preserve require.context call when unstable_disableModuleWrapping is enabled #1129
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## main #1129 +/- ##
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Coverage 83.09% 83.09%
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Files 206 206
Lines 10547 10548 +1
Branches 2617 2618 +1
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…ns (#30140) # Why - The dependency collection system needs extra customizations for tree shaking (tracking more import info, not mutating require context, etc.) and for supporting SSR externals (required for RSC). - Will pull in proposed changes such as facebook/metro#1129 in the future. <!-- Please describe the motivation for this PR, and link to relevant GitHub issues, forums posts, or feature requests. --> # How - Have ChatGPT rewrite the upstream collect dependencies module and tests in TypeScript. - No extra changes are applied on top of the module. # Test Plan - Pulled in the upstream tests to ensure compat with Metro. --------- Co-authored-by: Expo Bot <[email protected]>
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# Why > Most of the original PR has been landed in #30417 - Metro bundler does not have any form of graph-wide tree shaking built-in. This can lead to bundle sizes that are larger than they need to be, especially in the case of icon libraries. - This PR (which is partially an RFC) aims to add a system for removing unused imports and exports from a production bundle. <!-- Please describe the motivation for this PR, and link to relevant GitHub issues, forums posts, or feature requests. --> # How - Leverage the new "optimize graph" mode to perform holistic optimizations in the serializer. #30417 - Tree shaking can be enabled with the new env var `EXPO_UNSTABLE_TREE_SHAKING=1`. - This PR also adds a "barrel expansion" system which attempts to replace `export * from '...'` statements with `export { View, Image, etc } from '...'` statements to enable more graph reduction. - Empty modules (containing only comments and directives) are removed from the bundle. - Side-effecty imports (imports with zero specifiers, `import "foo"` and `import {} from "foo"`) are preserved unless marked otherwise by a `package.json`'s `sideEffects` field. - Custom imports such as `require.context` and `require.resolveWeak` are left in place. - Removed exports with source will trigger a recrawl to ensure any new unused imports/exports are recursively removed. - The feature is artificially forced to only run when `EXPO_UNSTABLE_TREE_SHAKING=1` is set, and when bundling for production. Tree shaking is disabled for SSR bundles. I may expand this to be web-only too just due to a lack of continuous testing for native runtimes. - Added some external fixes software-mansion/react-native-reanimated#6171 #30010 #29980 #29964 #29963 software-mansion/react-native-gesture-handler#2972 # Further work Some ideas that I've had but aren't implemented in this PR: - Use the worker farm to parallelize transformation in the serializer. This could be tricky because we'd need to convert the AST to a serial format then re-parse it back. - ~~Fork collectDependencies to fully track the import/exports so we can reuse the same import crawling code and references. This would also speed up the bundling as we could parallelize and cache the pass.~~ #30140 - Use a totally custom syntax for matching import/exports, e.g. `_$$_IMPORT_DEFAULT, _$$_IMPORT_ALL` (and some new export equivalents) to reduce the number of transforms we run in the serializer. All import/export's and the iife wrap could be run at transform-time and we'd simply be mutating a valid JS bundle in the serializer. This would be very challenging though and make it harder for users to contribute to the implementation. - ~~Upstream the hack on transformSyncRequire to support require.context with one parameter. facebook/metro#1129 - Detect if a module is CJS according to Node.js heuristic, e.g. `.cjs`, package exports, etc. then opt it out of tree shaking. - [ ] update source maps # Test Plan - Added an e2e tree shaking test for web. - Added mini-metro tests to account for the known and expected tree shaking behaviors. - Added mini-metro tests for side-effect handling (need more here). - Ensured all apps in expo/apps can be transformed and run with tree shaking enabled. --------- Co-authored-by: Expo Bot <[email protected]> Co-authored-by: Aman Mittal <[email protected]>
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Summary
One possible way to implement tree shaking would require calling collectDependencies with
unstable_disableModuleWrappingfor a first pass, and invoking it a second time with module wrapping. The issue with this is that the require.context mutation is mutated to a format that wouldn't work on subsequent runs.This PR will prevent the additional mutation of
require.context->require.Test plan
Tests continue working