Re: [PATCH] config.mak.dev: suppress C11 extension warning for Clang on Linux

[Junio C Hamano <gitster@pobox.com>]

Pablo <pabloosabaterr@gmail.com> writes:

> El jue, 7 may 2026 a las 4:16, Shardul Natu via GitGitGadget
> (<gitgitgadget@gmail.com>) escribió:
>>
>> From: Shnatu <snatu@google.com>
>>
>> When building Git with Clang on Linux with DEVELOPER=1, the build fails
>> because Clang treats C11 features used in glibc headers as extensions
>> and raises errors due to -std=gnu99, -pedantic, and -Werror.
>
> Hi Shnatu!
> This is already being discussed at:
> https://lore.kernel.org/git/20260505-b4-pks-ci-tolerate-glibc-generic-v1-1-5786386fe512@pks.im/T/#u
>
> You might want to check out that thread.
>
> Hope this helps,

Yes, they aim to solve the same issue, but the approach taken by
this patch to use -Wno-c11-extensions on clang may be with less
damage than the other approach that drops -std=gnu99 from Makefile.

The other approach uses the equivalent of this patch on the meson
side, so it may be doubly so that we should use -Wno-c11-extensions
on both build systems, no?


>> Specifically, glibc's string.h uses _Generic (a C11 feature) in macros
>> like strchr. When these macros are expanded in Git's C files, Clang
>> warns about them being C11 extensions.
>>
>> GCC does not exhibit this behavior because it suppresses pedantic
>> warnings for macros defined in system headers.
>>
>> To fix this, add -Wno-c11-extensions to DEVELOPER_CFLAGS when using
>> Clang, but restrict it to Linux (uname_S == Linux). This suppresses
>> the warning for glibc headers while keeping the build strict on other
>> platforms (like macOS) to catch accidental C11 usage in Git's own code.
>>
>> Signed-off-by: Shnatu <snatu@google.com>
>> ---
>>     config.mak.dev: suppress C11 extension warning for Clang on Linux
>>
>> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2291%2Fkiranani%2Fnext-2-v1
>> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2291/kiranani/next-2-v1
>> Pull-Request: https://github.com/git/git/pull/2291
>>
>>  config.mak.dev | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/config.mak.dev b/config.mak.dev
>> index c8dcf78779..f1dcf4329a 100644
>> --- a/config.mak.dev
>> +++ b/config.mak.dev
>> @@ -87,6 +87,9 @@ endif
>>  # The bug was fixed in Apple clang 12.
>>  #
>>  ifneq ($(filter clang1,$(COMPILER_FEATURES)),)     # if we are using clang
>> +ifeq ($(uname_S),Linux)
>> +DEVELOPER_CFLAGS += -Wno-c11-extensions
>> +endif
>>  ifeq ($(uname_S),Darwin)                           # if we are on darwin
>>  ifeq ($(filter clang12,$(COMPILER_FEATURES)),)     # if version < 12
>>  DEVELOPER_CFLAGS += -Wno-missing-braces
>>
>> base-commit: 4f69b47b940100b02630f745a52f9d9850f122b2
>> --
>> gitgitgadget
>>