chore: fallback to the original code after babel transform (#34635)

Author: pavelfeldman

packages/playwright/bundles/babel/src/babelBundleImpl.ts

@@ -118,15 +118,15 @@ function isTypeScript(filename: string) {
   return filename.endsWith('.ts') || filename.endsWith('.tsx') || filename.endsWith('.mts') || filename.endsWith('.cts');
 }
 
-export function babelTransform(code: string, filename: string, isModule: boolean, pluginsPrologue: [string, any?][], pluginsEpilogue: [string, any?][]): BabelFileResult {
+export function babelTransform(code: string, filename: string, isModule: boolean, pluginsPrologue: [string, any?][], pluginsEpilogue: [string, any?][]): BabelFileResult | null {
   if (isTransforming)
-    return {};
+    return null;
 
   // Prevent reentry while requiring plugins lazily.
   isTransforming = true;
   try {
     const options = babelTransformOptions(isTypeScript(filename), isModule, pluginsPrologue, pluginsEpilogue);
-    return babel.transform(code, { filename, ...options })!;
+    return babel.transform(code, { filename, ...options });
   } finally {
     isTransforming = false;
   }

packages/playwright/src/transform/babelBundle.ts

@@ -20,7 +20,7 @@ export const declare: typeof import('../../bundles/babel/node_modules/@types/bab
 export const types: typeof import('../../bundles/babel/node_modules/@types/babel__core').types = require('./babelBundleImpl').types;
 export const traverse: typeof import('../../bundles/babel/node_modules/@types/babel__traverse').default = require('./babelBundleImpl').traverse;
 export type BabelPlugin = [string, any?];
-export type BabelTransformFunction = (code: string, filename: string, isModule: boolean, pluginsPrefix: BabelPlugin[], pluginsSuffix: BabelPlugin[]) => BabelFileResult;
+export type BabelTransformFunction = (code: string, filename: string, isModule: boolean, pluginsPrefix: BabelPlugin[], pluginsSuffix: BabelPlugin[]) => BabelFileResult | null;
 export const babelTransform: BabelTransformFunction = require('./babelBundleImpl').babelTransform;
 export type BabelParseFunction = (code: string, filename: string, isModule: boolean) => ParseResult;
 export const babelParse: BabelParseFunction = require('./babelBundleImpl').babelParse;

packages/playwright/src/transform/transform.ts

@@ -232,9 +232,10 @@ export function transformHook(originalCode: string, filename: string, moduleUrl?
 
   const { babelTransform }: { babelTransform: BabelTransformFunction } = require('./babelBundle');
   transformData = new Map<string, any>();
-  const { code, map } = babelTransform(originalCode, filename, !!moduleUrl, pluginsPrologue, pluginsEpilogue);
-  if (!code)
-    return { code: '', serializedCache };
+  const babelResult = babelTransform(originalCode, filename, !!moduleUrl, pluginsPrologue, pluginsEpilogue);
+  if (!babelResult?.code)
+    return { code: originalCode, serializedCache };
+  const { code, map } = babelResult;
   const added = addToCache!(code, map, transformData);
   return { code, serializedCache: added.serializedCache };
 }