Fix using transform variable shadowing in for-of loops

src/compiler/transformers/esnext.ts

@@ -301,11 +301,12 @@ export function transformESNext(context: TransformationContext): (x: SourceFile
             // produces a shallow transformation to:
             //
             //  for (const x_1 of y) {
-            //    using x = x;
-            //    ...
+            //    using x = x_1;
+            //    { ... }
             //  }
             //
-            // before handing the shallow transformation back to the visitor for an in-depth transformation.
+            // where the original loop body is wrapped in an additional block scope
+            // to handle shadowing variables naturally through block scoping.
             const forInitializer = node.initializer;
             const forDecl = firstOrUndefined(forInitializer.declarations) || factory.createVariableDeclaration(factory.createTempVariable(/*recordTempVariable*/ undefined));
 
@@ -314,6 +315,26 @@ export function transformESNext(context: TransformationContext): (x: SourceFile
             const usingVar = factory.updateVariableDeclaration(forDecl, forDecl.name, /*exclamationToken*/ undefined, /*type*/ undefined, temp);
             const usingVarList = factory.createVariableDeclarationList([usingVar], isAwaitUsing ? NodeFlags.AwaitUsing : NodeFlags.Using);
             const usingVarStatement = factory.createVariableStatement(/*modifiers*/ undefined, usingVarList);
+
+            // Wrap the original loop body in an additional block scope to handle shadowing
+            // Don't create an extra block if the original statement is empty or contains only empty statements
+            const isEmptyBlock = isBlock(node.statement) && (
+                node.statement.statements.length === 0 ||
+                node.statement.statements.every(stmt => stmt.kind === SyntaxKind.EmptyStatement)
+            );
+            const shouldWrapInBlock = !isEmptyBlock;
+
+            const statements: Statement[] = [usingVarStatement];
+            if (shouldWrapInBlock) {
+                const wrappedStatement = isBlock(node.statement) ?
+                    node.statement :
+                    factory.createBlock([node.statement], /*multiLine*/ true);
+                statements.push(wrappedStatement);
+            }
+            else {
+                statements.push(...(isBlock(node.statement) ? node.statement.statements : [node.statement]));
+            }
+
             return visitNode(
                 factory.updateForOfStatement(
                     node,
@@ -322,15 +343,7 @@ export function transformESNext(context: TransformationContext): (x: SourceFile
                         factory.createVariableDeclaration(temp),
                     ], NodeFlags.Const),
                     node.expression,
-                    isBlock(node.statement) ?
-                        factory.updateBlock(node.statement, [
-                            usingVarStatement,
-                            ...node.statement.statements,
-                        ]) :
-                        factory.createBlock([
-                            usingVarStatement,
-                            node.statement,
-                        ], /*multiLine*/ true),
+                    factory.createBlock(statements, /*multiLine*/ true),
                 ),
                 visitor,
                 isStatement,

tests/baselines/reference/awaitUsingDeclarationsInForAwaitOf.3(target=es5).js

@@ -118,7 +118,9 @@ try {
         var env_1 = { stack: [], error: void 0, hasError: false };
         try {
             var _e = __addDisposableResource(env_1, _e_1, true);
-            ;
+            {
+                ;
+            }
         }
         catch (e_2) {
             env_1.error = e_2;
@@ -159,7 +161,9 @@ export function test() {
                 case 3:
                     _f.trys.push([3, 4, 5, 8]);
                     _b = __addDisposableResource(env_2, _b_1, true);
-                    ;
+                    {
+                        ;
+                    }
                     return [3 /*break*/, 8];
                 case 4:
                     e_3 = _f.sent();

tests/baselines/reference/awaitUsingDeclarationsInForOf.5(target=es5).js

@@ -107,7 +107,9 @@ for (var _i = 0, x_1 = x; _i < x_1.length; _i++) {
     var env_1 = { stack: [], error: void 0, hasError: false };
     try {
         var _a = __addDisposableResource(env_1, _a_1, true);
-        ;
+        {
+            ;
+        }
     }
     catch (e_1) {
         env_1.error = e_1;
@@ -135,7 +137,9 @@ export function test() {
                 case 2:
                     _b.trys.push([2, 3, 4, 7]);
                     _a = __addDisposableResource(env_2, _a_2, true);
-                    ;
+                    {
+                        ;
+                    }
                     return [3 /*break*/, 7];
                 case 3:
                     e_2 = _b.sent();

tests/baselines/reference/usingDeclarationsInForOfShadowing(target=es2015).errors.txt

@@ -0,0 +1,24 @@
+main.ts(12,7): error TS2481: Cannot initialize outer scoped variable 'baz' in the same scope as block scoped declaration 'baz'.
+
+
+==== main.ts (1 errors) ====
+    class Foo {}
+
+    for (using foo of []) {
+      const foo = new Foo();
+    }
+
+    for (using bar of []) {
+      let bar = "test";
+    }
+
+    for (using baz of []) {
+      var baz = 42;
+          ~~~
+!!! error TS2481: Cannot initialize outer scoped variable 'baz' in the same scope as block scoped declaration 'baz'.
+    }
+
+==== tslib.d.ts (0 errors) ====
+    export declare function __addDisposableResource<T>(env: any, value: T, async: boolean): T;
+    export declare function __disposeResources(env: any): void;
+

tests/baselines/reference/usingDeclarationsInForOfShadowing(target=es2015).js

@@ -0,0 +1,125 @@
+//// [tests/cases/conformance/statements/VariableStatements/usingDeclarations/usingDeclarationsInForOfShadowing.ts] ////
+
+//// [main.ts]
+class Foo {}
+
+for (using foo of []) {
+  const foo = new Foo();
+}
+
+for (using bar of []) {
+  let bar = "test";
+}
+
+for (using baz of []) {
+  var baz = 42;
+}
+
+//// [tslib.d.ts]
+export declare function __addDisposableResource<T>(env: any, value: T, async: boolean): T;
+export declare function __disposeResources(env: any): void;
+
+
+//// [main.js]
+var __addDisposableResource = (this && this.__addDisposableResource) || function (env, value, async) {
+    if (value !== null && value !== void 0) {
+        if (typeof value !== "object" && typeof value !== "function") throw new TypeError("Object expected.");
+        var dispose, inner;
+        if (async) {
+            if (!Symbol.asyncDispose) throw new TypeError("Symbol.asyncDispose is not defined.");
+            dispose = value[Symbol.asyncDispose];
+        }
+        if (dispose === void 0) {
+            if (!Symbol.dispose) throw new TypeError("Symbol.dispose is not defined.");
+            dispose = value[Symbol.dispose];
+            if (async) inner = dispose;
+        }
+        if (typeof dispose !== "function") throw new TypeError("Object not disposable.");
+        if (inner) dispose = function() { try { inner.call(this); } catch (e) { return Promise.reject(e); } };
+        env.stack.push({ value: value, dispose: dispose, async: async });
+    }
+    else if (async) {
+        env.stack.push({ async: true });
+    }
+    return value;
+};
+var __disposeResources = (this && this.__disposeResources) || (function (SuppressedError) {
+    return function (env) {
+        function fail(e) {
+            env.error = env.hasError ? new SuppressedError(e, env.error, "An error was suppressed during disposal.") : e;
+            env.hasError = true;
+        }
+        var r, s = 0;
+        function next() {
+            while (r = env.stack.pop()) {
+                try {
+                    if (!r.async && s === 1) return s = 0, env.stack.push(r), Promise.resolve().then(next);
+                    if (r.dispose) {
+                        var result = r.dispose.call(r.value);
+                        if (r.async) return s |= 2, Promise.resolve(result).then(next, function(e) { fail(e); return next(); });
+                    }
+                    else s |= 1;
+                }
+                catch (e) {
+                    fail(e);
+                }
+            }
+            if (s === 1) return env.hasError ? Promise.reject(env.error) : Promise.resolve();
+            if (env.hasError) throw env.error;
+        }
+        return next();
+    };
+})(typeof SuppressedError === "function" ? SuppressedError : function (error, suppressed, message) {
+    var e = new Error(message);
+    return e.name = "SuppressedError", e.error = error, e.suppressed = suppressed, e;
+});
+class Foo {
+}
+for (const foo_1 of []) {
+    const env_1 = { stack: [], error: void 0, hasError: false };
+    try {
+        const foo = __addDisposableResource(env_1, foo_1, false);
+        {
+            const foo = new Foo();
+        }
+    }
+    catch (e_1) {
+        env_1.error = e_1;
+        env_1.hasError = true;
+    }
+    finally {
+        __disposeResources(env_1);
+    }
+}
+for (const bar_1 of []) {
+    const env_2 = { stack: [], error: void 0, hasError: false };
+    try {
+        const bar = __addDisposableResource(env_2, bar_1, false);
+        {
+            let bar = "test";
+        }
+    }
+    catch (e_2) {
+        env_2.error = e_2;
+        env_2.hasError = true;
+    }
+    finally {
+        __disposeResources(env_2);
+    }
+}
+for (const baz_1 of []) {
+    const env_3 = { stack: [], error: void 0, hasError: false };
+    try {
+        const baz = __addDisposableResource(env_3, baz_1, false);
+        {
+            var baz = 42;
+        }
+    }
+    catch (e_3) {
+        env_3.error = e_3;
+        env_3.hasError = true;
+    }
+    finally {
+        __disposeResources(env_3);
+    }
+}

tests/baselines/reference/usingDeclarationsInForOfShadowing(target=es2017).errors.txt

@@ -0,0 +1,24 @@
+main.ts(12,7): error TS2481: Cannot initialize outer scoped variable 'baz' in the same scope as block scoped declaration 'baz'.
+
+
+==== main.ts (1 errors) ====
+    class Foo {}
+
+    for (using foo of []) {
+      const foo = new Foo();
+    }
+
+    for (using bar of []) {
+      let bar = "test";
+    }
+
+    for (using baz of []) {
+      var baz = 42;
+          ~~~
+!!! error TS2481: Cannot initialize outer scoped variable 'baz' in the same scope as block scoped declaration 'baz'.
+    }
+
+==== tslib.d.ts (0 errors) ====
+    export declare function __addDisposableResource<T>(env: any, value: T, async: boolean): T;
+    export declare function __disposeResources(env: any): void;
+