fix(43879): forbid async in the left hand in a for-of statement

Author: a-tarasyuk

src/compiler/checker.ts

@@ -41471,6 +41471,11 @@ namespace ts {
                 }
             }
 
+            if (isForOfStatement(forInOrOfStatement) && isIdentifier(forInOrOfStatement.initializer) && forInOrOfStatement.initializer.escapedText === "async") {
+                grammarErrorOnNode(forInOrOfStatement.initializer, Diagnostics.The_left_hand_side_of_a_for_of_statement_may_not_be_async);
+                return false;
+            }
+
             if (forInOrOfStatement.initializer.kind === SyntaxKind.VariableDeclarationList) {
                 const variableList = <VariableDeclarationList>forInOrOfStatement.initializer;
                 if (!checkGrammarVariableDeclarationList(variableList)) {

src/compiler/diagnosticMessages.json

@@ -319,6 +319,10 @@
         "category": "Error",
         "code": 1105
     },
+    "The left-hand side of a for-of statement may not be 'async'.": {
+        "category": "Error",
+        "code": 1106
+    },
     "Jump target cannot cross function boundary.": {
         "category": "Error",
         "code": 1107

tests/baselines/reference/parserForOfStatement22.errors.txt

@@ -0,0 +1,9 @@
+tests/cases/conformance/parser/ecmascript6/Iterators/parserForOfStatement22.ts(2,6): error TS1106: The left-hand side of a for-of statement may not be 'async'.
+
+
+==== tests/cases/conformance/parser/ecmascript6/Iterators/parserForOfStatement22.ts (1 errors) ====
+    var async;
+    for (async of [1, 2]) {}
+         ~~~~~
+!!! error TS1106: The left-hand side of a for-of statement may not be 'async'.
+    

tests/baselines/reference/parserForOfStatement22.js

@@ -0,0 +1,8 @@
+//// [parserForOfStatement22.ts]
+var async;
+for (async of [1, 2]) {}
+
+
+//// [parserForOfStatement22.js]
+var async;
+for (async of [1, 2]) { }

tests/baselines/reference/parserForOfStatement22.symbols

@@ -0,0 +1,7 @@
+=== tests/cases/conformance/parser/ecmascript6/Iterators/parserForOfStatement22.ts ===
+var async;
+>async : Symbol(async, Decl(parserForOfStatement22.ts, 0, 3))
+
+for (async of [1, 2]) {}
+>async : Symbol(async, Decl(parserForOfStatement22.ts, 0, 3))
+

tests/baselines/reference/parserForOfStatement22.types

@@ -0,0 +1,10 @@
+=== tests/cases/conformance/parser/ecmascript6/Iterators/parserForOfStatement22.ts ===
+var async;
+>async : any
+
+for (async of [1, 2]) {}
+>async : any
+>[1, 2] : number[]
+>1 : 1
+>2 : 2
+

tests/cases/conformance/parser/ecmascript6/Iterators/parserForOfStatement22.ts

@@ -0,0 +1,4 @@
+// @target: esnext
+
+var async;
+for (async of [1, 2]) {}