Fix closure capture for default parameter values

Ensure that default values of function parameters are scanned for variable captures before parameter names are added to the inner function scope. This fixes issues where closures in default parameter expressions could not capture outer variables. Adds new tests for closures in default parameter values.

Author: BlobMaster41

src/compiler.ts

@@ -7719,6 +7719,13 @@ export class Compiler extends DiagnosticEmitter {
         let funcExpr = <FunctionExpression>node;
         let decl = funcExpr.declaration;
         let params = decl.signature.parameters;
+        // Scan parameter default values for captures (before adding params to inner names)
+        for (let i = 0, k = params.length; i < k; i++) {
+          let paramInit = params[i].initializer;
+          if (paramInit) {
+            this.scanNodeForCaptures(paramInit, outerFlow, innerFunctionNames, captures);
+          }
+        }
         for (let i = 0, k = params.length; i < k; i++) {
           innerFunctionNames.add(params[i].name.text);
         }
@@ -7940,8 +7947,16 @@ export class Compiler extends DiagnosticEmitter {
     let captures = new Map<Local, i32>();
     let innerFunctionNames = new Set<string>();
 
-    // Add the function's own parameters to the inner names set
+    // Scan parameter default values for captures (before adding params to inner names)
     let params = declaration.signature.parameters;
+    for (let i = 0, k = params.length; i < k; i++) {
+      let paramInit = params[i].initializer;
+      if (paramInit) {
+        this.scanNodeForCaptures(paramInit, outerFlow, innerFunctionNames, captures);
+      }
+    }
+
+    // Add the function's own parameters to the inner names set
     for (let i = 0, k = params.length; i < k; i++) {
       innerFunctionNames.add(params[i].name.text);
     }
@@ -8415,8 +8430,9 @@ export class Compiler extends DiagnosticEmitter {
       case NodeKind.Empty:
         break;
 
-      // Class expression - scan members would be complex, but class expressions with closures are rare
+      // Class expressions are not supported (will error during compilation)
       case NodeKind.Class:
+      // Constructor keyword - not a capturable expression
       case NodeKind.Constructor:
         break;
 
@@ -8473,8 +8489,16 @@ export class Compiler extends DiagnosticEmitter {
     let capturedNames = new Map<string, null>();
     let innerFunctionNames = new Set<string>();
 
-    // Add the function's own parameters to the inner names set
+    // Scan parameter default values for captures (before adding params to inner names)
     let params = declaration.signature.parameters;
+    for (let i = 0, k = params.length; i < k; i++) {
+      let paramInit = params[i].initializer;
+      if (paramInit) {
+        this.collectCapturedNames(paramInit, innerFunctionNames, outerFlow, declaredVars, capturedNames);
+      }
+    }
+
+    // Add the function's own parameters to the inner names set
     for (let i = 0, k = params.length; i < k; i++) {
       innerFunctionNames.add(params[i].name.text);
     }
@@ -8639,6 +8663,13 @@ export class Compiler extends DiagnosticEmitter {
         let funcExpr = <FunctionExpression>node;
         let decl = funcExpr.declaration;
         let params = decl.signature.parameters;
+        // Scan parameter default values for captures (before adding params to inner names)
+        for (let i = 0, k = params.length; i < k; i++) {
+          let paramInit = params[i].initializer;
+          if (paramInit) {
+            this.collectCapturedNames(paramInit, innerFunctionNames, outerFlow, declaredVars, capturedNames);
+          }
+        }
         // Add the nested function's params to inner names
         for (let i = 0, k = params.length; i < k; i++) {
           innerFunctionNames.add(params[i].name.text);
@@ -8788,8 +8819,9 @@ export class Compiler extends DiagnosticEmitter {
       case NodeKind.Empty:
         break;
 
-      // Class expression - would need to scan members, but rare in closure context
+      // Class expressions are not supported (will error during compilation)
       case NodeKind.Class:
+      // Constructor keyword - not a capturable expression
       case NodeKind.Constructor:
         break;