fix(parser): report TS1243 for abstract async methods (#27192)

Report TS1243 when `abstract` and `async` are combined on a method in either order. The existing TypeScript conformance case covers both forms. Babel accepts `abstract async`, so the updated Babel snapshots record the resulting parser and semantic coverage difference.

crates/oxc_parser/src/modifiers.rs

@@ -698,12 +698,14 @@ const fn get_illegal_preceding_modifiers(kind: ModifierKind) -> ModifierKinds {
             ModifierKind::Async,
             ModifierKind::Declare,
         ]),
+        ModifierKind::Async => ModifierKinds::new([ModifierKind::Async, ModifierKind::Abstract]),
         ModifierKind::Abstract => ModifierKinds::new([
             ModifierKind::Abstract,
             ModifierKind::Override,
             ModifierKind::Accessor,
             ModifierKind::Static,
             ModifierKind::Private,
+            ModifierKind::Async,
         ]),
         ModifierKind::Export => ModifierKinds::new([
             ModifierKind::Export,
@@ -746,7 +748,7 @@ impl<'a, C: Config> ParserImpl<'a, C> {
             ModifierKind::Private,
             ModifierKind::Protected,
         ]);
-        use ModifierKind::{Abstract, Declare, Override, Private, Static};
+        use ModifierKind::{Abstract, Async, Declare, Override, Private, Static};
 
         let this_kind = modifier.kind;
         let this_kinds = ModifierKinds::new([this_kind]);
@@ -785,6 +787,9 @@ impl<'a, C: Config> ParserImpl<'a, C> {
             (Private, Abstract) | (Abstract, Private) => {
                 diagnostics::modifier_cannot_be_used_with_other_modifier(span, Private, Abstract)
             }
+            (Async, Abstract) | (Abstract, Async) => {
+                diagnostics::modifier_cannot_be_used_with_other_modifier(span, Async, Abstract)
+            }
             // `declare override`
             (Override, Declare) => {
                 diagnostics::modifier_cannot_be_used_with_other_modifier(span, Override, Declare)

tasks/coverage/snapshots/parser_babel.snap

@@ -2,7 +2,7 @@ commit: fd665901
 
 parser_babel Summary:
 AST Parsed     : 2239/2239 (100.00%)
-Positive Passed: 2223/2239 (99.29%)
+Positive Passed: 2222/2239 (99.24%)
 Negative Passed: 1732/1746 (99.20%)
 Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/cast/unparenthesized-assert-and-assign/input.ts
 
@@ -134,6 +134,24 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
  5 │ }
    ╰────
 
+Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/class/modifiers-methods-async/input.ts
+
+  × TS(1243): 'async' modifier cannot be used with 'abstract' modifier.
+   ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/modifiers-methods-async/input.ts:3:14]
+ 2 │ abstract class C {
+ 3 │     abstract async a();
+   ·              ─────
+ 4 │     static async s() {}
+   ╰────
+
+  × TS(1243): 'async' modifier cannot be used with 'abstract' modifier.
+   ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/modifiers-methods-async/input.ts:5:21]
+ 4 │     static async s() {}
+ 5 │     public abstract async pua();
+   ·                     ─────
+ 6 │     public static async pus() {}
+   ╰────
+
 Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/class/modifiers-override/input.ts
 
   × Identifier `show` has already been declared

tasks/coverage/snapshots/parser_typescript.snap

@@ -15926,6 +15926,22 @@ Expect to Parse: tasks/coverage/typescript/tsc/testdata/tests/cases/conformance/
  14 │ 
     ╰────
 
+  × TS(1243): 'async' modifier cannot be used with 'abstract' modifier.
+    ╭─[typescript/tsc/testdata/tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractMixedWithModifiers.ts:15:14]
+ 14 │ 
+ 15 │     abstract async foo_f();
+    ·              ─────
+ 16 │     async abstract foo_g();
+    ╰────
+
+  × TS(1243): 'async' modifier cannot be used with 'abstract' modifier.
+    ╭─[typescript/tsc/testdata/tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractMixedWithModifiers.ts:16:11]
+ 15 │     abstract async foo_f();
+ 16 │     async abstract foo_g();
+    ·           ────────
+ 17 │ }
+    ╰────
+
   × TS(2391): Function implementation is missing or not immediately following the declaration.
     ╭─[typescript/tsc/testdata/tests/cases/conformance/classes/classDeclarations/classAbstractKeyword/classAbstractOverloads.ts:15:5]
  14 │     

tasks/coverage/snapshots/semantic_babel.snap

@@ -2,7 +2,7 @@ commit: fd665901
 
 semantic_babel Summary:
 AST Parsed     : 2239/2239 (100.00%)
-Positive Passed: 2149/2239 (95.98%)
+Positive Passed: 2148/2239 (95.94%)
 semantic Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/comments/decorators/decorators-after-export/input.js
 Symbol flags mismatch for "_default":
 after transform: SymbolId(3): SymbolFlags(Class)
@@ -121,6 +121,10 @@ semantic Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/typescr
 Function implementation is missing or not immediately following the declaration.
 Function implementation is missing or not immediately following the declaration.
 
+semantic Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/class/modifiers-methods-async/input.ts
+'async' modifier cannot be used with 'abstract' modifier.
+'async' modifier cannot be used with 'abstract' modifier.
+
 semantic Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/class/modifiers-override/input.ts
 Identifier `show` has already been declared
 Identifier `size` has already been declared