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If a C23 compiler is detected, try asking for C17.

Browse Source 
Branches before 16 can't be compiled with a C23 compiler (see
deprecation warnings silenced by commit f9a56e72, and non-back-patchable
changes made in 16 by commit 1c27d16e).  Test __STDC_VERSION__, and if
it's above C17 then try appending -std=gnu17.  The test is done with the
user's CFLAGS, so an acceptable language version can also be configured
manually that way.

This is done in branches 15 and older, back to 9.2, per policy of
keeping them buildable with modern tools.

Discussion: https://postgr.es/m/87o72eo9iu.fsf%40gentoo.org
This commit is contained in:
Thomas Munro 2024-11-27 15:43:18 +13:00
parent 1c41731169
commit 0c7171b32e
2 changed files with 144 additions and 0 deletions
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124
configure vendored
View File

@ -3975,6 +3975,130 @@ else
fi
fi
# We use C constructs that became invalid in C23. Check if the compiler
# reports a standard higher than C17, with the flags selected above (so the
# user can control the language level explicitly to avoid the gcc/clang-only
# fallback logic below if preferred).
{ $as_echo "$as_me:$LINENO: checking whether $CC reports a C standard higher than ISO C17" >&5
$as_echo_n "checking whether $CC reports a C standard higher than ISO C17... " >&6; }
cat >conftest.$ac_ext <<_ACEOF
/* confdefs.h. */
_ACEOF
cat confdefs.h >>conftest.$ac_ext
cat >>conftest.$ac_ext <<_ACEOF
/* end confdefs.h. */
int
main ()
{
#if __STDC_VERSION__ > 201710L
choke me
#endif
;
return 0;
}
_ACEOF
rm -f conftest.$ac_objext
if { (ac_try="$ac_compile"
case "(($ac_try" in
*\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
*) ac_try_echo=$ac_try;;
esac
eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
$as_echo "$ac_try_echo") >&5
(eval "$ac_compile") 2>conftest.er1
ac_status=$?
grep -v '^ *+' conftest.er1 >conftest.err
rm -f conftest.er1
cat conftest.err >&5
$as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
(exit $ac_status); } && {
test -z "$ac_c_werror_flag" ||
test ! -s conftest.err
} && test -s conftest.$ac_objext; then
POSTC17=no
else
$as_echo "$as_me: failed program was:" >&5
sed 's/^/| /' conftest.$ac_ext >&5
POSTC17=yes
fi
rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
{ $as_echo "$as_me:$LINENO: result: ${POSTC17}" >&5
$as_echo "${POSTC17}" >&6; }
# If a too recent standard was detected with the user's CFLAGS, try asking for
# C17 with GNU extensions explicitly.
if test "$POSTC17" = yes; then
old_CFLAGS="$CFLAGS"
{ $as_echo "$as_me:$LINENO: checking whether $CC supports -std=gnu17" >&5
$as_echo_n "checking whether $CC supports -std=gnu17... " >&6; }
if test "${pgac_cv_prog_cc_cflags__std_gnu17+set}" = set; then
$as_echo_n "(cached) " >&6
else
pgac_save_CFLAGS=$CFLAGS
CFLAGS="$pgac_save_CFLAGS -std=gnu17"
ac_save_c_werror_flag=$ac_c_werror_flag
ac_c_werror_flag=yes
cat >conftest.$ac_ext <<_ACEOF
/* confdefs.h. */
_ACEOF
cat confdefs.h >>conftest.$ac_ext
cat >>conftest.$ac_ext <<_ACEOF
/* end confdefs.h. */
int
main ()
{
;
return 0;
}
_ACEOF
rm -f conftest.$ac_objext
if { (ac_try="$ac_compile"
case "(($ac_try" in
*\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
*) ac_try_echo=$ac_try;;
esac
eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
$as_echo "$ac_try_echo") >&5
(eval "$ac_compile") 2>conftest.er1
ac_status=$?
grep -v '^ *+' conftest.er1 >conftest.err
rm -f conftest.er1
cat conftest.err >&5
$as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
(exit $ac_status); } && {
test -z "$ac_c_werror_flag" ||
test ! -s conftest.err
} && test -s conftest.$ac_objext; then
pgac_cv_prog_cc_cflags__std_gnu17=yes
else
$as_echo "$as_me: failed program was:" >&5
sed 's/^/| /' conftest.$ac_ext >&5
pgac_cv_prog_cc_cflags__std_gnu17=no
fi
rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
ac_c_werror_flag=$ac_save_c_werror_flag
CFLAGS="$pgac_save_CFLAGS"
fi
{ $as_echo "$as_me:$LINENO: result: $pgac_cv_prog_cc_cflags__std_gnu17" >&5
$as_echo "$pgac_cv_prog_cc_cflags__std_gnu17" >&6; }
if test x"$pgac_cv_prog_cc_cflags__std_gnu17" = x"yes"; then
CFLAGS="$CFLAGS -std=gnu17"
fi
if test "$CFLAGS" = "$old_CFLAGS"; then
{ { $as_echo "$as_me:$LINENO: error: cannot proceed" >&5
$as_echo "$as_me: error: cannot proceed" >&2;}
{ (exit 1); exit 1; }; }
fi
fi
# Some versions of GCC support some additional useful warning flags.
# Check whether they are supported, and add them to CFLAGS if so.
# ICC pretends to be GCC but it's lying; it doesn't support these flags,

20
configure.in
View File

@ -407,6 +407,26 @@ else
fi
fi
# We use C constructs that became invalid in C23. Check if the compiler
# reports a standard higher than C17, with the flags selected above (so the
# user can control the language level explicitly to avoid the gcc/clang-only
# fallback logic below if preferred).
AC_MSG_CHECKING([whether $CC reports a C standard higher than ISO C17])
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [@%:@if __STDC_VERSION__ > 201710L
choke me
@%:@endif])], [POSTC17=no], [POSTC17=yes])
AC_MSG_RESULT(${POSTC17})
# If a too recent standard was detected with the user's CFLAGS, try asking for
# C17 with GNU extensions explicitly.
if test "$POSTC17" = yes; then
old_CFLAGS="$CFLAGS"
PGAC_PROG_CC_CFLAGS_OPT([-std=gnu17])
if test "$CFLAGS" = "$old_CFLAGS"; then
AC_MSG_ERROR([cannot proceed])
fi
fi
# Some versions of GCC support some additional useful warning flags.
# Check whether they are supported, and add them to CFLAGS if so.
# ICC pretends to be GCC but it's lying; it doesn't support these flags,