On 2024-05-28 08:02, Jakub Jelinek wrote:
even for C GCC updates the default
True, but C seems to be different, in that using a later-than-default
-std=whatever is more likely to help than hurt, because the C
standardization folks are more careful about compatibility. That's what
I've been experiencing with -std=gnu23, for example, even though C23 has
lots of changes from C17.
> Autoconf should go back to its 2.69 behavior and not mess with the C++
> version as that's more likely to hurt than help.
Yes.
OK, thanks, I installed the attached.
From 056518b94ecd487bcbefdb69046b3f52c4168222 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@xxxxxxxxxxx>
Date: Tue, 28 May 2024 09:31:11 -0700
Subject: [PATCH] AC_PROG_CXX no longer adjusts C++ language version
* lib/autoconf/c.m4 (_AC_CXX_CXX98_TEST_GLOBALS)
(_AC_CXX_CXX98_TEST_MAIN, _AC_CXX_CXX11_TEST_GLOBALS)
(_AC_CXX_CXX11_TEST_MAIN, _AC_CXX_CXX98_TEST_PROGRAM)
(_AC_CXX_CXX11_TEST_PROGRAM, _AC_CXX_CXX14_TEST_PROGRAM)
(_AC_CXX_CXX17_TEST_PROGRAM, _AC_CXX_CXX20_TEST_PROGRAM)
(_AC_CXX_CXX23_TEST_PROGRAM, _AC_CXX_CXX98_OPTIONS)
(_AC_CXX_CXX11_OPTIONS, _AC_CXX_CXX14_OPTIONS)
(_AC_CXX_CXX17_OPTIONS, _AC_CXX_CXX20_OPTIONS)
(_AC_CXX_CXX23_OPTIONS, _AC_PROG_CXX_STDCXX_EDITION_TRY)
(_AC_PROG_CXX_STDCXX_EDITION_TRY): Remove. All uses removed.
---
NEWS | 13 +-
doc/autoconf.texi | 29 ---
lib/autoconf/c.m4 | 439 ----------------------------------------------
3 files changed, 5 insertions(+), 476 deletions(-)
diff --git a/NEWS b/NEWS
index 4ba8f3fe..521bbd3a 100644
--- a/NEWS
+++ b/NEWS
@@ -16,14 +16,11 @@ GNU Autoconf NEWS - User visible changes.
C11 and later. Programs can use AC_C_VARARRAYS and __STDC_NO_VLA__
to use VLAs if available.
-*** AC_PROG_CXX now prefers C++23, C++20, C++17, C++14 if available.
- Older code may need to be updated, as some older features of C++ are
- removed in later standards.
-
-** Notable bug fixes
-
-*** AC_PROG_CXX no longer rejects C++20 compilers
-merely because C++20 is not upward-compatible with C++11.
+*** AC_PROG_CXX no longer attempts to switch to C++98 or C++11.
+ Instead, it uses the compiler's default, which you can override
+ by configuring with something like CXX='g++ -std=gnu++11'.
+ This reverts to Autoconf 2.69 behavior, and also fixes a bug where
+ AC_PROG_CXX rejected C++20 compilers.
* Noteworthy changes in release 2.72 (2023-12-22) [release]
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 37e0ae01..c36eefdb 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -7821,33 +7821,6 @@ where @var{options} are the appropriate set of options to use by
default. (It is important to use this construct rather than a normal
assignment, so that @code{CXXFLAGS} can still be overridden by the
person building the package. @xref{Preset Output Variables}.)
-
-If necessary, options are added to @code{CXX} to enable support for
-ISO Standard C++ features with extensions, preferring the newest edition
-of the C++ standard that is supported. Currently the newest edition
-Autoconf knows how to detect support for is C++23. After calling
-this macro, you can check whether the C++ compiler has been set to
-accept standard C++ by inspecting the shell variable @code{ac_prog_cxx_stdcxx}.
-Its value will be @samp{cxx23}, @samp{cxx20}, @samp{cxx17},
-@samp{cxx14}, @samp{cxx11} or @samp{cxx98},
-if the C++ compiler has been set to use the corresponding edition of the
-C++ standard, and @samp{no} if the compiler does not support compiling
-standard C++ at all.
-
-The tests for standard conformance are not comprehensive. They test
-the value of @code{__cplusplus} and a representative sample of the
-language features added in each version of the C++ standard. They
-do not test the C++ standard library, because this can be extremely
-slow, and because the C++ compiler might be generating code for a
-``freestanding environment'' (in which most of the C++ standard library
-is optional). If you need to know whether a particular C++ standard
-header exists, use @code{AC_CHECK_HEADER}.
-
-None of the options that may be added to @code{CXX} by this macro
-enable @emph{strict} conformance to the C++ standard. In particular,
-system-specific extensions are not disabled. (For example, for GNU
-C++, the @option{-std=gnu++@var{nn}} options may be used, but not the
-@option{-std=c++@var{nn}} options.)
@end defmac
@defmac AC_PROG_CXXCPP
@@ -21715,8 +21688,6 @@ standard. K&R C compilers are no longer of practical interest, though,
and Autoconf assumes at least C89, the first C standard,
which is sometimes called ``C90'' due to a delay in standardization.
C has since gone through the standards C99, C11, C17, and C23, and
-C++ has evolved in a similar way, with the standards
-C++98, C++11, C++14, C++17, C++20, and C++23.
Autoconf is compatible with all these standards.
Program portability is a huge topic, and this section can only briefly
diff --git a/lib/autoconf/c.m4 b/lib/autoconf/c.m4
index a0a2b487..456a6ba7 100644
--- a/lib/autoconf/c.m4
+++ b/lib/autoconf/c.m4
@@ -719,7 +719,6 @@ else
GXX=
fi
_AC_PROG_CXX_G
-_AC_PROG_CXX_STDCXX_EDITION
AC_LANG_POP(C++)dnl
])# AC_PROG_CXX
@@ -2542,441 +2541,3 @@ AC_DEFUN([_AC_OPENMP_SAFE_WD],
[AC@&t@_OPENMP clobbers files named 'mp' and 'penmp'.
Aborting configure because one of these files already exists.]))
fi])
-
-
-
-# ---------------------------------- #
-# 4b. C++ compiler characteristics. #
-# ---------------------------------- #
-
-# See the long comment at the beginning of section 4a for rationale
-# for these macros, and constraints on how the test programs should
-# be written.
-#
-# The C++98 freestanding headers are:
-# <cstdarg> <cstddef> <cstdlib> <exception> <limits> <new> <typeinfo>
-# C++11 adds:
-# <atomic> <cfloat> <ciso646> <climits> <cstdalign> <cstdbool>
-# <cstdint> <initializer_list> <type_traits>
-#
-# No other headers can safely be included. Therefore, almost no C++
-# standard library features are tested for. Use AC_CHECK_HEADER, etc.
-# if you need that.
-
-AC_DEFUN([_AC_CXX_CXX98_TEST_GLOBALS],
-[m4_divert_text([INIT_PREPARE],
-[[# Test code for whether the C++ compiler supports C++98 (global declarations)
-ac_cxx_conftest_cxx98_globals='
-// Does the compiler advertise C++98 conformance?
-#if !defined __cplusplus || __cplusplus < 199711L
-# error "Compiler does not advertise C++98 conformance"
-#endif
-
-// These inclusions are to reject old compilers that
-// lack the unsuffixed header files.
-#include <cstdlib>
-#include <exception>
-
-// <cassert> and <cstring> are *not* freestanding headers in C++98.
-extern void assert (int);
-namespace std {
- extern int strcmp (const char *, const char *);
-}
-
-// Namespaces, exceptions, and templates were all added after "C++ 2.0".
-using std::exception;
-using std::strcmp;
-
-namespace {
-
-void test_exception_syntax()
-{
- try {
- throw "test";
- } catch (const char *s) {
- // Extra parentheses suppress a warning when building autoconf itself,
- // due to lint rules shared with more typical C programs.
- assert (!(strcmp) (s, "test"));
- }
-}
-
-template <typename T> struct test_template
-{
- T const val;
- explicit test_template(T t) : val(t) {}
- template <typename U> T add(U u) { return static_cast<T>(u) + val; }
-};
-
-} // anonymous namespace
-'
-]])])
-
-AC_DEFUN([_AC_CXX_CXX98_TEST_MAIN],
-[m4_divert_text([INIT_PREPARE],
-[[# Test code for whether the C++ compiler supports C++98 (body of main)
-ac_cxx_conftest_cxx98_main='
- assert (argc);
- assert (! argv[0]);
-{
- test_exception_syntax ();
- test_template<double> tt (2.0);
- assert (tt.add (4) == 6.0);
- assert (true && !false);
-}
-'
-]])])
-
-AC_DEFUN([_AC_CXX_CXX11_TEST_GLOBALS],
-[m4_divert_text([INIT_PREPARE],
-[[# Test code for whether the C++ compiler supports C++11 (global declarations)
-ac_cxx_conftest_cxx11_globals='
-// Does the compiler advertise C++ 2011 conformance?
-#if !defined __cplusplus || __cplusplus < 201103L
-# error "Compiler does not advertise C++11 conformance"
-#endif
-
-namespace cxx11test
-{
- constexpr int get_val() { return 20; }
-
- struct testinit
- {
- int i;
- double d;
- };
-
- class delegate
- {
- public:
- delegate(int n) : n(n) {}
- delegate(): delegate(2354) {}
-
- virtual int getval() { return this->n; };
- protected:
- int n;
- };
-
- class overridden : public delegate
- {
- public:
- overridden(int n): delegate(n) {}
- virtual int getval() override final { return this->n * 2; }
- };
-
- class nocopy
- {
- public:
- nocopy(int i): i(i) {}
- nocopy() = default;
- nocopy(const nocopy&) = delete;
- nocopy & operator=(const nocopy&) = delete;
- private:
- int i;
- };
-
- // for testing lambda expressions
- template <typename Ret, typename Fn> Ret eval(Fn f, Ret v)
- {
- return f(v);
- }
-
- // for testing variadic templates and trailing return types
- template <typename V> auto sum(V first) -> V
- {
- return first;
- }
- template <typename V, typename... Args> auto sum(V first, Args... rest) -> V
- {
- return first + sum(rest...);
- }
-}
-'
-]])])
-
-AC_DEFUN([_AC_CXX_CXX11_TEST_MAIN],
-[m4_divert_text([INIT_PREPARE],
-[[# Test code for whether the C++ compiler supports C++11 (body of main)
-ac_cxx_conftest_cxx11_main='
-{
- // Test auto and decltype
- auto a1 = 6538;
- auto a2 = 48573953.4;
- auto a3 = "String literal";
-
- int total = 0;
- for (auto i = a3; *i; ++i) { total += *i; }
-
- decltype(a2) a4 = 34895.034;
-}
-{
- // Test constexpr
- short sa[cxx11test::get_val()] = { 0 };
-}
-{
- // Test initializer lists
- cxx11test::testinit il = { 4323, 435234.23544 };
-}
-{
- // Test range-based for
- int array[] = {9, 7, 13, 15, 4, 18, 12, 10, 5, 3,
- 14, 19, 17, 8, 6, 20, 16, 2, 11, 1};
- for (auto &x : array) { x += 23; }
-}
-{
- // Test lambda expressions
- using cxx11test::eval;
- assert (eval ([](int x) { return x*2; }, 21) == 42);
- double d = 2.0;
- assert (eval ([&](double x) { return d += x; }, 3.0) == 5.0);
- assert (d == 5.0);
- assert (eval ([=](double x) mutable { return d += x; }, 4.0) == 9.0);
- assert (d == 5.0);
-}
-{
- // Test use of variadic templates
- using cxx11test::sum;
- auto a = sum(1);
- auto b = sum(1, 2);
- auto c = sum(1.0, 2.0, 3.0);
-}
-{
- // Test constructor delegation
- cxx11test::delegate d1;
- cxx11test::delegate d2();
- cxx11test::delegate d3(45);
-}
-{
- // Test override and final
- cxx11test::overridden o1(55464);
-}
-{
- // Test nullptr
- char *c = nullptr;
-}
-{
- // Test template brackets
- test_template<::test_template<int>> v(test_template<int>(12));
-}
-{
- // Unicode literals. Do not test u8"..." as C++20 would reject it.
- char16_t const *utf16 = u"UTF-8 string \u2500";
- char32_t const *utf32 = U"UTF-32 string \u2500";
-}
-'
-]])])
-
-AC_DEFUN([_AC_CXX_CXX98_TEST_PROGRAM],
-[AC_REQUIRE([_AC_CXX_CXX98_TEST_GLOBALS])dnl
-AC_REQUIRE([_AC_CXX_CXX98_TEST_MAIN])dnl
-m4_divert_text([INIT_PREPARE],
-[[# Test code for whether the C compiler supports C++98 (complete).
-ac_cxx_conftest_cxx98_program="${ac_cxx_conftest_cxx98_globals}
-int
-main (int argc, char **argv)
-{
- int ok = 0;
- ${ac_cxx_conftest_cxx98_main}
- return ok;
-}
-"
-]])])
-
-AC_DEFUN([_AC_CXX_CXX11_TEST_PROGRAM],
-[AC_REQUIRE([_AC_CXX_CXX98_TEST_GLOBALS])dnl
-AC_REQUIRE([_AC_CXX_CXX98_TEST_MAIN])dnl
-AC_REQUIRE([_AC_CXX_CXX11_TEST_GLOBALS])dnl
-AC_REQUIRE([_AC_CXX_CXX11_TEST_MAIN])dnl
-m4_divert_text([INIT_PREPARE],
-[[# Test code for whether the C compiler supports C++11 (complete).
-ac_cxx_conftest_cxx11_program="${ac_cxx_conftest_cxx98_globals}
-${ac_cxx_conftest_cxx11_globals}
-
-int
-main (int argc, char **argv)
-{
- int ok = 0;
- ${ac_cxx_conftest_cxx98_main}
- ${ac_cxx_conftest_cxx11_main}
- return ok;
-}
-"
-]])])
-
-AC_DEFUN([_AC_CXX_CXX14_TEST_PROGRAM],
-[m4_divert_text([INIT_PREPARE],
-[[ac_cxx_conftest_cxx14_program='
-#if __cplusplus < 201402
-# error "Compiler does not advertise C++14 conformance"
-#endif
-
-int
-main ()
-{
- auto floating_point_literal_with_single_quotes = 0.123'\''456;
-}
-'
-]])])
-
-AC_DEFUN([_AC_CXX_CXX17_TEST_PROGRAM],
-[m4_divert_text([INIT_PREPARE],
-[[ac_cxx_conftest_cxx17_program='
-#if __cplusplus < 201707
-# error "Compiler does not advertise C++17 conformance"
-#endif
-
-int
-main ()
-{
- auto u8_expression_with_u8_character_literals = u8'\''x'\'' == u8'\''x'\'';
-}
-'
-]])])
-
-AC_DEFUN([_AC_CXX_CXX20_TEST_PROGRAM],
-[m4_divert_text([INIT_PREPARE],
-[[ac_cxx_conftest_cxx20_program='
-#if __cplusplus < 202002
-# error "Compiler does not advertise C++20 conformance"
-#endif
-
-#include <compare>
-
-int
-main ()
-{
- auto expression_with_three_way_comparison = 1 <=> 2;
-}
-'
-]])])
-
-AC_DEFUN([_AC_CXX_CXX23_TEST_PROGRAM],
-[m4_divert_text([INIT_PREPARE],
-[[ac_cxx_conftest_cxx23_program='
-#if __cplusplus < 202302
-# error "Compiler does not advertise C++23 conformance"
-#endif
-
-int
-main ()
-{
- auto expression_with_signed_size_literal = -1z < 0;
-}
-'
-]])])
-
-# _AC_CXX_CXX98_OPTIONS
-# ---------------------
-# Whitespace-separated list of options that might put the C++ compiler
-# into a mode conforming to ISO C++ 1998 with extensions. Do not try
-# "strictly conforming" modes (e.g. gcc's -std=c++98); they break some
-# systems' header files. If more than one option is needed, put
-# shell quotes around the group.
-#
-# GCC -std=gnu++98
-# Intel ICC -std=c++98
-# Note: because -std=c++98 puts GCC in strictly conforming mode,
-# this option must be tested *after* -std=gnu++98.
-# IBM XL C -qlanglvl=extended
-# HP aC++ -AA
-# Solaris N/A (default)
-# Tru64 N/A (default, but -std gnu could be used)
-m4_define([_AC_CXX_CXX98_OPTIONS], [
- -std=gnu++98
- -std=c++98
- -qlanglvl=extended
- -AA
-])
-
-# _AC_CXX_CXX11_OPTIONS
-# ---------------------
-# Whitespace-separated list of options that might put the C++ compiler
-# into a mode conforming to ISO C++ 2011 with extensions. Do not try
-# "strictly conforming" modes (e.g. gcc's -std=c++11); they break some
-# systems' header files. If more than one option is needed, put
-# shell quotes around the group.
-#
-# GCC -std=gnu++11, -std=gnu++0x
-# Intel ICC -std=c++11, -std=c++0x
-# Note: because -std=c++11 puts GCC in strictly conforming mode,
-# these options must be tested *after* -std=gnu++11.
-# IBM XL C -qlanglvl=extended0x (pre-V12.1)
-# HP aC++ -AA
-# Solaris N/A (no support)
-# Tru64 N/A (no support)
-m4_define([_AC_CXX_CXX11_OPTIONS], [
- -std=gnu++11
- -std=gnu++0x
- -std=c++11
- -std=c++0x
- -qlanglvl=extended0x
- -AA
-])
-
-# Similarly for C++14, C++17, C++20, C++23,
-# where -std=gnu++XX should be good enough.
-m4_define([_AC_CXX_CXX14_OPTIONS], [-std=gnu++14])
-m4_define([_AC_CXX_CXX17_OPTIONS], [-std=gnu++17])
-m4_define([_AC_CXX_CXX20_OPTIONS], [-std=gnu++20])
-m4_define([_AC_CXX_CXX23_OPTIONS], [-std=gnu++23])
-
-# _AC_PROG_CXX_STDCXX_EDITION_TRY(EDITION)
-# ----------------------------------------
-# Subroutine of _AC_PROG_CXX_STDCXX_EDITION. Not to be called directly.
-#
-# Check whether the C++ compiler accepts features of EDITION of the
-# C++ standard. EDITION should be a two-digit year (e.g. 98, 11).
-# (FIXME: Switch to four-digit years for futureproofing.)
-# This is done by compiling the test program defined by
-# _AC_C_CXX{EDITION}_TEST_PROGRAM, first with no additional
-# command-line options, and then with each of the options
-# in the space-separated list defined by _AC_C_CXX{EDITION}_OPTIONS.
-#
-# If we find a way to make the test program compile, set cache variable
-# ac_cv_prog_cxx_cxxEDITION to the options required (if any), and add those
-# options to $CXX. Set shell variable ac_prog_cxx_stdcxx to 'cxxEDITION',
-# and set shell variable ac_cv_prog_cxx_stdcxx to the options required.
-# (Neither of these variables is AC_SUBSTed. ac_cv_prog_cxx_stdcxx used
-# to be a cache variable and is preserved with this name for backward
-# compatibility.) Otherwise, ac_cv_prog_cxx_cxxEDITION is set to 'no'
-# and the other variables are not changed.
-#
-# If ac_prog_cxx_stdcxx is already set to a value other than 'no',
-# the shell code produced by this macro does nothing. This is so
-# _AC_PROG_CXX_STDCXX_EDITION can use m4_map to iterate through
-# all the editions.
-AC_DEFUN([_AC_PROG_CXX_STDCXX_EDITION_TRY],
-[AC_LANG_ASSERT([C++])]dnl
-[AC_REQUIRE([_AC_CXX_CXX$1_TEST_PROGRAM])]dnl
-[AS_IF([test x$ac_prog_cxx_stdcxx = xno],
-[AC_MSG_CHECKING([for $CXX option to enable C++$1 features])
-AC_CACHE_VAL(ac_cv_prog_cxx_cxx$1,
-[ac_cv_prog_cxx_cxx$1=no
-ac_save_CXX=$CXX
-AC_LANG_CONFTEST([AC_LANG_DEFINES_PROVIDED][$][ac_cxx_conftest_cxx$1_program])
-for ac_arg in '' m4_normalize(m4_defn([_AC_CXX_CXX$1_OPTIONS]))
-do
- CXX="$ac_save_CXX $ac_arg"
- _AC_COMPILE_IFELSE([], [ac_cv_prog_cxx_cxx$1=$ac_arg])
- test "x$ac_cv_prog_cxx_cxx$1" != "xno" && break
-done
-rm -f conftest.$ac_ext
-CXX=$ac_save_CXX])
-AS_IF([test "x$ac_cv_prog_cxx_cxx$1" = xno],
- [AC_MSG_RESULT([unsupported])],
- [AS_IF([test "x$ac_cv_prog_cxx_cxx$1" = x],
- [AC_MSG_RESULT([none needed])],
- [AC_MSG_RESULT([$ac_cv_prog_cxx_cxx$1])
- CXX="$CXX $ac_cv_prog_cxx_cxx$1"])
- ac_cv_prog_cxx_stdcxx=$ac_cv_prog_cxx_cxx$1
- ac_prog_cxx_stdcxx=cxx$1])])
-])
-
-# _AC_PROG_CXX_STDCXX_EDITION
-# ---------------------------
-# Detect the most recent edition of the ISO C++ standard that is
-# supported by the C++ compiler. Add command-line options to $CXX,
-# if necessary, to enable support for this edition. Set the shell
-# variable ac_prog_cxx_stdcxx to indicate the edition.
-AC_DEFUN([_AC_PROG_CXX_STDCXX_EDITION],
-[ac_prog_cxx_stdcxx=no
-m4_map([_AC_PROG_CXX_STDCXX_EDITION_TRY], [23, 20, 17, 14, 11, 98])])
--
2.43.0
