[hsusul]

Summary:

Fixes #59561. The root cause and fix follow the diagnosis in that issue.

Array-of-enum (mask) props such as Modal's supportedOrientations can end up with bits the JS value never listed. On iOS that lets a landscape-only modal rotate to portrait.

The generated <Name>MaskWrapped struct (from GeneratePropsH.js) declares its only member without an initializer. convertRawProp in propsConversions.h default-constructs the prop type (T result;), so result.value starts indeterminate. The generated fromRawValue then ORs each listed value into it (wrapped.value |= ...), which keeps whatever bits were already in that memory. The std::optional<T> and std::vector<T> overloads of fromRawValue default-construct T the same way.

This change gives the generated member a value initializer (value{}), so every default-constructed wrapper starts at an empty mask. The existing designated ({ .value = ... }) and braced ({static_cast<...>(...)}) initializers in the generated Props.cpp are unaffected. Fixing it in the generated type covers every site that default-constructs it, without changing convertRawProp for all other prop types.

Changelog:

[GENERAL] [FIXED] - Codegen array-of-enum props (e.g. Modal supportedOrientations) no longer start parsing from an uninitialized mask

Test Plan:

Updated the GeneratePropsH snapshots (unit and both e2e suites) to expect value{};. They fail before the generator change and pass after it:

$ yarn jest packages/react-native-codegen/src/generators/components/__tests__/GeneratePropsH-test.js packages/react-native-codegen/e2e/deep_imports/__tests__/components/GeneratePropsH-test.js packages/react-native-codegen/e2e/namespaced/__tests__/components/GeneratePropsH-test.js
# before
-   ArrayPropsNativeComponentSizesMask value{};
+   ArrayPropsNativeComponentSizesMask value;
Tests:       5 failed, 69 passed, 74 total
# after
Tests:       74 passed, 74 total

Runtime check of the generated code. I compiled the mask block that GeneratePropsH emits for the ARRAY_PROPS fixture (sizes: ['small', 'large']), with stub RawValue and PropsParserContext types and a copy of convertRawProp's T result; fromRawValue(...) pattern. I used clang++ -std=c++20 -O0 -ftrivial-auto-var-init=pattern so the indeterminate start value shows up the same way on every run:

# before
sizes=['small'] -> mask=0xaaaaaaab (expected 0x00000001), toString="small, large"
# after
sizes=['small'] -> mask=0x00000001 (expected 0x00000001), toString="small"

Also ran:

• yarn jest packages/react-native-codegen: 64 suites, 3130 tests, 1279 snapshots passed
• yarn flow-check: 0 errors
• yarn eslint --max-warnings 0 and prettier --check on GeneratePropsH.js: clean

Not run: an iOS or Android app build. I did not reproduce the Modal orientation behavior on a device or simulator. I did not regenerate the scripts/cxx-api snapshots. Those snapshots drop member initializers (for example bool visible{false} is recorded as bool visible), so I don't expect them to change.

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