feat(parser): better handling of invalid modifiers (#6482)

## What This PR Does

1. Recover on, and provide a better message for, invalid `export` modifier on constructor parameters. Before, an `unexpected token` error would be produced and the parser would panic. Now, the parser recovers and produces a message saying `'export' modifier cannot appear on a parameter.`
  ```ts
class Foo {
    constructor(export x: number) {}
}
  ```

2. Recover on, and provide a better message for, invalid modifiers on index signatures. Same recovery/message characteristics as above.
  ```ts
class Foo {
    public [x: string]: string;
}
```

crates/oxc_parser/src/diagnostics.rs

@@ -471,6 +471,12 @@ pub fn cannot_appear_on_a_parameter(modifier: &Modifier) -> OxcDiagnostic {
         .with_label(modifier.span)
 }
 
+/// TS(1071)
+pub fn cannot_appear_on_an_index_signature(modifier: &Modifier) -> OxcDiagnostic {
+    ts_error("1071", format!("'{}' modifier cannot appear on an index signature.", modifier.kind))
+        .with_label(modifier.span)
+}
+
 /// TS(18010)
 #[cold]
 pub fn accessibility_modifier_on_private_property(modifier: &Modifier) -> OxcDiagnostic {

crates/oxc_parser/src/ts/statement.rs

@@ -255,6 +255,7 @@ impl<'a> ParserImpl<'a> {
                 | Kind::Readonly
                 | Kind::Declare
                 | Kind::Override
+                | Kind::Export
         )) {
             return false;
         }

crates/oxc_parser/src/ts/types.rs

@@ -1269,14 +1269,14 @@ impl<'a> ParserImpl<'a> {
 
     pub(crate) fn parse_ts_index_signature_member(&mut self) -> Result<TSSignature<'a>> {
         let span = self.start_span();
-        let mut readonly = false;
-        while self.is_nth_at_modifier(0, false) {
-            if self.eat(Kind::Readonly) {
-                readonly = true;
-            } else {
-                return Err(self.unexpected());
-            }
-        }
+
+        let modifiers = self.parse_class_element_modifiers(false);
+        self.verify_modifiers(
+            &modifiers,
+            ModifierFlags::READONLY,
+            diagnostics::cannot_appear_on_an_index_signature,
+        );
+        let readonly = modifiers.contains(ModifierKind::Readonly);
 
         self.bump(Kind::LBrack);
         let index_name = self.parse_ts_index_signature_name()?;

tasks/coverage/snapshots/parser_typescript.snap

@@ -6629,7 +6629,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
  3 │     }
    ╰────
 
-  × Identifier expected. 'export' is a reserved word that cannot be used here.
+  × TS(1090): 'export' modifier cannot appear on a parameter.
    ╭─[typescript/tests/cases/compiler/constructorArgsErrors5.ts:2:18]
  1 │ class foo {
  2 │     constructor (export a: number) {
@@ -9223,7 +9223,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
  6 │ };
    ╰────
 
-  × Unexpected token
+  × TS(1071): 'public' modifier cannot appear on an index signature.
    ╭─[typescript/tests/cases/compiler/modifiersOnInterfaceIndexSignature1.ts:2:3]
  1 │ interface I {
  2 │   public [a: string]: number;
@@ -15079,7 +15079,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
  9 │ }
    ╰────
 
-  × Unexpected token
+  × 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;
@@ -15087,7 +15087,15 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
  13 │     static [s: number]: 42 | 233;
     ╰────
 
-  × Unexpected token
+  × 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;
+    ·     ──────
+ 14 │ }
+    ╰────
+
+  × 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;
@@ -15095,6 +15103,14 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
  8 │     static readonly [s: number]: 42 | 233
    ╰────
 
+  × 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
+   ·     ──────
+ 9 │ }
+   ╰────
+
   × Expected `,` but found `is`
      ╭─[typescript/tests/cases/conformance/controlFlow/assertionTypePredicates1.ts:163:20]
  162 │     get p1(): this is string;
@@ -20758,14 +20774,13 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/salsa/private
    · ─
    ╰────
 
-  × Expected a semicolon or an implicit semicolon after a statement, but found none
-   ╭─[typescript/tests/cases/conformance/parser/ecmascript5/IndexMemberDeclarations/parserIndexMemberDeclaration9.ts:2:10]
+  × TS(1071): 'export' modifier cannot appear on an index signature.
+   ╭─[typescript/tests/cases/conformance/parser/ecmascript5/IndexMemberDeclarations/parserIndexMemberDeclaration9.ts:2:4]
  1 │ class C {
  2 │    export [x: string]: string;
-   ·          ▲
+   ·    ──────
  3 │ }
    ╰────
-  help: Try insert a semicolon here
 
   × Unexpected token
    ╭─[typescript/tests/cases/conformance/parser/ecmascript5/IndexSignatures/parserIndexSignature1.ts:2:4]