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Autoconf, through the [`AC_PROG_CC`][] macro (called by libtool's [`LT_INIT`][]), tries to detect whether the C compiler needs options to enable C11 support (we require a C11 compiler). Autoconf development branch now understand hows to enable MSVC C11 support ([bug report][1], [patch][2]), which defaults to a C99 dialect. The code to detect C11 has also been fixed in the dev branch. We may use ac_prog_cc_stdc when Autoconf 2.73 is released. Note that clang-cl defaults to C17. It would be unfair to use Autoconf tests for missing or buggy C11 features if MSVC is in C99 mode, so we have to add `-std:c11` or `-std:c17` to `CFLAGS`. Our Autoconf tests can now expect a C11 compiler by default. The best-effort MSVC handling code can be removed once we switch to Autoconf 2.73. It works even if the user overwrites the `CFLAGS`, potentially disabling C11. [`AC_PROG_CC`]: https://www.gnu.org/software/autoconf/manual/autoconf-2.72/html_node/C-Compiler.html#index-AC_005fPROG_0 05fCC-1 [`LT_INIT`]: https://www.gnu.org/software/libtool/manual/html_node/LT_005fINIT.html [1]: https://lists.gnu.org/archive/html/autoconf/2024-04/msg00001.html [2]: http://git.savannah.gnu.org/gitweb/?p=autoconf.git;a=commit;h=e9fee73dba5d2156abc48734b5a9faff89dcdc11
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Autoconf, through the
AC_PROG_CCmacro (called by libtool'sLT_INIT), tries to detect whether the C compiler needs options to enable C11 support (we require a C11 compiler).Autoconf development branch now understand hows to enable MSVC C11 support (bug report, patch), which defaults to a C99 dialect. Note that clang-cl defaults to C17.
It would be unfair to use Autoconf tests for missing or buggy C11 features if MSVC is in C99 mode, so we have to add
-std:c11or-std:c17toCFLAGS.We can already re-organize our tests to assume C11, and, until Autoconf 2.73 is used, we can enable MSVC' C11 support by default. As it is still possible for the user to mess up the
CFLAGS, we can keep a convenience fallback re-enabling C11 in case it was disabled. I'm tempted to remove this fallback altogether (for instance, if the user inadvertently disables C11, Autoconf tests will use the C99 compiler until the fallback re-enabling C11 is reached…).The first and last commit should be reverted once we'll use Autoconf 2.73.
No change entry needed.