fix(parser): reject accessor modifiers on methods (#26617)

`class C { accessor x() {} }` was accepted as an ordinary method, silently dropping the `accessor` modifier. Reject it with TypeScript diagnostic TS1275 on methods, getters, setters, and constructors, while preserving valid auto-accessor fields and members named `accessor`.

crates/oxc_parser/src/diagnostics.rs

@@ -895,6 +895,12 @@ parser_diagnostics! {
             .with_allowed_modifier_help(allowed)
     };
 
+    accessor_only_on_property_declaration(modifier: Modifier, allowed: Option<ModifierKinds>) => {
+        ts_error("1275", "'accessor' modifier can only appear on a property declaration.")
+            .with_label(modifier.span())
+            .with_allowed_modifier_help(allowed)
+    };
+
     modifier_only_on_property_declaration_or_index_signature(modifier: Modifier, allowed: Option<ModifierKinds>) => {
         ts_error(
             "1024",

crates/oxc_parser/src/js/class.rs

@@ -507,9 +507,19 @@ impl<'a, C: Config> ParserImpl<'a, C> {
         self.check_method_definition_accessor(&method_definition);
         self.verify_modifiers(
             modifiers,
-            ModifierKinds::all_except([ModifierKind::Async, ModifierKind::Declare]),
+            ModifierKinds::all_except([
+                ModifierKind::Async,
+                ModifierKind::Declare,
+                ModifierKind::Accessor,
+            ]),
             false,
-            diagnostics::modifier_cannot_be_used_here,
+            |modifier, allowed| {
+                if modifier.kind == ModifierKind::Accessor {
+                    diagnostics::accessor_only_on_property_declaration(modifier, allowed)
+                } else {
+                    diagnostics::modifier_cannot_be_used_here(modifier, allowed)
+                }
+            },
         );
         ClassElement::MethodDefinition(method_definition)
     }
@@ -522,14 +532,26 @@ impl<'a, C: Config> ParserImpl<'a, C> {
         modifiers: &Modifiers,
         decorators: ArenaVec<'a, Decorator<'a>>,
     ) -> ClassElement<'a> {
-        if let Some(modifier) = modifiers.get(ModifierKind::Declare) {
-            self.error(diagnostics::declare_constructor(modifier.span()));
-        }
         self.verify_modifiers(
             modifiers,
-            ModifierKinds::all_except([ModifierKind::Readonly]),
+            ModifierKinds::all_except([
+                ModifierKind::Declare,
+                ModifierKind::Readonly,
+                ModifierKind::Accessor,
+            ]),
             false,
-            diagnostics::modifier_only_on_property_declaration_or_index_signature,
+            |modifier, _| match modifier.kind {
+                ModifierKind::Declare => diagnostics::declare_constructor(modifier.span()),
+                ModifierKind::Readonly => {
+                    diagnostics::modifier_only_on_property_declaration_or_index_signature(
+                        modifier, None,
+                    )
+                }
+                ModifierKind::Accessor => {
+                    diagnostics::accessor_only_on_property_declaration(modifier, None)
+                }
+                _ => unreachable!(),
+            },
         );
 
         let value = self.parse_method(
@@ -592,7 +614,11 @@ impl<'a, C: Config> ParserImpl<'a, C> {
         if generator.is_some() || matches!(self.cur_kind(), Kind::LParen | Kind::LAngle) {
             self.verify_modifiers(
                 modifiers,
-                ModifierKinds::all_except([ModifierKind::Declare, ModifierKind::Readonly]),
+                ModifierKinds::all_except([
+                    ModifierKind::Declare,
+                    ModifierKind::Readonly,
+                    ModifierKind::Accessor,
+                ]),
                 false,
                 |modifier, _| {
                     const ALLOWED: ModifierKinds = ModifierKinds::new([
@@ -615,6 +641,12 @@ impl<'a, C: Config> ParserImpl<'a, C> {
                                 Some(ALLOWED),
                             )
                         }
+                        ModifierKind::Accessor => {
+                            diagnostics::accessor_only_on_property_declaration(
+                                modifier,
+                                Some(ALLOWED),
+                            )
+                        }
                         _ => unreachable!(),
                     }
                 },

tasks/coverage/misc/fail/accessor-modifier-abstract-method.ts

@@ -0,0 +1 @@
+abstract class C { abstract accessor x(): void; }

tasks/coverage/misc/fail/accessor-modifier-async-method.ts

@@ -0,0 +1 @@
+class C { accessor async x() {} }

tasks/coverage/misc/fail/accessor-modifier-static-getter.ts

@@ -0,0 +1 @@
+class C { static accessor get x() { return 0; } }

tasks/coverage/misc/fail/accessor-modifier-static-method.ts

@@ -0,0 +1 @@
+class C { static accessor x() {} }

tasks/coverage/misc/fail/accessor-modifier-static-setter.ts

@@ -0,0 +1 @@
+class C { static accessor set x(value: number) {} }

tasks/coverage/misc/pass/accessor-modifier.ts

@@ -0,0 +1,16 @@
+class C {
+    accessor value = 0;
+    static accessor count = 0;
+    accessor() {}
+    static accessor() {}
+}
+
+class Fields {
+    accessor = 0;
+    static accessor = 0;
+}
+
+class Newline {
+    accessor
+    x() {}
+}

tasks/coverage/snapshots/codegen_misc.snap

@@ -1,3 +1,3 @@
 codegen_misc Summary:
-AST Parsed     : 109/109 (100.00%)
-Positive Passed: 109/109 (100.00%)
+AST Parsed     : 110/110 (100.00%)
+Positive Passed: 110/110 (100.00%)

tasks/coverage/snapshots/formatter_misc.snap

@@ -1,3 +1,3 @@
 formatter_misc Summary:
-AST Parsed     : 109/109 (100.00%)
-Positive Passed: 109/109 (100.00%)
+AST Parsed     : 110/110 (100.00%)
+Positive Passed: 110/110 (100.00%)

tasks/coverage/snapshots/lexer_misc.snap

@@ -1,3 +1,3 @@
 lexer_misc Summary:
-AST Parsed     : 331/331 (100.00%)
-Positive Passed: 331/331 (100.00%)
+AST Parsed     : 337/337 (100.00%)
+Positive Passed: 337/337 (100.00%)

tasks/coverage/snapshots/parser_misc.snap

@@ -1,7 +1,40 @@
 parser_misc Summary:
-AST Parsed     : 109/109 (100.00%)
-Positive Passed: 109/109 (100.00%)
-Negative Passed: 222/222 (100.00%)
+AST Parsed     : 110/110 (100.00%)
+Positive Passed: 110/110 (100.00%)
+Negative Passed: 227/227 (100.00%)
+
+  × TS(1275): 'accessor' modifier can only appear on a property declaration.
+   ╭─[misc/fail/accessor-modifier-abstract-method.ts:1:29]
+ 1 │ abstract class C { abstract accessor x(): void; }
+   ·                             ────────
+   ╰────
+  help: Allowed modifiers are: private, protected, public, static, abstract, override, async
+
+  × TS(1275): 'accessor' modifier can only appear on a property declaration.
+   ╭─[misc/fail/accessor-modifier-async-method.ts:1:11]
+ 1 │ class C { accessor async x() {} }
+   ·           ────────
+   ╰────
+  help: Allowed modifiers are: private, protected, public, static, abstract, override, async
+
+  × TS(1275): 'accessor' modifier can only appear on a property declaration.
+   ╭─[misc/fail/accessor-modifier-static-getter.ts:1:18]
+ 1 │ class C { static accessor get x() { return 0; } }
+   ·                  ────────
+   ╰────
+
+  × TS(1275): 'accessor' modifier can only appear on a property declaration.
+   ╭─[misc/fail/accessor-modifier-static-method.ts:1:18]
+ 1 │ class C { static accessor x() {} }
+   ·                  ────────
+   ╰────
+  help: Allowed modifiers are: private, protected, public, static, abstract, override, async
+
+  × TS(1275): 'accessor' modifier can only appear on a property declaration.
+   ╭─[misc/fail/accessor-modifier-static-setter.ts:1:18]
+ 1 │ class C { static accessor set x(value: number) {} }
+   ·                  ────────
+   ╰────
 
   × Cannot assign to 'arguments' in strict mode
    ╭─[misc/fail/arguments-eval-ambient.ts:2:13]

tasks/coverage/snapshots/parser_typescript.snap

@@ -17612,6 +17612,39 @@ Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/types/wit
  10 │     accessor i() {}
     ╰────
 
+  × TS(1275): 'accessor' modifier can only appear on a property declaration.
+    ╭─[typescript/tests/cases/conformance/classes/propertyMemberDeclarations/autoAccessorDisallowedModifiers.ts:10:5]
+  9 │     accessor static h: any;
+ 10 │     accessor i() {}
+    ·     ────────
+ 11 │     accessor get j() { return false; }
+    ╰────
+  help: Allowed modifiers are: private, protected, public, static, abstract, override, async
+
+  × TS(1275): 'accessor' modifier can only appear on a property declaration.
+    ╭─[typescript/tests/cases/conformance/classes/propertyMemberDeclarations/autoAccessorDisallowedModifiers.ts:11:5]
+ 10 │     accessor i() {}
+ 11 │     accessor get j() { return false; }
+    ·     ────────
+ 12 │     accessor set k(v: any) {}
+    ╰────
+
+  × TS(1275): 'accessor' modifier can only appear on a property declaration.
+    ╭─[typescript/tests/cases/conformance/classes/propertyMemberDeclarations/autoAccessorDisallowedModifiers.ts:12:5]
+ 11 │     accessor get j() { return false; }
+ 12 │     accessor set k(v: any) {}
+    ·     ────────
+ 13 │     accessor constructor() {}
+    ╰────
+
+  × TS(1275): 'accessor' modifier can only appear on a property declaration.
+    ╭─[typescript/tests/cases/conformance/classes/propertyMemberDeclarations/autoAccessorDisallowedModifiers.ts:13:5]
+ 12 │     accessor set k(v: any) {}
+ 13 │     accessor constructor() {}
+    ·     ────────
+ 14 │     accessor l?: any;
+    ╰────
+
   × TS(1276): An 'accessor' property cannot be declared optional.
     ╭─[typescript/tests/cases/conformance/classes/propertyMemberDeclarations/autoAccessorDisallowedModifiers.ts:14:15]
  13 │     accessor constructor() {}

tasks/coverage/snapshots/semantic_misc.snap

@@ -1,6 +1,6 @@
 semantic_misc Summary:
-AST Parsed     : 109/109 (100.00%)
-Positive Passed: 104/109 (95.41%)
+AST Parsed     : 110/110 (100.00%)
+Positive Passed: 105/110 (95.45%)
 semantic Error: tasks/coverage/misc/pass/declare-let-private.ts
 Bindings mismatch:
 after transform: ScopeId(0): ["private"]

tasks/coverage/snapshots/transformer_misc.snap

@@ -1,3 +1,3 @@
 transformer_misc Summary:
-AST Parsed     : 109/109 (100.00%)
-Positive Passed: 109/109 (100.00%)
+AST Parsed     : 110/110 (100.00%)
+Positive Passed: 110/110 (100.00%)