From e6ef75ece5727335eff9b1154525cd85d3176811 Mon Sep 17 00:00:00 2001
From: Ulrich Stark <github@ustark.de>
Date: Tue, 2 Sep 2025 20:57:02 +0200
Subject: [PATCH 1/3] fix(parser): improve diagnostics around modifier checks

---
 crates/oxc_parser/src/diagnostics.rs          |  27 ++++-
 crates/oxc_parser/src/js/class.rs             |  32 +++++
 crates/oxc_parser/src/modifiers.rs            |   5 +-
 crates/oxc_parser/src/ts/statement.rs         |  18 ++-
 crates/oxc_parser/src/ts/types.rs             |  14 ++-
 tasks/coverage/misc/fail/oxc-11713-13.ts      |   5 +-
 tasks/coverage/misc/fail/oxc-11713-23.ts      |   3 +
 tasks/coverage/misc/fail/oxc-11713-24.ts      |   3 +
 tasks/coverage/misc/fail/oxc-11713-25.ts      |   3 +
 tasks/coverage/misc/fail/oxc-11713-26.ts      |   1 +
 tasks/coverage/misc/fail/oxc-11713-27.ts      |   1 +
 tasks/coverage/snapshots/parser_babel.snap    | 112 ++++++++++++++++--
 tasks/coverage/snapshots/parser_misc.snap     |  80 +++++++------
 .../coverage/snapshots/parser_typescript.snap |  54 ++++++---
 14 files changed, 280 insertions(+), 78 deletions(-)
 create mode 100644 tasks/coverage/misc/fail/oxc-11713-23.ts
 create mode 100644 tasks/coverage/misc/fail/oxc-11713-24.ts
 create mode 100644 tasks/coverage/misc/fail/oxc-11713-25.ts
 create mode 100644 tasks/coverage/misc/fail/oxc-11713-26.ts
 create mode 100644 tasks/coverage/misc/fail/oxc-11713-27.ts

diff --git a/crates/oxc_parser/src/diagnostics.rs b/crates/oxc_parser/src/diagnostics.rs
index a7bc4ee0d0813..28ef47ae0d598 100644
--- a/crates/oxc_parser/src/diagnostics.rs
+++ b/crates/oxc_parser/src/diagnostics.rs
@@ -3,7 +3,7 @@ use std::borrow::Cow;
 use oxc_diagnostics::OxcDiagnostic;
 use oxc_span::Span;
 
-use crate::modifiers::Modifier;
+use crate::modifiers::{Modifier, ModifierKind};
 
 #[inline]
 fn ts_error<C, M>(code: C, message: M) -> OxcDiagnostic
@@ -536,6 +536,20 @@ pub fn modifier_cannot_be_used_here(modifier: &Modifier) -> OxcDiagnostic {
         .with_label(modifier.span)
 }
 
+#[cold]
+pub fn modifier_only_on_property_declaration_or_index_signature(
+    modifier: &Modifier,
+) -> OxcDiagnostic {
+    ts_error(
+        "1024",
+        format!(
+            "'{}' modifier can only appear on a property declaration or index signature.",
+            modifier.kind
+        ),
+    )
+    .with_label(modifier.span)
+}
+
 #[cold]
 pub fn accessibility_modifier_already_seen(modifier: &Modifier) -> OxcDiagnostic {
     ts_error("1028", "Accessibility modifier already seen.")
@@ -544,8 +558,15 @@ pub fn accessibility_modifier_already_seen(modifier: &Modifier) -> OxcDiagnostic
 }
 
 #[cold]
-pub fn export_modifier_must_precede_declare(modifier: &Modifier) -> OxcDiagnostic {
-    ts_error("1029", "'export' modifier must precede 'declare' modifier.").with_label(modifier.span)
+pub fn modifier_must_precede_other_modifier(
+    modifier: &Modifier,
+    other_modifier: ModifierKind,
+) -> OxcDiagnostic {
+    ts_error(
+        "1029",
+        format!("'{}' modifier must precede '{}' modifier.", modifier.kind, other_modifier),
+    )
+    .with_label(modifier.span)
 }
 
 #[cold]
diff --git a/crates/oxc_parser/src/js/class.rs b/crates/oxc_parser/src/js/class.rs
index e6201b021d905..7e8723133d0f4 100644
--- a/crates/oxc_parser/src/js/class.rs
+++ b/crates/oxc_parser/src/js/class.rs
@@ -278,6 +278,23 @@ impl<'a> ParserImpl<'a> {
             for decorator in decorators {
                 self.error(diagnostics::decorators_are_not_valid_here(decorator.span));
             }
+
+            let mut has_seen_readonly_modifier = false;
+            for modifier in modifiers.iter() {
+                match modifier.kind {
+                    ModifierKind::Readonly => has_seen_readonly_modifier = true,
+                    ModifierKind::Static => {
+                        if has_seen_readonly_modifier {
+                            self.error(diagnostics::modifier_must_precede_other_modifier(
+                                modifier,
+                                ModifierKind::Readonly,
+                            ));
+                        }
+                    }
+                    _ => self.error(diagnostics::cannot_appear_on_an_index_signature(modifier)),
+                }
+            }
+
             return ClassElement::TSIndexSignature(
                 self.parse_index_signature_declaration(span, &modifiers),
             );
@@ -476,6 +493,21 @@ impl<'a> ParserImpl<'a> {
         let optional = optional_span.is_some();
 
         if generator || matches!(self.cur_kind(), Kind::LParen | Kind::LAngle) {
+            for modifier in modifiers.iter() {
+                match modifier.kind {
+                    ModifierKind::Declare => {
+                        self.error(diagnostics::cannot_appear_on_class_elements(modifier));
+                    }
+                    ModifierKind::Readonly => {
+                        self.error(
+                            diagnostics::modifier_only_on_property_declaration_or_index_signature(
+                                modifier,
+                            ),
+                        );
+                    }
+                    _ => {}
+                }
+            }
             return self.parse_method_declaration(
                 span, r#type, generator, name, computed, optional, modifiers, decorators,
             );
diff --git a/crates/oxc_parser/src/modifiers.rs b/crates/oxc_parser/src/modifiers.rs
index 3a1d8ae8247ce..f28694639e056 100644
--- a/crates/oxc_parser/src/modifiers.rs
+++ b/crates/oxc_parser/src/modifiers.rs
@@ -309,7 +309,10 @@ impl<'a> ParserImpl<'a> {
             self.bump_any();
             let modifier = self.modifier(kind, self.end_span(span));
             if modifier.kind == ModifierKind::Export {
-                self.error(diagnostics::export_modifier_must_precede_declare(&modifier));
+                self.error(diagnostics::modifier_must_precede_other_modifier(
+                    &modifier,
+                    ModifierKind::Declare,
+                ));
             }
             self.check_for_duplicate_modifiers(flags, &modifier);
             flags.set(modifier_flags, true);
diff --git a/crates/oxc_parser/src/ts/statement.rs b/crates/oxc_parser/src/ts/statement.rs
index 7bdc75514eb98..336201cee3ff2 100644
--- a/crates/oxc_parser/src/ts/statement.rs
+++ b/crates/oxc_parser/src/ts/statement.rs
@@ -244,6 +244,18 @@ impl<'a> ParserImpl<'a> {
             /* permit_const_as_modifier */ true,
             /* stop_on_start_of_class_static_block */ false,
         );
+
+        if self.is_index_signature() {
+            self.verify_modifiers(
+                &modifiers,
+                ModifierFlags::READONLY,
+                diagnostics::cannot_appear_on_an_index_signature,
+            );
+            return TSSignature::TSIndexSignature(
+                self.parse_index_signature_declaration(span, &modifiers),
+            );
+        }
+
         self.verify_modifiers(
             &modifiers,
             ModifierFlags::READONLY,
@@ -258,12 +270,6 @@ impl<'a> ParserImpl<'a> {
             return self.parse_getter_setter_signature_member(span, TSMethodSignatureKind::Set);
         }
 
-        if self.is_index_signature() {
-            return TSSignature::TSIndexSignature(
-                self.parse_index_signature_declaration(span, &modifiers),
-            );
-        }
-
         self.parse_property_or_method_signature(span, &modifiers)
     }
 
diff --git a/crates/oxc_parser/src/ts/types.rs b/crates/oxc_parser/src/ts/types.rs
index 518e54f37e959..56c4e96949774 100644
--- a/crates/oxc_parser/src/ts/types.rs
+++ b/crates/oxc_parser/src/ts/types.rs
@@ -1178,6 +1178,15 @@ impl<'a> ParserImpl<'a> {
         let optional = self.eat(Kind::Question);
 
         if self.at(Kind::LParen) || self.at(Kind::LAngle) {
+            for modifier in modifiers.iter() {
+                if modifier.kind == ModifierKind::Readonly {
+                    self.error(
+                        diagnostics::modifier_only_on_property_declaration_or_index_signature(
+                            modifier,
+                        ),
+                    );
+                }
+            }
             let type_parameters = self.parse_ts_type_parameters();
             let (this_param, params) = self
                 .parse_formal_parameters(FunctionKind::Declaration, FormalParameterKind::Signature);
@@ -1213,11 +1222,6 @@ impl<'a> ParserImpl<'a> {
         span: u32,
         modifiers: &Modifiers<'a>,
     ) -> Box<'a, TSIndexSignature<'a>> {
-        self.verify_modifiers(
-            modifiers,
-            ModifierFlags::READONLY | ModifierFlags::STATIC,
-            diagnostics::cannot_appear_on_an_index_signature,
-        );
         self.expect(Kind::LBrack);
         let (params, comma_span) = self.parse_delimited_list(
             Kind::RBrack,
diff --git a/tasks/coverage/misc/fail/oxc-11713-13.ts b/tasks/coverage/misc/fail/oxc-11713-13.ts
index 0565fe2a8f8f9..4e07309ce2c16 100644
--- a/tasks/coverage/misc/fail/oxc-11713-13.ts
+++ b/tasks/coverage/misc/fail/oxc-11713-13.ts
@@ -1,2 +1,3 @@
-const [index: string]: number
-}
+interface Foo {
+  const [index: string]: number
+}
\ No newline at end of file
diff --git a/tasks/coverage/misc/fail/oxc-11713-23.ts b/tasks/coverage/misc/fail/oxc-11713-23.ts
new file mode 100644
index 0000000000000..f28bdeb442f8a
--- /dev/null
+++ b/tasks/coverage/misc/fail/oxc-11713-23.ts
@@ -0,0 +1,3 @@
+interface Foo {
+  readonly method();
+}
diff --git a/tasks/coverage/misc/fail/oxc-11713-24.ts b/tasks/coverage/misc/fail/oxc-11713-24.ts
new file mode 100644
index 0000000000000..bad13b0ba0196
--- /dev/null
+++ b/tasks/coverage/misc/fail/oxc-11713-24.ts
@@ -0,0 +1,3 @@
+class Foo {
+  declare method() {}
+}
diff --git a/tasks/coverage/misc/fail/oxc-11713-25.ts b/tasks/coverage/misc/fail/oxc-11713-25.ts
new file mode 100644
index 0000000000000..48cd98cf9ac63
--- /dev/null
+++ b/tasks/coverage/misc/fail/oxc-11713-25.ts
@@ -0,0 +1,3 @@
+class Foo {
+  readonly method() {}
+}
diff --git a/tasks/coverage/misc/fail/oxc-11713-26.ts b/tasks/coverage/misc/fail/oxc-11713-26.ts
new file mode 100644
index 0000000000000..d3231c30751c8
--- /dev/null
+++ b/tasks/coverage/misc/fail/oxc-11713-26.ts
@@ -0,0 +1 @@
+function foo(readonly parameter) {}
diff --git a/tasks/coverage/misc/fail/oxc-11713-27.ts b/tasks/coverage/misc/fail/oxc-11713-27.ts
new file mode 100644
index 0000000000000..fe5085465e3fb
--- /dev/null
+++ b/tasks/coverage/misc/fail/oxc-11713-27.ts
@@ -0,0 +1 @@
+class Foo { method(readonly parameter) {} }
diff --git a/tasks/coverage/snapshots/parser_babel.snap b/tasks/coverage/snapshots/parser_babel.snap
index 473f6387ac65a..36f840d2b30b5 100644
--- a/tasks/coverage/snapshots/parser_babel.snap
+++ b/tasks/coverage/snapshots/parser_babel.snap
@@ -3,7 +3,7 @@ commit: 41d96516
 parser_babel Summary:
 AST Parsed     : 2407/2423 (99.34%)
 Positive Passed: 2385/2423 (98.43%)
-Negative Passed: 1646/1755 (93.79%)
+Negative Passed: 1649/1755 (93.96%)
 Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/core/categorized/invalid-startindex-and-startline-specified-without-startcolumn/input.js
 
 Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/core/categorized/startline-and-startcolumn-specified/input.js
@@ -86,16 +86,10 @@ Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/ty
 
 Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/class/declare-initializer/input.ts
 
-Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/class/declare-method/input.ts
-
 Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/class/declare-readonly-field-initializer-w-annotation/input.ts
 
-Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/class/index-signature-errors/input.ts
-
 Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/class/invalid-modifiers-order/input.ts
 
-Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/class/method-readonly/input.ts
-
 Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/class/modifiers-incompatible/input.ts
 
 Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/class/modifiers-invalid-order/input.ts
@@ -12022,6 +12016,14 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
    ·         ───
    ╰────
 
+  × TS(1031): 'declare' modifier cannot appear on class elements of this kind.
+   ╭─[babel/packages/babel-parser/test/fixtures/estree/typescript/invalid-class-method-empty-body/input.js:4:3]
+ 3 │   #method();
+ 4 │   declare method();
+   ·   ───────
+ 5 │ }
+   ╰────
+
   × Function implementation is missing or not immediately following the declaration.
    ╭─[babel/packages/babel-parser/test/fixtures/estree/typescript/invalid-class-method-empty-body/input.js:2:3]
  1 │ class C {
@@ -12046,6 +12048,14 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
  5 │ }
    ╰────
 
+  × TS(1031): 'declare' modifier cannot appear on class elements of this kind.
+   ╭─[babel/packages/babel-parser/test/fixtures/estree/typescript/invalid-class-method-empty-body-babel-7/input.js:4:3]
+ 3 │   #method();
+ 4 │   declare method();
+   ·   ───────
+ 5 │ }
+   ╰────
+
   × Function implementation is missing or not immediately following the declaration.
    ╭─[babel/packages/babel-parser/test/fixtures/estree/typescript/invalid-class-method-empty-body-babel-7/input.js:2:3]
  1 │ class C {
@@ -12562,6 +12572,14 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
  4 │ }
    ╰────
 
+  × TS(1031): 'declare' modifier cannot appear on class elements of this kind.
+   ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/declare-method/input.ts:2:3]
+ 1 │ class A {
+ 2 │   declare foo() {}
+   ·   ───────
+ 3 │ }
+   ╰────
+
   × Expected a semicolon or an implicit semicolon after a statement, but found none
    ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/declare-new-line-abstract/input.ts:1:8]
  1 │ declare abstract
@@ -12660,6 +12678,22 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
  2 │ }
    ╰────
 
+  × TS(1024): 'readonly' modifier can only appear on a property declaration or index signature.
+   ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/generator-method-with-modifiers/input.ts:6:3]
+ 5 │   abstract *d() {}
+ 6 │   readonly *e() {}
+   ·   ────────
+ 7 │   declare *f() {}
+   ╰────
+
+  × TS(1031): 'declare' modifier cannot appear on class elements of this kind.
+   ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/generator-method-with-modifiers/input.ts:7:3]
+ 6 │   readonly *e() {}
+ 7 │   declare *f() {}
+   ·   ───────
+ 8 │   protected *g() {}
+   ╰────
+
   × TS(1245): Method 'd' cannot have an implementation because it is marked abstract.
    ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/generator-method-with-modifiers/input.ts:5:13]
  4 │   static *c() {}
@@ -12691,6 +12725,22 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
  2 │ }
    ╰────
 
+  × TS(1029): 'static' modifier must precede 'readonly' modifier.
+   ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/index-signature-errors/input.ts:2:14]
+ 1 │ class C {
+ 2 │     readonly static [x: string]: any;
+   ·              ──────
+ 3 │ }
+   ╰────
+
+  × TS(1024): 'readonly' modifier can only appear on a property declaration or index signature.
+   ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/method-readonly/input.ts:2:5]
+ 1 │ class C {
+ 2 │     readonly m() {}
+   ·     ────────
+ 3 │ }
+   ╰────
+
   × The keyword 'private' is reserved
    ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/modifier-name-parameters/input.ts:2:15]
  1 │ class Foo {
@@ -12772,6 +12822,38 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
  4 │ }
    ╰────
 
+  × TS(1024): 'readonly' modifier can only appear on a property declaration or index signature.
+   ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/optional-generator-method-with-invalid-modifiers/input.ts:3:3]
+ 2 │   abstract *d?() { }
+ 3 │   readonly *e?() { }
+   ·   ────────
+ 4 │   declare *f?() { }
+   ╰────
+
+  × TS(1031): 'declare' modifier cannot appear on class elements of this kind.
+   ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/optional-generator-method-with-invalid-modifiers/input.ts:4:3]
+ 3 │   readonly *e?() { }
+ 4 │   declare *f?() { }
+   ·   ───────
+ 5 │ }
+   ╰────
+
+  × TS(1024): 'readonly' modifier can only appear on a property declaration or index signature.
+    ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/optional-generator-method-with-invalid-modifiers/input.ts:9:3]
+  8 │   abstract *[d?.d]?() { }
+  9 │   readonly *[e?.e]?() { }
+    ·   ────────
+ 10 │   declare *[f?.f]?() { }
+    ╰────
+
+  × TS(1031): 'declare' modifier cannot appear on class elements of this kind.
+    ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/optional-generator-method-with-invalid-modifiers/input.ts:10:3]
+  9 │   readonly *[e?.e]?() { }
+ 10 │   declare *[f?.f]?() { }
+    ·   ───────
+ 11 │ }
+    ╰────
+
   × TS(1245): Method 'd' cannot have an implementation because it is marked abstract.
    ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/optional-generator-method-with-invalid-modifiers/input.ts:2:13]
  1 │ class C {
@@ -13433,6 +13515,14 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
  8 │   readonly g();
    ╰────
 
+  × TS(1024): 'readonly' modifier can only appear on a property declaration or index signature.
+   ╭─[babel/packages/babel-parser/test/fixtures/typescript/interface/invalid-modifiers-method/input.ts:8:3]
+ 7 │   abstract f();
+ 8 │   readonly g();
+   ·   ────────
+ 9 │ }
+   ╰────
+
   × TS(1070): 'private' modifier cannot appear on a type member.
    ╭─[babel/packages/babel-parser/test/fixtures/typescript/interface/invalid-modifiers-method-babel-7/input.ts:2:3]
  1 │ interface Foo {
@@ -13481,6 +13571,14 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
  8 │   readonly g();
    ╰────
 
+  × TS(1024): 'readonly' modifier can only appear on a property declaration or index signature.
+   ╭─[babel/packages/babel-parser/test/fixtures/typescript/interface/invalid-modifiers-method-babel-7/input.ts:8:3]
+ 7 │   abstract f();
+ 8 │   readonly g();
+   ·   ────────
+ 9 │ }
+   ╰────
+
   × TS(1070): 'private' modifier cannot appear on a type member.
    ╭─[babel/packages/babel-parser/test/fixtures/typescript/interface/invalid-modifiers-property/input.ts:2:3]
  1 │ interface Foo {
diff --git a/tasks/coverage/snapshots/parser_misc.snap b/tasks/coverage/snapshots/parser_misc.snap
index d1fae1c473f3b..47f4a0e40091b 100644
--- a/tasks/coverage/snapshots/parser_misc.snap
+++ b/tasks/coverage/snapshots/parser_misc.snap
@@ -1,7 +1,7 @@
 parser_misc Summary:
 AST Parsed     : 49/49 (100.00%)
 Positive Passed: 49/49 (100.00%)
-Negative Passed: 78/78 (100.00%)
+Negative Passed: 83/83 (100.00%)
 
   × Cannot assign to 'arguments' in strict mode
    ╭─[misc/fail/arguments-eval.ts:1:10]
@@ -197,26 +197,12 @@ Negative Passed: 78/78 (100.00%)
  3 │ }
    ╰────
 
-  × Missing initializer in destructuring declaration
-   ╭─[misc/fail/oxc-11713-13.ts:1:7]
- 1 │ const [index: string]: number
-   ·       ───────────────────────
- 2 │ }
-   ╰────
-
-  × Unexpected token
-   ╭─[misc/fail/oxc-11713-13.ts:2:1]
- 1 │ const [index: string]: number
- 2 │ }
-   · ─
-   ╰────
-
-  × TS(1070): 'const' modifier cannot appear on a type member.
-   ╭─[misc/fail/oxc-11713-14.ts:2:2]
- 1 │ const foo: {
- 2 │     const [index: string] : string
-   ·     ─────
- 3 │ } = {};
+  × TS(1071): 'const' modifier cannot appear on an index signature.
+   ╭─[misc/fail/oxc-11713-13.ts:2:3]
+ 1 │ interface Foo {
+ 2 │   const [index: string]: number
+   ·   ─────
+ 3 │ }
    ╰────
 
   × TS(1071): 'const' modifier cannot appear on an index signature.
@@ -259,14 +245,6 @@ Negative Passed: 78/78 (100.00%)
  3 │ }
    ╰────
 
-  × TS(1070): 'default' modifier cannot appear on a type member.
-   ╭─[misc/fail/oxc-11713-19.ts:2:2]
- 1 │ interface Foo {
- 2 │     default [index: string]: number
-   ·     ───────
- 3 │ }
-   ╰────
-
   × TS(1071): 'default' modifier cannot appear on an index signature.
    ╭─[misc/fail/oxc-11713-19.ts:2:2]
  1 │ interface Foo {
@@ -283,14 +261,6 @@ Negative Passed: 78/78 (100.00%)
  3 │ }
    ╰────
 
-  × TS(1070): 'default' modifier cannot appear on a type member.
-   ╭─[misc/fail/oxc-11713-20.ts:2:2]
- 1 │ const foo: {
- 2 │     default [index: string] : string
-   ·     ───────
- 3 │ } = {};
-   ╰────
-
   × TS(1071): 'default' modifier cannot appear on an index signature.
    ╭─[misc/fail/oxc-11713-20.ts:2:2]
  1 │ const foo: {
@@ -315,6 +285,42 @@ Negative Passed: 78/78 (100.00%)
  3 │ }
    ╰────
 
+  × TS(1024): 'readonly' modifier can only appear on a property declaration or index signature.
+   ╭─[misc/fail/oxc-11713-23.ts:2:3]
+ 1 │ interface Foo {
+ 2 │   readonly method();
+   ·   ────────
+ 3 │ }
+   ╰────
+
+  × TS(1031): 'declare' modifier cannot appear on class elements of this kind.
+   ╭─[misc/fail/oxc-11713-24.ts:2:3]
+ 1 │ class Foo {
+ 2 │   declare method() {}
+   ·   ───────
+ 3 │ }
+   ╰────
+
+  × TS(1024): 'readonly' modifier can only appear on a property declaration or index signature.
+   ╭─[misc/fail/oxc-11713-25.ts:2:3]
+ 1 │ class Foo {
+ 2 │   readonly method() {}
+   ·   ────────
+ 3 │ }
+   ╰────
+
+  × A parameter property is only allowed in a constructor implementation.
+   ╭─[misc/fail/oxc-11713-26.ts:1:14]
+ 1 │ function foo(readonly parameter) {}
+   ·              ──────────────────
+   ╰────
+
+  × A parameter property is only allowed in a constructor implementation.
+   ╭─[misc/fail/oxc-11713-27.ts:1:20]
+ 1 │ class Foo { method(readonly parameter) {} }
+   ·                    ──────────────────
+   ╰────
+
   × TS(1090): 'private' modifier cannot appear on a parameter.
    ╭─[misc/fail/oxc-11713-3.ts:1:14]
  1 │ function foo(private parameter) {}
diff --git a/tasks/coverage/snapshots/parser_typescript.snap b/tasks/coverage/snapshots/parser_typescript.snap
index ac9277903f2b4..c0455902a1ace 100644
--- a/tasks/coverage/snapshots/parser_typescript.snap
+++ b/tasks/coverage/snapshots/parser_typescript.snap
@@ -3,7 +3,7 @@ commit: 261630d6
 parser_typescript Summary:
 AST Parsed     : 8814/8816 (99.98%)
 Positive Passed: 8803/8816 (99.85%)
-Negative Passed: 1435/3535 (40.59%)
+Negative Passed: 1437/3535 (40.65%)
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/ExportAssignment7.ts
 
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/ExportAssignment8.ts
@@ -2270,8 +2270,6 @@ Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/classes/p
 
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/classes/propertyMemberDeclarations/defineProperty.ts
 
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/classes/propertyMemberDeclarations/derivedUninitializedPropertyDeclaration.ts
-
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/classes/propertyMemberDeclarations/initializerReferencingConstructorLocals.ts
 
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/classes/propertyMemberDeclarations/initializerReferencingConstructorParameters.ts
@@ -3608,8 +3606,6 @@ Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ec
 
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/MemberFunctionDeclarations/parserMemberFunctionDeclaration3.ts
 
-Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/MemberFunctionDeclarations/parserMemberFunctionDeclaration5.ts
-
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/MemberVariableDeclarations/parserMemberVariableDeclaration3.ts
 
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/ModuleDeclarations/parserModuleDeclaration1.d.ts
@@ -9972,14 +9968,6 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  6 │ };
    ╰────
 
-  × TS(1070): 'public' modifier cannot appear on a type member.
-   ╭─[typescript/tests/cases/compiler/modifiersOnInterfaceIndexSignature1.ts:2:3]
- 1 │ interface I {
- 2 │   public [a: string]: number;
-   ·   ──────
- 3 │ }
-   ╰────
-
   × TS(1071): 'public' modifier cannot appear on an index signature.
    ╭─[typescript/tests/cases/compiler/modifiersOnInterfaceIndexSignature1.ts:2:3]
  1 │ interface I {
@@ -16088,6 +16076,22 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  11 │     readonly #quxMethod() { return  3; }       // Error
     ╰────
 
+  × TS(1024): 'readonly' modifier can only appear on a property declaration or index signature.
+    ╭─[typescript/tests/cases/conformance/classes/members/privateNames/privateNamesIncompatibleModifiers.ts:11:5]
+ 10 │     protected #bazMethod() { return  3; }      // Error
+ 11 │     readonly #quxMethod() { return  3; }       // Error
+    ·     ────────
+ 12 │     declare #whatMethod()                      // Error
+    ╰────
+
+  × TS(1031): 'declare' modifier cannot appear on class elements of this kind.
+    ╭─[typescript/tests/cases/conformance/classes/members/privateNames/privateNamesIncompatibleModifiers.ts:12:5]
+ 11 │     readonly #quxMethod() { return  3; }       // Error
+ 12 │     declare #whatMethod()                      // Error
+    ·     ───────
+ 13 │     async #asyncMethod() { return 1; }         //OK
+    ╰────
+
   × TS(18010): An accessibility modifier cannot be used with a private identifier.
     ╭─[typescript/tests/cases/conformance/classes/members/privateNames/privateNamesIncompatibleModifiers.ts:17:5]
  16 │ 
@@ -16437,6 +16441,14 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  12 │ };
     ╰────
 
+  × TS(1031): 'declare' modifier cannot appear on class elements of this kind.
+    ╭─[typescript/tests/cases/conformance/classes/propertyMemberDeclarations/derivedUninitializedPropertyDeclaration.ts:15:5]
+ 14 │ class BOther extends A {
+ 15 │     declare m() { return 2 } // not allowed on methods
+    ·     ───────
+ 16 │     declare nonce: any; // ok, even though it's not in the base
+    ╰────
+
   × Function implementation is missing or not immediately following the declaration.
    ╭─[typescript/tests/cases/conformance/classes/propertyMemberDeclarations/memberFunctionDeclarations/memberFunctionOverloadMixingStaticAndInstance.ts:3:12]
  2 │     foo();
@@ -16593,7 +16605,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  9 │ }
    ╰────
 
-  × TS(1070): 'static' modifier cannot appear on a type member.
+  × TS(1071): 'static' modifier cannot appear on an index signature.
     ╭─[typescript/tests/cases/conformance/classes/staticIndexSignature/staticIndexSignature4.ts:12:5]
  11 │ interface IB {
  12 │     static [s: string]: number;
@@ -16601,7 +16613,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  13 │     static [s: number]: 42 | 233;
     ╰────
 
-  × TS(1070): 'static' modifier cannot appear on a type member.
+  × TS(1071): 'static' modifier cannot appear on an index signature.
     ╭─[typescript/tests/cases/conformance/classes/staticIndexSignature/staticIndexSignature4.ts:13:5]
  12 │     static [s: string]: number;
  13 │     static [s: number]: 42 | 233;
@@ -16609,7 +16621,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  14 │ }
     ╰────
 
-  × TS(1070): 'static' modifier cannot appear on a type member.
+  × TS(1071): 'static' modifier cannot appear on an index signature.
    ╭─[typescript/tests/cases/conformance/classes/staticIndexSignature/staticIndexSignature5.ts:7:5]
  6 │ interface I {
  7 │     static readonly [s: string]: number;
@@ -16617,7 +16629,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  8 │     static readonly [s: number]: 42 | 233
    ╰────
 
-  × TS(1070): 'static' modifier cannot appear on a type member.
+  × TS(1071): 'static' modifier cannot appear on an index signature.
    ╭─[typescript/tests/cases/conformance/classes/staticIndexSignature/staticIndexSignature5.ts:8:5]
  7 │     static readonly [s: string]: number;
  8 │     static readonly [s: number]: 42 | 233
@@ -23542,6 +23554,14 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  3 │ }
    ╰────
 
+  × TS(1031): 'declare' modifier cannot appear on class elements of this kind.
+   ╭─[typescript/tests/cases/conformance/parser/ecmascript5/MemberFunctionDeclarations/parserMemberFunctionDeclaration5.ts:2:5]
+ 1 │ class C {
+ 2 │     declare Foo() { }
+   ·     ───────
+ 3 │ }
+   ╰────
+
   × Identifier `public` has already been declared
    ╭─[typescript/tests/cases/conformance/parser/ecmascript5/MemberFunctionDeclarations/parserMemberFunctionDeclarationAmbiguities1.ts:2:3]
  1 │ class C {

From 070828aef5bb7ebc6dde69839ee9a4f24b19cb13 Mon Sep 17 00:00:00 2001
From: Ulrich Stark <github@ustark.de>
Date: Mon, 8 Sep 2025 20:19:42 +0200
Subject: [PATCH 2/3] branch off the more specific TS(1028) diagnostic from the
 general TS(1030) diagnostic like TypeScript does

---
 crates/oxc_parser/src/modifiers.rs            | 14 ++++----
 tasks/coverage/snapshots/parser_babel.snap    | 12 +++----
 .../coverage/snapshots/parser_typescript.snap | 32 +++++++++----------
 3 files changed, 29 insertions(+), 29 deletions(-)

diff --git a/crates/oxc_parser/src/modifiers.rs b/crates/oxc_parser/src/modifiers.rs
index f28694639e056..f59af5c472769 100644
--- a/crates/oxc_parser/src/modifiers.rs
+++ b/crates/oxc_parser/src/modifiers.rs
@@ -471,14 +471,14 @@ impl<'a> ParserImpl<'a> {
     }
 
     fn check_for_duplicate_modifiers(&mut self, seen_flags: ModifierFlags, modifier: &Modifier) {
-        if seen_flags.contains(modifier.kind.into())
-            || (matches!(
-                modifier.kind,
-                ModifierKind::Public | ModifierKind::Protected | ModifierKind::Private
-            ) && seen_flags.intersects(
-                ModifierFlags::PUBLIC | ModifierFlags::PROTECTED | ModifierFlags::PRIVATE,
-            ))
+        if matches!(
+            modifier.kind,
+            ModifierKind::Public | ModifierKind::Protected | ModifierKind::Private
+        ) && seen_flags
+            .intersects(ModifierFlags::PUBLIC | ModifierFlags::PROTECTED | ModifierFlags::PRIVATE)
         {
+            self.error(diagnostics::accessibility_modifier_already_seen(modifier));
+        } else if seen_flags.contains(modifier.kind.into()) {
             self.error(diagnostics::modifier_already_seen(modifier));
         }
     }
diff --git a/tasks/coverage/snapshots/parser_babel.snap b/tasks/coverage/snapshots/parser_babel.snap
index 36f840d2b30b5..bab61b35bbe73 100644
--- a/tasks/coverage/snapshots/parser_babel.snap
+++ b/tasks/coverage/snapshots/parser_babel.snap
@@ -12606,7 +12606,7 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
    ╰────
   help: Remove the duplicate modifier.
 
-  × TS(1030): 'public' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/duplicates-accessibility/input.ts:2:10]
  1 │ class Foo {
  2 │   public public a;
@@ -12615,7 +12615,7 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
    ╰────
   help: Remove the duplicate modifier.
 
-  × TS(1030): 'public' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/duplicates-accessibility/input.ts:3:11]
  2 │   public public a;
  3 │   private public b;
@@ -12624,7 +12624,7 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
    ╰────
   help: Remove the duplicate modifier.
 
-  × TS(1030): 'private' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/duplicates-accessibility/input.ts:4:13]
  3 │   private public b;
  4 │   protected private c;
@@ -12633,7 +12633,7 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
    ╰────
   help: Remove the duplicate modifier.
 
-  × TS(1030): 'protected' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/duplicates-accessibility/input.ts:5:10]
  4 │   protected private c;
  5 │   public protected d;
@@ -12642,7 +12642,7 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
    ╰────
   help: Remove the duplicate modifier.
 
-  × TS(1030): 'protected' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/duplicates-accessibility/input.ts:6:10]
  5 │   public protected d;
  6 │   public protected private e;
@@ -12651,7 +12651,7 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
    ╰────
   help: Remove the duplicate modifier.
 
-  × TS(1030): 'private' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[babel/packages/babel-parser/test/fixtures/typescript/class/duplicates-accessibility/input.ts:6:20]
  5 │   public protected d;
  6 │   public protected private e;
diff --git a/tasks/coverage/snapshots/parser_typescript.snap b/tasks/coverage/snapshots/parser_typescript.snap
index c0455902a1ace..ff71113812e38 100644
--- a/tasks/coverage/snapshots/parser_typescript.snap
+++ b/tasks/coverage/snapshots/parser_typescript.snap
@@ -6742,7 +6742,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  3 │     }
    ╰────
 
-  × TS(1030): 'public' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[typescript/tests/cases/compiler/constructorArgsErrors3.ts:2:25]
  1 │ class foo {
  2 │     constructor (public public a: number) {
@@ -6751,7 +6751,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
    ╰────
   help: Remove the duplicate modifier.
 
-  × TS(1030): 'public' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[typescript/tests/cases/compiler/constructorArgsErrors4.ts:2:26]
  1 │ class foo {
  2 │     constructor (private public a: number) {
@@ -10222,7 +10222,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  2 │     .then((role: Role) =>
    ╰────
 
-  × TS(1030): 'public' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[typescript/tests/cases/compiler/multipleClassPropertyModifiersErrors.ts:2:9]
  1 │ class C {
  2 │     public public p1;
@@ -10231,7 +10231,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
    ╰────
   help: Remove the duplicate modifier.
 
-  × TS(1030): 'private' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[typescript/tests/cases/compiler/multipleClassPropertyModifiersErrors.ts:3:10]
  2 │     public public p1;
  3 │     private private p2;
@@ -16243,7 +16243,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  3 │ }
    ╰────
 
-  × TS(1030): 'public' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
     ╭─[typescript/tests/cases/conformance/classes/propertyMemberDeclarations/accessibilityModifiers.ts:39:13]
  38 │ class E {
  39 │     private public protected property;
@@ -16252,7 +16252,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
     ╰────
   help: Remove the duplicate modifier.
 
-  × TS(1030): 'protected' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
     ╭─[typescript/tests/cases/conformance/classes/propertyMemberDeclarations/accessibilityModifiers.ts:39:20]
  38 │ class E {
  39 │     private public protected property;
@@ -16261,7 +16261,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
     ╰────
   help: Remove the duplicate modifier.
 
-  × TS(1030): 'protected' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
     ╭─[typescript/tests/cases/conformance/classes/propertyMemberDeclarations/accessibilityModifiers.ts:40:12]
  39 │     private public protected property;
  40 │     public protected method() { }
@@ -16270,7 +16270,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
     ╰────
   help: Remove the duplicate modifier.
 
-  × TS(1030): 'protected' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
     ╭─[typescript/tests/cases/conformance/classes/propertyMemberDeclarations/accessibilityModifiers.ts:41:13]
  40 │     public protected method() { }
  41 │     private protected get getter() { return 0; }
@@ -16279,7 +16279,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
     ╰────
   help: Remove the duplicate modifier.
 
-  × TS(1030): 'public' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
     ╭─[typescript/tests/cases/conformance/classes/propertyMemberDeclarations/accessibilityModifiers.ts:42:12]
  41 │     private protected get getter() { return 0; }
  42 │     public public set setter(a: number) { }
@@ -22470,7 +22470,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  3 │ }
    ╰────
 
-  × TS(1030): 'public' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[typescript/tests/cases/conformance/parser/ecmascript5/ConstructorDeclarations/parserConstructorDeclaration6.ts:2:10]
  1 │ class C {
  2 │   public public constructor() { }
@@ -22479,7 +22479,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
    ╰────
   help: Remove the duplicate modifier.
 
-  × TS(1030): 'private' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[typescript/tests/cases/conformance/parser/ecmascript5/ConstructorDeclarations/parserConstructorDeclaration7.ts:2:10]
  1 │ class C {
  2 │   public private constructor() { }
@@ -23510,7 +23510,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  3 │ }
    ╰────
 
-  × TS(1030): 'public' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[typescript/tests/cases/conformance/parser/ecmascript5/MemberAccessorDeclarations/parserMemberAccessorDeclaration7.ts:2:12]
  1 │ class C {
  2 │     public public get Foo() { }
@@ -23528,7 +23528,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  3 │ }
    ╰────
 
-  × TS(1030): 'public' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[typescript/tests/cases/conformance/parser/ecmascript5/MemberFunctionDeclarations/parserMemberFunctionDeclaration1.ts:2:12]
  1 │ class C {
  2 │     public public Foo() { }
@@ -23618,7 +23618,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  13 │ }
     ╰────
 
-  × TS(1030): 'public' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[typescript/tests/cases/conformance/parser/ecmascript5/MemberVariableDeclarations/parserMemberVariableDeclaration1.ts:2:10]
  1 │ class C {
  2 │   public public Foo;
@@ -23831,7 +23831,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
  2 │ }
    ╰────
 
-  × TS(1030): 'public' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[typescript/tests/cases/conformance/parser/ecmascript5/Protected/Protected4.ts:2:13]
  1 │ class C {
  2 │   protected public m() { }
@@ -23840,7 +23840,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmasc
    ╰────
   help: Remove the duplicate modifier.
 
-  × TS(1030): 'private' modifier already seen.
+  × TS(1028): Accessibility modifier already seen.
    ╭─[typescript/tests/cases/conformance/parser/ecmascript5/Protected/Protected7.ts:2:13]
  1 │ class C {
  2 │   protected private m() { }

From ac3e7d843eb1892adb06de63adaeb4ec99292070 Mon Sep 17 00:00:00 2001
From: Ulrich Stark <github@ustark.de>
Date: Mon, 8 Sep 2025 21:08:26 +0200
Subject: [PATCH 3/3] remove incorrect code to parse modifiers on typescript
 this parameter

---
 crates/oxc_parser/src/js/function.rs  |  4 +-
 crates/oxc_parser/src/ts/statement.rs |  7 +--
 crates/oxc_parser/src/ts/types.rs     | 87 +--------------------------
 3 files changed, 4 insertions(+), 94 deletions(-)

diff --git a/crates/oxc_parser/src/js/function.rs b/crates/oxc_parser/src/js/function.rs
index 21fe0335490b3..f1d0c825e2355 100644
--- a/crates/oxc_parser/src/js/function.rs
+++ b/crates/oxc_parser/src/js/function.rs
@@ -49,9 +49,7 @@ impl<'a> ParserImpl<'a> {
         self.expect(Kind::LParen);
         let this_param = if self.is_ts && self.at(Kind::This) {
             let param = self.parse_ts_this_parameter();
-            if !self.at(Kind::RParen) {
-                self.expect(Kind::Comma);
-            }
+            self.bump(Kind::Comma);
             Some(param)
         } else {
             None
diff --git a/crates/oxc_parser/src/ts/statement.rs b/crates/oxc_parser/src/ts/statement.rs
index 336201cee3ff2..e9106f9786491 100644
--- a/crates/oxc_parser/src/ts/statement.rs
+++ b/crates/oxc_parser/src/ts/statement.rs
@@ -561,14 +561,11 @@ impl<'a> ParserImpl<'a> {
 
     pub(crate) fn parse_ts_this_parameter(&mut self) -> TSThisParameter<'a> {
         let span = self.start_span();
-        self.parse_class_element_modifiers(true);
-
-        let this_span = self.start_span();
         self.bump_any();
-        let this = self.end_span(this_span);
+        let this_span = self.end_span(span);
 
         let type_annotation = self.parse_ts_type_annotation();
-        self.ast.ts_this_parameter(self.end_span(span), this, type_annotation)
+        self.ast.ts_this_parameter(self.end_span(span), this_span, type_annotation)
     }
 
     pub(crate) fn at_start_of_ts_declaration(&mut self) -> bool {
diff --git a/crates/oxc_parser/src/ts/types.rs b/crates/oxc_parser/src/ts/types.rs
index 56c4e96949774..5c04a117077b8 100644
--- a/crates/oxc_parser/src/ts/types.rs
+++ b/crates/oxc_parser/src/ts/types.rs
@@ -6,7 +6,7 @@ use oxc_syntax::operator::UnaryOperator;
 use crate::{
     Context, ParserImpl, diagnostics,
     lexer::Kind,
-    modifiers::{Modifier, ModifierFlags, ModifierKind, Modifiers},
+    modifiers::{ModifierFlags, ModifierKind, Modifiers},
 };
 
 use super::{super::js::FunctionKind, statement::CallOrConstructorSignature};
@@ -1274,91 +1274,6 @@ impl<'a> ParserImpl<'a> {
         }
     }
 
-    pub(crate) fn parse_class_element_modifiers(
-        &mut self,
-        is_constructor_parameter: bool,
-    ) -> Modifiers<'a> {
-        if !self.is_ts {
-            return Modifiers::empty();
-        }
-
-        let mut flags = ModifierFlags::empty();
-        let mut modifiers = None;
-
-        loop {
-            if !self.is_at_modifier(is_constructor_parameter) {
-                break;
-            }
-
-            if let Ok(kind) = ModifierKind::try_from(self.cur_kind()) {
-                let modifier = Modifier { kind, span: self.cur_token().span() };
-                let new_flag = ModifierFlags::from(kind);
-                if flags.contains(new_flag) {
-                    self.error(diagnostics::accessibility_modifier_already_seen(&modifier));
-                } else {
-                    flags.insert(new_flag);
-                    modifiers.get_or_insert_with(|| self.ast.vec()).push(modifier);
-                }
-            } else {
-                break;
-            }
-
-            self.bump_any();
-        }
-
-        Modifiers::new(modifiers, flags)
-    }
-
-    fn is_at_modifier(&mut self, is_constructor_parameter: bool) -> bool {
-        if !matches!(
-            self.cur_kind(),
-            Kind::Public
-                | Kind::Protected
-                | Kind::Private
-                | Kind::Static
-                | Kind::Abstract
-                | Kind::Readonly
-                | Kind::Declare
-                | Kind::Override
-                | Kind::Export
-        ) {
-            return false;
-        }
-
-        let checkpoint = self.checkpoint();
-        self.bump_any();
-        let next = self.cur_token();
-
-        if next.is_on_new_line() {
-            self.rewind(checkpoint);
-            return false;
-        }
-
-        let followed_by_any_member = matches!(next.kind(), Kind::PrivateIdentifier | Kind::LBrack)
-            || next.kind().is_literal_property_name();
-        if followed_by_any_member {
-            self.rewind(checkpoint);
-            return true;
-        }
-
-        let followed_by_class_member = !is_constructor_parameter && next.kind() == Kind::Star;
-        if followed_by_class_member {
-            self.rewind(checkpoint);
-            return true;
-        }
-
-        // allow `...` for error recovery
-        let followed_by_parameter = is_constructor_parameter
-            && matches!(next.kind(), Kind::LCurly | Kind::LBrack | Kind::Dot3);
-        if followed_by_parameter {
-            self.rewind(checkpoint);
-            return true;
-        }
-
-        self.rewind(checkpoint);
-        false
-    }
-
     fn parse_js_doc_unknown_or_nullable_type(&mut self) -> TSType<'a> {
         let span = self.start_span();
         self.bump_any(); // bump `?`