(e: KclError, being_declared: &Option<String>) -> KclError {
+    let KclError::UndefinedValue { name, mut details } = e else {
+        return e;
+    };
+    // TODO after June 26th: replace this with a let-chain,
+    // which will be available in Rust 1.88
+    // https://rust-lang.github.io/rfcs/2497-if-let-chains.html
+    match (&being_declared, &name) {
+        (Some(name0), Some(name1)) if name0 == name1 => {
+            details.message = format!("You can't use `{name0}` because you're currently trying to define it. Use a different variable here instead.");
+        }
+        _ => {}
+    }
+    KclError::UndefinedValue { details, name }
+}
+
 impl Node<AscribedExpression> {
     #[async_recursion]
     pub async fn get_result(&self, exec_state: &mut ExecState, ctx: &ExecutorContext) -> Result<KclValue, KclError> {

rust/kcl-lib/tests/var_ref_in_own_def/artifact_commands.snap

@@ -28,5 +28,30 @@ description: Artifact commands var_ref_in_own_def.kcl
       "object_id": "[uuid]",
       "hidden": true
     }
+  },
+  {
+    "cmdId": "[uuid]",
+    "range": [],
+    "command": {
+      "type": "make_plane",
+      "origin": {
+        "x": 0.0,
+        "y": 0.0,
+        "z": 0.0
+      },
+      "x_axis": {
+        "x": 1.0,
+        "y": 0.0,
+        "z": 0.0
+      },
+      "y_axis": {
+        "x": 0.0,
+        "y": 1.0,
+        "z": 0.0
+      },
+      "size": 60.0,
+      "clobber": false,
+      "hide": true
+    }
   }
 ]

rust/kcl-lib/tests/var_ref_in_own_def/artifact_graph_flowchart.snap.md

@@ -1,3 +1,5 @@
 ```mermaid
 flowchart LR
+  1["Plane<br>[95, 112, 0]"]
+    %% [ProgramBodyItem { index: 0 }, VariableDeclarationDeclaration, VariableDeclarationInit, PipeBodyItem { index: 0 }]
 ```

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

@@ -13,11 +13,13 @@ description: Result of parsing var_ref_in_own_def.kcl
           "id": {
             "commentStart": 0,
             "end": 0,
-            "name": "x",
+            "name": "sketch001",
             "start": 0,
             "type": "Identifier"
           },
           "init": {
+            "body": [
+              {
                 "callee": {
                   "abs_path": false,
                   "commentStart": 0,
@@ -25,7 +27,7 @@ description: Result of parsing var_ref_in_own_def.kcl
                   "name": {
                     "commentStart": 0,
                     "end": 0,
-                "name": "cos",
+                    "name": "startSketchOn",
                     "start": 0,
                     "type": "Identifier"
                   },
@@ -45,7 +47,7 @@ description: Result of parsing var_ref_in_own_def.kcl
                   "name": {
                     "commentStart": 0,
                     "end": 0,
-                "name": "x",
+                    "name": "XY",
                     "start": 0,
                     "type": "Identifier"
                   },
@@ -55,13 +57,105 @@ description: Result of parsing var_ref_in_own_def.kcl
                   "type": "Name"
                 }
               },
+              {
+                "arguments": [
+                  {
+                    "type": "LabeledArg",
+                    "label": null,
+                    "arg": {
+                      "abs_path": false,
+                      "commentStart": 0,
+                      "end": 0,
+                      "name": {
+                        "commentStart": 0,
+                        "end": 0,
+                        "name": "sketch001",
+                        "start": 0,
+                        "type": "Identifier"
+                      },
+                      "path": [],
+                      "start": 0,
+                      "type": "Name",
+                      "type": "Name"
+                    }
+                  }
+                ],
+                "callee": {
+                  "abs_path": false,
+                  "commentStart": 0,
+                  "end": 0,
+                  "name": {
+                    "commentStart": 0,
+                    "end": 0,
+                    "name": "startProfileAt",
+                    "start": 0,
+                    "type": "Identifier"
+                  },
+                  "path": [],
+                  "start": 0,
+                  "type": "Name"
+                },
+                "commentStart": 0,
+                "end": 0,
+                "start": 0,
+                "type": "CallExpressionKw",
+                "type": "CallExpressionKw",
+                "unlabeled": {
+                  "commentStart": 0,
+                  "elements": [
+                    {
+                      "commentStart": 0,
+                      "end": 0,
+                      "raw": "20",
+                      "start": 0,
+                      "type": "Literal",
+                      "type": "Literal",
+                      "value": {
+                        "value": 20.0,
+                        "suffix": "None"
+                      }
+                    },
+                    {
+                      "argument": {
+                        "commentStart": 0,
+                        "end": 0,
+                        "raw": "20",
+                        "start": 0,
+                        "type": "Literal",
+                        "type": "Literal",
+                        "value": {
+                          "value": 20.0,
+                          "suffix": "None"
+                        }
+                      },
+                      "commentStart": 0,
+                      "end": 0,
+                      "operator": "-",
+                      "start": 0,
+                      "type": "UnaryExpression",
+                      "type": "UnaryExpression"
+                    }
+                  ],
+                  "end": 0,
+                  "start": 0,
+                  "type": "ArrayExpression",
+                  "type": "ArrayExpression"
+                }
+              }
+            ],
+            "commentStart": 0,
+            "end": 0,
+            "start": 0,
+            "type": "PipeExpression",
+            "type": "PipeExpression"
+          },
           "start": 0,
           "type": "VariableDeclarator"
         },
         "end": 0,
         "kind": "const",
         "preComments": [
-          "// This won't work, because `x` is being referenced in its own definition."
+          "// This won't work, because `sketch001` is being referenced in its own definition."
         ],
         "start": 0,
         "type": "VariableDeclaration",

rust/kcl-lib/tests/var_ref_in_own_def/execution_error.snap

@@ -4,10 +4,11 @@ description: Error from executing var_ref_in_own_def.kcl
 ---
 KCL UndefinedValue error
 
-  × undefined value: `x` is not defined
+  × undefined value: You can't use `sketch001` because you're currently trying
-   ╭─[2:9]
+  │ to define it. Use a different variable here instead.
- 1 │ // This won't work, because `x` is being referenced in its own definition.
+   ╭─[3:32]
- 2 │ x = cos(x)
+ 2 │ sketch001 = startSketchOn(XY)
-   ·         ┬
+ 3 │   |> startProfileAt([20, -20], sketch001)
+   ·                                ────┬────
    ·                                    ╰── tests/var_ref_in_own_def/input.kcl
    ╰────

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

@@ -1,2 +1,3 @@
-// This won't work, because `x` is being referenced in its own definition.
+// This won't work, because `sketch001` is being referenced in its own definition.
-x = cos(x)
+sketch001 = startSketchOn(XY)
+  |> startProfileAt([20, -20], sketch001)

rust/kcl-lib/tests/var_ref_in_own_def/ops.snap

@@ -2,4 +2,18 @@
 source: kcl-lib/src/simulation_tests.rs
 description: Operations executed var_ref_in_own_def.kcl
 ---
-[]
+[
+  {
+    "type": "StdLibCall",
+    "name": "startSketchOn",
+    "unlabeledArg": {
+      "value": {
+        "type": "Plane",
+        "artifact_id": "[uuid]"
+      },
+      "sourceRange": []
+    },
+    "labeledArgs": {},
+    "sourceRange": []
+  }
+]

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

@@ -2,5 +2,6 @@
 source: kcl-lib/src/simulation_tests.rs
 description: Result of unparsing var_ref_in_own_def.kcl
 ---
-// This won't work, because `x` is being referenced in its own definition.
+// This won't work, because `sketch001` is being referenced in its own definition.
-x = cos(x)
+sketch001 = startSketchOn(XY)
+  |> startProfileAt([20, -20], sketch001)