fix(transformer/class-properties): align setPublicClassFields with TypeScript's useDefineForClassFields: false

crates/oxc_transformer/src/es2022/class_properties/class.rs

@@ -276,6 +276,12 @@ impl<'a> ClassProperties<'a, '_> {
             }
         }
 
+        // When `self.set_public_class_fields` is true, we don't need to convert instance properties
+        // without initializers, that means `instance_prop_count != 0` but `instance_inits` may be empty.
+        if instance_inits.is_empty() {
+            return;
+        }
+
         // Scope that instance property initializers will be inserted into.
         // This is usually class constructor, but can also be a `_super` function which is created.
         let instance_inits_scope_id;

crates/oxc_transformer/src/es2022/class_properties/prop_decl.rs

@@ -24,11 +24,20 @@ impl<'a> ClassProperties<'a, '_> {
         ctx: &mut TraverseCtx<'a>,
     ) {
         // Get value
-        let value = prop.value.take().unwrap_or_else(|| ctx.ast.void_0(SPAN));
+        let value = prop.value.take();
 
         let init_expr = if let PropertyKey::PrivateIdentifier(ident) = &mut prop.key {
+            let value = value.unwrap_or_else(|| ctx.ast.void_0(SPAN));
             self.create_private_instance_init_assignment(ident, value, ctx)
         } else {
+            let value = match value {
+                Some(value) => value,
+                // Do not need to convert property to `assignee.prop = void 0` if no initializer exists.
+                // This is to align `TypeScript` with `useDefineForClassFields: false`.
+                None if self.private_fields_as_properties => return,
+                None => ctx.ast.void_0(SPAN),
+            };
+
             // Convert to assignment or `_defineProperty` call, depending on `loose` option
             let this = ctx.ast.expression_this(SPAN);
             self.create_init_assignment(prop, value, this, false, ctx)
@@ -85,17 +94,23 @@ impl<'a> ClassProperties<'a, '_> {
         // Get value.
         // Transform it to replace `this` and references to class name with temp var for class.
         // Also transform `super`.
-        let value = match prop.value.take() {
-            Some(mut value) => {
-                self.transform_static_initializer(&mut value, ctx);
-                value
-            }
-            None => ctx.ast.void_0(SPAN),
-        };
+        let value = prop.value.take().map(|mut value| {
+            self.transform_static_initializer(&mut value, ctx);
+            value
+        });
 
         if let PropertyKey::PrivateIdentifier(ident) = &mut prop.key {
+            let value = value.unwrap_or_else(|| ctx.ast.void_0(SPAN));
             self.insert_private_static_init_assignment(ident, value, ctx);
         } else {
+            let value = match value {
+                Some(value) => value,
+                // Do not need to convert property to `assignee.prop = void 0` if no initializer exists.
+                // This is to align `TypeScript` with `useDefineForClassFields: false`.
+                None if self.private_fields_as_properties => return,
+                None => ctx.ast.void_0(SPAN),
+            };
+
             // Convert to assignment or `_defineProperty` call, depending on `loose` option
             let class_details = self.current_class();
             let class_binding = if class_details.is_declaration {
@@ -200,6 +215,9 @@ impl<'a> ClassProperties<'a, '_> {
 // Used for both instance and static properties
 impl<'a> ClassProperties<'a, '_> {
     /// `assignee.prop = value` or `_defineProperty(assignee, "prop", value)`
+    /// `#[inline]` because the caller has been checked `self.set_public_class_fields`.
+    /// After inlining, the two `self.set_public_class_fields` checks may be folded into one.
+    #[inline]
     fn create_init_assignment(
         &mut self,
         prop: &mut PropertyDefinition<'a>,

tasks/transform_conformance/overrides/babel-plugin-transform-class-properties/test/fixtures/compile-to-class/constructor-collision-ignores-types-loose/output.js

@@ -1,6 +1,5 @@
 class C {
   constructor(T) {
-    this.x = void 0;
     this.y = 0;
   }
 }

tasks/transform_conformance/overrides/babel-plugin-transform-class-properties/test/fixtures/public-loose/instance-undefined/output.js

@@ -1,5 +1 @@
-class Foo {
-  constructor() {
-    this.bar = void 0;
-  }
-}
+class Foo { }

tasks/transform_conformance/overrides/babel-plugin-transform-class-properties/test/fixtures/public-loose/preserve-comments/output.js

@@ -1,6 +1 @@
-class C {
-  constructor() {
-    this.a = void 0;
-  }
-}
-C.b = void 0;
+class C { }

tasks/transform_conformance/overrides/babel-plugin-transform-class-properties/test/fixtures/public-loose/static-undefined/output.js

@@ -1,2 +1 @@
 class Foo {}
-Foo.bar = void 0;

tasks/transform_conformance/snapshots/babel_exec.snap.md

@@ -2,7 +2,7 @@ commit: 578ac4df
 
 node: v22.14.0
 
-Passed: 320 of 406 (78.82%)
+Passed: 319 of 406 (78.57%)
 
 Failures:
 
@@ -58,6 +58,10 @@ AssertionError: expected function to throw an error, but it didn't
 AssertionError: expected '_Class' to be 'Foo' // Object.is equality
     at ./tasks/transform_conformance/fixtures/babel/babel-plugin-transform-class-properties-test-fixtures-public-loose-static-infer-name-exec.test.js:8:19
 
+./fixtures/babel/babel-plugin-transform-class-properties-test-fixtures-public-loose-static-undefined-exec.test.js
+AssertionError: expected false to be true // Object.is equality
+    at ./tasks/transform_conformance/fixtures/babel/babel-plugin-transform-class-properties-test-fixtures-public-loose-static-undefined-exec.test.js:5:23
+
 ./fixtures/babel/babel-plugin-transform-class-properties-test-fixtures-public-static-infer-name-exec.test.js
 AssertionError: expected '_Class' to be 'Foo' // Object.is equality
     at ./tasks/transform_conformance/fixtures/babel/babel-plugin-transform-class-properties-test-fixtures-public-static-infer-name-exec.test.js:9:19