feat(napi/transform): support enabling removeClassFieldsWithoutInitializer

Author: Dunqing

napi/transform/index.d.ts

@@ -427,6 +427,42 @@ export interface TypeScriptOptions {
   onlyRemoveTypeImports?: boolean
   allowNamespaces?: boolean
   allowDeclareFields?: boolean
+  /**
+   * When enabled, class fields without initializers are removed.
+   *
+   * For example:
+   * ```ts
+   * class Foo {
+   *    x: number;
+   *    y: number = 0;
+   * }
+   * ```
+   * // transform into
+   * ```js
+   * class Foo {
+   *    x: number;
+   *    y: number = 0;
+   * }
+   * ```
+   *
+   * The option is used to align with the behavior of TypeScript's `useDefineForClassFields: false` option.
+   * When you want to enable this, you also need to set [`crate::CompilerAssumptions::set_public_class_fields`]
+   * to `true`. The `set_public_class_fields: true` + `remove_class_fields_without_initializer: true` is
+   * equivalent to `useDefineForClassFields: false` in TypeScript.
+   *
+   * When `set_public_class_fields: true`, the above example transforms into:
+   *
+   * ```js
+   * class Foo {
+   *   constructor() {
+   *    this.y = 0;
+   *  }
+   * }
+   * ```
+   *
+   * Defaults to `false`.
+   */
+  removeClassFieldsWithoutInitializer?: boolean
   /**
    * Also generate a `.d.ts` declaration file for TypeScript files.
    *

napi/transform/src/transformer.rs

@@ -220,6 +220,40 @@ pub struct TypeScriptOptions {
     pub only_remove_type_imports: Option<bool>,
     pub allow_namespaces: Option<bool>,
     pub allow_declare_fields: Option<bool>,
+    /// When enabled, class fields without initializers are removed.
+    ///
+    /// For example:
+    /// ```ts
+    /// class Foo {
+    ///    x: number;
+    ///    y: number = 0;
+    /// }
+    /// ```
+    /// // transform into
+    /// ```js
+    /// class Foo {
+    ///    x: number;
+    ///    y: number = 0;
+    /// }
+    /// ```
+    ///
+    /// The option is used to align with the behavior of TypeScript's `useDefineForClassFields: false` option.
+    /// When you want to enable this, you also need to set [`crate::CompilerAssumptions::set_public_class_fields`]
+    /// to `true`. The `set_public_class_fields: true` + `remove_class_fields_without_initializer: true` is
+    /// equivalent to `useDefineForClassFields: false` in TypeScript.
+    ///
+    /// When `set_public_class_fields: true`, the above example transforms into:
+    ///
+    /// ```js
+    /// class Foo {
+    ///   constructor() {
+    ///    this.y = 0;
+    ///  }
+    /// }
+    /// ```
+    ///
+    /// Defaults to `false`.
+    pub remove_class_fields_without_initializer: Option<bool>,
     /// Also generate a `.d.ts` declaration file for TypeScript files.
     ///
     /// The source file must be compliant with all
@@ -252,8 +286,9 @@ impl From<TypeScriptOptions> for oxc::transformer::TypeScriptOptions {
             allow_namespaces: options.allow_namespaces.unwrap_or(ops.allow_namespaces),
             allow_declare_fields: options.allow_declare_fields.unwrap_or(ops.allow_declare_fields),
             optimize_const_enums: false,
-            // TODO: Implement
-            remove_class_fields_without_initializer: false,
+            remove_class_fields_without_initializer: options
+                .remove_class_fields_without_initializer
+                .unwrap_or(ops.remove_class_fields_without_initializer),
             rewrite_import_extensions: options.rewrite_import_extensions.and_then(|value| {
                 match value {
                     Either::A(v) => {

napi/transform/test/transform.test.ts

@@ -340,3 +340,61 @@ describe('worker', () => {
     expect(code).toBe(0);
   });
 });
+
+describe('typescript', () => {
+  describe('options', () => {
+    test('removeClassFieldsWithoutInitializer', () => {
+      const code = `
+        class Foo {
+          a: number;
+          b: number = 1;
+        }
+      `;
+      const ret = transform('test.ts', code, {
+        typescript: {
+          removeClassFieldsWithoutInitializer: true,
+        },
+      });
+      expect(ret.code).toMatchInlineSnapshot(`
+        "class Foo {
+        	b = 1;
+        }
+        "
+      `);
+    });
+
+    test('align `useDefineForClassFields: false`', () => {
+      const code = `
+        class Foo {
+          a: number;
+          b: number = 1;
+          @dec
+          c: number;
+        }
+      `;
+      const ret = transform('test.ts', code, {
+        assumptions: {
+          setPublicClassFields: true,
+        },
+        target: 'es2020',
+        typescript: {
+          removeClassFieldsWithoutInitializer: true,
+        },
+        decorator: {
+          legacy: true,
+        },
+      });
+      expect(ret.code).toMatchInlineSnapshot(`
+        "import _decorate from "@oxc-project/runtime/helpers/decorate";
+        class Foo {
+        	constructor() {
+        		this.b = 1;
+        		this.c = void 0;
+        	}
+        }
+        _decorate([dec], Foo.prototype, "c", void 0);
+        "
+      `);
+    });
+  });
+});