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fix(fmt): patch base.h consteval gate via prepare_command for Xcode 26.x #2961

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fix(fmt): patch base.h consteval gate via prepare_command for Xcode 26.x #2961

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2c20800
fix(fmt): set FMT_USE_CONSTEVAL=0 in fmt.podspec for Xcode 26.x compa…
tvinhas May 13, 2026
3c6ea99
fix(fmt): patch base.h via prepare_command instead of xcconfig -D
tvinhas May 13, 2026
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27 changes: 27 additions & 0 deletions packages/react-native/third-party-podspecs/fmt.podspec
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,33 @@ Pod::Spec.new do |spec|
:git => fmt_git_url,
:tag => "11.0.2"
}
# Patch fmt's existing "Apple clang < 14 broken" gate at
# `include/fmt/base.h:122` to catch ALL Apple clang versions. fmt 11.0.2's
# consteval `basic_format_string` constructor is rejected by Xcode 26.x's
# stricter constexpr evaluator, breaking the compile of `Pods/fmt/src/format.cc`
# at `format-inl.h:59`, `60`, `1387`, `1391`, `1394`, etc. with:
#
# error: call to consteval function 'fmt::basic_format_string<...>'
# is not a constant expression
#
# fmt already disables consteval for compilers it considers broken
# (Apple clang < 14, MSVC VS2019 < 16.10 etc. — see `base.h:113-132`) by
# forcing the `FMT_USE_CONSTEVAL=0` branch of its config chain. Widening
# the existing Apple-clang branch to drop the `< 14000029L` upper bound
# adds Xcode 26.x to that broken-list and falls back to fmt's constexpr
# path, which compiles cleanly. Notes:
#
# - An xcconfig `GCC_PREPROCESSOR_DEFINITIONS = FMT_USE_CONSTEVAL=0`
# alone does NOT work: fmt's chain in `base.h:113-132` has no
# `#ifndef FMT_USE_CONSTEVAL` guard and unconditionally redefines the
# macro to `1` on any compiler that sets `__cpp_consteval`. Patching
# the source is the only path that survives the preprocessor.
# - Long-term fix is a fmt 11.1+ bump (fmt's own upstream addressed the
# stricter-eval interaction there). This `sed` is the minimal,
# reversible workaround until that lands.
spec.prepare_command = <<-CMD
/usr/bin/sed -i.bak 's|defined(__apple_build_version__) && __apple_build_version__ < 14000029L|defined(__apple_build_version__)|' include/fmt/base.h
CMD
spec.pod_target_xcconfig = {
"CLANG_CXX_LANGUAGE_STANDARD" => rct_cxx_language_standard(),
"GCC_WARN_INHIBIT_ALL_WARNINGS" => "YES" # Disable warnings because we don't control this library
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