feat(test runner): support tsconfig.extends array (#22975)

Fixes #22151.

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

@@ -39,6 +39,7 @@ interface Tsconfig {
     strict?: boolean;
     allowJs?: boolean;
   };
+  references?: any[];
 }
 
 export interface TsConfigLoaderResult {
@@ -123,20 +124,19 @@ export function walkForTsConfig(
 
 function loadTsconfig(
   configFilePath: string,
-  existsSync: (path: string) => boolean = fs.existsSync,
-  readFileSync: (filename: string) => string = (filename: string) =>
-    fs.readFileSync(filename, "utf8")
 ): Tsconfig | undefined {
-  if (!existsSync(configFilePath)) {
+  if (!fs.existsSync(configFilePath)) {
     return undefined;
   }
 
-  const configString = readFileSync(configFilePath);
+  const configString = fs.readFileSync(configFilePath, 'utf-8');
   const cleanedJson = StripBom(configString);
-  let config: Tsconfig = json5.parse(cleanedJson);
-  let extendedConfig = config.extends;
+  const parsedConfig: Tsconfig = json5.parse(cleanedJson);
 
-  if (extendedConfig) {
+  let config: Tsconfig = {};
+
+  const extendsArray = Array.isArray(parsedConfig.extends) ? parsedConfig.extends : (parsedConfig.extends ? [parsedConfig.extends] : []);
+  for (let extendedConfig of extendsArray) {
     if (
       typeof extendedConfig === "string" &&
       extendedConfig.indexOf(".json") === -1
@@ -148,7 +148,7 @@ function loadTsconfig(
     if (
       extendedConfig.indexOf("/") !== -1 &&
       extendedConfig.indexOf(".") !== -1 &&
-      !existsSync(extendedConfigPath)
+      !fs.existsSync(extendedConfigPath)
     ) {
       extendedConfigPath = path.join(
         currentDir,
@@ -158,7 +158,7 @@ function loadTsconfig(
     }
 
     const base =
-      loadTsconfig(extendedConfigPath, existsSync, readFileSync) || {};
+      loadTsconfig(extendedConfigPath) || {};
 
     // baseUrl should be interpreted as relative to the base tsconfig,
     // but we need to update it so it is relative to the original tsconfig being loaded
@@ -170,16 +170,14 @@ function loadTsconfig(
       );
     }
 
-    config = {
-      ...base,
-      ...config,
-      compilerOptions: {
-        ...base.compilerOptions,
-        ...config.compilerOptions,
-      },
-    };
+    config = mergeConfigs(config, base);
   }
 
+  config = mergeConfigs(config, parsedConfig);
+  // The only top-level property that is excluded from inheritance is "references".
+  // https://www.typescriptlang.org/tsconfig#extends
+  config.references = parsedConfig.references;
+
   if (path.basename(configFilePath) === 'jsconfig.json' && config.compilerOptions?.allowJs === undefined) {
     config.compilerOptions = config.compilerOptions || {};
     config.compilerOptions.allowJs = true;
@@ -188,6 +186,17 @@ function loadTsconfig(
   return config;
 }
 
+function mergeConfigs(base: Tsconfig, override: Tsconfig): Tsconfig {
+  return {
+    ...base,
+    ...override,
+    compilerOptions: {
+      ...base.compilerOptions,
+      ...override.compilerOptions,
+    },
+  };
+}
+
 function StripBom(string: string) {
 	if (typeof string !== 'string') {
 		throw new TypeError(`Expected a string, got ${typeof string}`);

tests/playwright-test/resolver.spec.ts

@@ -469,3 +469,39 @@ test('should respect path resolver for JS and TS files from jsconfig.json', asyn
   expect(result.passed).toBe(2);
   expect(result.exitCode).toBe(0);
 });
+
+test('should support extends in tsconfig.json', async ({ runInlineTest }) => {
+  const result = await runInlineTest({
+    'tsconfig.json': `{
+      "extends": ["./tsconfig.base1.json", "./tsconfig.base2.json"],
+    }`,
+    'tsconfig.base1.json': `{
+      "extends": "./tsconfig.base.json",
+    }`,
+    'tsconfig.base2.json': `{
+      "compilerOptions": {
+        "baseUrl": "dir",
+      },
+    }`,
+    'tsconfig.base.json': `{
+      "compilerOptions": {
+        "paths": {
+          "util/*": ["./foo/bar/util/*"],
+        },
+      },
+    }`,
+    'a.test.ts': `
+      const { foo } = require('util/file');
+      import { test, expect } from '@playwright/test';
+      test('test', ({}, testInfo) => {
+        expect(foo).toBe('foo');
+      });
+    `,
+    'dir/foo/bar/util/file.ts': `
+      module.exports = { foo: 'foo' };
+    `,
+  });
+
+  expect(result.passed).toBe(1);
+  expect(result.exitCode).toBe(0);
+});