react · robhogan · Sep 2, 2026 · Sep 2, 2026
diff --git a/.flowconfig b/.flowconfig
@@ -1,6 +1,6 @@
 [ignore]
 <PROJECT_ROOT>/packages/.*/build/.*
-<PROJECT_ROOT>/\.hg/.*
+<PROJECT_ROOT>/\.\(hg\|sl\|git\)/.*
 # this transient dep bundles tests with their package, which flow attempts to parse
 # and crashes out as the test includes purposely malformed json
 <PROJECT_ROOT>\(/.*\)?/node_modules/resolve/test/.*

diff --git a/packages/metro-babel-transformer/src/index.js b/packages/metro-babel-transformer/src/index.js
@@ -25,7 +25,7 @@ type BabelTransformOptions = NonNullable<
 >;
 
 export type CustomTransformOptions = {
-  [string]: unknown,
+  [key: string]: unknown,
   __proto__: null,
   ...
 };
@@ -80,7 +80,7 @@ export type BabelTransformerCacheKeyOptions = Readonly<{
 }>;
 
 export type BabelTransformer = Readonly<{
-  transform: BabelTransformerArgs => Readonly<{
+  transform: (transformerArgs: BabelTransformerArgs) => Readonly<{
     ast: BabelNodeFile,
     // Deprecated, will be removed in a future breaking release. Function maps
     // will be generated by an input Babel plugin instead and written into
@@ -92,12 +92,10 @@ export type BabelTransformer = Readonly<{
   getCacheKey?: (options?: BabelTransformerCacheKeyOptions) => string,
 }>;
 
-function transform({
-  filename,
-  options,
-  plugins,
-  src,
-}: BabelTransformerArgs): ReturnType<BabelTransformer['transform']> {
+function transform(
+  opts: BabelTransformerArgs,
+): ReturnType<BabelTransformer['transform']> {
+  const {filename, options, plugins, src} = opts;
   const OLD_BABEL_ENV = process.env.BABEL_ENV;
   process.env.BABEL_ENV = options.dev
     ? 'development'

diff --git a/packages/metro-babel-transformer/types/index.d.ts b/packages/metro-babel-transformer/types/index.d.ts
@@ -6,7 +6,7 @@
  *
  * @noformat
  * @oncall react_native
- * @generated SignedSource<<c71ff6c13c916919d1340d231518de8f>>
+ * @generated SignedSource<<2503f88efd80b39e4d860870017af66d>>
  *
  * This file was translated from Flow by scripts/generateTypeScriptDefinitions.js
  * Original file: packages/metro-babel-transformer/src/index.js
@@ -24,7 +24,7 @@ type BabelTransformOptions = NonNullable<
   Parameters<typeof transformFromAstSync>[2]
 >;
 export type CustomTransformOptions = {
-  [$$Key$$: string]: unknown;
+  [key: string]: unknown;
 };
 export type TransformProfile = 'default' | 'hermes-stable' | 'hermes-canary';
 type BabelTransformerOptions = Readonly<{
@@ -85,15 +85,15 @@ export type BabelTransformerCacheKeyOptions = Readonly<{
   enableBabelRCLookup?: boolean;
 }>;
 export type BabelTransformer = Readonly<{
-  transform: ($$PARAM_0$$: BabelTransformerArgs) => Readonly<{
+  transform: (transformerArgs: BabelTransformerArgs) => Readonly<{
     ast: BabelNodeFile;
     functionMap?: BabelFileFunctionMapMetadata;
     metadata?: MetroBabelFileMetadata;
   }>;
   getCacheKey?: (options?: BabelTransformerCacheKeyOptions) => string;
 }>;
 declare function transform(
-  $$PARAM_0$$: BabelTransformerArgs,
+  opts: BabelTransformerArgs,
 ): ReturnType<BabelTransformer['transform']>;
 /**
  * Generates a cache key component based on the user's Babel configuration files.

diff --git a/packages/metro-config/src/types.js b/packages/metro-config/src/types.js
@@ -108,7 +108,7 @@ type ResolverConfigT = {
   dependencyExtractor: ?string,
   emptyModulePath: string,
   enableGlobalPackages: boolean,
-  extraNodeModules: {[name: string]: string, ...},
+  extraNodeModules: {[packageName: string]: string, ...},
   hasteImplModulePath: ?string,
   nodeModulesPaths: ReadonlyArray<string>,
   platforms: ReadonlyArray<string>,
@@ -139,7 +139,7 @@ type SerializerConfigT = {
     delta: DeltaResult<>,
   ) => unknown,
   getModulesRunBeforeMainModule: (entryFilePath: string) => Array<string>,
-  getPolyfills: ({platform: ?string, ...}) => ReadonlyArray<string>,
+  getPolyfills: (ctx: {platform: ?string, ...}) => ReadonlyArray<string>,
   getRunModuleStatement: (
     moduleId: number | string,
     globalPrefix: string,
@@ -178,10 +178,13 @@ type CacheStoresConfigT = ReadonlyArray<CacheStore<TransformResult<>>>;
 
 type ServerConfigT = {
   /** @deprecated */
-  enhanceMiddleware: (Middleware, MetroServer) => Middleware | Server,
+  enhanceMiddleware: (
+    middleware: Middleware,
+    server: MetroServer,
+  ) => Middleware | Server,
   forwardClientLogs: boolean,
   port: number,
-  rewriteRequestUrl: string => string,
+  rewriteRequestUrl: (url: string) => string,
   unstable_serverRoot: ?string,
   useGlobalHotkey: boolean,
   verifyConnections: boolean,
@@ -196,16 +199,16 @@ type ServerConfigT = {
 };
 
 type SymbolicatorConfigT = {
-  customizeFrame: ({
+  customizeFrame: (frame: {
     +file: ?string,
     +lineNumber: ?number,
     +column: ?number,
     +methodName: ?string,
     ...
   }) => ?{+collapse?: boolean} | Promise<?{+collapse?: boolean}>,
   customizeStack: (
-    Array<IntermediateStackFrame>,
-    unknown,
+    symbolicatedStack: Array<IntermediateStackFrame>,
+    extraData: unknown,
   ) => Array<IntermediateStackFrame> | Promise<Array<IntermediateStackFrame>>,
 };
 
@@ -230,7 +233,9 @@ type WatcherConfigT = {
 export type InputConfigT = Partial<
   Readonly<
     MetalConfigT & {
-      cacheStores: CacheStoresConfigT | (MetroCache => CacheStoresConfigT),
+      cacheStores:
+        | CacheStoresConfigT
+        | ((metroCache: MetroCache) => CacheStoresConfigT),
       resolver: Readonly<Partial<ResolverConfigT>>,
       server: Readonly<Partial<ServerConfigT>>,
       serializer: Readonly<Partial<SerializerConfigT>>,

diff --git a/packages/metro-config/types/types.d.ts b/packages/metro-config/types/types.d.ts
@@ -6,7 +6,7 @@
  *
  * @noformat
  * @oncall react_native
- * @generated SignedSource<<9c62bc2ca711f9693edc135a382a382a>>
+ * @generated SignedSource<<45e0111f05ce2350b8be53c72dd0c8c7>>
  *
  * This file was translated from Flow by scripts/generateTypeScriptDefinitions.js
  * Original file: packages/metro-config/src/types.js
@@ -97,7 +97,7 @@ type ResolverConfigT = {
   dependencyExtractor: null | undefined | string;
   emptyModulePath: string;
   enableGlobalPackages: boolean;
-  extraNodeModules: {[name: string]: string};
+  extraNodeModules: {[packageName: string]: string};
   hasteImplModulePath: null | undefined | string;
   nodeModulesPaths: ReadonlyArray<string>;
   platforms: ReadonlyArray<string>;
@@ -130,7 +130,7 @@ type SerializerConfigT = {
     delta: DeltaResult,
   ) => unknown;
   getModulesRunBeforeMainModule: (entryFilePath: string) => Array<string>;
-  getPolyfills: ($$PARAM_0$$: {
+  getPolyfills: (ctx: {
     platform: null | undefined | string;
   }) => ReadonlyArray<string>;
   getRunModuleStatement: (
@@ -178,12 +178,12 @@ type CacheStoresConfigT = ReadonlyArray<CacheStore<TransformResult>>;
 type ServerConfigT = {
   /** @deprecated */
   enhanceMiddleware: (
-    $$PARAM_0$$: Middleware,
-    $$PARAM_1$$: MetroServer,
+    middleware: Middleware,
+    server: MetroServer,
   ) => Middleware | Server;
   forwardClientLogs: boolean;
   port: number;
-  rewriteRequestUrl: ($$PARAM_0$$: string) => string;
+  rewriteRequestUrl: (url: string) => string;
   unstable_serverRoot: null | undefined | string;
   useGlobalHotkey: boolean;
   verifyConnections: boolean;
@@ -197,7 +197,7 @@ type ServerConfigT = {
       };
 };
 type SymbolicatorConfigT = {
-  customizeFrame: ($$PARAM_0$$: {
+  customizeFrame: (frame: {
     readonly file: null | undefined | string;
     readonly lineNumber: null | undefined | number;
     readonly column: null | undefined | number;
@@ -206,8 +206,8 @@ type SymbolicatorConfigT = {
     | (null | undefined | {readonly collapse?: boolean})
     | Promise<null | undefined | {readonly collapse?: boolean}>;
   customizeStack: (
-    $$PARAM_0$$: Array<IntermediateStackFrame>,
-    $$PARAM_1$$: unknown,
+    symbolicatedStack: Array<IntermediateStackFrame>,
+    extraData: unknown,
   ) => Array<IntermediateStackFrame> | Promise<Array<IntermediateStackFrame>>;
 };
 type WatcherConfigT = {
@@ -227,7 +227,7 @@ export type InputConfigT = Partial<
     MetalConfigT & {
       cacheStores:
         | CacheStoresConfigT
-        | (($$PARAM_0$$: MetroCache) => CacheStoresConfigT);
+        | ((metroCache: MetroCache) => CacheStoresConfigT);
       resolver: Readonly<Partial<ResolverConfigT>>;
       server: Readonly<Partial<ServerConfigT>>;
       serializer: Readonly<Partial<SerializerConfigT>>;

diff --git a/packages/metro-file-map/src/cache/DiskCacheManager.js b/packages/metro-file-map/src/cache/DiskCacheManager.js
@@ -50,10 +50,9 @@ export class DiskCacheManager implements CacheManager {
   #tryWrite: ?() => Promise<void>;
   #stopListening: ?() => void;
 
-  constructor(
-    {buildParameters}: CacheManagerFactoryOptions,
-    {autoSave = {}, cacheDirectory, cacheFilePrefix}: DiskCacheConfig,
-  ) {
+  constructor(opts: CacheManagerFactoryOptions, config: DiskCacheConfig) {
+    const {buildParameters} = opts;
+    const {autoSave = {}, cacheDirectory, cacheFilePrefix} = config;
     this.#cachePath = DiskCacheManager.getCacheFilePath(
       buildParameters,
       cacheFilePrefix,
@@ -103,12 +102,9 @@ export class DiskCacheManager implements CacheManager {
 
   async write(
     getSnapshot: () => CacheData,
-    {
-      changedSinceCacheRead,
-      eventSource,
-      onWriteError,
-    }: CacheManagerWriteOptions,
+    opts: CacheManagerWriteOptions,
   ): Promise<void> {
+    const {changedSinceCacheRead, eventSource, onWriteError} = opts;
     // Initialise a writer function using a promise queue to ensure writes are
     // sequenced.
     const tryWrite = (this.#tryWrite = () => {

diff --git a/packages/metro-file-map/src/flow-types.js b/packages/metro-file-map/src/flow-types.js
@@ -96,7 +96,7 @@ export type ChangedFileMetadata = Readonly<{
 }>;
 
 export type ChangeEvent = Readonly<{
-  logger: ?RootPerfLogger,
+  logger?: ?RootPerfLogger,
   changes: ReadonlyFileSystemChanges<Readonly<ChangedFileMetadata>>,
   rootDir: string,
 }>;
@@ -110,7 +110,7 @@ export type ChangeEventMetadata = {
 export type Console = typeof global.console;
 
 export type CrawlerOptions = {
-  abortSignal: ?AbortSignal,
+  abortSignal?: ?AbortSignal,
   computeSha1: boolean,
   console: Console,
   extensions: ReadonlyArray<string>,
@@ -328,8 +328,8 @@ export interface FileSystem {
     mixedStartPath: string,
     subpath: string,
     opts: {
-      breakOnSegment: ?string,
-      invalidatedBy: ?Set<string>,
+      breakOnSegment?: ?string,
+      invalidatedBy?: ?Set<string>,
       subpathType: 'f' | 'd',
     },
   ): ?{

diff --git a/packages/metro-file-map/src/plugins/HastePlugin.js b/packages/metro-file-map/src/plugins/HastePlugin.js
@@ -80,10 +80,11 @@ export default class HastePlugin
     this.#failValidationOnConflicts = options.failValidationOnConflicts;
   }
 
-  async initialize({
-    files,
-  }: FileMapPluginInitOptions<null, string | null>): Promise<void> {
+  async initialize(
+    opts: FileMapPluginInitOptions<null, string | null>,
+  ): Promise<void> {
     this.#perfLogger?.point('constructHasteMap_start');
+    const files = opts.files;
     let hasteFiles = 0;
     for (const {
       baseName,

diff --git a/packages/metro-file-map/types/cache/DiskCacheManager.d.ts b/packages/metro-file-map/types/cache/DiskCacheManager.d.ts
@@ -6,7 +6,7 @@
  *
  * @noformat
  * @oncall react_native
- * @generated SignedSource<<9cdec2a3b7a46f0a893dd5dc392a5294>>
+ * @generated SignedSource<<1276c0a64e0ad55f32baa402baf919da>>
  *
  * This file was translated from Flow by scripts/generateTypeScriptDefinitions.js
  * Original file: packages/metro-file-map/src/cache/DiskCacheManager.js
@@ -30,10 +30,7 @@ type DiskCacheConfig = Readonly<{
   cacheDirectory?: null | undefined | string;
 }>;
 export declare class DiskCacheManager implements CacheManager {
-  constructor(
-    $$PARAM_0$$: CacheManagerFactoryOptions,
-    $$PARAM_1$$: DiskCacheConfig,
-  );
+  constructor(opts: CacheManagerFactoryOptions, config: DiskCacheConfig);
   static getCacheFilePath(
     buildParameters: BuildParameters,
     cacheFilePrefix?: null | undefined | string,
@@ -43,7 +40,7 @@ export declare class DiskCacheManager implements CacheManager {
   read(): Promise<null | undefined | CacheData>;
   write(
     getSnapshot: () => CacheData,
-    $$PARAM_1$$: CacheManagerWriteOptions,
+    opts: CacheManagerWriteOptions,
   ): Promise<void>;
   end(): Promise<void>;
 }
diff --git a/packages/metro-file-map/types/flow-types.d.ts b/packages/metro-file-map/types/flow-types.d.ts
@@ -6,7 +6,7 @@
  *
  * @noformat
  * @oncall react_native
- * @generated SignedSource<<b3646c81d37188726a1fc27777dcbede>>
+ * @generated SignedSource<<ffc6f9b096f7d4a23bbd86997a3044d6>>
  *
  * This file was translated from Flow by scripts/generateTypeScriptDefinitions.js
  * Original file: packages/metro-file-map/src/flow-types.js
@@ -80,7 +80,7 @@ export type ChangedFileMetadata = Readonly<{
   modifiedTime?: null | undefined | number;
 }>;
 export type ChangeEvent = Readonly<{
-  logger: null | undefined | RootPerfLogger;
+  logger?: null | undefined | RootPerfLogger;
   changes: ReadonlyFileSystemChanges<Readonly<ChangedFileMetadata>>;
   rootDir: string;
 }>;
@@ -91,7 +91,7 @@ export type ChangeEventMetadata = {
 };
 export type Console = typeof global.console;
 export type CrawlerOptions = {
-  abortSignal: null | undefined | AbortSignal;
+  abortSignal?: null | undefined | AbortSignal;
   computeSha1: boolean;
   console: Console;
   extensions: ReadonlyArray<string>;
@@ -289,8 +289,8 @@ export interface FileSystem {
     mixedStartPath: string,
     subpath: string,
     opts: {
-      breakOnSegment: null | undefined | string;
-      invalidatedBy: null | undefined | Set<string>;
+      breakOnSegment?: null | undefined | string;
+      invalidatedBy?: null | undefined | Set<string>;
       subpathType: 'f' | 'd';
     },
   ): null | undefined | {absolutePath: string; containerRelativePath: string};

diff --git a/packages/metro-file-map/types/plugins/HastePlugin.d.ts b/packages/metro-file-map/types/plugins/HastePlugin.d.ts
@@ -6,7 +6,7 @@
  *
  * @noformat
  * @oncall react_native
- * @generated SignedSource<<3d1462ab2325a09553e02b69b5de84eb>>
+ * @generated SignedSource<<d1c8a8bc5a39d65b817f19d70211260b>>
  *
  * This file was translated from Flow by scripts/generateTypeScriptDefinitions.js
  * Original file: packages/metro-file-map/src/plugins/HastePlugin.js
@@ -44,7 +44,7 @@ declare class HastePlugin
   readonly name: 'haste';
   constructor(options: HasteMapOptions);
   initialize(
-    $$PARAM_0$$: FileMapPluginInitOptions<null, string | null>,
+    opts: FileMapPluginInitOptions<null, string | null>,
   ): Promise<void>;
   getSerializableSnapshot(): null;
   getModule(

diff --git a/packages/metro-resolver/src/types.js b/packages/metro-resolver/src/types.js
@@ -140,7 +140,7 @@ export type ResolutionContext = Readonly<{
    * @deprecated, prefer `fileSystemLookup`
    */
   doesFileExist: DoesFileExist,
-  extraNodeModules: ?{[string]: string, ...},
+  extraNodeModules: ?{[packageName: string]: string, ...},
 
   /** Is resolving for a development bundle. */
   dev: boolean,
@@ -239,6 +239,6 @@ export type CustomResolver = (
 
 export type CustomResolverOptions = {
   __proto__: null,
-  +[string]: unknown,
+  +[key: string]: unknown,
   ...
 };