fix(test runner): allow directory imports with path mapping

This regressed in microsoft#32078.

packages/playwright/src/third_party/tsconfig-loader.ts

@@ -53,9 +53,13 @@ export interface LoadedTsConfig {
 }
 
 export function loadTsConfig(configPath: string): LoadedTsConfig[] {
-  const references: LoadedTsConfig[] = [];
-  const config = innerLoadTsConfig(configPath, references);
-  return [config, ...references];
+  try {
+    const references: LoadedTsConfig[] = [];
+    const config = innerLoadTsConfig(configPath, references);
+    return [config, ...references];
+  } catch (e) {
+    throw new Error(`Failed to load tsconfig file at ${configPath}:\n${e.message}`);
+  }
 }
 
 function resolveConfigFile(baseConfigFile: string, referencedConfigFile: string) {

packages/playwright/src/transform/transform.ts

@@ -136,8 +136,13 @@ export function resolveHook(filename: string, specifier: string): string | undef
     return;
 
   if (isRelativeSpecifier(specifier))
-    return resolveImportSpecifierExtension(path.resolve(path.dirname(filename), specifier));
+    return resolveImportSpecifierExtension(path.resolve(path.dirname(filename), specifier), false);
 
+  /**
+   * 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
+   * However, if path-mapping doesn't yield a result, TypeScript falls back to the default resolution through node_modules.
+   */
   const isTypeScript = filename.endsWith('.ts') || filename.endsWith('.tsx');
   const tsconfigs = loadAndValidateTsconfigsForFile(filename);
   for (const tsconfig of tsconfigs) {
@@ -179,7 +184,7 @@ 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);
         if (existing) {
           longestPrefixLength = keyPrefix.length;
           pathMatchedByLongestPrefix = existing;
@@ -193,7 +198,7 @@ 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);
   }
 }
 

packages/playwright/src/util.ts

@@ -307,6 +307,20 @@ function folderIsModule(folder: string): boolean {
   return require(packageJsonPath).type === 'module';
 }
 
+const packageJsonMainFieldCache = new Map<string, string | undefined>();
+
+function getMainFieldFromPackageJson(packageJsonPath: string) {
+  if (!packageJsonMainFieldCache.has(packageJsonPath)) {
+    let mainField: string | undefined;
+    try {
+      mainField = JSON.parse(fs.readFileSync(packageJsonPath, 'utf8')).main;
+    } catch {
+    }
+    packageJsonMainFieldCache.set(packageJsonPath, mainField);
+  }
+  return packageJsonMainFieldCache.get(packageJsonPath);
+}
+
 // This follows the --moduleResolution=bundler strategy from tsc.
 // https://devblogs.microsoft.com/typescript/announcing-typescript-5-0-beta/#moduleresolution-bundler
 const kExtLookups = new Map([
@@ -316,7 +330,7 @@ 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): string | undefined {
   if (fileExists(resolved))
     return resolved;
 
@@ -332,13 +346,33 @@ export function resolveImportSpecifierExtension(resolved: string): string | unde
   }
 
   if (dirExists(resolved)) {
+    const packageJsonPath = path.join(resolved, 'package.json');
+
+    if (isPathMapping) {
+      // After TypeScript path mapping, here's how directory imports are resolved
+      // with "moduleResolution:bundler" setting:
+      //  - `package.json#exports` is not respected, because it's not a proper module
+      //  - `package.json#main` is respected according to "folder as module" Node.js behavior
+      //  - `index.js` default is respected according to "folder as module" Node.js behavior
+      //
+      // More info:
+      //  - https://www.typescriptlang.org/docs/handbook/modules/reference.html#directory-modules-index-file-resolution
+      //  - https://nodejs.org/dist/latest-v20.x/docs/api/modules.html#folders-as-modules
+
+      const mainField = getMainFieldFromPackageJson(packageJsonPath);
+      const mainFieldResolved = mainField ? resolveImportSpecifierExtension(path.resolve(resolved, mainField), isPathMapping) : undefined;
+      return mainFieldResolved || resolveImportSpecifierExtension(path.join(resolved, 'index'), isPathMapping);
+    }
+
     // If we import a package, let Node.js figure out the correct import based on package.json.
-    if (fileExists(path.join(resolved, 'package.json')))
+    // This also covers the "main" field for "folder as module".
+    if (fileExists(packageJsonPath))
       return resolved;
 
-    // Otherwise, try to find a corresponding index file.
+    // Fallback to "folder as module" Node.js behavior.
+    // https://nodejs.org/dist/latest-v20.x/docs/api/modules.html#folders-as-modules
     const dirImport = path.join(resolved, 'index');
-    return resolveImportSpecifierExtension(dirImport);
+    return resolveImportSpecifierExtension(dirImport, isPathMapping);
   }
 }
 

tests/playwright-test/playwright-test-fixtures.ts

@@ -367,8 +367,8 @@ export const test = base
 const TSCONFIG = {
   'compilerOptions': {
     'target': 'ESNext',
-    'moduleResolution': 'node',
-    'module': 'commonjs',
+    'moduleResolution': 'bundler',
+    'module': 'esnext',
     'strict': true,
     'esModuleInterop': true,
     'allowSyntheticDefaultImports': true,