Xcode 26.4b1/b2/b3/RC • FMT Compile Errors (it needs upgrading) • REPRO **IS** included despite the erroneous label

Description

FMT needs upgrading so that it will compile with Xcode 26.4b1.

I modified the FMT and RCT-Folly pod specs to use 12.1.0 and the compilation succeeded.

I am not 100% sure but I'm suspecting this fmtlib/fmt#4065 may be the fix for the problem.

We currently depend on the legacy architecture so would be hoping this fix would qualify for an 0.81.x release.

NOTE: I did not need to fork the reproducer or use as a template because no changes were required to produce the problem.

Steps to reproduce

npm install
cd ReproducerApp/ios
pod install
DEVELOPER_DIR=/Applications/Xcode\ 26.4b1.app/Contents/Developer/ xed .
Select the simulator and build

React Native Version

0.83.1

Affected Platforms

Build - MacOS

Output of `npx @react-native-community/cli info`

brettbest@Bretts-MacBook-Pro ~/D/r/ReproducerApp (main)> DEVELOPER_DIR=/Applications/Xcode\ 26.4b1.app/Contents/Developer/ npx @react-native-community/cli info
info Fetching system and libraries information...
System:
  OS: macOS 26.4
  CPU: (12) arm64 Apple M2 Pro
  Memory: 144.23 MB / 16.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 24.13.0
    path: /Users/brettbest/.local/share/mise/installs/node/24.13.0/bin/node
  Yarn:
    version: 1.22.22
    path: /opt/homebrew/bin/yarn
  npm:
    version: 11.6.2
    path: /Users/brettbest/.local/share/mise/installs/node/24.13.0/bin/npm
  Watchman:
    version: 2026.01.12.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /opt/homebrew/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 25.4
      - iOS 26.4
      - macOS 26.4
      - tvOS 26.4
      - visionOS 26.4
      - watchOS 26.4
  Android SDK: Not Found
IDEs:
  Android Studio: Not Found
  Xcode:
    version: 26.4/17E5159k
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 25.0.2
    path: /opt/homebrew/opt/openjdk/bin/javac
  Ruby:
    version: 3.3.0
    path: /Users/brettbest/.local/share/mise/installs/ruby/3.3.0/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 20.0.0
    wanted: 20.0.0
  react:
    installed: 19.2.0
    wanted: 19.2.0
  react-native:
    installed: 0.83.1
    wanted: 0.83.1
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: true
  newArchEnabled: true

info React Native v0.84.0 is now available (your project is running on v0.83.1).
info Changelog: https://github.com/facebook/react-native/releases/tag/v0.84.0
info Diff: https://react-native-community.github.io/upgrade-helper/?from=0.83.1&to=0.84.0
info For more info, check out "https://reactnative.dev/docs/upgrading?os=macos".

Stacktrace or Logs

/Users/brettbest/Developer/reproducer-react-native/ReproducerApp/ios/Pods/fmt/include/fmt/format-inl.h:59:24 Call to consteval function 'fmt::basic_format_string<char, fmt::basic_string_view<char> &, const char (&)[3]>::basic_format_string<FMT_COMPILE_STRING, 0>' is not a constant expression

/Users/brettbest/Developer/reproducer-react-native/ReproducerApp/ios/Pods/fmt/include/fmt/format-inl.h:60:22 Call to consteval function 'fmt::basic_format_string<char, const char (&)[7], int &>::basic_format_string<FMT_COMPILE_STRING, 0>' is not a constant expression

/Users/brettbest/Developer/reproducer-react-native/ReproducerApp/ios/Pods/fmt/include/fmt/format-inl.h:1387:35 Call to consteval function 'fmt::basic_format_string<char, unsigned int &>::basic_format_string<FMT_COMPILE_STRING, 0>' is not a constant expression

/Users/brettbest/Developer/reproducer-react-native/ReproducerApp/ios/Pods/fmt/include/fmt/format-inl.h:1391:33 Call to consteval function 'fmt::basic_format_string<char, unsigned int &>::basic_format_string<FMT_COMPILE_STRING, 0>' is not a constant expression

/Users/brettbest/Developer/reproducer-react-native/ReproducerApp/ios/Pods/fmt/include/fmt/format-inl.h:1394:33 Call to consteval function 'fmt::basic_format_string<char, int>::basic_format_string<FMT_COMPILE_STRING, 0>' is not a constant expression

MANDATORY Reproducer

https://github.com/Brett-Best/rn-fmt-reproducer

Screenshots and Videos

RCT_USE_PREBUILT_RNCORE=0 RCT_USE_RN_DEP=0 bundle exec pod install

I have used the latest template and using the above modification to my original steps the issue reproduces.

https://github.com/Brett-Best/rn-fmt-reproducer-v2 (no changes needed)

@leotm

@leotm I cloned the latest react native commit down and did the following:

yarn install
node scripts/releases/prepare-ios-prebuilds.js -s
node scripts/releases/prepare-ios-prebuilds.js -w
node scripts/releases/prepare-ios-prebuilds.js -b -p ios-simulator -r debug

In the output you can find FMT fails to compile:

In file included from /Users/brettbest/Developer/react-native/packages/react-native/third-party/fmt/target/src/format.cc:8:
/Users/brettbest/Developer/react-native/packages/react-native/third-party/fmt/target/include/fmt/format-inl.h:1387:35: error: call to consteval function 'fmt::basic_format_string<char, unsigned int
      &>::basic_format_string<FMT_COMPILE_STRING, 0>' is not a constant expression
 1387 |         out = fmt::format_to(out, FMT_STRING("{:x}"), value);

I derived the steps from https://github.com/facebook/react-native/blob/972a30db4ce19609dddc8553afc2c2c2844e5442/.github/workflows/prebuild-ios-dependencies.yml.

It also looks like the Xcode version is determined by using https://github.com/facebook/react-native/blob/972a30db4ce19609dddc8553afc2c2c2844e5442/.github/workflows/prebuild-ios-dependencies.yml#L74-L76 and then which appears to be https://github.com/facebook/react-native/blob/972a30db4ce19609dddc8553afc2c2c2844e5442/.github/actions/setup-xcode/action.yml#L7

I wasn't actually able to find any run of that workflow but might've been looking in the wrong place.

However, I was able to verify that the prebuilds for RN 0.84.1 which come from here are built with Xcode 16.4.

This can be checked by looking at rn-fmt-reproducer-v2/ReproducerApp/ios/Pods/ReactNativeDependencies/framework/packages/react-native/ReactNativeDependencies.xcframework/ios-arm64/ReactNativeDependencies.framework/Info.plist and the DTXcode/DTXcodeBuild keys.

Xcode 16.4 was released almost a year ago on 27 May 2025 and doesn't use the latest SDK.

RCT_USE_PREBUILT_RNCORE=0 RCT_USE_RN_DEP=0

thanks can repro via the full opt-out

:::info
If you need to build React Native from source (for example, to opt out of Hermes V1), you can disable precompiled binaries by setting RCT_USE_PREBUILT_RNCORE=0 when installing pods.
:::

https://reactnative.dev/blog/2026/02/11/react-native-0.84#precompiled-binaries-on-ios-by-default

was only partially opting out 🙈 oops

RCT_USE_PREBUILT_RNCORE=0 ... Removing React-Core-prebuilt
RCT_USE_PREBUILT_RNCORE=0 RCT_USE_RN_DEP=0 ... Removing ReactNativeDependencies
clear in the Podfile.lock diff

looks like RCT_USE_RN_DEP was mentioned after all in the full opt-in earlier
https://reactnative.dev/blog/2025/12/10/react-native-0.83#experimental---debug-your-precompiled-binaries-on-ios

can see what's going on now w the flags
https://github.com/facebook/react-native/blob/main/packages/react-native/scripts/ios-prebuild/__docs__/README.md
https://github.com/facebook/react-native/blob/main/packages/react-native/scripts/cocoapods/rncore.rb
https://github.com/facebook/react-native/blob/main/packages/react-native/scripts/react_native_pods.rb
https://github.com/facebook/react-native/blob/main/packages/react-native/scripts/cocoapods/rndependencies.rb

the FMT bump (direct or via RCT-Folly) makes sense

Bump fmt to 12.1.0 to fix xcode 26.4 (react#56099)

Bump fmt to 12.1.0 to fix xcode 26.4 (#56099)

@leotm

@leotm thanks for fixing this. Will patch versions to RN 82, 83 and 84 be released soon? 🙏

i usd last version react native 0.84, and i get this error on my xcode, it is after update my xcode to last version. After this moment i try to start project with version 0.83.2 and i get this error too.

I had a big task to complete, but for some reason I decided to update my Xcode, and after that, my projects won't launch. Since the company I work for is downsizing, I'll likely be fired simply because my projects won't launch((

Also, for some reason xcworkspace won't launch for me. GG WP

@alexeevayaan

This patch might do the trick for now:

diff --git a/node_modules/react-native/third-party-podspecs/RCT-Folly.podspec b/node_modules/react-native/third-party-podspecs/RCT-Folly.podspec
index 8852179..040c4f0 100644
--- a/node_modules/react-native/third-party-podspecs/RCT-Folly.podspec
+++ b/node_modules/react-native/third-party-podspecs/RCT-Folly.podspec
@@ -25,7 +25,7 @@ Pod::Spec.new do |spec|
   spec.dependency "DoubleConversion"
   spec.dependency "glog"
   spec.dependency "fast_float", "8.0.0"
-  spec.dependency "fmt", "11.0.2"
+  spec.dependency "fmt", "12.1.0"
   spec.compiler_flags = '-Wno-documentation -faligned-new'
   spec.source_files = 'folly/String.cpp',
                       'folly/Conv.cpp',
diff --git a/node_modules/react-native/third-party-podspecs/fmt.podspec b/node_modules/react-native/third-party-podspecs/fmt.podspec
index 2f38990..a40c575 100644
--- a/node_modules/react-native/third-party-podspecs/fmt.podspec
+++ b/node_modules/react-native/third-party-podspecs/fmt.podspec
@@ -8,14 +8,14 @@ fmt_git_url = fmt_config[:git]
 
 Pod::Spec.new do |spec|
   spec.name = "fmt"
-  spec.version = "11.0.2"
+  spec.version = "12.1.0"
   spec.license = { :type => "MIT" }
   spec.homepage = "https://github.com/fmtlib/fmt"
   spec.summary = "{fmt} is an open-source formatting library for C++. It can be used as a safe and fast alternative to (s)printf and iostreams."
   spec.authors = "The fmt contributors"
   spec.source = {
     :git => fmt_git_url,
-    :tag => "11.0.2"
+    :tag => "12.1.0"
   }
   spec.pod_target_xcconfig = {
     "CLANG_CXX_LANGUAGE_STANDARD" => rct_cxx_language_standard(),

I'm still testing it out, but sharing it now as I don't want @alexeevayaan to get fired...

Hey, I currently use slightly extended patch, to include the Android change from the original fix. I tested on both XCode 26.4, 26.3, Android studio using both dev and prod builds, and everything looks correct.

diff --git a/node_modules/react-native/third-party-podspecs/RCT-Folly.podspec b/node_modules/react-native/third-party-podspecs/RCT-Folly.podspec
index 8852179..040c4f0 100644
--- a/node_modules/react-native/third-party-podspecs/RCT-Folly.podspec
+++ b/node_modules/react-native/third-party-podspecs/RCT-Folly.podspec
@@ -25,7 +25,7 @@ Pod::Spec.new do |spec|
   spec.dependency "DoubleConversion"
   spec.dependency "glog"
   spec.dependency "fast_float", "8.0.0"
-  spec.dependency "fmt", "11.0.2"
+  spec.dependency "fmt", "12.1.0"
   spec.compiler_flags = '-Wno-documentation -faligned-new'
   spec.source_files = 'folly/String.cpp',
                       'folly/Conv.cpp',
diff --git a/node_modules/react-native/third-party-podspecs/fmt.podspec b/node_modules/react-native/third-party-podspecs/fmt.podspec
index 2f38990..765acce 100644
--- a/node_modules/react-native/third-party-podspecs/fmt.podspec
+++ b/node_modules/react-native/third-party-podspecs/fmt.podspec
@@ -3,19 +3,23 @@
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.

+# PATCHED: bumped fmt 11.0.2 → 12.1.0 to fix Xcode 26.4 consteval build failure (Clang 22).
+# See: https://github.com/facebook/react-native/issues/55601
+# Remove this patch when React Native updates fmt to 12.1.0 or later.
+
 fmt_config = get_fmt_config()
 fmt_git_url = fmt_config[:git]

 Pod::Spec.new do |spec|
   spec.name = "fmt"
-  spec.version = "11.0.2"
+  spec.version = "12.1.0"
   spec.license = { :type => "MIT" }
   spec.homepage = "https://github.com/fmtlib/fmt"
   spec.summary = "{fmt} is an open-source formatting library for C++. It can be used as a safe and fast alternative to (s)printf and iostreams."
   spec.authors = "The fmt contributors"
   spec.source = {
     :git => fmt_git_url,
-    :tag => "11.0.2"
+    :tag => "12.1.0"
   }
   spec.pod_target_xcconfig = {
     "CLANG_CXX_LANGUAGE_STANDARD" => rct_cxx_language_standard(),
diff --git a/node_modules/react-native/gradle/libs.versions.toml b/node_modules/react-native/gradle/libs.versions.toml
index f0902b7..cb88f66 100644
--- a/node_modules/react-native/gradle/libs.versions.toml
+++ b/node_modules/react-native/gradle/libs.versions.toml
@@ -43,7 +43,7 @@ yoga-proguard-annotations = "1.19.0"
 boost="1_83_0"
 doubleconversion="1.1.6"
 fastFloat="8.0.0"
-fmt="11.0.2"
+fmt="12.1.0"
 folly="2024.11.18.00"
 glog="0.3.5"
 gflags="2.2.0"

I added a fix to my Podfile to get around this.

# Workaround for Xcode 26: newer Apple Clang breaks consteval in fmt 11.0.2.

# Patch base.h to disable consteval since the header doesn't check for pre-defined FMT_USE_CONSTEVAL.

fmt_base = File.join(installer.sandbox.root, 'fmt', 'include', 'fmt', 'base.h')

if File.exist?(fmt_base)
 content = File.read(fmt_base)
  unless content.include?('Xcode 26 workaround')
    patched = content.gsub(
      /^(#elif defined\(__cpp_consteval\)\n#  define FMT_USE_CONSTEVAL) 1/,
      "// Xcode 26 workaround: disable consteval\n\\1 0"
    )
    if patched != content
      File.chmod(0644, fmt_base)
      File.write(fmt_base, patched)
    end
  end
end

For those on RN 0.83.x who can't upgrade to 0.84 yet, here's a minimal patch-package workaround that adds a prepare_command to the fmt.podspec to disable consteval in base.h:

diff --git a/node_modules/react-native/third-party-podspecs/fmt.podspec b/node_modules/react-native/third-party-podspecs/fmt.podspec
index 2f38990..9b02e48 100644
--- a/node_modules/react-native/third-party-podspecs/fmt.podspec
+++ b/node_modules/react-native/third-party-podspecs/fmt.podspec
@@ -26,4 +26,11 @@ Pod::Spec.new do |spec|
   spec.public_header_files = "include/fmt/*.h"
   spec.header_mappings_dir = "include"
   spec.source_files = ["include/fmt/*.h", "src/format.cc"]
+
+  # TODO: Remove after upgrading React Native past 0.83.x
+  # Fix fmt 11.0.2 consteval build error with Xcode 26.4 (facebook/react-native#55601)
+  # Fixed in RN 0.84+ which bumps fmt to a compatible version.
+  spec.prepare_command = <<~SCRIPT
+    perl -i -pe 's/^#  define FMT_USE_CONSTEVAL 1$/#  define FMT_USE_CONSTEVAL 0/' include/fmt/base.h
+  SCRIPT
 end

Save as patches/react-native+0.83.4.patch (adjust version as needed), then:

cd ios && rm -rf Pods/fmt Pods/Local\ Podspecs/fmt.podspec.json && pod install

This sets FMT_USE_CONSTEVAL to 0, which disables consteval in fmt's base.h. Only compile-time format string validation is affected (moves to runtime constexpr path) — no runtime behavior change for valid format strings.

Tested with Xcode 26.4 + RN 0.83.4.

for react native 0.80.0 what is the exact solution for this problem where my macos v is 26.4

I added a fix to my Podfile to get around this.

# Workaround for Xcode 26: newer Apple Clang breaks consteval in fmt 11.0.2.

# Patch base.h to disable consteval since the header doesn't check for pre-defined FMT_USE_CONSTEVAL.

fmt_base = File.join(installer.sandbox.root, 'fmt', 'include', 'fmt', 'base.h')

if File.exist?(fmt_base)
 content = File.read(fmt_base)
  unless content.include?('Xcode 26 workaround')
    patched = content.gsub(
      /^(#elif defined\(__cpp_consteval\)\n#  define FMT_USE_CONSTEVAL) 1/,
      "// Xcode 26 workaround: disable consteval\n\\1 0"
    )
    if patched != content
      File.chmod(0644, fmt_base)
      File.write(fmt_base, patched)
    end
  end
end

This worked for me. Thanks

I added a fix to my Podfile to get around this.

# Workaround for Xcode 26: newer Apple Clang breaks consteval in fmt 11.0.2.

# Patch base.h to disable consteval since the header doesn't check for pre-defined FMT_USE_CONSTEVAL.

fmt_base = File.join(installer.sandbox.root, 'fmt', 'include', 'fmt', 'base.h')

if File.exist?(fmt_base)
 content = File.read(fmt_base)
  unless content.include?('Xcode 26 workaround')
    patched = content.gsub(
      /^(#elif defined\(__cpp_consteval\)\n#  define FMT_USE_CONSTEVAL) 1/,
      "// Xcode 26 workaround: disable consteval\n\\1 0"
    )
    if patched != content
      File.chmod(0644, fmt_base)
      File.write(fmt_base, patched)
    end
  end
end

This worked for me. Thanks

your fix will work. but you will need to remember to remove it when you will upgrade react native.
My fix above using patch package ties the version and when you will upgrade, you will get a notification to remove the patch.

fix(ios): upgrade fmt to 12.1.0 for Xcode 26 compatibility

fix(ios): upgrade fmt to 12.1.0 for Xcode 26.4 compatibility (#10905)

Fix build issues when using Xcode 26.4

this fixed the issue for me

installer.pods_project.targets.each do |target|
      target.build_configurations.each do |config|

        # fmt/base.h unconditionally redefines FMT_USE_CONSTEVAL based on __cplusplus,
        # so preprocessor defines are overwritten. The reliable fix is to compile fmt
        # in C++17 mode: FMT_CPLUSPLUS (201703L) < 201709L → FMT_USE_CONSTEVAL = 0.
        # All other pods stay in C++20 (React-perflogger needs std::unordered_map::contains).

        if target.name == 'fmt'
          config.build_settings['CLANG_CXX_LANGUAGE_STANDARD'] = 'c++17'
        end
        
      end
    end

fix(ios): upgrade fmt to 12.1.0 for Xcode 26.4 compatibility (#10905)

@leotm thanks for fixing this. Will patch versions to RN 82, 83 and 84 be released soon? 🙏

0.83 likely yes (active support), 0.81 likely no (unsupported)

We accepts pick requests only for versions of React Native that are currently supported
The release crew evaluates each pick on a case-by-case basis
The release crew have a lot of flexibility so long as they feel the change would significantly improve the quality or stability of a version of React Native

if we feel the latter, i've opened pick requests for 0.82 (end of cycle, unsupported 2026-04-06) and 0.84 (active support)

otherwise already picked for v0.85.0-rc.6 and i verified in one of the latest 0.86 nightlies

full details in the support policy and feel free to keep track of things here

@roidayan1

I solved it that way on 0.81.6:

linkage = ENV['USE_FRAMEWORKS']
if linkage != nil
  Pod::UI.puts "Configuring Pod with #{linkage}ally linked Frameworks".green
  use_frameworks! :linkage => linkage.to_sym
end

# Bumpt fmt version to 12.1.0 to avoid build failure with Xcode 26.4+
# Patch both fmt.podspec and RCT-Folly.podspec before CocoaPods resolves dependencies
# TODO: remove after updating RN
fmt_podspec_path = File.join(__dir__, '..', 'node_modules', 'react-native', 'third-party-podspecs', 'fmt.podspec')
folly_podspec_path = File.join(__dir__, '..', 'node_modules', 'react-native', 'third-party-podspecs', 'RCT-Folly.podspec')

if File.exist?(fmt_podspec_path)
  fmt_content = File.read(fmt_podspec_path)
  fmt_content.gsub!('"11.0.2"', '"12.1.0"')
  File.write(fmt_podspec_path, fmt_content)
end

if File.exist?(folly_podspec_path)
  folly_content = File.read(folly_podspec_path)
  folly_content.gsub!('spec.dependency "fmt", "11.0.2"', 'spec.dependency "fmt", "12.1.0"')
  File.write(folly_podspec_path, folly_content)
end

target 'xyz' do

but like the patch from @roidayan1 better :) Thanks.

RN 0.78.3 helped

# TODO: remove it later
# Bump fmt version to 12.1.0 to avoid build failure with Xcode 16.4+
# Patch all react-native podspecs that pin fmt to 11.0.2 before CocoaPods resolves dependencies
rn_path = File.join(__dir__, '..', 'node_modules', 'react-native')
Dir.glob(File.join(rn_path, '**', '*.podspec')).each do |podspec_path|
  content = File.read(podspec_path)
  if content.include?('"fmt", "11.0.2"') || (podspec_path.end_with?('fmt.podspec') && content.include?('"11.0.2"'))
    content.gsub!('"fmt", "11.0.2"', '"fmt", "12.1.0"')
    content.gsub!(/"11\.0\.2"/, '"12.1.0"') if podspec_path.end_with?('fmt.podspec')
    File.write(podspec_path, content)
  end
end

fix: Xcode 26 fmt consteval 빌드 에러 우회

Fix Xcode 26 fmt consteval build failure with Podfile patch

fix(mobile): add Expo Config Plugin for fmt Xcode 26 fix

Bump fmt to 12.1.0 to fix xcode 26.4 (#56099)

rn: 0.81.4
xcode: 26.4
AI fixed with adding this on Podfile;

   installer.pods_project.targets.each do |target|
      if target.name == 'fmt'
        target.build_configurations.each do |config|
          config.build_settings['CLANG_CXX_LANGUAGE_STANDARD'] = 'c++17'
        end
      end
    end

But i think i need to upgrade rn.

feat: Apple Sign In対応 & iOS 1.0.1 (build 2) & build/を.gitignoreへ追加

chore(examples): patch fmt consteval for Xcode 26.4 in example-expo-53 (

Fix iOS build on Xcode 26.4: force fmt pod to C++17

Fix iOS build on Xcode 26.4 and lift CI Xcode cap (#841)

rn: 0.81.4 xcode: 26.4 AI fixed with adding this on Podfile;

   installer.pods_project.targets.each do |target|
      if target.name == 'fmt'
        target.build_configurations.each do |config|
          config.build_settings['CLANG_CXX_LANGUAGE_STANDARD'] = 'c++17'
        end
      end
    end

But i think i need to upgrade rn.

I tried this, then build work fine :)

post_install do |installer|
    # Fix fmt 11.0.2 consteval errors with Xcode 26 / Clang 17+.
    # base.h unconditionally `#define`s FMT_USE_CONSTEVAL inside its detection
    # chain, so a -D flag is overwritten. Patch the header to force it to 0.
    fmt_base_h = "#{Pod::Config.instance.installation_root}/Pods/fmt/include/fmt/base.h"
    if File.exist?(fmt_base_h)
      text = File.read(fmt_base_h)
      marker = '// FMT_USE_CONSTEVAL override for Xcode 26 / Clang 17+'
      if text.include?(marker)
        puts "ℹ️ fmt/base.h already patched"
      else
        needle = "#if FMT_USE_CONSTEVAL\n#  define FMT_CONSTEVAL consteval"
        raise "fmt/base.h structure unexpected; cannot patch FMT_USE_CONSTEVAL" unless text.include?(needle)
        replacement = "#{marker}\n#undef FMT_USE_CONSTEVAL\n#define FMT_USE_CONSTEVAL 0\n#{needle}"
        File.write(fmt_base_h, text.sub(needle, replacement))
        puts "🔧 Patched fmt/base.h to force FMT_USE_CONSTEVAL=0"
      end
    else
      puts "ℹ️ fmt/base.h not found (skipping consteval patch)"
    end
end

Fix fmt consteval build error with Xcode 26 (Apple Clang 17+)

fix(bare-rn/ios): force C++17 on fmt/RCT-Folly pods to dodge consteva…

Feat/android 15 upgrade (#171)

fix(ios): fmt consteval patch only on Xcode 26.4+

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Xcode 26.4b1/b2/b3/RC • FMT Compile Errors (it needs upgrading) • REPRO IS included despite the erroneous label #55601

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React Native Version

Affected Platforms

Output of `npx @react-native-community/cli info`

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Xcode 26.4b1/b2/b3/RC • FMT Compile Errors (it needs upgrading) • REPRO **IS** included despite the erroneous label #55601

Description

Description

Steps to reproduce

React Native Version

Affected Platforms

Output of npx @react-native-community/cli info

Stacktrace or Logs

MANDATORY Reproducer

Screenshots and Videos

Activity

Brett-Best commented on Mar 13, 2026

Brett-Best commented on Mar 13, 2026

leotm commented on Mar 14, 2026

jenskuhrjorgensen commented on Mar 25, 2026

alexeevayaan commented on Mar 25, 2026

alexeevayaan commented on Mar 25, 2026

alexeevayaan commented on Mar 25, 2026

jenskuhrjorgensen commented on Mar 25, 2026

vladimirivanoviliev commented on Mar 25, 2026

chrisbeaver commented on Mar 25, 2026

roidayan1 commented on Mar 26, 2026

Maanooz18 commented on Mar 26, 2026

StaniEbo commented on Mar 26, 2026

roidayan1 commented on Mar 26, 2026

Diaa-Ghonim commented on Mar 27, 2026

leotm commented on Mar 27, 2026

lorenc-tomasz commented on Mar 30, 2026

Iuriy-Budnikov commented on Apr 6, 2026

zhouxlin commented on Apr 15, 2026

ambadah commented on Apr 27, 2026

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Xcode 26.4b1/b2/b3/RC • FMT Compile Errors (it needs upgrading) • REPRO IS included despite the erroneous label #55601

Output of `npx @react-native-community/cli info`