merge bitcoin#24460: update ax_cxx_compile_stdcxx to serial 14

kwvg · kwvg · commit 1f4c0b50ee0e · 2025-02-12T16:57:46.000Z
diff --git a/build-aux/m4/ax_cxx_compile_stdcxx.m4 b/build-aux/m4/ax_cxx_compile_stdcxx.m4
@@ -10,14 +10,13 @@
 #
 #   Check for baseline language coverage in the compiler for the specified
 #   version of the C++ standard.  If necessary, add switches to CXX and
-#   CXXCPP to enable support.  VERSION may be '11' (for the C++11 standard),
-#   '14' (for the C++14 standard), '17' (for the C++17 standard) or
-#   '20' (for the C++20 standard)
+#   CXXCPP to enable support.  VERSION may be '11', '14', '17', or '20' for
+#   the respective C++ standard version.
 #
 #   The second argument, if specified, indicates whether you insist on an
 #   extended mode (e.g. -std=gnu++11) or a strict conformance mode (e.g.
 #   -std=c++11).  If neither is specified, you get whatever works, with
-#   preference for an extended mode.
+#   preference for no added switch, and then for an extended mode.
 #
 #   The third argument, if specified 'mandatory' or if left unspecified,
 #   indicates that baseline support for the specified C++ standard is
@@ -36,25 +35,24 @@
 #   Copyright (c) 2015 Moritz Klammler <moritz@klammler.eu>
 #   Copyright (c) 2016, 2018 Krzesimir Nowak <qdlacz@gmail.com>
 #   Copyright (c) 2019 Enji Cooper <yaneurabeya@gmail.com>
+#   Copyright (c) 2020 Jason Merrill <jason@redhat.com>
+#   Copyright (c) 2021 Jörn Heusipp <osmanx@problemloesungsmaschine.de>
 #
 #   Copying and distribution of this file, with or without modification, are
 #   permitted in any medium without royalty provided the copyright notice
 #   and this notice are preserved.  This file is offered as-is, without any
 #   warranty.
 
-#serial 11
+#serial 14
 
 dnl  This macro is based on the code from the AX_CXX_COMPILE_STDCXX_11 macro
 dnl  (serial version number 13).
 
-dnl  Modifications:
-dnl  Add support for C++20, with no new tests
-
 AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
   m4_if([$1], [11], [ax_cxx_compile_alternatives="11 0x"],
         [$1], [14], [ax_cxx_compile_alternatives="14 1y"],
         [$1], [17], [ax_cxx_compile_alternatives="17 1z"],
-        [$1], [20], [ax_cxx_compile_alternatives="20 2a"],
+        [$1], [20], [ax_cxx_compile_alternatives="20"],
         [m4_fatal([invalid first argument `$1' to AX_CXX_COMPILE_STDCXX])])dnl
   m4_if([$2], [], [],
         [$2], [ext], [],
@@ -67,6 +65,16 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
   AC_LANG_PUSH([C++])dnl
   ac_success=no
 
+  m4_if([$2], [], [dnl
+    AC_CACHE_CHECK(whether $CXX supports C++$1 features by default,
+		   ax_cv_cxx_compile_cxx$1,
+      [AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
+        [ax_cv_cxx_compile_cxx$1=yes],
+        [ax_cv_cxx_compile_cxx$1=no])])
+    if test x$ax_cv_cxx_compile_cxx$1 = xyes; then
+      ac_success=yes
+    fi])
+
   m4_if([$2], [noext], [], [dnl
   if test x$ac_success = xno; then
     for alternative in ${ax_cxx_compile_alternatives}; do
@@ -145,33 +153,28 @@ m4_define([_AX_CXX_COMPILE_STDCXX_testbody_11],
   _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
 )
 
-
 dnl  Test body for checking C++14 support
 
 m4_define([_AX_CXX_COMPILE_STDCXX_testbody_14],
   _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
   _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
 )
 
+dnl  Test body for checking C++17 support
+
 m4_define([_AX_CXX_COMPILE_STDCXX_testbody_17],
   _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
   _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
   _AX_CXX_COMPILE_STDCXX_testbody_new_in_17
 )
 
+dnl  Test body for checking C++20 support
 
-dnl Test body for checking C++20 support: R modification
 m4_define([_AX_CXX_COMPILE_STDCXX_testbody_20],
-#ifndef __cplusplus
-#error "This is not a C++ compiler"
-dnl value from 2020-01-14 draft, clang 11 has 202002L
-#elif __cplusplus < 201703L
-#error "This is not a C++20 compiler"
-#else
   _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
   _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
   _AX_CXX_COMPILE_STDCXX_testbody_new_in_17
-#endif
+  _AX_CXX_COMPILE_STDCXX_testbody_new_in_20
 )
 
 
@@ -272,7 +275,7 @@ namespace cxx11
     }
 
     int
-    test(const int c, volatile int v) // 'volatile is deprecated in C++20'
+    test(const int c, volatile int v)
     {
       static_assert(is_same<int, decltype(0)>::value == true, "");
       static_assert(is_same<int, decltype(c)>::value == false, "");
@@ -970,3 +973,33 @@ namespace cxx17
 #endif  // __cplusplus < 201703L
 
 ]])
+
+
+dnl  Tests for new features in C++20
+
+m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_20], [[
+
+#ifndef __cplusplus
+
+#error "This is not a C++ compiler"
+
+#elif __cplusplus < 202002L
+
+#error "This is not a C++20 compiler"
+
+#else
+
+#include <version>
+
+namespace cxx20
+{
+
+// As C++20 supports feature test macros in the standard, there is no
+// immediate need to actually test for feature availability on the
+// Autoconf side.
+
+}  // namespace cxx20
+
+#endif  // __cplusplus < 202002L
+
+]])
