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Commit3f302f0

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If a C23 compiler is detected, try asking for C17.
Branches before 16 can't be compiled with a C23 compiler (seedeprecation warnings silenced by commitf9a56e7, and non-back-patchablechanges made in 16 by commit1c27d16). Test __STDC_VERSION__, and ifit's above C17 then try appending -std=gnu17. The test is done with theuser's CFLAGS, so an acceptable language version can also be configuredmanually that way.This is done in branches 15 and older, back to 9.2, per policy ofkeeping them buildable with modern tools.Discussion:https://postgr.es/m/87o72eo9iu.fsf%40gentoo.org
1 parent15a89e2 commit3f302f0

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2 files changed

+97
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lines changed

2 files changed

+97
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‎configure

Lines changed: 77 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -5247,6 +5247,83 @@ else
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BITCODE_CXXFLAGS="-O2 $BITCODE_CXXFLAGS"
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fi
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# We use C constructs that became invalid in C23. Check if the compiler
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# reports a standard higher than C17, with the flags selected above (so the
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# user can control the language level explicitly to avoid the gcc/clang-only
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# fallback logic below if preferred).
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{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CC reports a C standard higher than ISO C17" >&5
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$as_echo_n "checking whether $CC reports a C standard higher than ISO C17... " >&6; }
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cat confdefs.h - <<_ACEOF >conftest.$ac_ext
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/* end confdefs.h. */
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int
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main ()
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{
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#if __STDC_VERSION__ > 201710L
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choke me
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#endif
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;
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return 0;
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}
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_ACEOF
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if ac_fn_c_try_compile "$LINENO"; then :
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POSTC17=no
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else
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POSTC17=yes
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fi
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rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
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{ $as_echo "$as_me:${as_lineno-$LINENO}: result: ${POSTC17}" >&5
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$as_echo "${POSTC17}" >&6; }
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# If a too recent standard was detected with the user's CFLAGS, try asking for
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# C17 with GNU extensions explicitly.
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if test "$POSTC17" = yes; then
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old_CFLAGS="$CFLAGS"
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{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -std=gnu17, for CFLAGS" >&5
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$as_echo_n "checking whether ${CC} supports -std=gnu17, for CFLAGS... " >&6; }
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if ${pgac_cv_prog_CC_cflags__std_gnu17+:} false; then :
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$as_echo_n "(cached) " >&6
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else
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pgac_save_CFLAGS=$CFLAGS
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pgac_save_CC=$CC
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CC=${CC}
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CFLAGS="${CFLAGS} -std=gnu17"
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ac_save_c_werror_flag=$ac_c_werror_flag
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ac_c_werror_flag=yes
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cat confdefs.h - <<_ACEOF >conftest.$ac_ext
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/* end confdefs.h. */
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int
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main ()
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{
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;
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return 0;
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}
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_ACEOF
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if ac_fn_c_try_compile "$LINENO"; then :
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pgac_cv_prog_CC_cflags__std_gnu17=yes
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else
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pgac_cv_prog_CC_cflags__std_gnu17=no
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fi
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rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
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ac_c_werror_flag=$ac_save_c_werror_flag
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CFLAGS="$pgac_save_CFLAGS"
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CC="$pgac_save_CC"
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fi
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{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CC_cflags__std_gnu17" >&5
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$as_echo "$pgac_cv_prog_CC_cflags__std_gnu17" >&6; }
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if test x"$pgac_cv_prog_CC_cflags__std_gnu17" = x"yes"; then
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CFLAGS="${CFLAGS} -std=gnu17"
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fi
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if test "$CFLAGS" = "$old_CFLAGS"; then
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as_fn_error $? "cannot proceed" "$LINENO" 5
5324+
fi
5325+
fi
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# C[XX]FLAGS we determined above will be added back at the end
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user_CFLAGS=$CFLAGS
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CFLAGS=""

‎configure.in

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Original file line numberDiff line numberDiff line change
@@ -452,6 +452,26 @@ else
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BITCODE_CXXFLAGS="-O2 $BITCODE_CXXFLAGS"
453453
fi
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# We use C constructs that became invalid in C23. Check if the compiler
456+
# reports a standard higher than C17, with the flags selected above (so the
457+
# user can control the language level explicitly to avoid the gcc/clang-only
458+
# fallback logic below if preferred).
459+
AC_MSG_CHECKING([whether $CC reports a C standard higher than ISO C17])
460+
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [@%:@if __STDC_VERSION__ > 201710L
461+
choke me
462+
@%:@endif])], [POSTC17=no], [POSTC17=yes])
463+
AC_MSG_RESULT(${POSTC17})
464+
465+
# If a too recent standard was detected with the user's CFLAGS, try asking for
466+
# C17 with GNU extensions explicitly.
467+
if test "$POSTC17" = yes; then
468+
old_CFLAGS="$CFLAGS"
469+
PGAC_PROG_CC_CFLAGS_OPT([-std=gnu17])
470+
if test "$CFLAGS" = "$old_CFLAGS"; then
471+
AC_MSG_ERROR([cannot proceed])
472+
fi
473+
fi
474+
455475
# C[XX]FLAGS we determined above will be added back at the end
456476
user_CFLAGS=$CFLAGS
457477
CFLAGS=""

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