Repository: vercel/next.js
Pull request: [Turbopack] Fix AST traversal for `this` in function default parameters

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Include FunctionField::Params in the AST traversal check to correctly identify when `this` appears within a function's scope. Previously only checked FunctionField::Body, missing `this` usage in default parameters.

Fixes #83739

Changed files:
filename: turbopack/crates/turbopack-ecmascript/src/analyzer/graph.rs
patch: @@ -2075,6 +2075,7 @@ impl VisitAstPath for Analyzer<'_> {
                     | AstParentKind::ClassDecl(ClassDeclField::Class)
                     | AstParentKind::ClassExpr(ClassExprField::Class)
                     | AstParentKind::Function(FunctionField::Body)
+                    | AstParentKind::Function(FunctionField::Params(_))
             )
         }) {
             // We are in some scope that will rebind this

filename: turbopack/crates/turbopack-tests/tests/execution/turbopack/basic/this-in-default-params/input/index.js
patch: @@ -0,0 +1,38 @@
+it('should handle this in default parameters for function declaration', () => {
+  function withDefault(value = this.prop) {
+    return value
+  }
+
+  const obj = { prop: 42 }
+  expect(withDefault.call(obj)).toBe(42)
+})
+
+it('should handle this in default parameters for function expression', () => {
+  const funcExpr = function (value = this.prop) {
+    return value
+  }
+
+  const obj = { prop: 55 }
+  expect(funcExpr.call(obj)).toBe(55)
+})
+
+it('should handle this in default parameters for arrow function', () => {
+  const obj = {
+    prop: 77,
+    test() {
+      const arrow = (value = this.prop) => value
+      return arrow()
+    },
+  }
+  expect(obj.test()).toBe(77)
+})
+
+it('should handle this in default parameters for object method', () => {
+  const obj = {
+    prop: 100,
+    method(value = this.prop) {
+      return value
+    },
+  }
+  expect(obj.method()).toBe(100)
+})