Add Buck CLI override for feature flag defaults#56507
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Summary:
Adds a mechanism to override React Native feature flag default values via a Buck command line argument, without modifying source files.
A `genrule` in the featureflags BUCK target always interposes on `ReactNativeFeatureFlagsDefaults.h` before compilation. When `react_native.feature_flag_defaults` is set to a JSON object via `--config`, a Python script rewrites the return values in the matching method bodies. When unset, the header passes through unmodified.
The Python script matches each override against the full method signature shape (`<returnType> <flagName>() override { ... return <value>; }`) with lenient whitespace, and fails the build if any requested flag name is not found in the header.
Usage:
```
buck2 build --config 'react_native.feature_flag_defaults={"enableViewCulling":true}' //target
buck2 build --config 'react_native.feature_flag_defaults={"enableViewCulling":true,"preparedTextCacheSize":500}' //target
```
This modifies defaults only — app-level providers still take priority.
Changelog: [Internal]
Reviewed By: robhogan
Differential Revision: D101484355
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Closing as this has been merged in fed907b |
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Summary:
Adds a mechanism to override React Native feature flag default values via a Buck command line argument, without modifying source files.
A
genrulein the featureflags BUCK target always interposes onReactNativeFeatureFlagsDefaults.hbefore compilation. Whenreact_native.feature_flag_defaultsis set to a JSON object via--config, a Python script rewrites the return values in the matching method bodies. When unset, the header passes through unmodified.The Python script matches each override against the full method signature shape (
<returnType> <flagName>() override { ... return <value>; }) with lenient whitespace, and fails the build if any requested flag name is not found in the header.Usage:
This modifies defaults only — app-level providers still take priority.
Changelog: [Internal]
Reviewed By: robhogan
Differential Revision: D101484355