Allow of in await using declarations in for-of loops (#55558)

Author: Andarist

src/compiler/parser.ts

@@ -6892,7 +6892,8 @@ namespace Parser {
             if (
                 token() === SyntaxKind.VarKeyword || token() === SyntaxKind.LetKeyword || token() === SyntaxKind.ConstKeyword ||
                 token() === SyntaxKind.UsingKeyword && lookAhead(nextTokenIsBindingIdentifierOrStartOfDestructuringOnSameLineDisallowOf) ||
-                token() === SyntaxKind.AwaitKeyword && lookAhead(nextTokenIsUsingKeywordThenBindingIdentifierOrStartOfObjectDestructuringOnSameLineDisallowOf)
+                // this one is meant to allow of
+                token() === SyntaxKind.AwaitKeyword && lookAhead(nextTokenIsUsingKeywordThenBindingIdentifierOrStartOfObjectDestructuringOnSameLine)
             ) {
                 initializer = parseVariableDeclarationList(/*inForStatementInitializer*/ true);
             }
@@ -7308,10 +7309,6 @@ namespace Parser {
         return lookAhead(nextTokenIsBindingIdentifierOrStartOfDestructuringOnSameLine);
     }
 
-    function nextTokenIsUsingKeywordThenBindingIdentifierOrStartOfObjectDestructuringOnSameLineDisallowOf() {
-        return nextTokenIsUsingKeywordThenBindingIdentifierOrStartOfObjectDestructuringOnSameLine(/*disallowOf*/ true);
-    }
-
     function nextTokenIsUsingKeywordThenBindingIdentifierOrStartOfObjectDestructuringOnSameLine(disallowOf?: boolean) {
         if (nextToken() === SyntaxKind.UsingKeyword) {
             return nextTokenIsBindingIdentifierOrStartOfDestructuringOnSameLine(disallowOf);

tests/baselines/reference/awaitUsingDeclarationsInForAwaitOf.2.errors.txt

@@ -0,0 +1,13 @@
+awaitUsingDeclarationsInForAwaitOf.2.ts(4,32): error TS2448: Block-scoped variable 'of' used before its declaration.
+
+
+==== awaitUsingDeclarationsInForAwaitOf.2.ts (1 errors) ====
+    // https://github.com/microsoft/TypeScript/issues/55555
+    
+    async function test() {
+      for await (await using of of of) {};
+                                   ~~
+!!! error TS2448: Block-scoped variable 'of' used before its declaration.
+!!! related TS2728 awaitUsingDeclarationsInForAwaitOf.2.ts:4:26: 'of' is declared here.
+    }
+    

tests/baselines/reference/awaitUsingDeclarationsInForAwaitOf.2.js

@@ -0,0 +1,16 @@
+//// [tests/cases/conformance/statements/VariableStatements/usingDeclarations/awaitUsingDeclarationsInForAwaitOf.2.ts] ////
+
+//// [awaitUsingDeclarationsInForAwaitOf.2.ts]
+// https://github.com/microsoft/TypeScript/issues/55555
+
+async function test() {
+  for await (await using of of of) {};
+}
+
+
+//// [awaitUsingDeclarationsInForAwaitOf.2.js]
+// https://github.com/microsoft/TypeScript/issues/55555
+async function test() {
+    for await (await using of of of) { }
+    ;
+}

tests/baselines/reference/awaitUsingDeclarationsInForOf.2.errors.txt

@@ -9,6 +9,6 @@ async function main() {
 
 //// [awaitUsingDeclarationsInForOf.2.js]
 async function main() {
-    for (await using of of[]) {
+    for (await using of of []) {
     }
 }

tests/baselines/reference/awaitUsingDeclarationsInForOf.2.js

@@ -0,0 +1,16 @@
+awaitUsingDeclarationsInForOf.4.ts(4,8): error TS2853: 'await using' statements are only allowed at the top level of a file when that file is a module, but this file has no imports or exports. Consider adding an empty 'export {}' to make this file a module.
+awaitUsingDeclarationsInForOf.4.ts(4,26): error TS2448: Block-scoped variable 'of' used before its declaration.
+
+
+==== awaitUsingDeclarationsInForOf.4.ts (2 errors) ====
+    // https://github.com/microsoft/TypeScript/issues/55555
+    
+    {
+      for (await using of of of) {};
+           ~~~~~
+!!! error TS2853: 'await using' statements are only allowed at the top level of a file when that file is a module, but this file has no imports or exports. Consider adding an empty 'export {}' to make this file a module.
+                             ~~
+!!! error TS2448: Block-scoped variable 'of' used before its declaration.
+!!! related TS2728 awaitUsingDeclarationsInForOf.4.ts:4:20: 'of' is declared here.
+    }
+    

tests/baselines/reference/awaitUsingDeclarationsInForOf.4.errors.txt

@@ -0,0 +1,16 @@
+//// [tests/cases/conformance/statements/VariableStatements/usingDeclarations/awaitUsingDeclarationsInForOf.4.ts] ////
+
+//// [awaitUsingDeclarationsInForOf.4.ts]
+// https://github.com/microsoft/TypeScript/issues/55555
+
+{
+  for (await using of of of) {};
+}
+
+
+//// [awaitUsingDeclarationsInForOf.4.js]
+// https://github.com/microsoft/TypeScript/issues/55555
+{
+    for (await using of of of) { }
+    ;
+}

tests/baselines/reference/awaitUsingDeclarationsInForOf.4.js

@@ -0,0 +1,10 @@
+// @target: esnext
+// @module: esnext
+// @lib: esnext
+// @noTypesAndSymbols: true
+
+// https://github.com/microsoft/TypeScript/issues/55555
+
+async function test() {
+  for await (await using of of of) {};
+}

tests/cases/conformance/statements/VariableStatements/usingDeclarations/awaitUsingDeclarationsInForAwaitOf.2.ts

@@ -0,0 +1,10 @@
+// @target: esnext
+// @module: esnext
+// @lib: esnext
+// @noTypesAndSymbols: true
+
+// https://github.com/microsoft/TypeScript/issues/55555
+
+{
+  for (await using of of of) {};
+}