fix: embedded debug bundle in Expo dev mode - #391
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June 22, 2026 11:31
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Pull request overview
This PR fixes Expo iOS framework Debug embedded bundle behavior so embedded bundles are generated with dev-mode transforms disabled, and refines Debug bundle URL resolution to prefer Metro when available while allowing an embedded-bundle fallback when Metro is unavailable.
Changes:
- Force embedded framework Debug bundling to pass
--dev falseviaEXTRA_PACKAGER_ARGS(CI/local scripts + Expo config-plugin rewrite). - Update iOS runtime bundle URL resolution behavior/docs to “Metro first in Debug, embedded fallback when enabled”.
- Add/adjust regression tests for the config-plugin rewrite and SwiftPM bundle URL resolver behavior; add Node test coverage for Detox simulator device selection.
Reviewed changes
Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| scripts/ci-local-ios-e2e-common.sh | Ensures Detox/CI embedded bundle builds disable dev transforms via EXTRA_PACKAGER_ARGS. |
| packages/react-native-brownfield/src/expo-config-plugin/ios/xcodeHelpers.ts | Injects --dev false into the rewritten Xcode bundling phase for framework targets. |
| packages/react-native-brownfield/src/expo-config-plugin/ios/tests/xcodeHelpers.test.ts | Adds assertions ensuring the rewrite includes the new EXTRA_PACKAGER_ARGS export. |
| packages/react-native-brownfield/ios/Vanilla/ReactNativeHostRuntime.swift | Uses fallbackURLProvider: { nil } for Metro URL detection; clarifies Debug embedded fallback semantics. |
| packages/react-native-brownfield/ios/Expo/ExpoHostRuntime.swift | Same Metro URL fallback behavior for Expo runtime delegate; updates Debug fallback docs. |
| packages/react-native-brownfield/ios/ReactNativeBrownfield.swift | Updates API docs to match “Debug fallback when Metro unavailable”. |
| packages/react-native-brownfield/ios/swiftpm/Sources/BrownfieldBundleSupport/BrownfieldBundleURLResolver.swift | Changes Debug resolution to prefer Metro when available, with optional embedded fallback. |
| packages/react-native-brownfield/ios/swiftpm/Tests/BrownfieldBundleSupportTests/BrownfieldBundleURLResolverTests.swift | Splits/updates tests to cover Metro-first + embedded-fallback behavior. |
| apps/brownfield-example-shared-tests/package.json | Enables Node test runner for .test.cjs files. |
| apps/brownfield-example-shared-tests/e2e/expoPostMessageBrownfield.e2e.js | Refactors E2E navigation into a helper (but currently leaves Detox sync disabled). |
| apps/brownfield-example-shared-tests/detox-ios-simulator-device.cjs | Refactors simulator selection to prefer installed simulators over uncreated device types. |
| apps/brownfield-example-shared-tests/detox-ios-simulator-device.test.cjs | Adds Node tests for simulator device selection behavior. |
| .changeset/expo-debug-embedded-bundle.md | Changeset documenting the patch release. |
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| export function rewriteBundleReactNativePhaseScriptForFrameworkTarget( | ||
| shellScript: string | ||
| ): string { | ||
| const debugBundlingOverride = `# Brownfield framework packaging must embed JS in Debug builds. | ||
| if [[ "$CONFIGURATION" = *Debug* ]]; then |
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Summary
--dev falseto the React Native bundling script.Root cause
Expo debug bundles generated for embedded framework use were still emitted with JS dev mode enabled. When the host app loaded that embedded bundle without the Expo/Metro dev server, Expo devtools code attempted to create dev-server websocket endpoints and threw
Cannot create devtools websocket connections in embedded environments.Impact
Debug framework packaging can still embed JS, but the embedded bundle now behaves like a server-independent bundle instead of depending on Expo dev-server-only runtime paths.
Validation
EXTRA_PACKAGER_ARGSoverride.yarn workspace @callstack/react-native-brownfield testbrownfield-navigation-drift, turbotypecheck, turbolint