fix: use es6 as fallback module type in babel-swc-loader (#1321)

Author: jbroma

.changeset/sharp-bars-peel.md

@@ -0,0 +1,5 @@
+---
+"@callstack/repack": patch
+---
+
+Fix bundling with `babel-swc-loader` when `disableImportExportTransform` is set to `true` in RN babel preset

packages/repack/src/loaders/babelSwcLoader/__tests__/babelSwcLoader.test.ts

@@ -1,4 +1,4 @@
-import { partitionTransforms } from '../babelSwcLoader.js';
+import { buildFinalSwcConfig, partitionTransforms } from '../babelSwcLoader.js';
 
 type TransformEntry = [string, Record<string, any> | undefined];
 
@@ -66,3 +66,27 @@ describe('partitionTransforms', () => {
     expect(result).toMatchSnapshot('empty arrays');
   });
 });
+
+describe('buildFinalSwcConfig', () => {
+  it('uses module.type from swcConfig when transform-modules-commonjs is present', () => {
+    const result = buildFinalSwcConfig({
+      swcConfig: { module: { type: 'commonjs' } },
+      includedSwcTransforms: [],
+      lazyImports: false,
+      sourceType: 'module',
+    });
+
+    expect(result.module?.type).toBe('commonjs');
+  });
+
+  it('falls back to es6 module.type when transform-modules-commonjs is not present', () => {
+    const result = buildFinalSwcConfig({
+      swcConfig: {},
+      includedSwcTransforms: [],
+      lazyImports: false,
+      sourceType: 'module',
+    });
+
+    expect(result.module?.type).toBe('es6');
+  });
+});

packages/repack/src/loaders/babelSwcLoader/babelSwcLoader.ts

@@ -55,6 +55,41 @@ export function partitionTransforms(
   return { includedSwcTransforms, supportedSwcTransforms, swcConfig };
 }
 
+export interface BuildFinalSwcConfigOptions {
+  swcConfig: SwcLoaderOptions;
+  includedSwcTransforms: string[];
+  lazyImports: boolean | string[];
+  sourceType: 'module' | 'script' | undefined;
+}
+
+export function buildFinalSwcConfig(
+  options: BuildFinalSwcConfigOptions
+): SwcLoaderOptions {
+  const { swcConfig, includedSwcTransforms, lazyImports, sourceType } = options;
+  return {
+    ...swcConfig,
+    // set env based on babel transforms
+    env: {
+      // node supports everything and does not include
+      // any transforms by default, so it can as a template
+      targets: { node: 24 },
+      include: includedSwcTransforms,
+    },
+    // set lazy imports based on loader options
+    module: {
+      ...swcConfig.module,
+      lazy: lazyImports,
+      // if type is not set, this means that we are not using
+      // transform-modules-commonjs babel plugin, which can be disabled
+      // in babel config through `disableImportExportTransform` option in the RN preset
+      // we use 'es6' as a fallback here to achieve the desired behaviour of
+      // keeping ES modules as they are found in the source code
+      type: swcConfig.module?.type ?? 'es6',
+    },
+    isModule: sourceType === 'module',
+  };
+}
+
 export default async function babelSwcLoader(
   this: LoaderContext<BabelSwcLoaderOptions>,
   source: string,
@@ -118,23 +153,12 @@ export default async function babelSwcLoader(
       hermesParserOverrides: options.hermesParserOverrides,
     });
 
-    const finalSwcConfig: SwcLoaderOptions = {
-      ...swcConfig,
-      // set env based on babel transforms
-      env: {
-        // node supports everything and does not include
-        // any transforms by default, so it can as a template
-        targets: { node: 24 },
-        include: includedSwcTransforms,
-      },
-      // set lazy imports based on loader options
-      module: {
-        ...swcConfig.module,
-        lazy: lazyImports,
-        type: swcConfig.module!.type,
-      },
-      isModule: babelResult.sourceType === 'module',
-    };
+    const finalSwcConfig = buildFinalSwcConfig({
+      swcConfig,
+      includedSwcTransforms,
+      lazyImports,
+      sourceType: babelResult.sourceType,
+    });
 
     const swcResult = swc.transformSync(babelResult?.code!, {
       ...finalSwcConfig,