Merge pull request #1 from a-chabot/a-chabot/private-methods-compiler-flag

feat: gate private method transform behind enablePrivateMethods compi…

Author: a-chabot

packages/@lwc/compiler/src/options.ts

@@ -149,6 +149,8 @@ export interface TransformOptions {
     experimentalErrorRecoveryMode?: boolean;
     /** Full module path for a feature flag to import and enforce at runtime (e.g., '@salesforce/featureFlag/name'). */
     componentFeatureFlagModulePath?: string;
+    /** Flag to enable the private method round-trip transform. When false or omitted, private methods pass through to standard Babel handling. */
+    enablePrivateMethods?: boolean;
 }
 
 type OptionalTransformKeys =
@@ -164,6 +166,7 @@ type OptionalTransformKeys =
     | 'experimentalDynamicDirective'
     | 'dynamicImports'
     | 'componentFeatureFlagModulePath'
+    | 'enablePrivateMethods'
     | 'instrumentation';
 
 type RequiredTransformOptions = RecursiveRequired<Omit<TransformOptions, OptionalTransformKeys>>;

packages/@lwc/compiler/src/transformers/__tests__/transform-javascript.spec.ts

@@ -224,6 +224,38 @@ describe('unnecessary registerDecorators', () => {
     });
 });
 
+describe('enablePrivateMethods', () => {
+    const source = `
+        import { LightningElement } from 'lwc';
+        export default class Foo extends LightningElement {
+            #secret() { return 42; }
+            connectedCallback() { this.#secret(); }
+        }
+    `;
+
+    it('should transform and restore private methods when enabled', async () => {
+        const { code } = await transform(source, 'foo.js', {
+            ...BASE_TRANSFORM_OPTIONS,
+            enablePrivateMethods: true,
+        });
+        expect(code).toContain('#secret');
+        expect(code).not.toContain('__lwc_component_class_internal_private_');
+    });
+
+    it('should reject private methods when disabled', async () => {
+        await expect(
+            transform(source, 'foo.js', {
+                ...BASE_TRANSFORM_OPTIONS,
+                enablePrivateMethods: false,
+            })
+        ).rejects.toThrow();
+    });
+
+    it('should reject private methods when omitted', async () => {
+        await expect(transform(source, 'foo.js', BASE_TRANSFORM_OPTIONS)).rejects.toThrow();
+    });
+});
+
 describe('sourcemaps', () => {
     it("should generate inline sourcemaps when the output config includes the 'inline' option for sourcemaps", () => {
         const source = `

packages/@lwc/compiler/src/transformers/javascript.ts

@@ -48,6 +48,7 @@ export default function scriptTransform(
         dynamicImports,
         outputConfig: { sourcemap },
         enableLightningWebSecurityTransforms,
+        enablePrivateMethods,
         namespace,
         name,
         instrumentation,
@@ -68,10 +69,10 @@ export default function scriptTransform(
     };
 
     const plugins: babel.PluginItem[] = [
-        LwcPrivateMethodTransform,
+        ...(enablePrivateMethods ? [LwcPrivateMethodTransform as babel.PluginItem] : []),
         [lwcClassTransformPlugin, lwcBabelPluginOptions],
         [babelClassPropertiesPlugin, { loose: true }],
-        LwcReversePrivateMethodTransform,
+        ...(enablePrivateMethods ? [LwcReversePrivateMethodTransform as babel.PluginItem] : []),
     ];
 
     if (!isAPIFeatureEnabled(APIFeature.DISABLE_OBJECT_REST_SPREAD_TRANSFORMATION, apiVersion)) {

packages/@lwc/rollup-plugin/src/index.ts

@@ -74,6 +74,7 @@ export interface RollupLwcOptions {
      * @example '@salesforce/featureFlag/name'
      */
     componentFeatureFlagModulePath?: string;
+    enablePrivateMethods?: boolean;
 }
 
 const PLUGIN_NAME = 'rollup-plugin-lwc-compiler';
@@ -198,6 +199,7 @@ export default function lwc(pluginOptions: RollupLwcOptions = {}): Plugin {
         apiVersion,
         defaultModules = DEFAULT_MODULES,
         componentFeatureFlagModulePath,
+        enablePrivateMethods,
     } = pluginOptions;
 
     return {
@@ -395,6 +397,7 @@ export default function lwc(pluginOptions: RollupLwcOptions = {}): Plugin {
                 targetSSR,
                 ssrMode,
                 componentFeatureFlagModulePath,
+                enablePrivateMethods,
             });
 
             if (warnings) {