fix(compiler): closure transform generated parent_this even when no…

…t used (#6531)

This is a small code cleanup as part of addressing #4925.

We only generate the `parent_this` variable used in generated closure classes when needed. If the inflight closure never accesses `this` then we don't generated `parent_this`. The code avoids traversing into inner classes inside the closure when searching for `this` accesses, making it a bit cleaner and more efficient.

This relates to #4925 because it solves the problem of accessing `this` (for assignment into `parent_this`) before the `super()` call in a ctor.

## Checklist

- [x] Title matches [Winglang's style guide](https://www.winglang.io/contributing/start-here/pull_requests#how-are-pull-request-titles-formatted)
- [x] Description explains motivation and solution
- [ ] Tests added (always)
- [ ] Docs updated (only required for features)
- [ ] Added `pr/e2e-full` label if this feature requires end-to-end testing

*By submitting this pull request, I confirm that my contribution is made under the terms of the [Wing Cloud Contribution License](https://github.com/winglang/wing/blob/main/CONTRIBUTION_LICENSE.md)*.

libs/wingc/src/closure_transform.rs

@@ -156,16 +156,12 @@ impl Fold for ClosureTransformer {
 				let class_fields: Vec<ClassField> = vec![];
 				let class_init_params: Vec<FunctionParameter> = vec![];
 
+				let parent_this = format!("{}_{}", PARENT_THIS_NAME, self.closure_counter);
+				let mut this_transform = RenameThisTransformer::new(&parent_this.as_str());
 				let new_func_def = if self.inside_scope_with_this {
 					// If we are inside a class, we transform inflight closures with an extra
 					// `let __parent_this_${CLOSURE_COUNT} = this;` statement before the class definition, and replace references
 					// to `this` with `__parent_this_${CLOSURE_COUNT}` so that they can access the parent class's fields.
-					let parent_this = format!("{}_{}", PARENT_THIS_NAME, self.closure_counter);
-					let mut this_transform = RenameThisTransformer {
-						from: "this",
-						to: parent_this.as_str(),
-						inside_class: false,
-					};
 					this_transform.fold_function_definition(func_def)
 				} else {
 					func_def
@@ -226,11 +222,8 @@ impl Fold for ClosureTransformer {
 
 				// If we are inside a scope with "this", add define `let __parent_this_${CLOSURE_COUNT} = this` which can be
 				// used by the newly-created preflight classes
-				if self.inside_scope_with_this {
-					let parent_this_name = Symbol::new(
-						format!("{}_{}", PARENT_THIS_NAME, self.closure_counter),
-						WingSpan::for_file(file_id),
-					);
+				if self.inside_scope_with_this && this_transform.performed_renames {
+					let parent_this_name = Symbol::new(parent_this, WingSpan::for_file(file_id));
 					let this_name = Symbol::new("this", WingSpan::for_file(file_id));
 					let parent_this_def = Stmt {
 						kind: StmtKind::Let {
@@ -331,34 +324,31 @@ impl Fold for ClosureTransformer {
 struct RenameThisTransformer<'a> {
 	from: &'a str,
 	to: &'a str,
-	// The transform shouldn't change references to `this` inside inflight classes since
-	// they refer to different objects.
-	inside_class: bool,
+	performed_renames: bool,
 }
 
-impl Default for RenameThisTransformer<'_> {
-	fn default() -> Self {
+impl<'a> RenameThisTransformer<'a> {
+	fn new(to: &'a str) -> Self {
 		Self {
 			from: "this",
-			to: PARENT_THIS_NAME,
-			inside_class: false,
+			to,
+			performed_renames: false,
 		}
 	}
 }
 
 impl<'a> Fold for RenameThisTransformer<'a> {
 	fn fold_class(&mut self, node: Class) -> Class {
-		let old_inside_class = self.inside_class;
-		self.inside_class = true;
-		let new_class = fold::fold_class(self, node);
-		self.inside_class = old_inside_class;
-		new_class
+		// The transform shouldn't change references to `this` inside inflight classes since
+		// they refer to different objects. Skip inner class.
+		node
 	}
 
 	fn fold_reference(&mut self, node: Reference) -> Reference {
 		match node {
 			Reference::Identifier(ident) => {
-				if !self.inside_class && ident.name == self.from {
+				if ident.name == self.from {
+					self.performed_renames = true;
 					Reference::Identifier(Symbol {
 						name: self.to.to_string(),
 						span: ident.span,

libs/wingc/src/jsify/snapshots/closure_field.snap

@@ -113,7 +113,6 @@ class $Root extends $stdlib.std.Resource {
     class MyResource extends $stdlib.std.Resource {
       constructor($scope, $id, ) {
         super($scope, $id);
-        const __parent_this_1 = this;
         class $Closure1 extends $stdlib.std.AutoIdResource {
           _id = $stdlib.core.closureId();
           constructor($scope, $id, ) {

libs/wingc/src/jsify/snapshots/lift_inside_preflight_method.snap

@@ -82,7 +82,6 @@ class $Root extends $stdlib.std.Resource {
       }
       defineBucket(name) {
         const b = this.node.root.new("@winglang/sdk.cloud.Bucket", cloud.Bucket, this, name);
-        const __parent_this_1 = this;
         class $Closure1 extends $stdlib.std.AutoIdResource {
           _id = $stdlib.core.closureId();
           constructor($scope, $id, ) {

tools/hangar/__snapshots__/test_corpus/valid/calling_inflight_variants.test.w_compile_tf-aws.md

@@ -117,7 +117,6 @@ class $Root extends $stdlib.std.Resource {
     class Foo extends $stdlib.std.Resource {
       constructor($scope, $id, ) {
         super($scope, $id);
-        const __parent_this_1 = this;
         class $Closure1 extends $stdlib.std.AutoIdResource {
           _id = $stdlib.core.closureId();
           constructor($scope, $id, ) {

tools/hangar/__snapshots__/test_corpus/valid/capture_reassigable_class_field.test.w_compile_tf-aws.md

@@ -163,7 +163,6 @@ class $Root extends $stdlib.std.Resource {
       constructor($scope, $id, ) {
         super($scope, $id);
         this.bucket = this.node.root.new("@winglang/sdk.cloud.Bucket", cloud.Bucket, this, "Bucket");
-        const __parent_this_1 = this;
         class $Closure1 extends $stdlib.std.AutoIdResource {
           _id = $stdlib.core.closureId();
           constructor($scope, $id, ) {

tools/hangar/__snapshots__/test_corpus/valid/doubler.test.w_compile_tf-aws.md

@@ -328,7 +328,6 @@ class $Root extends $stdlib.std.Resource {
         super($scope, $id);
       }
       makeFunc(handler) {
-        const __parent_this_2 = this;
         class $Closure2 extends $stdlib.std.AutoIdResource {
           _id = $stdlib.core.closureId();
           constructor($scope, $id, ) {

tools/hangar/__snapshots__/test_corpus/valid/inflight_class_definitions.test.w_compile_tf-aws.md

@@ -343,7 +343,6 @@ class $Root extends $stdlib.std.Resource {
             });
           }
         }
-        const __parent_this_2 = this;
         class $Closure2 extends $stdlib.std.AutoIdResource {
           _id = $stdlib.core.closureId();
           constructor($scope, $id, ) {

tools/hangar/__snapshots__/test_corpus/valid/inflight_closure_inside_preflight_closure.test.w_compile_tf-aws.md

@@ -69,7 +69,6 @@ class $Root extends $stdlib.std.Resource {
       constructor($scope, $id, ) {
         super($scope, $id);
         const foo = (() => {
-          const __parent_this_1 = this;
           class $Closure1 extends $stdlib.std.AutoIdResource {
             _id = $stdlib.core.closureId();
             constructor($scope, $id, ) {

tools/hangar/__snapshots__/test_corpus/valid/inflights_calling_inflights.test.w_compile_tf-aws.md

@@ -388,7 +388,6 @@ class $Root extends $stdlib.std.Resource {
     class MyResource extends $stdlib.std.Resource {
       constructor($scope, $id, ) {
         super($scope, $id);
-        const __parent_this_4 = this;
         class $Closure4 extends $stdlib.std.AutoIdResource {
           _id = $stdlib.core.closureId();
           constructor($scope, $id, ) {

tools/hangar/__snapshots__/test_corpus/valid/mutation_after_class_init.test.w_compile_tf-aws.md

@@ -349,7 +349,6 @@ class $Root extends $stdlib.std.Resource {
       constructor($scope, $id, ) {
         super($scope, $id);
         this.data = this.node.root.new("@winglang/sdk.cloud.Bucket", cloud.Bucket, this, "Bucket");
-        const __parent_this_1 = this;
         class $Closure1 extends $stdlib.std.AutoIdResource {
           _id = $stdlib.core.closureId();
           constructor($scope, $id, ) {

tools/hangar/__snapshots__/test_corpus/valid/symbol_shadow.test.w_compile_tf-aws.md

@@ -133,7 +133,6 @@ class $Root extends $stdlib.std.Resource {
         super($scope, $id);
         const s = "inResource";
         $helpers.assert($helpers.eq(s, "inResource"), "s == \"inResource\"");
-        const __parent_this_2 = this;
         class $Closure2 extends $stdlib.std.AutoIdResource {
           _id = $stdlib.core.closureId();
           constructor($scope, $id, ) {