fix: Windows (Git Bash) local development environment compatibility

[stevenkeith-consensys]

Description

Local development on Windows with Git Bash was broken at three independent layers. All root causes are platform-native path separators (\ vs /) or line endings (CRLF vs LF) leaking into code that assumed POSIX conventions:

1. App crashed at startup with [runtime not ready]: ReferenceError: Property 'require' doesn't exist. The ignore and overrides path checks in babel.config.js used forward slashes only, and Metro hands Babel backslash-separated paths on Windows. Babel therefore transformed files it must never touch — the SES lockdown files and the expo/virtual/streams.js Metro polyfill — injecting require("@babel/runtime/helpers/...") into code that executes before Metro's module system defines require. Fixed with a posixPath separator-normalizing helper used by every path check. This also restores the 12 overrides compatibility transforms (private methods, CJS interop) that were silently not being applied on Windows.

2. yarn watch failed with Cannot find module 'C:\Program Files\Git\update-expo-channel.js'. When Yarn spawns ./scripts/build.sh on Windows, bash receives a backslash-separated BASH_SOURCE[0], so the ${BASH_SOURCE[0]%/*} trim found no /, the cd failed, and __DIRNAME__ was silently empty (/update-expo-channel.js then gets MSYS-converted to the Git install root — hence the misleading error). Fixed by normalizing backslashes before dirname in the four scripts that resolve their own directory.

3. Device targeting and env loading corrupted by CRLF: adb.exe emits CRLF, so $(adb get-state) captures device\r and equality checks fail; a CRLF .js.env exports every value with a trailing \r. Fixed by stripping \r at the read sites. The metro.config.js perps-controller originModulePath checks were also forward-slash-only and now match either separator.

Every fix is a no-op on macOS/Linux: backslash normalization doesn't alter POSIX paths, and CR stripping doesn't alter LF files. Verified by running old vs. new logic side-by-side on POSIX-style inputs with byte-identical results, plus a unit test of the Babel config path checks against both path styles.

Changelog

CHANGELOG entry: null

Related issues

Fixes: N/A (developer-environment fix, no tracking issue)

Manual testing steps

Feature: Local development on Windows with Git Bash

  Scenario: developer starts the Metro watcher
    Given a Windows machine with Git Bash and a cloned repo with yarn setup:expo completed
    When the developer runs `yarn watch:clean`
    Then Metro starts and reaches "Waiting on http://localhost:8081"
    And no "Cannot find module 'C:\Program Files\Git\update-expo-channel.js'" error occurs

  Scenario: developer runs the app on an Android emulator
    Given Metro is running and the expo dev build is installed on a booted emulator
    When the developer launches MetaMask on the emulator
    Then the app boots to the wallet with no red screen
    And logcat shows `Running "MetaMask"` with no "[runtime not ready]" ReferenceError

  Scenario: macOS developer is unaffected
    Given a macOS machine
    When the developer runs `yarn watch:clean` and `yarn install:ios:dev`
    Then behavior is identical to before this change (all fixes are no-ops on POSIX paths)

Verified on Windows 11 + Git Bash: Metro bundles all 17,393 modules from a clean cache and the app boots on an Android 16 (API 36) emulator. Checks run locally: ESLint on changed JS files, prettier --check, bash -n on all changed scripts, and a Jest smoke run (Jest shares babel.config.js; the one failing test in scripts/worktree-create.test.ts fails identically on main on Windows and is unrelated).

Screenshots/Recordings

Before

Red screen on app launch (Android emulator, Windows host):
[runtime not ready]: ReferenceError: Property 'require' doesn't exist

After

App boots to the wallet normally; logcat shows Running "MetaMask". N/A for UI screenshots — developer-tooling change with no user-facing UI.

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Mobile Coding Standards.
• I've completed the PR template to the best of my ability
• I've included tests if applicable
• I've documented my code using JSDoc format if applicable
• I've applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Performance checks (if applicable)

• I've tested on Android
  • Ideally on a mid-range device; emulator is acceptable
• I've tested with a power user scenario
  • Use these power-user SRPs to import wallets with many accounts and tokens
• I've instrumented key operations with Sentry traces for production performance metrics
  • See trace() for usage and addToken for an example

For performance guidelines and tooling, see the Performance Guide.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

🤖 Generated with Claude Code

[github-actions]

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❌ @stevenkeith-consensys

[mm-token-exchange-service]

PR template — items to address before "Ready for review"

Warnings — informational, address before merging:

• Pre-merge author checklist has unchecked items (e.g. "I've applied the right labels on the PR (see labeling guidelines). Not required for external contributors."). Every box must be consciously checked — see docs/readme/ready-for-review.md.

See docs/readme/ready-for-review.md for the full Definition of Ready for Review.

[github-actions]

🔍 Smart E2E Test Selection

• Selected E2E tags: None (no tests recommended)
• Selected Performance tags: None (no tests recommended)
• Risk Level: low
• AI Confidence: 92%

click to see 🤖 AI reasoning details

E2E Test Selection:
All 8 changed files are Windows compatibility fixes for build tooling and bundler configuration:

1. babel.config.js: Adds a posixPath() helper to normalize Windows backslash separators to forward slashes before regex path matching. On macOS/Linux (CI environment), this is a no-op - the behavior is identical. No Babel transformation logic changed.

2. metro.config.js: Changes String.includes() to regex with [\\/] for path separator matching. Again, functionally identical on macOS/Linux CI. No module resolution logic changed.

3. scripts/build.sh, generate-attributions.sh, install-android-dev-app.sh, install-ios-dev-app.sh: Developer-facing shell scripts with Windows/Git Bash path normalization fixes. These are local development tools, not CI pipeline scripts.

4. scripts/lib/dev-device-target.sh: CRLF stripping for adb output and .js.env loading on Windows. Local development tooling.

5. scripts/lib/download-gha-expo-dev-build.sh: Only changes a help text comment to add Windows install instructions - purely cosmetic.

None of these changes affect:

• App source code or UI components
• Controllers or Engine
• Test infrastructure (page objects, flows, selectors, smoke specs)
• CI workflow files
• Any user-facing functionality

The changes are purely build tooling improvements for Windows developer compatibility, with no functional impact on macOS/Linux CI environments where E2E tests run. No E2E test tags are warranted.

Performance Test Selection:
No performance-sensitive code was changed. All modifications are Windows compatibility fixes in build scripts (babel.config.js, metro.config.js, shell scripts) that have no functional impact on macOS/Linux CI environments where performance tests run. No app rendering, data fetching, or user flow code was modified.

View GitHub Actions results

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[ghgoodreau]

FEEDBACK

1. babel.config.js: normalization is a convention, not an invariant — and there's a clear judo move (blocker)
   The fix edits 13 call sites so each one individually remembers to call posixPath(f). Nothing enforces this. The next contributor who adds an override will copy the pre-existing muscle-memory pattern (f) => !!f?.includes('/node_modules/...') from an old PR or another repo, and Windows silently breaks again — the exact failure mode this PR fixes, with no test to catch it (see finding 3).

The stronger structure is one line away, and it also collapses most of the file. Nine of the twelve overrides are byte-identical except for the path — all applying @babel/plugin-transform-private-methods — so the whole block should be data plus one factory:

const pathIncludes = (needle) => (f) => posixPath(f).includes(needle); const privateMethodsLoose = [ ['@babel/plugin-transform-private-methods', { loose: true }], ]; const PRIVATE_METHODS_PATHS = [ '/node_modules/marked', '/node_modules/@metamask/profile-sync-controller', '/node_modules/@metamask/notification-services-controller', '/node_modules/@metamask/bridge-controller', '/node_modules/@metamask/rpc-errors', '/app/core/redux/ReduxService.ts', '/app/core/Engine/Engine.ts', '/app/core/NavigationService/NavigationService.ts', '/app/core/OAuthService/OAuthLoginHandlers', ]; overrides: [ ...PRIVATE_METHODS_PATHS.map((p) => ({ test: pathIncludes(p), plugins: privateMethodsLoose, })), // hyperliquid + secp256k1 (commonjs) and SnapsExecutionWebView (inline-import) // stay as three explicit entries, using pathIncludes for their tests. ],

This turns roughly 70 lines of repeated lambdas into ~25, deletes the repetition rather than normalizing it in place, and makes it structurally impossible to forget normalization for the common case. The ignore entry should also route through a helper rather than open-coding four regexes against a locally-normalized variable.

One deeper option worth a note in the PR (investigate, don't block on it): Babel normalizes string MatchPatterns cross-platform itself (its pattern-to-regex compiles separators as [\/]). If the function tests were replaced with string patterns, posixPath could be deleted entirely. The prefix/suffix matching semantics of string patterns need verification, so the factory above is the safe, verifiable move.

2. Missing test the PR claims to have (blocker)

The PR body says the fix was verified with "a unit test of the Babel config path checks against both path styles" — but the diff contains no test file (the 8 changed files are the two configs and six scripts; babel.config.tests.js in the repo is a Babel configuration for Jest, not a test). Either commit that test or correct the description. Given finding 1 — a convention that will regress silently the moment someone forgets it — a committed test asserting the ignore/override checks match both C:...\ses.cjs and /.../ses.cjs styles is the cheap permanent guard and should ship with this PR.

3. metro.config.js: duplicated regex and a second idiom for the same problem

The exact expression /[\\/]@metamask[\\/]perps-controller[\\/]/.test(context.originModulePath ?? '') is pasted twice, ~15 lines apart. Extract it once:

const isPerpsControllerOrigin = (context) => /[\\/]@metamask[\\/]perps-controller[\\/]/.test(context.originModulePath ?? '');

More importantly, this file solves separator-independence with a regex character class while babel.config.js solves it with normalize-then-includes. Two sibling config files, same problem, two idioms — pick one (normalize-then-includes is the more legible of the two) so the next Windows path bug has one obvious fix pattern to copy. Also note the new regex is subtly stricter than the old .includes('@metamask/perps-controller') — it now requires a trailing separator. That's fine (origin paths are files inside the package) and arguably an improvement, but it's an unstated behavior change; a word in the comment would help.

FIX REQUIRED FOR MAC BUILD

the first yarn watch:clean run on the untouched PR branch failed immediately with METAMASK_ENVIRONMENT '' is not valid, even with a valid .js.env present. The cause is the PR's CRLF fix itself:

source <(tr -d '\r' < "$JS_ENV_FILE")

macOS ships bash 3.2, and both scripts/build.sh and scripts/lib/dev-device-target.sh run under #!/bin/bash, so Homebrew bash doesn't save you. On bash 3.2, source of a process substitution silently reads zero bytes for a file of this size — I confirmed with a minimal repro: sourcing the 259-line .js.env.example through <(tr -d '\r' ...) loads nothing, while eval "$(tr -d '\r' < file)" loads everything correctly. So the PR's claim "every fix is a no-op on macOS/Linux" is false — it breaks yarn watch and the device-targeting env load for every macOS developer. This is a must-fix review comment. The fix is one line in each of the two files:

eval "$(tr -d '\r' < "$JS_ENV_FILE")"

I applied that patch in the test worktree (both call sites) to continue; everything after that worked.