fix(react-native): disable fmt consteval for Xcode 26.4 builds#275
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Kristopher Johnson (kristopherjohnson) wants to merge 1 commit intomainfrom
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fix(react-native): disable fmt consteval for Xcode 26.4 builds#275Kristopher Johnson (kristopherjohnson) wants to merge 1 commit intomainfrom
Kristopher Johnson (kristopherjohnson) wants to merge 1 commit intomainfrom
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Compile the fmt pod as C++17 in a post_install hook so __cpp_consteval is not defined, which forces fmt to skip the consteval FMT_STRING code path entirely and fall back to runtime format-string validation. Scoped to the fmt target only — RCT-Folly, React-Core, and the rest of RN keep their C++20 settings. Without this, `react-native run-ios` (Debug or Release) fails on Xcode 26.4 with errors like: call to consteval function 'fmt::basic_format_string<...>' is not a constant expression This mirrors the fix landed in the SDK monorepo's example app (getditto/ditto#22248, backported to releases/stable/sdk-4.14 in #22327). Remove when React Native upgrades to a build that bundles fmt >= 11.1. See SDKS-3242.
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Pull request overview
Updates the React Native iOS quickstart’s CocoaPods configuration to work around an Xcode 26.4 clang + fmt 11.0.2 consteval compilation failure, while keeping the rest of React Native on C++20.
Changes:
- Adds a
post_installoverride to force thefmtpod target to compile as C++17. - Documents the rationale, upstream reference, and removal condition (when RN bundles fmt ≥ 11.1).
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Kristopher Johnson (kristopherjohnson)
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Alyssa Evans (alycda) and
Aaron LaBeau (biozal)
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Summary
Apply the fmt-consteval Xcode 26.4 fix to the React Native quickstart's
Podfile.Without this,
react-native run-ios(Debug or Release) on Xcode 26.4 fails to compile the bundledfmt11.0.2 Pod with:The post_install hook compiles only the
fmttarget as C++17 so__cpp_constevalisn't defined, which causes fmt to skip its constevalFMT_STRINGpath and fall back to runtime format-string validation. RCT-Folly, React-Core, and the rest of RN keep their C++20 settings.This mirrors the fix the SDK team landed in the monorepo's example app:
releases/stable/sdk-4.14)Confirmed locally on Xcode 26.4: with the snippet in place,
react-native run-ios --device 'KJ iPhone XR' --mode Releasebuilds, installs, and launches successfully. Without it, the same command fails on the consteval errors above.Remove this hook once React Native bundles
fmt >= 11.1(which has the upstream consteval fix).Linear
Closes SDKS-3595
Test plan
cd react-native/ios && pod installsucceedscd react-native && npx react-native run-ios --simulator 'iPhone 16'builds clean (no consteval errors)