Xcode 16 Homebrew GCC 14.2 breaks with CMake

Readme.md

With macOS 14.6 and 15.0, Xcode 16 breaks with CMake and Homebrew GCC 14.2.

The error is revealed in this simple project.

CXX=g++-14 cmake -Bbuild

cmake --build build

Workaround

The workaround is to specify SDKROOT so that CMake uses the compatible SDK with GCC 14.2, until Homebrew updates its platform environment. Create a file ~/gcc.sh and source ~/gcc.sh to use GCC:

export CC=gcc-14 CXX=g++-14 FC=gfortran-14

export SDKROOT=/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/

In general in my projects I have CMake print CMAKE_OSX_SYSROOT so when users run into an issue I can help them more quickly.

Configure output

-- The CXX compiler identification is GNU 14.2.0
-- Checking whether CXX compiler has -isysroot
-- Checking whether CXX compiler has -isysroot - yes
-- Checking whether CXX compiler supports OSX deployment target flag
-- Checking whether CXX compiler supports OSX deployment target flag - yes
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /opt/homebrew/bin/g++-14 - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- CMAKE_OSX_SYSROOT /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk

CMake build errors

Lots of build errors if using CMake, starting with:

/opt/homebrew/bin/g++-14   -O3 -DNDEBUG -arch arm64 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.0.sdk -fdiagnostics-color=always -MD -MT CMakeFiles/main.dir/main.cpp.o -MF CMakeFiles/main.dir/main.cpp.o.d -o CMakeFiles/main.dir/main.cpp.o -c d69faebbc56da9714798087b56de925a/main.cpp
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/_wchar.h:90,
                 from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/wchar.h:67,
                 from /opt/homebrew/Cellar/gcc/14.2.0/include/c++/14/cwchar:44,
                 from /opt/homebrew/Cellar/gcc/14.2.0/include/c++/14/bits/postypes.h:40,
                 from /opt/homebrew/Cellar/gcc/14.2.0/include/c++/14/iosfwd:42,
                 from /opt/homebrew/Cellar/gcc/14.2.0/include/c++/14/ios:40,
                 from /opt/homebrew/Cellar/gcc/14.2.0/include/c++/14/ostream:40,
                 from /opt/homebrew/Cellar/gcc/14.2.0/include/c++/14/iostream:41,
                 from d69faebbc56da9714798087b56de925a/main.cpp:1:
/opt/homebrew/Cellar/gcc/14.2.0/lib/gcc/current/gcc/aarch64-apple-darwin23/14/include-fixed/stdio.h:83:8: error: 'FILE' does not name a type
   83 | extern FILE *__stdinp;
      |        ^~~~
/opt/homebrew/Cellar/gcc/14.2.0/lib/gcc/current/gcc/aarch64-apple-darwin23/14/include-fixed/stdio.h:81:1: note: 'FILE' is defined in header '<cstdio>'; this is probably fixable by adding '#include <cstdio>'
   80 | #include <sys/_types/_seek_set.h>
  +++ |+#include <cstdio>
   81 |
/opt/homebrew/Cellar/gcc/14.2.0/lib/gcc/current/gcc/aarch64-apple-darwin23/14/include-fixed/stdio.h:84:8: error: 'FILE' does not name a type
   84 | extern FILE *__stdoutp;
      |        ^~~~
/opt/homebrew/Cellar/gcc/14.2.0/lib/gcc/current/gcc/aarch64-apple-darwin23/14/include-fixed/stdio.h:84:8: note: 'FILE' is defined in header '<cstdio>'; this is probably fixable by adding '#include <cstdio>'
/opt/homebrew/Cellar/gcc/14.2.0/lib/gcc/current/gcc/aarch64-apple-darwin23/14/include-fixed/stdio.h:85:8: error: 'FILE' does not name a type
   85 | extern FILE *__stderrp;

Regular command line is OK

g++-14 main.cpp -v

works, output ends with

 /opt/homebrew/Cellar/gcc/14.2.0/bin/../libexec/gcc/aarch64-apple-darwin23/14/collect2 -demangle -syslibroot /Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/ -dynamic -arch arm64 -platform_version macos 15.0.0 0.0 -o a.out -L/opt/homebrew/Cellar/gcc/14.2.0/bin/../lib/gcc/current/gcc/aarch64-apple-darwin23/14 -L/opt/homebrew/Cellar/gcc/14.2.0/bin/../lib/gcc/current/gcc -L/opt/homebrew/Cellar/gcc/14.2.0/bin/../lib/gcc/current/gcc/aarch64-apple-darwin23/14/../../.. -lemutls_w -lheapt_w /var/folders/dh/k7c2gppn12v3w0plnf_xz94c0000gn/T//ccarxhZd.o -lstdc++ -lgcc -lSystem -no_compact_unwind -rpath @loader_path -rpath /opt/homebrew/Cellar/gcc/14.2.0/lib/gcc/current/gcc/aarch64-apple-darwin23/14 -rpath /opt/homebrew/Cellar/gcc/14.2.0/lib/gcc/current/gcc -rpath /opt/homebrew/Cellar/gcc/14.2.0/lib/gcc/current

CMakeLists.txt

cmake_minimum_required(VERSION 3.20)

project(min LANGUAGES CXX)

message(STATUS "CMAKE_OSX_SYSROOT ${CMAKE_OSX_SYSROOT}")

foreach(i IN ITEMS OS_NAME OS_VERSION OS_RELEASE OS_PLATFORM)
  cmake_host_system_information(RESULT ${i} QUERY ${i})
  message(STATUS "${i}: ${${i}}")
endforeach()

add_executable(main main.cpp)

main.cpp

#include <iostream>

int main(){ return 0; }

@PKua007 Most likely this is the current issue on iains gcc-14 branch.
iains/gcc-14-branch#11

Not sure however who will take care to bring this to Homebrew as soon as fixed.