explicitly disallow using in ambient contexts (microsoft#61781)

codeOwlAI · Jun 5, 2025 · Jun 5, 2025 · Jun 6, 2025 · Jun 6, 2025 · Jun 6, 2025
commit 1e2494566eb6d352844e00b34b15d67c025d307d
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -52856,17 +52856,28 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         }
 
         const blockScopeFlags = declarationList.flags & NodeFlags.BlockScoped;
-        if ((blockScopeFlags === NodeFlags.Using || blockScopeFlags === NodeFlags.AwaitUsing) && isForInStatement(declarationList.parent)) {
-            return grammarErrorOnNode(
-                declarationList,
-                blockScopeFlags === NodeFlags.Using ?
-                    Diagnostics.The_left_hand_side_of_a_for_in_statement_cannot_be_a_using_declaration :
-                    Diagnostics.The_left_hand_side_of_a_for_in_statement_cannot_be_an_await_using_declaration,
-            );
-        }
+        if (blockScopeFlags === NodeFlags.Using || blockScopeFlags === NodeFlags.AwaitUsing) {
+            if (isForInStatement(declarationList.parent)) {
+                return grammarErrorOnNode(
+                    declarationList,
+                    blockScopeFlags === NodeFlags.Using ?
+                        Diagnostics.The_left_hand_side_of_a_for_in_statement_cannot_be_a_using_declaration :
+                        Diagnostics.The_left_hand_side_of_a_for_in_statement_cannot_be_an_await_using_declaration,
+                );
+            }
 
-        if (blockScopeFlags === NodeFlags.AwaitUsing) {
-            return checkAwaitGrammar(declarationList);
+            if (declarationList.flags & NodeFlags.Ambient) {
+                return grammarErrorOnNode(
+                    declarationList,
+                    blockScopeFlags === NodeFlags.Using ?
+                        Diagnostics.using_declarations_are_not_allowed_in_ambient_contexts :
+                        Diagnostics.await_using_declarations_are_not_allowed_in_ambient_contexts,
+                );
+            }
+
+            if (blockScopeFlags === NodeFlags.AwaitUsing) {
+                return checkAwaitGrammar(declarationList);
+            }
         }
 
         return false;

diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
@@ -1837,6 +1837,14 @@
         "category": "Error",
         "code": 1544
     },
+    "'using' declarations are not allowed in ambient contexts.": {
+        "category": "Error",
+        "code": 1545
+    },
+    "'await using' declarations are not allowed in ambient contexts.": {
+        "category": "Error",
+        "code": 1546
+    },
 
     "The types of '{0}' are incompatible between these types.": {
         "category": "Error",

diff --git a/tests/baselines/reference/awaitUsingDeclarations.16.errors.txt b/tests/baselines/reference/awaitUsingDeclarations.16.errors.txt
@@ -0,0 +1,24 @@
+awaitUsingDeclarations.16.ts(2,5): error TS1546: 'await using' declarations are not allowed in ambient contexts.
+awaitUsingDeclarations.16.ts(3,5): error TS1546: 'await using' declarations are not allowed in ambient contexts.
+awaitUsingDeclarations.16.ts(6,5): error TS1546: 'await using' declarations are not allowed in ambient contexts.
+awaitUsingDeclarations.16.ts(7,5): error TS1546: 'await using' declarations are not allowed in ambient contexts.
+
+
+==== awaitUsingDeclarations.16.ts (4 errors) ====
+    declare namespace N {
+        await using x: { [Symbol.asyncDispose](): Promise<void> };
+        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS1546: 'await using' declarations are not allowed in ambient contexts.
+        await using y: null;
+        ~~~~~~~~~~~~~~~~~~~
+!!! error TS1546: 'await using' declarations are not allowed in ambient contexts.
+    }
+    declare module 'M' {
+        await using x: { [Symbol.asyncDispose](): Promise<void> };
+        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS1546: 'await using' declarations are not allowed in ambient contexts.
+        await using y: null;
+        ~~~~~~~~~~~~~~~~~~~
+!!! error TS1546: 'await using' declarations are not allowed in ambient contexts.
+    }
+
diff --git a/tests/baselines/reference/awaitUsingDeclarations.16.js b/tests/baselines/reference/awaitUsingDeclarations.16.js
@@ -0,0 +1,14 @@
+//// [tests/cases/conformance/statements/VariableStatements/usingDeclarations/awaitUsingDeclarations.16.ts] ////
+
+//// [awaitUsingDeclarations.16.ts]
+declare namespace N {
+    await using x: { [Symbol.asyncDispose](): Promise<void> };
+    await using y: null;
+}
+declare module 'M' {
+    await using x: { [Symbol.asyncDispose](): Promise<void> };
+    await using y: null;
+}
+
+
+//// [awaitUsingDeclarations.16.js]
diff --git a/tests/baselines/reference/usingDeclarations.16.errors.txt b/tests/baselines/reference/usingDeclarations.16.errors.txt
@@ -0,0 +1,24 @@
+usingDeclarations.16.ts(2,5): error TS1545: 'using' declarations are not allowed in ambient contexts.
+usingDeclarations.16.ts(3,5): error TS1545: 'using' declarations are not allowed in ambient contexts.
+usingDeclarations.16.ts(6,5): error TS1545: 'using' declarations are not allowed in ambient contexts.
+usingDeclarations.16.ts(7,5): error TS1545: 'using' declarations are not allowed in ambient contexts.
+
+
+==== usingDeclarations.16.ts (4 errors) ====
+    declare namespace N {
+        using x: { [Symbol.dispose](): void };
+        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS1545: 'using' declarations are not allowed in ambient contexts.
+        using y: null;
+        ~~~~~~~~~~~~~
+!!! error TS1545: 'using' declarations are not allowed in ambient contexts.
+    }
+    declare module 'M' {
+        using x: { [Symbol.dispose](): void };
+        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS1545: 'using' declarations are not allowed in ambient contexts.
+        using y: null;
+        ~~~~~~~~~~~~~
+!!! error TS1545: 'using' declarations are not allowed in ambient contexts.
+    }
+
diff --git a/tests/baselines/reference/usingDeclarations.16.js b/tests/baselines/reference/usingDeclarations.16.js
@@ -0,0 +1,14 @@
+//// [tests/cases/conformance/statements/VariableStatements/usingDeclarations/usingDeclarations.16.ts] ////
+
+//// [usingDeclarations.16.ts]
+declare namespace N {
+    using x: { [Symbol.dispose](): void };
+    using y: null;
+}
+declare module 'M' {
+    using x: { [Symbol.dispose](): void };
+    using y: null;
+}
+
+
+//// [usingDeclarations.16.js]
diff --git a/.../conformance/statements/VariableStatements/usingDeclarations/awaitUsingDeclarations.16.ts b/.../conformance/statements/VariableStatements/usingDeclarations/awaitUsingDeclarations.16.ts
@@ -0,0 +1,13 @@
+// @target: esnext
+// @module: esnext
+// @lib: esnext
+// @noTypesAndSymbols: true
+
+declare namespace N {
+    await using x: { [Symbol.asyncDispose](): Promise<void> };
+    await using y: null;
+}
+declare module 'M' {
+    await using x: { [Symbol.asyncDispose](): Promise<void> };
+    await using y: null;
+}
diff --git a/...cases/conformance/statements/VariableStatements/usingDeclarations/usingDeclarations.16.ts b/...cases/conformance/statements/VariableStatements/usingDeclarations/usingDeclarations.16.ts
@@ -0,0 +1,13 @@
+// @target: esnext
+// @module: esnext
+// @lib: esnext
+// @noTypesAndSymbols: true
+
+declare namespace N {
+    using x: { [Symbol.dispose](): void };
+    using y: null;
+}
+declare module 'M' {
+    using x: { [Symbol.dispose](): void };
+    using y: null;
+}