[Due for payment 2026-03-19] [$250] Enable Platform Shaking for React Native Bundle Size Optimization

[roryabraham]

Proposal

Enable Platform Shaking for React Native Bundle Size Optimization

Problem

The app’s Hermes Bytecode (HBC) bundle is larger than necessary. The Metro bundler and Babel transformer are using default configurations that do not enable Metro’s import support, which prevents Metro from performing platform-specific code elimination.
Additionally, the app includes expo/metro-config in metro.config.js, which is unnecessary since we do not use the Expo CLI. A larger bundle size leads to slower app startup times and higher memory consumption.

Solution

Enable platform shaking by aligning Metro and Babel configurations and removing the unnecessary Expo Metro config dependency. This allows Metro to exclude unused, platform-specific code from the final bundle.

Results

With these changes, we reduced the bundle size from 37.1 MB to 34.2 MB (~2.9 MB reduction, approximately 8%).
We still need to test this on ad-hoc builds to confirm all works correctly

Draft PR -> https://github.com/Expensify/App/pull/80110/files
Inspiration -> https://x.com/thymikee/status/2013321153700340183

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[melvin-bot]

⚠️ Looks like this issue was linked to a Deploy Blocker here

If you are the assigned CME please investigate whether the linked PR caused a regression and leave a comment with the results.

If a regression has occurred and you are the assigned CM follow the instructions here.

If this regression could have been avoided please consider also proposing a recommendation to the PR checklist so that we can avoid it in the future.

[dukenv0307]

@roryabraham, please remove the Reviewing label and bump to Daily as payment is due

[melvin-bot]

Triggered auto assignment to @CortneyOfstad (Bug), see https://stackoverflow.com/c/expensify/questions/14418 for more details. Please add this bug to a GH project, as outlined in the SO.