fix(parser): reject generators in ambient contexts and overload signatures (TS1221/TS1222) (#22848)

A generator (`function*` / `*method`) is not allowed in an ambient context
(TS1221), and a generator overload signature with no body is not allowed
(TS1222). Mirrors tsc's `checkGrammarForGenerator`:

    declare function* f(): any;              // now TS1221
    declare namespace N { function* g(); }   // now TS1221
    declare class C { *m(); }                // now TS1221
    function* f(): any;                       // overload → now TS1222
    function* f() { yield 1; }

    function* f() { yield 1; }               // normal generator → still valid

The check lives in `parse_function` next to the TS1183 implementation-in-ambient
check and keys off `ctx.has_ambient()` / `body.is_none()`. Class methods are
covered too (`class.rs` does not check generators, so there is no duplicate
diagnostic).

Also fixes a latent bug: `parse_ts_declare_function` hard-coded `generator: false`
and never consumed the `*`, so `declare function* f()` silently dropped the
generator flag. It now eats the `*` and threads the flag through (which is what
lets TS1221 fire there).

parser_typescript +7 negative-pass (generatorInAmbientContext1-4, generatorOverloads1-3);
positive/AST stay 100%.

crates/oxc_parser/src/diagnostics.rs

@@ -1228,6 +1228,16 @@ pub fn implementation_in_ambient(span: Span) -> OxcDiagnostic {
     ts_error("1183", "An implementation cannot be declared in ambient contexts.").with_label(span)
 }
 
+#[cold]
+pub fn generator_in_ambient_context(span: Span) -> OxcDiagnostic {
+    ts_error("1221", "Generators are not allowed in an ambient context.").with_label(span)
+}
+
+#[cold]
+pub fn overload_signature_generator(span: Span) -> OxcDiagnostic {
+    ts_error("1222", "An overload signature cannot be declared as a generator.").with_label(span)
+}
+
 #[cold]
 pub fn initializers_not_allowed_in_ambient_contexts(span: Span) -> OxcDiagnostic {
     ts_error("1039", "Initializers are not allowed in ambient contexts.").with_label(span)

crates/oxc_parser/src/js/function.rs

@@ -302,6 +302,14 @@ impl<'a, C: Config> ParserImpl<'a, C> {
         {
             self.error(diagnostics::implementation_in_ambient(Span::empty(body.span.start)));
         }
+
+        if generator {
+            if ctx.has_ambient() {
+                self.error(diagnostics::generator_in_ambient_context(self.end_span(span)));
+            } else if body.is_none() {
+                self.error(diagnostics::overload_signature_generator(self.end_span(span)));
+            }
+        }
         self.verify_modifiers(
             modifiers,
             ModifierKinds::new([ModifierKind::Declare, ModifierKind::Async]),

crates/oxc_parser/src/ts/statement.rs

@@ -583,13 +583,14 @@ impl<'a, C: Config> ParserImpl<'a, C> {
     ) -> Box<'a, Function<'a>> {
         let r#async = modifiers.contains(ModifierKind::Async);
         self.expect(Kind::Function);
+        let generator = self.eat(Kind::Star);
         let func_kind = FunctionKind::TSDeclaration;
-        let id = self.parse_function_id(func_kind, r#async, false);
+        let id = self.parse_function_id(func_kind, r#async, generator);
         self.parse_function(
             start_span,
             id,
             r#async,
-            false,
+            generator,
             func_kind,
             FormalParameterKind::FormalParameter,
             modifiers,

tasks/coverage/snapshots/parser_babel.snap

@@ -12788,6 +12788,14 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
    ╰────
   help: Allowed modifiers are: private, protected, public, static, abstract, override, async
 
+  × TS(1221): Generators are not allowed in an ambient context.
+   ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/generator-method-with-modifiers/input.ts:7:13]
+ 6 │   readonly *e() {}
+ 7 │   declare *f() {}
+   ·             ─────
+ 8 │   protected *g() {}
+   ╰────
+
   × TS(1183): An implementation cannot be declared in ambient contexts.
    ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/generator-method-with-modifiers/input.ts:7:16]
  6 │   readonly *e() {}
@@ -13085,6 +13093,14 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
    ╰────
   help: Allowed modifiers are: private, protected, public, static, abstract, override, async
 
+  × TS(1221): Generators are not allowed in an ambient context.
+   ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/optional-generator-method-with-invalid-modifiers/input.ts:4:14]
+ 3 │   readonly *e?() { }
+ 4 │   declare *f?() { }
+   ·              ──────
+ 5 │ }
+   ╰────
+
   × TS(1183): An implementation cannot be declared in ambient contexts.
    ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/optional-generator-method-with-invalid-modifiers/input.ts:4:17]
  3 │   readonly *e?() { }
@@ -13119,6 +13135,14 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
     ╰────
   help: Allowed modifiers are: private, protected, public, static, abstract, override, async
 
+  × TS(1221): Generators are not allowed in an ambient context.
+    ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/optional-generator-method-with-invalid-modifiers/input.ts:10:19]
+  9 │   readonly *[e?.e]?() { }
+ 10 │   declare *[f?.f]?() { }
+    ·                   ──────
+ 11 │ }
+    ╰────
+
   × TS(1183): An implementation cannot be declared in ambient contexts.
     ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/optional-generator-method-with-invalid-modifiers/input.ts:10:22]
   9 │   readonly *[e?.e]?() { }

tasks/coverage/snapshots/parser_typescript.snap

@@ -3,7 +3,7 @@ commit: e5509e21
 parser_typescript Summary:
 AST Parsed     : 9779/9779 (100.00%)
 Positive Passed: 9779/9779 (100.00%)
-Negative Passed: 1621/2640 (61.40%)
+Negative Passed: 1628/2640 (61.67%)
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/FunctionDeclaration3.ts
 
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/FunctionDeclaration4.ts
@@ -1302,20 +1302,6 @@ Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/es6/yield
 
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/es6/yieldExpressions/YieldStarExpression1_es6.ts
 
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/es6/yieldExpressions/generatorInAmbientContext1.ts
-
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/es6/yieldExpressions/generatorInAmbientContext2.ts
-
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/es6/yieldExpressions/generatorInAmbientContext3.d.ts
-
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/es6/yieldExpressions/generatorInAmbientContext4.d.ts
-
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/es6/yieldExpressions/generatorOverloads1.ts
-
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/es6/yieldExpressions/generatorOverloads2.ts
-
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/es6/yieldExpressions/generatorOverloads3.ts
-
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck9.ts
 
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/es7/exponentiationOperator/compoundExponentiationAssignmentLHSCanBeAssigned1.ts
@@ -19988,6 +19974,94 @@ Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/types/wit
  3 │ }
    ╰────
 
+  × TS(1221): Generators are not allowed in an ambient context.
+   ╭─[typescript/tests/cases/conformance/es6/yieldExpressions/generatorInAmbientContext1.ts:2:15]
+ 1 │ declare class C {
+ 2 │     *generator(): any;
+   ·               ────────
+ 3 │ }
+   ╰────
+
+  × TS(1221): Generators are not allowed in an ambient context.
+   ╭─[typescript/tests/cases/conformance/es6/yieldExpressions/generatorInAmbientContext2.ts:2:5]
+ 1 │ declare namespace M {
+ 2 │     function *generator(): any;
+   ·     ───────────────────────────
+ 3 │ }
+   ╰────
+
+  × TS(1221): Generators are not allowed in an ambient context.
+   ╭─[typescript/tests/cases/conformance/es6/yieldExpressions/generatorInAmbientContext3.d.ts:2:15]
+ 1 │ declare class C {
+ 2 │     *generator(): any;
+   ·               ────────
+ 3 │ }
+   ╰────
+
+  × TS(1221): Generators are not allowed in an ambient context.
+   ╭─[typescript/tests/cases/conformance/es6/yieldExpressions/generatorInAmbientContext4.d.ts:2:5]
+ 1 │ declare namespace M {
+ 2 │     function *generator(): any;
+   ·     ───────────────────────────
+ 3 │ }
+   ╰────
+
+  × TS(1222): An overload signature cannot be declared as a generator.
+   ╭─[typescript/tests/cases/conformance/es6/yieldExpressions/generatorOverloads1.ts:2:5]
+ 1 │ namespace M {
+ 2 │     function* f(s: string): Iterable<any>;
+   ·     ──────────────────────────────────────
+ 3 │     function* f(s: number): Iterable<any>;
+   ╰────
+
+  × TS(1222): An overload signature cannot be declared as a generator.
+   ╭─[typescript/tests/cases/conformance/es6/yieldExpressions/generatorOverloads1.ts:3:5]
+ 2 │     function* f(s: string): Iterable<any>;
+ 3 │     function* f(s: number): Iterable<any>;
+   ·     ──────────────────────────────────────
+ 4 │     function* f(s: any): Iterable<any> { }
+   ╰────
+
+  × TS(1221): Generators are not allowed in an ambient context.
+   ╭─[typescript/tests/cases/conformance/es6/yieldExpressions/generatorOverloads2.ts:2:5]
+ 1 │ declare namespace M {
+ 2 │     function* f(s: string): Iterable<any>;
+   ·     ──────────────────────────────────────
+ 3 │     function* f(s: number): Iterable<any>;
+   ╰────
+
+  × TS(1221): Generators are not allowed in an ambient context.
+   ╭─[typescript/tests/cases/conformance/es6/yieldExpressions/generatorOverloads2.ts:3:5]
+ 2 │     function* f(s: string): Iterable<any>;
+ 3 │     function* f(s: number): Iterable<any>;
+   ·     ──────────────────────────────────────
+ 4 │     function* f(s: any): Iterable<any>;
+   ╰────
+
+  × TS(1221): Generators are not allowed in an ambient context.
+   ╭─[typescript/tests/cases/conformance/es6/yieldExpressions/generatorOverloads2.ts:4:5]
+ 3 │     function* f(s: number): Iterable<any>;
+ 4 │     function* f(s: any): Iterable<any>;
+   ·     ───────────────────────────────────
+ 5 │ }
+   ╰────
+
+  × TS(1222): An overload signature cannot be declared as a generator.
+   ╭─[typescript/tests/cases/conformance/es6/yieldExpressions/generatorOverloads3.ts:2:7]
+ 1 │ class C {
+ 2 │     *f(s: string): Iterable<any>;
+   ·       ───────────────────────────
+ 3 │     *f(s: number): Iterable<any>;
+   ╰────
+
+  × TS(1222): An overload signature cannot be declared as a generator.
+   ╭─[typescript/tests/cases/conformance/es6/yieldExpressions/generatorOverloads3.ts:3:7]
+ 2 │     *f(s: string): Iterable<any>;
+ 3 │     *f(s: number): Iterable<any>;
+   ·       ───────────────────────────
+ 4 │     *f(s: any): Iterable<any> { }
+   ╰────
+
   × A 'yield' expression is only allowed in a generator body.
    ╭─[typescript/tests/cases/conformance/es6/yieldExpressions/generatorTypeCheck32.ts:2:29]
  1 │ var s: string;