Restore base config merge in metro-config

[huntie]

Summary

Reverts #36777.

This is motivated by reducing user friction when the widespread assumption is for @react-native/metro-config to export a complete Metro config, as with Expo/rnx-kit, and like previously understood uses of metro-config. See react/metro#1010 (comment) for further notes.

Fixes:

• sourceExts and assetExts missing from resolver  metro#1010
• @react-native/metro-config doesn't export default assetExts and sourceExts anymore. #38069
• how to configure metro.config.js in 0.72.0 kristerkari/react-native-svg-transformer#276

Note that we do not intend for @react-native/metro-config to directly export assetExts etc — these can be accessed on the resolver property from the full config object.

Changelog: [General][Changed] @react-native/metro-config now includes all base config values from metro-config

Test Plan

Steps

• Using a new React Native 0.72 project.
  • Use yarn link to substitute @react-native/metro-config with local version.
  • Use yarn link to substitute @react-native-community/cli-plugin-metro with local fork.
    • This is modified to log the final config to the terminal.
  • Expand watchFolders in Metro config.
  • yarn start

✅ Produces functionally identical final config

(Diff before and after changes)

✅ App builds

Differential Revision: D47055973

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D47055973

[huntie]

@kelset@cipolleschi@hoxyq Do you know if package version bumps are performed as part of the release process? Or should I increment the version here (to be subsequently bumped in the template)?

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	9,045,226	-1
android	hermes	armeabi-v7a	8,294,498	-1
android	hermes	x86	9,561,418	-2
android	hermes	x86_64	9,403,753	+0
android	jsc	arm64-v8a	9,604,418	-1
android	jsc	armeabi-v7a	8,731,133	-1
android	jsc	x86	9,691,465	+0
android	jsc	x86_64	9,937,808	+0

Base commit: c803a5b
Branch: main

[kelset]

@kelset@cipolleschi@hoxyq Do you know if package version bumps are performed as part of the release process? Or should I increment the version here (to be subsequently bumped in the template)?

yes they are done as part of the release process, please don't bump here.

[kelset]

separate question: how does this change affect existing users on 0.72? will everything keep working as expected, or would they need to change anything?

'cause that will affect if we can cherry-pick in 0.72.

[huntie]

@kelset Ah yeah of course, ty 👍🏻

[robhogan]

separate question: how does this change affect existing users on 0.72? will everything keep working as expected, or would they need to change anything?
'cause that will affect if we can cherry-pick in 0.72.

This is non-breaking as I see it, so should be fine to pick - we'll just be exporting a complete config object rather than a loose, partial one.

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D47055973

[github-actions]

This pull request was successfully merged by @huntie in bbcedd3.

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