fix(transformer/typescript): preserve computed-key static block when class has an empty constructor (#21562)

## Summary

When a TypeScript class used a computed-key static property together with a constructor that has no parameter-property assignments, the early return in `transform_class_fields` dropped the `computed_key_assignment_static_block` that initializes the temp var, leaving it declared but never assigned.

```ts
export class SampleClass {
  static [Symbol.toPrimitive] = "test"
  constructor() {}
}
```

previously emitted:

```js
let _Symbol$toPrimitive;
export class SampleClass {
  static {
    this[_Symbol$toPrimitive] = "test";
  }
  constructor() {}
}
```

Now emits (matching TypeScript's own output under `useDefineForClassFields: false`):

```js
let _Symbol$toPrimitive;
export class SampleClass {
  static {
    _Symbol$toPrimitive = Symbol.toPrimitive;
  }
  static {
    this[_Symbol$toPrimitive] = "test";
  }
  constructor() {}
}
```

## Test plan

- Added fixtures `computed-static-property-with-constructor` (exact repro) and `computed-static-property-with-constructor-super` (super() + multiple computed keys) under `babel-plugin-transform-typescript`.
- Verified output against `tsc` 5.7 with `useDefineForClassFields: false`.

Closes rolldown/rolldown#9121

crates/oxc_transformer/src/typescript/class.rs

@@ -1,6 +1,6 @@
 use oxc_allocator::{TakeIn, Vec as ArenaVec};
 use oxc_ast::ast::*;
-use oxc_semantic::ScopeFlags;
+use oxc_semantic::{ScopeFlags, ScopeId};
 use oxc_span::SPAN;
 use oxc_str::Ident;
 use oxc_syntax::operator::AssignmentOperator;
@@ -100,6 +100,10 @@ impl<'a> TypeScript<'a> {
             )
         });
 
+        // Static blocks created below must be parented to the class body scope,
+        // not the current traversal scope (which is the scope enclosing the class).
+        let class_scope_id = class.scope_id();
+
         let mut constructor = None;
         let mut property_assignments = Vec::new();
         let mut computed_key_assignments = Vec::new();
@@ -123,7 +127,7 @@ impl<'a> TypeScript<'a> {
                             // `class C { static x = 1; }` -> `class C { static { this.x = 1; } }`
                             // `class C { static [x] = 1; }` -> `let _x; class C { static { this[_x] = 1; } }`
                             let body = ctx.ast.vec1(assignment);
-                            *element = Self::create_class_static_block(body, ctx);
+                            *element = Self::create_class_static_block(body, class_scope_id, ctx);
                         } else {
                             property_assignments.push(assignment);
                         }
@@ -170,7 +174,7 @@ impl<'a> TypeScript<'a> {
                     .ast
                     .expression_sequence(SPAN, ctx.ast.vec_from_iter(computed_key_assignments));
                 let statement = ctx.ast.statement_expression(SPAN, sequence_expression);
-                Self::create_class_static_block(ctx.ast.vec1(statement), ctx)
+                Self::create_class_static_block(ctx.ast.vec1(statement), class_scope_id, ctx)
             });
 
         if let Some(constructor) = constructor {
@@ -179,8 +183,13 @@ impl<'a> TypeScript<'a> {
             let params_assignment = Self::convert_constructor_params(params, ctx);
             property_assignments.splice(0..0, params_assignment);
 
-            // Exit if there are no property and parameter assignments
             if property_assignments.is_empty() {
+                // No property/parameter assignments to inject, but computed-key temp
+                // inits still need their static block (e.g. `static [expr] = value` +
+                // empty `constructor()`), otherwise the temp var is left uninitialized.
+                if let Some(element) = computed_key_assignment_static_block {
+                    class.body.body.insert(0, element);
+                }
                 return;
             }
 
@@ -429,21 +438,22 @@ impl<'a> TypeScript<'a> {
         )
     }
 
-    /// Create `static { body }`
+    /// Create `static { body }` as a child of `class_scope_id`.
+    ///
+    /// The enclosing traversal scope is the scope around the class, not the class body,
+    /// so pass `class.scope_id()` explicitly to parent the static block correctly.
     #[inline]
     fn create_class_static_block(
         body: ArenaVec<'a, Statement<'a>>,
+        class_scope_id: ScopeId,
         ctx: &mut TraverseCtx<'a>,
     ) -> ClassElement<'a> {
-        let scope_id = ctx.insert_scope_below_statements(
-            &body,
+        let scope_id = ctx.insert_scope_below_statement_from_scope_id(
+            &body[0],
+            class_scope_id,
             ScopeFlags::StrictMode | ScopeFlags::ClassStaticBlock,
         );
 
-        ctx.ast.class_element_static_block_with_scope_id(
-            SPAN,
-            ctx.ast.vec_from_iter(body),
-            scope_id,
-        )
+        ctx.ast.class_element_static_block_with_scope_id(SPAN, body, scope_id)
     }
 }

tasks/transform_conformance/snapshots/oxc.snap.md

@@ -1,6 +1,6 @@
 commit: c543b031
 
-Passed: 220/367
+Passed: 222/369
 
 # All Passed:
 * babel-plugin-transform-class-static-block
@@ -69,7 +69,7 @@ after transform: SymbolId(0): [ReferenceId(0), ReferenceId(2), ReferenceId(6), R
 rebuilt        : SymbolId(0): [ReferenceId(0), ReferenceId(2), ReferenceId(6), ReferenceId(10)]
 
 
-# babel-plugin-transform-typescript (15/48)
+# babel-plugin-transform-typescript (17/50)
 * allow-declare-fields-false/input.ts
 Unresolved references mismatch:
 after transform: ["dce"]
@@ -614,32 +614,8 @@ Scope parent mismatch:
 after transform: ScopeId(12): Some(ScopeId(0))
 rebuilt        : ScopeId(2): Some(ScopeId(1))
 Scope parent mismatch:
-after transform: ScopeId(11): Some(ScopeId(0))
-rebuilt        : ScopeId(3): Some(ScopeId(1))
-Scope parent mismatch:
-after transform: ScopeId(13): Some(ScopeId(0))
-rebuilt        : ScopeId(5): Some(ScopeId(4))
-Scope parent mismatch:
-after transform: ScopeId(16): Some(ScopeId(0))
-rebuilt        : ScopeId(8): Some(ScopeId(7))
-Scope parent mismatch:
-after transform: ScopeId(14): Some(ScopeId(0))
-rebuilt        : ScopeId(9): Some(ScopeId(7))
-Scope parent mismatch:
-after transform: ScopeId(15): Some(ScopeId(0))
-rebuilt        : ScopeId(10): Some(ScopeId(7))
-Scope parent mismatch:
 after transform: ScopeId(17): Some(ScopeId(0))
 rebuilt        : ScopeId(12): Some(ScopeId(11))
-Scope parent mismatch:
-after transform: ScopeId(18): Some(ScopeId(0))
-rebuilt        : ScopeId(17): Some(ScopeId(15))
-Scope parent mismatch:
-after transform: ScopeId(19): Some(ScopeId(0))
-rebuilt        : ScopeId(19): Some(ScopeId(15))
-Scope parent mismatch:
-after transform: ScopeId(20): Some(ScopeId(0))
-rebuilt        : ScopeId(20): Some(ScopeId(15))
 Unresolved reference IDs mismatch for "dce":
 after transform: [ReferenceId(0), ReferenceId(1), ReferenceId(4), ReferenceId(9), ReferenceId(12), ReferenceId(14), ReferenceId(17)]
 rebuilt        : [ReferenceId(5)]

tasks/transform_conformance/tests/babel-plugin-transform-typescript/test/fixtures/computed-static-property-with-constructor-super/input.ts

@@ -0,0 +1,8 @@
+class Sub extends Base {
+	static [x()] = 1;
+	static [y()] = 2;
+
+	constructor(a: number) {
+		super(a);
+	}
+}

tasks/transform_conformance/tests/babel-plugin-transform-typescript/test/fixtures/computed-static-property-with-constructor-super/options.json

@@ -0,0 +1,8 @@
+{
+  "assumptions": {
+    "setPublicClassFields": true
+  },
+  "plugins": [
+    ["transform-typescript"]
+  ]
+}

tasks/transform_conformance/tests/babel-plugin-transform-typescript/test/fixtures/computed-static-property-with-constructor-super/output.js

@@ -0,0 +1,15 @@
+let _x, _y;
+class Sub extends Base {
+  static {
+    _x = x(), _y = y();
+  }
+  static {
+    this[_x] = 1;
+  }
+  static {
+    this[_y] = 2;
+  }
+  constructor(a) {
+    super(a);
+  }
+}

tasks/transform_conformance/tests/babel-plugin-transform-typescript/test/fixtures/computed-static-property-with-constructor/input.ts

@@ -0,0 +1,5 @@
+export class SampleClass {
+	static [Symbol.toPrimitive] = "test";
+
+	constructor() {}
+}

tasks/transform_conformance/tests/babel-plugin-transform-typescript/test/fixtures/computed-static-property-with-constructor/options.json

@@ -0,0 +1,8 @@
+{
+  "assumptions": {
+    "setPublicClassFields": true
+  },
+  "plugins": [
+    ["transform-typescript"]
+  ]
+}

tasks/transform_conformance/tests/babel-plugin-transform-typescript/test/fixtures/computed-static-property-with-constructor/output.js

@@ -0,0 +1,10 @@
+let _Symbol$toPrimitive;
+export class SampleClass {
+  static {
+    _Symbol$toPrimitive = Symbol.toPrimitive;
+  }
+  static {
+    this[_Symbol$toPrimitive] = "test";
+  }
+  constructor() {}
+}