metro-file-map: Remove micromatch by robhogan · Pull Request #2000 · react/metro

robhogan · 2026-09-29T21:19:08Z

Security

This was originally filed a cleanup PR but the need is more acute due to CVE-2026-93687, a CVE on braces, which is a dependency of micromatch. This PR removes Metro's only direct or indirect dependency on braces in prod (there are still some in devDependencies, mostly via Jest).

Context

The watcher backends filter change events by matching each relative path against globs with micromatch. Those globs aren't configurable - Metro builds them from extensions, plus **/package.json and the health check file prefix - so all micromatch ever checks is an extension, a base name or a prefix. We don't need the flexibility of globs here, and being explicit is faster, easier to reason about, and drops a dependency.

Change

This replaces the watchers' globs option with included - a set of extensions, basenames and basenamePrefixes checked with Set lookups and startsWith. Extensions are compared using path.extname, the same as the Node crawler:

metro/packages/metro-file-map/src/crawlers/node/index.js

Lines 78 to 79 in 13604e0

    
           const ext = path.extname(name).substr(1); 
        
           if (!isSymbolicLink && !exts.has(ext)) {

It also removes the watchers' dot option, which Metro always set to true, and the unused Glob type. With that, micromatch is no longer a dependency of metro-file-map. The watcher backends are only reachable through metro-file-map/private/*, and Expo uses neither them nor the removed types.

Changelog

 - **[Security]**: Fix CVE on micromatch/braces by removing the dependency

Test plan

New unit test for isIncluded. integration-test.js drives each watcher backend against a real temporary tree with an extension, a file name and a prefix in included, so it exercises this directly.

The watcher backends filter change events by matching each relative path against globs with `micromatch`. Those globs aren't configurable - Metro builds them from `extensions`, plus `**/package.json` and the health check file prefix - so all micromatch ever checks is an extension, a file name or a prefix. This replaces the watchers' `globs` option with `included`, a set of extensions, basenames and basename prefixes checked with `Set` lookups and `startsWith`. Extensions are compared using `path.extname`, the same as the Node crawler: https://github.com/react/metro/blob/13604e0207e02c6aed7fbff97af439ed2df5fd1f/packages/metro-file-map/src/crawlers/node/index.js#L78-L79 It also removes the watchers' `dot` option, which Metro always set to `true`, and the unused `Glob` type. With that, `micromatch` is no longer a dependency of `metro-file-map`. The watcher backends are only reachable through `metro-file-map/private/*`, and Expo uses neither them nor the removed types. Changelog: Internal Test plan: New unit test for `isIncluded`. `integration-test.js` drives each watcher backend against a real temporary tree with an extension, a file name and a prefix in `included`, so it exercises this directly.

Copilot

Copilot review overview

🟢 Approval recommended

The replacement preserves intended watcher semantics and is supported by focused unit and backend integration coverage.

Review effort: Balanced
Findings: None

What changed in this PR

Removes micromatch from production watcher filtering, replacing glob matching with explicit extension, basename, and prefix checks.

Changes:

Introduces typed inclusion rules shared by all watcher backends.
Removes obsolete glob and dotfile options.
Adds unit and integration coverage for the new filtering behavior.

File	Description
`WatchmanWatcher.js`	Uses explicit inclusion filtering.
`NativeWatcher.js`	Uses explicit inclusion filtering.
`FallbackWatcher.js`	Uses explicit inclusion filtering.
`common.js`	Implements `isIncluded`.
`AbstractWatcher.js`	Stores inclusion configuration.
`Watcher.js`	Constructs extension, basename, and prefix rules.
`flow-types.js`	Defines the new inclusion API.
`package.json`	Removes `micromatch`.
`WatchmanWatcher-test.js`	Updates Watchman fixtures.
`NativeWatcher-test.js`	Updates native watcher fixtures.
`FallbackWatcher-test.js`	Updates fallback watcher fixtures.
`integration-test.js`	Exercises inclusion rules across backends.
`common-test.js`	Tests inclusion matching semantics.

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`Watcher` always watches `package.json` files, whatever `extensions` says, because they're crucial for module resolution. Neither crawler does the same, so with `json` absent from `extensions` they're skipped at startup. `FileMap` then checks every regular file change against `extensions` again, which drops the `package.json` events the watcher backend let through. This passes the same basenames to both crawlers. The Node crawler checks them alongside extensions. The Watchman crawler adds a `name` term for any basename whose extension isn't in `extensions`, and widens the `suffix` generator to cover it. With crawling and watching agreeing on which files to include, the watcher backends' `included` filter from #2000 is the only one needed, so this removes `FileMap`'s `hasWatchedExtension` recheck. There's no difference for a default Metro config, where `json` is in `sourceExts`. Changelog: [Fix] Include `package.json` files in the file map even when `json` is not in `sourceExts`, `assetExts` or `watcher.additionalExts`. Test plan: New `planQuery` tests for basenames, including that they don't change the query when `extensions` already covers them. The crawler integration test runs both crawlers against a real fixture tree with a `package.json` and only `js` in `extensions`. The `FileMap` test for the removed recheck is deleted, since `common-test.js` covers the backends' filter.

# Why Cherry-pick of #51093 onto `sdk-58`. It ports react/metro#2000 to `@expo/metro-file-map`. `micromatch` depends on `braces`, which has a CVE ([GHSA-vfj7-8cjw-p6xm](GHSA-vfj7-8cjw-p6xm)). The fork only uses `micromatch` to filter watcher change events, against globs it builds itself from `extensions`, `package.json` and the health check file prefix. None of them are configurable, so all it ever checks is an extension, a file name or a prefix. # How The same change as on `main`. The watchers' `globs` option is replaced by `included`, a set of `extensions`, `basenames` and `basenamePrefixes` checked with `Set` lookups and `startsWith`. A file matches an extension when its basename ends with `.` followed by that extension, as the `**/*.<ext>` globs did with `dot: true`. This keeps `.env` matching the `env` extension that `@expo/metro-config` adds to `watcher.additionalExts`, which `path.extname` would miss. The watchers' `dot` option, which was always `true`, and the unused `Glob` type are removed, and with them the `micromatch` and `@types/micromatch` dependencies. One difference from upstream: the fork's `healthCheckFilePrefix` is nullable, so a null prefix now adds no prefix match rather than a literal `**/null*` glob. Both commits from #51093 cherry-picked cleanly. The `.changeset` file is replaced by a `CHANGELOG.md` entry, because `sdk-58` does not use changesets. # Test Plan New unit test for `isIncluded`, ported from upstream and extended with dotfile and multi-part extension cases. A one-off script checked `isIncluded` against `micromatch.some(path, globs, {dot: true})` on 21 edge cases (`.env`, `.env.local`, `.envrc`, `src/.js`, `a.d.ts`, `a.js.map`, `a..js`, …) with no mismatches. On this branch, `pnpm test` (725 tests), `pnpm typecheck` and `pnpm lint` pass in `packages/@expo/metro-file-map`, and `pnpm install --frozen-lockfile` accepts the lockfile. The CLI E2E suite exercises the watchers through the injected file map, including `.env` reloads in `hmr-env-vars.test.ts`. # Checklist - [x] I added a `CHANGELOG.md` entry. - [ ] Docs: not applicable.

#2000 replaced the watchers' globs with `included`, comparing extensions using `path.extname`. That isn't quite what the `**/*.<ext>` globs did with `dot: true` - `path.extname('.env')` is `''`, so `.env` no longer matches an `env` extension, and a multi-part extension like `d.ts` never matches. That's a regression for Expo, which adds `env` to `watcher.additionalExts` so that editing `.env` triggers a reload: https://github.com/expo/expo/blob/7c9b0878c1942d24552adfab7de396c9e4a69103/packages/@expo/metro-config/src/ExpoMetroConfig.ts#L345 This matches an extension when the basename ends with `.` followed by that extension, after any dot, which is what the globs matched. Changelog: Internal (#2000 is unreleased) Test plan: Extended `common-test.js` with dotfile and multi-part extension cases. Compared against `micromatch.some(path, globs, {dot: true})` with the globs Metro used to build, on 21 edge-case paths (`.env`, `.env.local`, `.envrc`, `src/.js`, `a.d.ts`, `a.js.map`, `a..js`, ...), with no mismatches. Found by Expo's `hmr-env-vars` E2E test failing on the port of #2000 to Expo's file map, expo/expo#51093, which carries the same fix.

# Why Port of react/metro#2000 + react/metro#2024 to `@expo/metro-file-map`. `micromatch` depends on `braces`, which has a CVE ([GHSA-vfj7-8cjw-p6xm](GHSA-vfj7-8cjw-p6xm)). The fork only uses `micromatch` to filter watcher change events, against globs it builds itself from `extensions`, `package.json` and the health check file prefix. None of them are configurable, so all it ever checks is an extension, a file name or a prefix. # How This replaces the watchers' `globs` option with `included`, a set of `extensions`, `basenames` and `basenamePrefixes` checked with `Set` lookups and `startsWith`. A file matches an extension when its basename ends with `.` followed by that extension, so `.env` matches `env` and `foo.d.ts` matches `d.ts`. It also removes the watchers' `dot` option, which was always `true`, and the unused `Glob` type. With that, `micromatch` and `@types/micromatch` are no longer dependencies of `@expo/metro-file-map`. One difference from upstream: the fork's `healthCheckFilePrefix` is nullable, so a null prefix now adds no prefix match rather than a literal `**/null*` glob. # Test Plan New unit test for `isIncluded`, ported from upstream. `pnpm test`, `pnpm typecheck` and `pnpm lint` pass in `packages/@expo/metro-file-map`. The CLI E2E suite exercises the watchers through the injected file map. # Checklist - [x] I added a changeset and followed [this short guide](https://github.com/expo/expo/blob/main/CONTRIBUTING.md#-before-submitting) - [ ] This diff will work correctly for `npx expo prebuild` & EAS Build (eg: updated a module plugin). - [ ] Conforms with the [Documentation Writing Style Guide](https://github.com/expo/expo/blob/main/guides/Expo%20Documentation%20Writing%20Style%20Guide.md)

# Why Cherry-pick of #51093 onto `sdk-58`. It ports react/metro#2000 and its follow-up react/metro#2024 to `@expo/metro-file-map`. `micromatch` depends on `braces`, which has a CVE ([GHSA-vfj7-8cjw-p6xm](GHSA-vfj7-8cjw-p6xm)). The fork only uses `micromatch` to filter watcher change events, against globs it builds itself from `extensions`, `package.json` and the health check file prefix. None of them are configurable, so all it ever checks is an extension, a file name or a prefix. # How The same change as on `main`. The watchers' `globs` option is replaced by `included`, a set of `extensions`, `basenames` and `basenamePrefixes` checked with `Set` lookups and `startsWith`. A file matches an extension when its basename ends with `.` followed by that extension, as the `**/*.<ext>` globs did with `dot: true`. This keeps `.env` matching the `env` extension that `@expo/metro-config` adds to `watcher.additionalExts`, which `path.extname` would miss. The watchers' `dot` option, which was always `true`, and the unused `Glob` type are removed, and with them the `micromatch` and `@types/micromatch` dependencies. One difference from upstream: the fork's `healthCheckFilePrefix` is nullable, so a null prefix now adds no prefix match rather than a literal `**/null*` glob. The merged commit from #51093 (52acc2c) cherry-picked cleanly. The `.changeset` file is replaced by a `CHANGELOG.md` entry, because `sdk-58` does not use changesets. # Test Plan New unit test for `isIncluded`, ported from upstream and extended with dotfile and multi-part extension cases. A one-off script checked `isIncluded` against `micromatch.some(path, globs, {dot: true})` on 21 edge cases (`.env`, `.env.local`, `.envrc`, `src/.js`, `a.d.ts`, `a.js.map`, `a..js`, …) with no mismatches. On this branch, `pnpm test` (725 tests), `pnpm typecheck` and `pnpm lint` pass in `packages/@expo/metro-file-map`, and `pnpm install --frozen-lockfile` accepts the lockfile. The CLI E2E suite exercises the watchers through the injected file map, including `.env` reloads in `hmr-env-vars.test.ts`. # Checklist - [x] I added a `CHANGELOG.md` entry. - [ ] Docs: not applicable. (cherry picked from commit 52acc2c)

`Watcher` always watches `package.json` files, whatever `extensions` says, because they're crucial for module resolution. Neither crawler does the same, so with `json` absent from `extensions` they're skipped at startup. `FileMap` then checks every regular file change against `extensions` again, which drops the `package.json` events the watcher backend let through. This passes the same basenames to both crawlers. The Node crawler checks them alongside extensions. The Watchman crawler adds a `name` term for any basename whose extension isn't in `extensions`, and widens the `suffix` generator to cover it. With crawling and watching agreeing on which files to include, the watcher backends' `included` filter from #2000 is the only one needed, so this removes `FileMap`'s `hasWatchedExtension` recheck. There's no difference for a default Metro config, where `json` is in `sourceExts`. Changelog: [Fix] Include `package.json` files in the file map even when `json` is not in `sourceExts`, `assetExts` or `watcher.additionalExts`. Test plan: New `planQuery` tests for basenames, including that they don't change the query when `extensions` already covers them. The crawler integration test runs both crawlers against a real fixture tree with a `package.json` and only `js` in `extensions`. The `FileMap` test for the removed recheck is deleted, since `common-test.js` covers the backends' filter.

# Why Cherry-pick of #51093 onto `sdk-58`. It ports react/metro#2000 and its follow-up react/metro#2024 to `@expo/metro-file-map`. `micromatch` depends on `braces`, which has a CVE ([GHSA-vfj7-8cjw-p6xm](GHSA-vfj7-8cjw-p6xm)). The fork only uses `micromatch` to filter watcher change events, against globs it builds itself from `extensions`, `package.json` and the health check file prefix. None of them are configurable, so all it ever checks is an extension, a file name or a prefix. # How The same change as on `main`. The watchers' `globs` option is replaced by `included`, a set of `extensions`, `basenames` and `basenamePrefixes` checked with `Set` lookups and `startsWith`. A file matches an extension when its basename ends with `.` followed by that extension, as the `**/*.<ext>` globs did with `dot: true`. This keeps `.env` matching the `env` extension that `@expo/metro-config` adds to `watcher.additionalExts`, which `path.extname` would miss. The watchers' `dot` option, which was always `true`, and the unused `Glob` type are removed, and with them the `micromatch` and `@types/micromatch` dependencies. One difference from upstream: the fork's `healthCheckFilePrefix` is nullable, so a null prefix now adds no prefix match rather than a literal `**/null*` glob. The merged commit from #51093 (52acc2c) cherry-picked cleanly. The `.changeset` file is replaced by a `CHANGELOG.md` entry, because `sdk-58` does not use changesets. # Test Plan New unit test for `isIncluded`, ported from upstream and extended with dotfile and multi-part extension cases. A one-off script checked `isIncluded` against `micromatch.some(path, globs, {dot: true})` on 21 edge cases (`.env`, `.env.local`, `.envrc`, `src/.js`, `a.d.ts`, `a.js.map`, `a..js`, …) with no mismatches. On this branch, `pnpm test` (725 tests), `pnpm typecheck` and `pnpm lint` pass in `packages/@expo/metro-file-map`, and `pnpm install --frozen-lockfile` accepts the lockfile. The CLI E2E suite exercises the watchers through the injected file map, including `.env` reloads in `hmr-env-vars.test.ts`. # Checklist - [x] I added a `CHANGELOG.md` entry. - [ ] Docs: not applicable. (cherry picked from commit 52acc2c)

# Why Cherry-pick of #51093 onto `sdk-57`. It ports react/metro#2000 and its follow-up react/metro#2024 to `@expo/metro-file-map`. `micromatch` depends on `braces`, which has a CVE ([GHSA-vfj7-8cjw-p6xm](GHSA-vfj7-8cjw-p6xm)). The fork only uses `micromatch` to filter watcher change events, against globs it builds itself from `extensions`, `package.json` and the health check file prefix. None of them are configurable, so all it ever checks is an extension, a file name or a prefix. # How The same change as on `main`. The watchers' `globs` option is replaced by `included`, a set of `extensions`, `basenames` and `basenamePrefixes` checked with `Set` lookups and `startsWith`. A file matches an extension when its basename ends with `.` followed by that extension, as the `**/*.<ext>` globs did with `dot: true`. This keeps `.env` matching the `env` extension that `@expo/metro-config` adds to `watcher.additionalExts`, which `path.extname` would miss. The watchers' `dot` option, which was always `true`, and the unused `Glob` type are removed, and with them the `micromatch` and `@types/micromatch` dependencies. One difference from upstream: the fork's `healthCheckFilePrefix` is nullable, so a null prefix now adds no prefix match rather than a literal `**/null*` glob. The merged commit from #51093 (52acc2c) cherry-picked cleanly. The `.changeset` file is replaced by a `CHANGELOG.md` entry, because `sdk-57` does not use changesets. # Test Plan New unit test for `isIncluded`, ported from upstream and extended with dotfile and multi-part extension cases. A one-off script checked `isIncluded` against `micromatch.some(path, globs, {dot: true})` on 21 edge cases (`.env`, `.env.local`, `.envrc`, `src/.js`, `a.d.ts`, `a.js.map`, `a..js`, …) with no mismatches. On this branch, `pnpm test` (725 tests), `pnpm typecheck` and `pnpm lint` pass in `packages/@expo/metro-file-map`, and `pnpm install --frozen-lockfile` accepts the lockfile. The CLI E2E suite exercises the watchers through the injected file map, including `.env` reloads in `hmr-env-vars.test.ts`. # Checklist - [x] I added a `CHANGELOG.md` entry. - [ ] Docs: not applicable. (cherry picked from commit 52acc2c)

# Why Cherry-pick of #51093 onto `sdk-56`. It ports react/metro#2000 and its follow-up react/metro#2024 to `@expo/metro-file-map`. `micromatch` depends on `braces`, which has a CVE ([GHSA-vfj7-8cjw-p6xm](GHSA-vfj7-8cjw-p6xm)). The fork only uses `micromatch` to filter watcher change events, against globs it builds itself from `extensions`, `package.json` and the health check file prefix. None of them are configurable, so all it ever checks is an extension, a file name or a prefix. # How The same change as on `main`. The watchers' `globs` option is replaced by `included`, a set of `extensions`, `basenames` and `basenamePrefixes` checked with `Set` lookups and `startsWith`. A file matches an extension when its basename ends with `.` followed by that extension, as the `**/*.<ext>` globs did with `dot: true`. This keeps `.env` matching the `env` extension that `@expo/metro-config` adds to `watcher.additionalExts`, which `path.extname` would miss. The watchers' `dot` option, which was always `true`, and the unused `Glob` type are removed, and with them the `micromatch` and `@types/micromatch` dependencies. One difference from upstream: the fork's `healthCheckFilePrefix` is nullable, so a null prefix now adds no prefix match rather than a literal `**/null*` glob. The cherry-pick of the merged commit from #51093 (52acc2c) had one conflict. `FallbackWatcher.test.ts` doesn't exist on `sdk-56`, and the pick only updated the watcher options it passes, so I resolved it by keeping the file deleted. The `.changeset` file is replaced by a `CHANGELOG.md` entry, because `sdk-56` does not use changesets. # Test Plan New unit test for `isIncluded`, ported from upstream and extended with dotfile and multi-part extension cases. A one-off script checked `isIncluded` against `micromatch.some(path, globs, {dot: true})` on 21 edge cases (`.env`, `.env.local`, `.envrc`, `src/.js`, `a.d.ts`, `a.js.map`, `a..js`, …) with no mismatches. On this branch, `pnpm test` (720 tests), `pnpm typecheck` and `pnpm lint` pass in `packages/@expo/metro-file-map`, and `pnpm install --frozen-lockfile` with pnpm 10 (as CI uses on this branch) accepts the lockfile. The CLI E2E suite exercises the watchers through the injected file map, including `.env` reloads in `hmr-env-vars.test.ts`. # Checklist - [x] I added a `CHANGELOG.md` entry. - [ ] Docs: not applicable. (cherry picked from commit 52acc2c)

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metro-file-map: Always include package.json, drop the extension recheck #2022

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[metro-file-map] Remove micromatch expo/expo#51093

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[metro-file-map][sdk-58] Remove micromatch (#51093) expo/expo#51096

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metro-file-map: Restore change events for dotfiles like .env #2024

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[metro-file-map][sdk-57] Remove micromatch (#51093) expo/expo#51097

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[metro-file-map][sdk-56] Remove micromatch (#51093) expo/expo#51098

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[0.83.x] Backport micromatch removal and dotfile/multipart watcher fix together #2027

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[0.83.x] Backport paired watcher matching fixes and remove micromatch #2028

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	const ext = path.extname(name).substr(1);
	if (!isSymbolicLink && !exts.has(ext)) {

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