feat(semantic): check for type annotations on left side of for..in and for..of iterators

crates/oxc_semantic/src/checker/mod.rs

@@ -53,10 +53,12 @@ pub fn check<'a>(node: &AstNode<'a>, ctx: &SemanticBuilder<'a>) {
         AstKind::ForInStatement(stmt) => {
             js::check_function_declaration(&stmt.body, false, ctx);
             js::check_for_statement_left(&stmt.left, true, node, ctx);
+            ts::check_for_statement_left(&stmt.left, true, ctx);
         }
         AstKind::ForOfStatement(stmt) => {
             js::check_function_declaration(&stmt.body, false, ctx);
             js::check_for_statement_left(&stmt.left, false, node, ctx);
+            ts::check_for_statement_left(&stmt.left, false, ctx);
         }
         AstKind::WhileStatement(WhileStatement { body, .. })
         | AstKind::DoWhileStatement(DoWhileStatement { body, .. })

crates/oxc_semantic/src/checker/typescript.rs

@@ -479,3 +479,27 @@ pub fn check_object_property(prop: &ObjectProperty, ctx: &SemanticBuilder<'_>) {
         }
     }
 }
+
+/// The left-hand side of a 'for...of' statement cannot use a type annotation. (2483)
+fn type_annotation_in_for_left(span: Span, is_for_in: bool) -> OxcDiagnostic {
+    let for_of_or_in = if is_for_in { "for...in" } else { "for...of" };
+    ts_error(
+        "2483",
+        format!(
+            "The left-hand side of a '{for_of_or_in}' statement cannot use a type annotation.",
+        ),
+    ).with_label(span).with_help("This iterator's type will be inferred from the iterable. You can safely remove the type annotation.")
+}
+
+pub fn check_for_statement_left(left: &ForStatementLeft, is_for_in: bool, ctx: &SemanticBuilder) {
+    let ForStatementLeft::VariableDeclaration(decls) = left else {
+        return;
+    };
+
+    for decl in &decls.declarations {
+        if decl.id.type_annotation.is_some() {
+            let span = decl.id.span();
+            ctx.error(type_annotation_in_for_left(span, is_for_in));
+        }
+    }
+}

tasks/coverage/snapshots/parser_typescript.snap

@@ -3,7 +3,7 @@ commit: a709f989
 parser_typescript Summary:
 AST Parsed     : 6469/6479 (99.85%)
 Positive Passed: 6458/6479 (99.68%)
-Negative Passed: 1228/5715 (21.49%)
+Negative Passed: 1234/5715 (21.59%)
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/ClassDeclaration10.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/ClassDeclaration11.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/ClassDeclaration13.ts
@@ -854,10 +854,8 @@ Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/firstMatchRe
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/fixTypeParameterInSignatureWithRestParameters.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/fixingTypeParametersRepeatedly2.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/flatArrayNoExcessiveStackDepth.ts
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/forIn.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/forIn2.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/forInStatement2.ts
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/forInStatement4.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/forInStatement7.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/forInStrictNullChecksNoError.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/forwardDeclaredCommonTypes01.ts
@@ -3850,14 +3848,12 @@ Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ec
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserES5ForOfStatement15.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserES5ForOfStatement16.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserES5ForOfStatement20.ts
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserES5ForOfStatement5.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserES5ForOfStatement8.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserES5ForOfStatement9.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserEmptyStatement1.d.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserExpressionStatement1.d.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserForInStatement1.d.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserForInStatement4.ts
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserForInStatement5.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserForInStatement8.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserForStatement1.d.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserForStatement2.ts
@@ -3962,7 +3958,6 @@ Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ec
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript6/Iterators/parserForOfStatement15.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript6/Iterators/parserForOfStatement16.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript6/Iterators/parserForOfStatement20.ts
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript6/Iterators/parserForOfStatement5.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript6/Iterators/parserForOfStatement8.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript6/Iterators/parserForOfStatement9.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/pedantic/noUncheckedIndexedAccess.ts
@@ -4071,7 +4066,6 @@ Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/statement
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/statements/for-inStatements/for-inStatementsDestructuring2.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/statements/for-inStatements/for-inStatementsDestructuring3.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/statements/for-inStatements/for-inStatementsDestructuring4.ts
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/statements/for-ofStatements/ES5For-of17.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/statements/for-ofStatements/ES5For-of26.ts
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/statements/for-ofStatements/ES5For-of27.ts
@@ -7901,6 +7895,24 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
  30 │ }
     ╰────
 
+  × TS(2483): The left-hand side of a 'for...in' statement cannot use a type annotation.
+   ╭─[typescript/tests/cases/compiler/forIn.ts:2:10]
+ 1 │ var arr = null;
+ 2 │ for (var i:number in arr) { // error
+   ·          ────────
+ 3 │     var x1 = arr[i];
+   ╰────
+  help: This iterator's type will be inferred from the iterable. You can safely remove the type annotation.
+
+  × TS(2483): The left-hand side of a 'for...in' statement cannot use a type annotation.
+   ╭─[typescript/tests/cases/compiler/forInStatement4.ts:2:10]
+ 1 │ var expr: any;
+ 2 │ for (var a: number in expr) {
+   ·          ─────────
+ 3 │ }
+   ╰────
+  help: This iterator's type will be inferred from the iterable. You can safely remove the type annotation.
+
   × Identifier `foo3` has already been declared
     ╭─[typescript/tests/cases/compiler/funClodule.ts:15:10]
  14 │ 
@@ -21644,6 +21656,14 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
  2 │ }
    ╰────
 
+  × TS(2483): The left-hand side of a 'for...of' statement cannot use a type annotation.
+   ╭─[typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserES5ForOfStatement5.ts:1:10]
+ 1 │ for (var a: number of X) {
+   ·          ─────────
+ 2 │ }
+   ╰────
+  help: This iterator's type will be inferred from the iterable. You can safely remove the type annotation.
+
   × Only a single declaration is allowed in a `for...of` statement
    ╭─[typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserES5ForOfStatement6.ts:1:6]
  1 │ for (var a = 1, b = 2 of X) {
@@ -21658,6 +21678,22 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
  2 │ }
    ╰────
 
+  × TS(2483): The left-hand side of a 'for...of' statement cannot use a type annotation.
+   ╭─[typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserES5ForOfStatement7.ts:1:10]
+ 1 │ for (var a: number = 1, b: string = "" of X) {
+   ·          ─────────
+ 2 │ }
+   ╰────
+  help: This iterator's type will be inferred from the iterable. You can safely remove the type annotation.
+
+  × TS(2483): The left-hand side of a 'for...of' statement cannot use a type annotation.
+   ╭─[typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserES5ForOfStatement7.ts:1:25]
+ 1 │ for (var a: number = 1, b: string = "" of X) {
+   ·                         ─────────
+ 2 │ }
+   ╰────
+  help: This iterator's type will be inferred from the iterable. You can safely remove the type annotation.
+
   × Unexpected token
    ╭─[typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserForInStatement2.ts:1:10]
  1 │ for (var in X) {
@@ -21672,6 +21708,14 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
  2 │ }
    ╰────
 
+  × TS(2483): The left-hand side of a 'for...in' statement cannot use a type annotation.
+   ╭─[typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserForInStatement5.ts:1:10]
+ 1 │ for (var a: number in X) {
+   ·          ─────────
+ 2 │ }
+   ╰────
+  help: This iterator's type will be inferred from the iterable. You can safely remove the type annotation.
+
   × Only a single declaration is allowed in a `for...in` statement
    ╭─[typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserForInStatement6.ts:1:6]
  1 │ for (var a = 1, b = 2 in X) {
@@ -21686,6 +21730,22 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
  2 │ }
    ╰────
 
+  × TS(2483): The left-hand side of a 'for...in' statement cannot use a type annotation.
+   ╭─[typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserForInStatement7.ts:1:10]
+ 1 │ for (var a: number = 1, b: string = "" in X) {
+   ·          ─────────
+ 2 │ }
+   ╰────
+  help: This iterator's type will be inferred from the iterable. You can safely remove the type annotation.
+
+  × TS(2483): The left-hand side of a 'for...in' statement cannot use a type annotation.
+   ╭─[typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserForInStatement7.ts:1:25]
+ 1 │ for (var a: number = 1, b: string = "" in X) {
+   ·                         ─────────
+ 2 │ }
+   ╰────
+  help: This iterator's type will be inferred from the iterable. You can safely remove the type annotation.
+
   × Unexpected token
    ╭─[typescript/tests/cases/conformance/parser/ecmascript5/Statements/parserForStatement4.ts:1:6]
  1 │ for (a = 1 in b) {
@@ -22151,6 +22211,14 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
  2 │ }
    ╰────
 
+  × TS(2483): The left-hand side of a 'for...of' statement cannot use a type annotation.
+   ╭─[typescript/tests/cases/conformance/parser/ecmascript6/Iterators/parserForOfStatement5.ts:1:10]
+ 1 │ for (var a: number of X) {
+   ·          ─────────
+ 2 │ }
+   ╰────
+  help: This iterator's type will be inferred from the iterable. You can safely remove the type annotation.
+
   × Only a single declaration is allowed in a `for...of` statement
    ╭─[typescript/tests/cases/conformance/parser/ecmascript6/Iterators/parserForOfStatement6.ts:1:6]
  1 │ for (var a = 1, b = 2 of X) {
@@ -22165,6 +22233,22 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
  2 │ }
    ╰────
 
+  × TS(2483): The left-hand side of a 'for...of' statement cannot use a type annotation.
+   ╭─[typescript/tests/cases/conformance/parser/ecmascript6/Iterators/parserForOfStatement7.ts:1:10]
+ 1 │ for (var a: number = 1, b: string = "" of X) {
+   ·          ─────────
+ 2 │ }
+   ╰────
+  help: This iterator's type will be inferred from the iterable. You can safely remove the type annotation.
+
+  × TS(2483): The left-hand side of a 'for...of' statement cannot use a type annotation.
+   ╭─[typescript/tests/cases/conformance/parser/ecmascript6/Iterators/parserForOfStatement7.ts:1:25]
+ 1 │ for (var a: number = 1, b: string = "" of X) {
+   ·                         ─────────
+ 2 │ }
+   ╰────
+  help: This iterator's type will be inferred from the iterable. You can safely remove the type annotation.
+
   × Expected `,` but found `?`
    ╭─[typescript/tests/cases/conformance/parser/ecmascript6/ShorthandPropertyAssignment/parserShorthandPropertyAssignment1.ts:3:11]
  2 │ var name:any, id: any;
@@ -23101,6 +23185,15 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
  38 │ }
     ╰────
 
+  × TS(2483): The left-hand side of a 'for...in' statement cannot use a type annotation.
+    ╭─[typescript/tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts:10:10]
+  9 │ 
+ 10 │ for (var idx : number in {}) { }
+    ·          ────────────
+ 11 │ 
+    ╰────
+  help: This iterator's type will be inferred from the iterable. You can safely remove the type annotation.
+
   × Unexpected token
    ╭─[typescript/tests/cases/conformance/statements/for-ofStatements/ES5For-of12.ts:1:6]
  1 │ for ([""] of [[""]]) { }