feat: provide extends directive for configs

packages/metro-config/package.json

@@ -13,6 +13,7 @@
   },
   "license": "MIT",
   "dependencies": {
+    "@topoconfig/extends": "^0.12.0",
     "connect": "^3.6.5",
     "cosmiconfig": "^5.0.5",
     "jest-validate": "^29.6.3",

packages/metro-config/src/__tests__/__snapshots__/loadConfig-test.js.snap

@@ -543,6 +543,187 @@ Object {
 }
 `;
 
+exports[`loadConfig can populate \`extends\` references 1`] = `
+Object {
+  "cacheStores": Array [],
+  "cacheVersion": "foo",
+  "maxWorkers": 2,
+  "projectRoot": "/",
+  "reporter": null,
+  "resetCache": false,
+  "resolver": Object {
+    "assetExts": Array [
+      "bmp",
+      "gif",
+      "jpg",
+      "jpeg",
+      "png",
+      "psd",
+      "svg",
+      "webp",
+      "m4v",
+      "mov",
+      "mp4",
+      "mpeg",
+      "mpg",
+      "webm",
+      "aac",
+      "aiff",
+      "caf",
+      "m4a",
+      "mp3",
+      "wav",
+      "html",
+      "pdf",
+      "yaml",
+      "yml",
+      "otf",
+      "ttf",
+      "zip",
+    ],
+    "assetResolutions": Array [
+      "1",
+      "1.5",
+      "2",
+      "3",
+      "4",
+    ],
+    "blockList": /\\(\\\\/__tests__\\\\/\\.\\*\\)\\$/,
+    "dependencyExtractor": undefined,
+    "disableHierarchicalLookup": false,
+    "emptyModulePath": "metro-runtime/src/modules/empty-module",
+    "enableGlobalPackages": false,
+    "extraNodeModules": Object {},
+    "hasteImplModulePath": undefined,
+    "nodeModulesPaths": Array [],
+    "platforms": Array [
+      "ios",
+      "android",
+      "windows",
+      "web",
+    ],
+    "requireCycleIgnorePatterns": Array [
+      /\\(\\^\\|\\\\/\\|\\\\\\\\\\)node_modules\\(\\$\\|\\\\/\\|\\\\\\\\\\)/,
+    ],
+    "resolveRequest": null,
+    "resolverMainFields": Array [
+      "browser",
+      "main",
+    ],
+    "sourceExts": Array [
+      "js",
+      "jsx",
+      "json",
+      "ts",
+      "tsx",
+    ],
+    "unstable_conditionNames": Array [
+      "require",
+      "import",
+    ],
+    "unstable_conditionsByPlatform": Object {
+      "web": Array [
+        "browser",
+      ],
+    },
+    "unstable_enablePackageExports": false,
+    "unstable_enableSymlinks": true,
+    "useWatchman": true,
+  },
+  "serializer": Object {
+    "createModuleIdFactory": [Function],
+    "customSerializer": null,
+    "experimentalSerializerHook": [Function],
+    "getModulesRunBeforeMainModule": [Function],
+    "getPolyfills": [Function],
+    "getRunModuleStatement": [Function],
+    "isThirdPartyModule": [Function],
+    "polyfillModuleNames": Array [],
+    "processModuleFilter": [Function],
+  },
+  "server": Object {
+    "enhanceMiddleware": [Function],
+    "forwardClientLogs": true,
+    "port": 8081,
+    "rewriteRequestUrl": [Function],
+    "unstable_serverRoot": null,
+    "useGlobalHotkey": true,
+    "verifyConnections": false,
+  },
+  "stickyWorkers": true,
+  "symbolicator": Object {
+    "customizeFrame": [Function],
+    "customizeStack": [Function],
+  },
+  "transformer": Object {
+    "allowOptionalDependencies": false,
+    "assetPlugins": Array [],
+    "assetRegistryPath": "missing-asset-registry-path",
+    "asyncRequireModulePath": "metro-runtime/src/modules/asyncRequire",
+    "babelTransformerPath": "metro-babel-transformer",
+    "dynamicDepsInPackages": "throwAtRuntime",
+    "enableBabelRCLookup": true,
+    "enableBabelRuntime": true,
+    "getTransformOptions": [Function],
+    "globalPrefix": "",
+    "hermesParser": false,
+    "minifierConfig": Object {
+      "compress": Object {
+        "reduce_funcs": false,
+      },
+      "mangle": Object {
+        "toplevel": false,
+      },
+      "output": Object {
+        "ascii_only": true,
+        "quote_style": 3,
+        "wrap_iife": true,
+      },
+      "sourceMap": Object {
+        "includeSources": false,
+      },
+      "toplevel": false,
+    },
+    "minifierPath": "metro-minify-terser",
+    "optimizationSizeLimit": 153600,
+    "publicPath": "/assets",
+    "transformVariants": Object {
+      "default": Object {},
+    },
+    "unstable_allowRequireContext": false,
+    "unstable_compactOutput": false,
+    "unstable_dependencyMapReservedName": null,
+    "unstable_disableModuleWrapping": false,
+    "unstable_disableNormalizePseudoGlobals": false,
+    "unstable_workerThreads": false,
+    "workerPath": "metro/src/DeltaBundler/Worker",
+  },
+  "transformerPath": "",
+  "unstable_perfLoggerFactory": [Function],
+  "watchFolders": Array [
+    "/",
+  ],
+  "watcher": Object {
+    "additionalExts": Array [
+      "cjs",
+      "mjs",
+    ],
+    "healthCheck": Object {
+      "enabled": false,
+      "filePrefix": ".metro-health-check",
+      "interval": 30000,
+      "timeout": 5000,
+    },
+    "unstable_workerThreads": false,
+    "watchman": Object {
+      "deferStates": Array [
+        "hg.update",
+      ],
+    },
+  },
+}
+`;
+
 exports[`loadConfig injects \`metro-cache\` into the \`cacheStores\` callback 1`] = `
 Object {
   "cacheStores": Array [],

packages/metro-config/src/__tests__/loadConfig-test.js

@@ -16,6 +16,8 @@ jest.mock('cosmiconfig');
 const getDefaultConfig = require('../defaults');
 const {loadConfig} = require('../loadConfig');
 const cosmiconfig = require('cosmiconfig');
+const fs = require('fs');
+const os = require('os');
 const path = require('path');
 const prettyFormat = require('pretty-format');
 const stripAnsi = require('strip-ansi');
@@ -152,6 +154,38 @@ describe('loadConfig', () => {
     expect(cosmiconfig.hasLoadBeenCalled()).toBeTruthy();
   });
 
+  it('can populate `extends` references', async () => {
+    const temp = fs.mkdtempSync(path.join(os.tmpdir(), 'temp-'));
+    await fs.promises.writeFile(
+      path.resolve(temp, 'config.json'),
+      '{"extends": "./base.json"}',
+      'utf8',
+    );
+    await fs.promises.writeFile(
+      path.resolve(temp, 'base.json'),
+      '{"cacheVersion": "foo"}',
+      'utf8',
+    );
+
+    const config: any = {
+      reporter: null,
+      maxWorkers: 2,
+      cacheStores: [],
+      transformerPath: '',
+      resolver: {
+        emptyModulePath: 'metro-runtime/src/modules/empty-module',
+      },
+      extends: path.resolve(temp, 'config.json'),
+    };
+
+    cosmiconfig.setResolvedConfig(config);
+
+    const result = await loadConfig({});
+
+    expect(result).toMatchSnapshot();
+    expect(result.cacheVersion).toBe('foo');
+  });
+
   it('can load the config with no config present', async () => {
     cosmiconfig.setReturnNull(true);