fix(test runner): align with typescript behaviour for resolving index.js and package.json through path mapping

Co-Authored-By: Dmitry Gozman <dgozman@gmail.com>

packages/playwright-ct-core/src/vitePlugin.ts

@@ -249,7 +249,7 @@ function vitePlugin(registerSource: string, templateDir: string, buildInfo: Buil
 
     async writeBundle(this: PluginContext) {
       for (const importInfo of importInfos.values()) {
-        const importPath = resolveHook(importInfo.filename, importInfo.importSource);
+        const importPath = resolveHook(importInfo.filename, importInfo.importSource, true);
         if (!importPath)
           continue;
         const deps = new Set<string>();

packages/playwright-ct-core/src/viteUtils.ts

@@ -147,13 +147,13 @@ export async function populateComponentsFromTests(componentRegistry: ComponentRe
     for (const importInfo of importList)
       componentRegistry.set(importInfo.id, importInfo);
     if (componentsByImportingFile)
-      componentsByImportingFile.set(file, importList.map(i => resolveHook(i.filename, i.importSource)).filter(Boolean) as string[]);
+      componentsByImportingFile.set(file, importList.map(i => resolveHook(i.filename, i.importSource, true)).filter(Boolean) as string[]);
   }
 }
 
 export function hasJSComponents(components: ImportInfo[]): boolean {
   for (const component of components) {
-    const importPath = resolveHook(component.filename, component.importSource);
+    const importPath = resolveHook(component.filename, component.importSource, true);
     const extname = importPath ? path.extname(importPath) : '';
     if (extname === '.js' || (importPath && !extname && fs.existsSync(importPath + '.js')))
       return true;
@@ -183,7 +183,7 @@ export function transformIndexFile(id: string, content: string, templateDir: str
   lines.push(registerSource);
 
   for (const value of importInfos.values()) {
-    const importPath = resolveHook(value.filename, value.importSource) || value.importSource;
+    const importPath = resolveHook(value.filename, value.importSource, true) || value.importSource;
     lines.push(`const ${value.id} = () => import('${importPath?.replaceAll(path.sep, '/')}').then((mod) => mod.${value.remoteName || 'default'});`);
   }
 

packages/playwright/src/transform/esmLoader.ts

@@ -26,7 +26,7 @@ import { fileIsModule } from '../util';
 async function resolve(specifier: string, context: { parentURL?: string }, defaultResolve: Function) {
   if (context.parentURL && context.parentURL.startsWith('file://')) {
     const filename = url.fileURLToPath(context.parentURL);
-    const resolved = resolveHook(filename, specifier);
+    const resolved = resolveHook(filename, specifier, true);
     if (resolved !== undefined)
       specifier = url.pathToFileURL(resolved).toString();
   }

packages/playwright/src/transform/transform.ts

@@ -92,15 +92,21 @@ function loadAndValidateTsconfigsForFile(file: string): ParsedTsConfigData[] {
 const pathSeparator = process.platform === 'win32' ? ';' : ':';
 const builtins = new Set(Module.builtinModules);
 
-export function resolveHook(filename: string, specifier: string): string | undefined {
+export function resolveHook(filename: string, specifier: string, isESM: boolean): string | undefined {
   if (specifier.startsWith('node:') || builtins.has(specifier))
     return;
   if (!shouldTransform(filename))
     return;
 
   if (isRelativeSpecifier(specifier))
-    return resolveImportSpecifierExtension(path.resolve(path.dirname(filename), specifier));
+    return resolveImportSpecifierExtension(path.resolve(path.dirname(filename), specifier), false, isESM);
 
+  /**
+   * TypeScript discourages path-mapping into node_modules
+   *    (https://www.typescriptlang.org/docs/handbook/modules/reference.html#paths-should-not-point-to-monorepo-packages-or-node_modules-packages).
+   * It seems like TypeScript tries path-mapping first, but does not look at the `package.json` or `index.js` files in ESM.
+   * If path-mapping doesn't yield a result, TypeScript falls back to the default resolution (typically node_modules).
+   */
   const isTypeScript = filename.endsWith('.ts') || filename.endsWith('.tsx');
   const tsconfigs = loadAndValidateTsconfigsForFile(filename);
   for (const tsconfig of tsconfigs) {
@@ -142,7 +148,7 @@ export function resolveHook(filename: string, specifier: string): string | undef
         if (value.includes('*'))
           candidate = candidate.replace('*', matchedPartOfSpecifier);
         candidate = path.resolve(tsconfig.pathsBase!, candidate);
-        const existing = resolveImportSpecifierExtension(candidate);
+        const existing = resolveImportSpecifierExtension(candidate, true, isESM);
         if (existing) {
           longestPrefixLength = keyPrefix.length;
           pathMatchedByLongestPrefix = existing;
@@ -156,7 +162,7 @@ export function resolveHook(filename: string, specifier: string): string | undef
   if (path.isAbsolute(specifier)) {
     // Handle absolute file paths like `import '/path/to/file'`
     // Do not handle module imports like `import 'fs'`
-    return resolveImportSpecifierExtension(specifier);
+    return resolveImportSpecifierExtension(specifier, false, isESM);
   }
 }
 
@@ -238,7 +244,7 @@ function installTransformIfNeeded() {
   const originalResolveFilename = (Module as any)._resolveFilename;
   function resolveFilename(this: any, specifier: string, parent: Module, ...rest: any[]) {
     if (parent) {
-      const resolved = resolveHook(parent.filename, specifier);
+      const resolved = resolveHook(parent.filename, specifier, false);
       if (resolved !== undefined)
         specifier = resolved;
     }

packages/playwright/src/util.ts

@@ -304,7 +304,7 @@ const kExtLookups = new Map([
   ['.mjs', ['.mts']],
   ['', ['.js', '.ts', '.jsx', '.tsx', '.cjs', '.mjs', '.cts', '.mts']],
 ]);
-export function resolveImportSpecifierExtension(resolved: string): string | undefined {
+export function resolveImportSpecifierExtension(resolved: string, isPathMapping: boolean, isESM: boolean): string | undefined {
   if (fileExists(resolved))
     return resolved;
 
@@ -321,12 +321,16 @@ export function resolveImportSpecifierExtension(resolved: string): string | unde
 
   if (dirExists(resolved)) {
     // If we import a package, let Node.js figure out the correct import based on package.json.
-    if (fileExists(path.join(resolved, 'package.json')))
+    // TypeScript does not interpret package.json for path mappings: https://www.typescriptlang.org/docs/handbook/modules/reference.html#paths-should-not-point-to-monorepo-packages-or-node_modules-packages
+    if (!isPathMapping && fileExists(path.join(resolved, 'package.json')))
       return resolved;
 
-    // Otherwise, try to find a corresponding index file.
-    const dirImport = path.join(resolved, 'index');
-    return resolveImportSpecifierExtension(dirImport);
+    // Following TypeScript's path mapping logic, index files are still resolved in CommonJS.
+    const shouldNotResolveIndex = isPathMapping && isESM;
+    if (!shouldNotResolveIndex) {
+      const dirImport = path.join(resolved, 'index');
+      return resolveImportSpecifierExtension(dirImport, isPathMapping, isESM);
+    }
   }
 }
 

tests/playwright-test/resolver.spec.ts

@@ -693,3 +693,65 @@ test('should respect --tsconfig option', async ({ runInlineTest }) => {
   expect(result.exitCode).toBe(0);
   expect(result.output).not.toContain(`Could not`);
 });
+
+
+test('should resolve index.js in CJS after path mapping', async ({ runInlineTest }) => {
+  test.info().annotations.push({ type: 'issue', description: 'https://github.com/microsoft/playwright/issues/31811' });
+
+  const result = await runInlineTest({
+    '@acme/lib/index.js': `
+      exports.greet = () => console.log('hello playwright');
+    `,
+    '@acme/lib/index.d.ts': `
+      export const greet: () => void;
+    `,
+    'tests/hello.test.ts': `
+      import { greet } from '@acme/lib';
+      import { test } from '@playwright/test';
+      test('hello', async ({}) => {
+        greet();
+      });
+    `,
+    'tests/tsconfig.json': JSON.stringify({
+      compilerOptions: {
+        'paths': {
+          '@acme/*': ['../@acme/*'],
+        }
+      }
+    })
+  });
+
+  expect(result.exitCode).toBe(0);
+  expect(result.passed).toBe(1);
+});
+
+test('should not resolve index.js in ESM after path mapping', async ({ runInlineTest }) => {
+  test.info().annotations.push({ type: 'issue', description: 'https://github.com/microsoft/playwright/issues/31811' });
+
+  const result = await runInlineTest({
+    '@acme/lib/index.js': `
+      export const greet = () => console.log('hello playwright');
+    `,
+    '@acme/lib/index.d.ts': `
+      export const greet: () => void;
+    `,
+    'tests/hello.test.ts': `
+      import { greet } from '@acme/lib';
+      import { test } from '@playwright/test';
+      test('hello', async ({}) => {
+        greet();
+      });
+    `,
+    'tests/tsconfig.json': JSON.stringify({
+      compilerOptions: {
+        'paths': {
+          '@acme/*': ['../@acme/*'],
+        }
+      }
+    }),
+    'package.json': JSON.stringify({ type: 'module' }),
+  });
+
+  expect(result.exitCode).toBe(1);
+  expect(result.output).toContain(`Cannot find package '@acme/lib'`);
+});