fix(semantic): allow new.target in class field initializers (#18349)

## Summary

- Allow `new.target` in class field initializers per the ES2022 spec
- `new.target` evaluates to `undefined` in this context, same as in static blocks
- This aligns Oxc with Babel's behavior

## Background

TypeScript incorrectly disallows `new.target` in class field initializers. Their validation was implemented in 2016 ([PR #12783](https://github.com/Microsoft/TypeScript/pull/12783)) before class fields were standardized, and was never updated when ES2022 landed.

The ES spec explicitly allows this - see the [TC39 class-fields proposal](https://github.com/tc39/proposal-class-fields) and [Babel issue #6243](https://github.com/babel/babel/issues/6243).

## Test case

```javascript
class X {
  static a = new.target;              // ✓ allowed (evaluates to undefined)
  static b = () => new.target;        // ✓ allowed (arrow inherits from field context)
  e = new.target;                     // ✓ allowed
  f = () => new.target;               // ✓ allowed
}
```

## Test plan

- [x] Babel conformance test `es2022/class-properties/new-target` now passes
- [x] `cargo test -p oxc_semantic --lib` passes
- [x] `just check lint test` passes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

crates/oxc_semantic/src/checker/javascript.rs

@@ -512,19 +512,50 @@ pub fn check_meta_property(prop: &MetaProperty, ctx: &SemanticBuilder<'_>) {
                 if ctx.source_type.is_commonjs() {
                     return;
                 }
-                let mut in_function_scope = false;
-                for scope_id in ctx.scoping.scope_ancestors(ctx.current_scope_id) {
-                    let flags = ctx.scoping.scope_flags(scope_id);
-                    // In arrow functions, new.target is inherited from the surrounding scope.
-                    if flags.contains(ScopeFlags::Arrow) {
-                        continue;
-                    }
-                    if flags.intersects(ScopeFlags::Function | ScopeFlags::ClassStaticBlock) {
-                        in_function_scope = true;
-                        break;
+
+                // Check if we're in a valid context for new.target:
+                // 1. Inside a function (including constructor)
+                // 2. Inside a class static block
+                // 3. Inside a class field initializer (new.target evaluates to undefined)
+                //
+                // Arrow functions inherit new.target from their surrounding scope,
+                // so we skip them and continue checking the enclosing context.
+
+                let mut in_valid_context = false;
+
+                // First, check AST ancestors for class field initializers.
+                // We need to do this because class fields don't have their own scope.
+                for node_kind in ctx.nodes.ancestor_kinds(ctx.current_node_id) {
+                    match node_kind {
+                        // Regular functions have their own new.target binding.
+                        // Use scope-based check from here.
+                        AstKind::Function(_) => break,
+                        // Class field initializers allow new.target (evaluates to undefined).
+                        // This includes arrow functions nested inside the initializer.
+                        AstKind::PropertyDefinition(_) | AstKind::AccessorProperty(_) => {
+                            in_valid_context = true;
+                            break;
+                        }
+                        _ => {}
                     }
                 }
-                if !in_function_scope {
+
+                // If not in a class field, fall back to scope-based check
+                if !in_valid_context {
+                    for scope_id in ctx.scoping.scope_ancestors(ctx.current_scope_id) {
+                        let flags = ctx.scoping.scope_flags(scope_id);
+                        // In arrow functions, new.target is inherited from the surrounding scope.
+                        if flags.contains(ScopeFlags::Arrow) {
+                            continue;
+                        }
+                        if flags.intersects(ScopeFlags::Function | ScopeFlags::ClassStaticBlock) {
+                            in_valid_context = true;
+                            break;
+                        }
+                    }
+                }
+
+                if !in_valid_context {
                     ctx.error(diagnostics::new_target(prop.span));
                 }
             }

crates/oxc_semantic/src/diagnostics.rs

@@ -121,7 +121,9 @@ pub fn module_code(x0: &str, span1: Span) -> OxcDiagnostic {
 #[cold]
 pub fn new_target(span: Span) -> OxcDiagnostic {
     OxcDiagnostic::error("Unexpected new.target expression")
-        .with_help("new.target is only allowed in constructors and functions invoked using the `new` operator")
+        .with_help(
+            "new.target is only allowed in constructors, functions, and class field initializers",
+        )
         .with_label(span)
 }
 

tasks/coverage/snapshots/parser_babel.snap

@@ -2,7 +2,7 @@ commit: fc58af40
 
 parser_babel Summary:
 AST Parsed     : 2221/2227 (99.73%)
-Positive Passed: 2205/2227 (99.01%)
+Positive Passed: 2206/2227 (99.06%)
 Negative Passed: 1649/1689 (97.63%)
 Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/es2026/explicit-resource-management/invalid-for-using-of-no-initializer/input.js
 
@@ -84,80 +84,6 @@ Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/ty
 
 Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/typescript/types/invalid-import-type-options-with-spread-element/input.ts
 
-Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/es2022/class-properties/new-target/input.js
-
-  × Unexpected new.target expression
-   ╭─[babel/packages/babel-parser/test/fixtures/es2022/class-properties/new-target/input.js:2:14]
- 1 │ class X {
- 2 │   static a = new.target;
-   ·              ──────────
- 3 │   static b = (foo = 1 + bar(new.target));
-   ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
-
-  × Unexpected new.target expression
-   ╭─[babel/packages/babel-parser/test/fixtures/es2022/class-properties/new-target/input.js:3:29]
- 2 │   static a = new.target;
- 3 │   static b = (foo = 1 + bar(new.target));
-   ·                             ──────────
- 4 │   static c = () => new.target;
-   ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
-
-  × Unexpected new.target expression
-   ╭─[babel/packages/babel-parser/test/fixtures/es2022/class-properties/new-target/input.js:4:20]
- 3 │   static b = (foo = 1 + bar(new.target));
- 4 │   static c = () => new.target;
-   ·                    ──────────
- 5 │   static d = (foo = new.target) => {};
-   ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
-
-  × Unexpected new.target expression
-   ╭─[babel/packages/babel-parser/test/fixtures/es2022/class-properties/new-target/input.js:5:21]
- 4 │   static c = () => new.target;
- 5 │   static d = (foo = new.target) => {};
-   ·                     ──────────
- 6 │   e = new.target;
-   ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
-
-  × Unexpected new.target expression
-   ╭─[babel/packages/babel-parser/test/fixtures/es2022/class-properties/new-target/input.js:6:7]
- 5 │   static d = (foo = new.target) => {};
- 6 │   e = new.target;
-   ·       ──────────
- 7 │   f = (foo = 1 + bar(new.target));
-   ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
-
-  × Unexpected new.target expression
-   ╭─[babel/packages/babel-parser/test/fixtures/es2022/class-properties/new-target/input.js:7:22]
- 6 │   e = new.target;
- 7 │   f = (foo = 1 + bar(new.target));
-   ·                      ──────────
- 8 │   g = () => new.target;
-   ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
-
-  × Unexpected new.target expression
-   ╭─[babel/packages/babel-parser/test/fixtures/es2022/class-properties/new-target/input.js:8:13]
- 7 │   f = (foo = 1 + bar(new.target));
- 8 │   g = () => new.target;
-   ·             ──────────
- 9 │   h = (foo = new.target) => {};
-   ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
-
-  × Unexpected new.target expression
-    ╭─[babel/packages/babel-parser/test/fixtures/es2022/class-properties/new-target/input.js:9:14]
-  8 │   g = () => new.target;
-  9 │   h = (foo = new.target) => {};
-    ·              ──────────
- 10 │ }
-    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
-
 Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/es2022/class-static-block/duplicate-function-var-name/input.js
 
   × Identifier `x` has already been declared
@@ -956,14 +882,14 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
  1 │ const x = new.target;
    ·           ──────────
    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Unexpected new.target expression
    ╭─[babel/packages/babel-parser/test/fixtures/core/opts/allowNewTargetOutsideFunction-false-2/input.js:1:17]
  1 │ const y = () => new.target;
    ·                 ──────────
    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × TS(1108): A 'return' statement can only be used within a function body.
    ╭─[babel/packages/babel-parser/test/fixtures/core/opts/allowReturnOutsideFunction-true-invalid-in-static-block/input.js:3:5]
@@ -3132,7 +3058,7 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
    ·   ──────────
  3 │ }
    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × The only valid meta property for new is new.target
    ╭─[babel/packages/babel-parser/test/fixtures/es2015/meta-properties/new-invalid-prop/input.js:2:3]
@@ -3147,7 +3073,7 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
  1 │ new.target
    · ──────────
    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Keywords cannot contain escape characters
    ╭─[babel/packages/babel-parser/test/fixtures/es2015/meta-properties/new-target-invalid-escaped-new/input.js:1:16]
@@ -8250,7 +8176,7 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
  1 │ var x = new.target;
    ·         ──────────
    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Expected `(` but found `}`
    ╭─[babel/packages/babel-parser/test/fixtures/es2022/class-properties/no-ctor/input.js:3:1]
@@ -9953,7 +9879,7 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
  1 │ var x = new.target;
    ·         ──────────
    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × The only valid meta property for new is new.target
    ╭─[babel/packages/babel-parser/test/fixtures/esprima/es2015-meta-property/unknown-property/input.js:1:22]

tasks/coverage/snapshots/parser_test262.snap

@@ -20523,7 +20523,7 @@ Negative Passed: 4581/4581 (100.00%)
     ·   ──────────
  38 │ };
     ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Unexpected new.target expression
     ╭─[test262/test/language/global-code/new.target.js:21:1]
@@ -20531,7 +20531,7 @@ Negative Passed: 4581/4581 (100.00%)
  21 │ new.target;
     · ──────────
     ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × TS(1108): A 'return' statement can only be used within a function body.
     ╭─[test262/test/language/global-code/return.js:23:1]
@@ -24730,7 +24730,7 @@ Negative Passed: 4581/4581 (100.00%)
  16 │ new.target;
     · ──────────
     ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × The keyword 'public' is reserved
     ╭─[test262/test/language/module-code/early-strict-mode.js:15:5]

tasks/coverage/snapshots/parser_typescript.snap

@@ -16683,7 +16683,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
    ·           ──────────
  2 │ const b = () => new.target;
    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Unexpected new.target expression
    ╭─[typescript/tests/cases/conformance/es6/newTarget/invalidNewTarget.es5.ts:2:17]
@@ -16692,7 +16692,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
    ·                 ──────────
  3 │ 
    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Unexpected new.target expression
    ╭─[typescript/tests/cases/conformance/es6/newTarget/invalidNewTarget.es5.ts:5:6]
@@ -16701,16 +16701,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
    ·      ──────────
  6 │     c() { return new.target; }
    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
-
-  × Unexpected new.target expression
-    ╭─[typescript/tests/cases/conformance/es6/newTarget/invalidNewTarget.es5.ts:9:15]
-  8 │     set e(_) { _ = new.target; }
-  9 │     f = () => new.target;
-    ·               ──────────
- 10 │ 
-    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Unexpected new.target expression
     ╭─[typescript/tests/cases/conformance/es6/newTarget/invalidNewTarget.es5.ts:11:13]
@@ -16719,16 +16710,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
     ·             ──────────
  12 │     static g() { return new.target; }
     ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
-
-  × Unexpected new.target expression
-    ╭─[typescript/tests/cases/conformance/es6/newTarget/invalidNewTarget.es5.ts:15:22]
- 14 │     static set i(_) { _ = new.target; }
- 15 │     static j = () => new.target;
-    ·                      ──────────
- 16 │ }
-    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Unexpected new.target expression
     ╭─[typescript/tests/cases/conformance/es6/newTarget/invalidNewTarget.es5.ts:19:6]
@@ -16737,7 +16719,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
     ·      ──────────
  20 │     k() { return new.target; },
     ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Unexpected new.target expression
     ╭─[typescript/tests/cases/conformance/es6/newTarget/invalidNewTarget.es5.ts:23:8]
@@ -16746,7 +16728,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
     ·        ──────────
  24 │ };
     ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Unexpected new.target expression
    ╭─[typescript/tests/cases/conformance/es6/newTarget/invalidNewTarget.es6.ts:1:11]
@@ -16754,7 +16736,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
    ·           ──────────
  2 │ const b = () => new.target;
    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Unexpected new.target expression
    ╭─[typescript/tests/cases/conformance/es6/newTarget/invalidNewTarget.es6.ts:2:17]
@@ -16763,7 +16745,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
    ·                 ──────────
  3 │ 
    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Unexpected new.target expression
    ╭─[typescript/tests/cases/conformance/es6/newTarget/invalidNewTarget.es6.ts:5:6]
@@ -16772,16 +16754,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
    ·      ──────────
  6 │     c() { return new.target; }
    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
-
-  × Unexpected new.target expression
-    ╭─[typescript/tests/cases/conformance/es6/newTarget/invalidNewTarget.es6.ts:9:15]
-  8 │     set e(_) { _ = new.target; }
-  9 │     f = () => new.target;
-    ·               ──────────
- 10 │ 
-    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Unexpected new.target expression
     ╭─[typescript/tests/cases/conformance/es6/newTarget/invalidNewTarget.es6.ts:11:13]
@@ -16790,16 +16763,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
     ·             ──────────
  12 │     static g() { return new.target; }
     ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
-
-  × Unexpected new.target expression
-    ╭─[typescript/tests/cases/conformance/es6/newTarget/invalidNewTarget.es6.ts:15:22]
- 14 │     static set i(_) { _ = new.target; }
- 15 │     static j = () => new.target;
-    ·                      ──────────
- 16 │ }
-    ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Unexpected new.target expression
     ╭─[typescript/tests/cases/conformance/es6/newTarget/invalidNewTarget.es6.ts:19:6]
@@ -16808,7 +16772,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
     ·      ──────────
  20 │     k() { return new.target; },
     ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Unexpected new.target expression
     ╭─[typescript/tests/cases/conformance/es6/newTarget/invalidNewTarget.es6.ts:23:8]
@@ -16817,7 +16781,7 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
     ·        ──────────
  24 │ };
     ╰────
-  help: new.target is only allowed in constructors and functions invoked using the `new` operator
+  help: new.target is only allowed in constructors, functions, and class field initializers
 
   × Expected `:` but found `,`
    ╭─[typescript/tests/cases/conformance/es6/shorthandPropertyAssignment/objectLiteralShorthandPropertiesErrorFromNotUsingIdentifier.ts:3:20]

tasks/coverage/snapshots/semantic_babel.snap

@@ -2,7 +2,7 @@ commit: fc58af40
 
 semantic_babel Summary:
 AST Parsed     : 2227/2227 (100.00%)
-Positive Passed: 1939/2227 (87.07%)
+Positive Passed: 1940/2227 (87.11%)
 semantic Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/comments/decorators/decorators-after-export/input.js
 Symbol span mismatch for "C":
 after transform: SymbolId(0): Span { start: 65, end: 66 }
@@ -76,16 +76,6 @@ Symbol scope ID mismatch for "_await":
 after transform: SymbolId(3): ScopeId(2)
 rebuilt        : SymbolId(2): ScopeId(0)
 
-semantic Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/es2022/class-properties/new-target/input.js
-Unexpected new.target expression
-Unexpected new.target expression
-Unexpected new.target expression
-Unexpected new.target expression
-Unexpected new.target expression
-Unexpected new.target expression
-Unexpected new.target expression
-Unexpected new.target expression
-
 semantic Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/es2022/class-static-block/duplicate-function-var-name/input.js
 Identifier `x` has already been declared