Fix macOS build failure with GCC 15#2095
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Defining _XOPEN_SOURCE on Darwin lowers __DARWIN_C_LEVEL, hiding quick_exit/at_quick_exit. GCC 15's libstdc++ <cstdlib> unconditionally does 'using ::quick_exit;', which fails to compile when those symbols are hidden. Defining _DARWIN_C_SOURCE alongside _XOPEN_SOURCE restores full Darwin visibility while keeping the POSIX/SUSv2 definitions cctz needs elsewhere. Scoped to __APPLE__ only; no effect on other platforms. Fixes abseil#2027
…EN_SOURCE" This reverts commit c7f471f.
…PEN_SOURCE" This reverts commit 5b123e1.
Contributor
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This code is forked from https://github.com/google/cctz, can you please open a PR there? |
Contributor
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This also seems like maybe the fix to google/cctz#265 was just too wide? Could we just add Apple to the exclusion list? The original issue was to fix a problem in QNX |
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Thanks for the guidance — opened google/cctz#343 with the narrower Closing this PR since the fix belongs upstream. Per devbww's note on |
Contributor
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If everything goes smoothly it shouldn't take more than a few days :) |
mkruskal-google
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Jun 29, 2026
* Exclude Apple platforms from _XOPEN_SOURCE definition _XOPEN_SOURCE 500 was added in #266 to fix a QNX-specific compile error. On Apple platforms, defining it lowers __DARWIN_C_LEVEL, hiding C11 additions like quick_exit/at_quick_exit. GCC 15's libstdc++ <cstdlib> unconditionally re-exports these symbols, which fails to compile when they're hidden by this macro. Add __APPLE__ to the existing exclusion list alongside FreeBSD and OpenBSD, consistent with how those platforms are already handled. See abseil/abseil-cpp#2095 * Add temporary CI workflow to verify macOS GCC15 build * Fix CI workflow: use mkdir -p to avoid build dir conflict * Fix CI workflow: rename build dir to avoid case-insensitive collision with Bazel BUILD file * Fix CI workflow: disable BUILD_TESTING to skip GTest/benchmark deps * Fix missing #endif causing unterminated #if compile error * Revert "Exclude Apple platforms from _XOPEN_SOURCE definition" This reverts commit 3ae438d. * Reapply "Exclude Apple platforms from _XOPEN_SOURCE definition" This reverts commit 433ab0e. * Remove temporary CI verification workflow
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Fixes #2027
Problem
Building Abseil on macOS with Homebrew GCC 15 fails with:
error: 'quick_exit' has not been declared in '::'error: 'at_quick_exit' has not been declared in '::'Root cause
_XOPEN_SOURCE 500, defined intime_zone_format.ccto expose SUSv2/POSIXdefinitions, lowers
__DARWIN_C_LEVELon Darwin, hiding C11 additions likequick_exit/at_quick_exit. GCC 15's libstdc++<cstdlib>now unconditionallyre-exports these into the global namespace, which fails when the underlying
declarations are hidden.
Fix
Define
_DARWIN_C_SOURCEalongside_XOPEN_SOURCE, scoped to__APPLE__only,restoring both POSIX and C11 visibility on Darwin without affecting other
platforms (Linux/FreeBSD/OpenBSD behavior unchanged).
Testing
Verified with a CI workflow on a macos-latest runner + Homebrew GCC 15: