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fix(ios): force fmt 12.1.0 in the example so it compiles on Xcode 26.4+ #349

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mfazekas merged 1 commit into from
Jul 17, 2026
+24 −17
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fix(ios): force fmt 12.1.0 in the example so it compiles on Xcode 26.4+ #349

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41 changes: 24 additions & 17 deletions example/ios/Podfile
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,30 @@ require Pod::Executable.execute_command('node', ['-p',
platform :ios, min_ios_version_supported
prepare_react_native_project!

# fmt `consteval` build error on Xcode 26.4+ (Apple clang 21): RN 0.80's bundled fmt 11.0.2
# fails to compile (expo/expo#44229, facebook/react-native#55601), and it predates both the
# FMT_USE_CONSTEVAL escape hatch (fmt 11.1) and the real code fix (fmt 12.x, shipped with
# RN 0.83+). Force fmt 12.1.0 — the exact version RN 0.86 ships — by rewriting the vendored
# podspecs before dependency resolution (RCT-Folly exact-pins fmt, so its podspec must be
# relaxed too). Re-runs on every `pod install`, so it survives `yarn install` re-extraction.
# Drop this once the example is on RN >= 0.83.
rn_podspecs = File.expand_path('../node_modules/react-native/third-party-podspecs', __dir__)
{
'fmt.podspec' => [['"11.0.2"', '"12.1.0"']],
'RCT-Folly.podspec' => [['spec.dependency "fmt", "11.0.2"', 'spec.dependency "fmt", "12.1.0"']],
}.each do |file, subs|
path = File.join(rn_podspecs, file)
contents = File.read(path)
patched = subs.reduce(contents) { |c, (from, to)| c.gsub(from, to) }
if patched != contents
File.write(path, patched)
Pod::UI.puts "Forced fmt 12.1.0 in #{file} (Xcode 26.4+ consteval fix)".green
end
# CocoaPods reuses cached podspec JSONs even when the .podspec changed underneath it
cached = File.join(__dir__, 'Pods', 'Local Podspecs', "#{file}.json")
File.delete(cached) if File.exist?(cached) && File.read(cached).include?('11.0.2')
end

linkage = ENV['USE_FRAMEWORKS']
if linkage != nil
Pod::UI.puts "Configuring Pod with #{linkage}ally linked Frameworks".green
Expand All @@ -34,22 +58,5 @@ target 'RiveExample' do
# :ccache_enabled => true
)

# fmt `consteval` build error on Xcode 26.4+ (Apple clang 21): the compiler rejects
# fmt's compile-time FMT_STRING (basic_format_string's consteval ctor) as a
# non-constant-expression. Disable fmt's consteval path via FMT_USE_CONSTEVAL=0 while
# keeping C++20 — this is the interim workaround Expo recommends (expo/expo#44229) and
# mirrors what fmt itself does for broken-consteval compilers (fmt/base.h sets
# FMT_USE_CONSTEVAL 0 for e.g. Apple clang < 14). Preferred over compiling the fmt pod as
# C++17 because it keeps the whole graph on a single C++ standard. Real fix is upstream in
# React Native 0.83+ (fmtlib/fmt#4740, facebook/react-native#55601); remove once we bump.
installer.pods_project.targets.each do |target|
next unless target.name == 'fmt'
target.build_configurations.each do |bc|
defs = bc.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] || ['$(inherited)']
defs = [defs] unless defs.is_a?(Array)
defs << 'FMT_USE_CONSTEVAL=0' unless defs.include?('FMT_USE_CONSTEVAL=0')
bc.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] = defs
end
end
end
end
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