From 04c71e680ce8d47abca807597aa353e03273eb0a Mon Sep 17 00:00:00 2001
From: Olly Betts <olly@survex.com>
Date: Thu, 19 Jan 2023 17:40:13 +1300
Subject: AX_CXX_COMPILE_STDCXX: Fix MSVC with C++17 or later

MSVC defaults to C++14 and needs -std:c++NN to enable support for
newer versions so add that to the list of options to try.
---
 m4/ax_cxx_compile_stdcxx.m4 | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

(limited to 'm4')

diff --git a/m4/ax_cxx_compile_stdcxx.m4 b/m4/ax_cxx_compile_stdcxx.m4
index a3d964c..a2e068a 100644
--- a/m4/ax_cxx_compile_stdcxx.m4
+++ b/m4/ax_cxx_compile_stdcxx.m4
@@ -43,7 +43,7 @@
 #   and this notice are preserved.  This file is offered as-is, without any
 #   warranty.
 
-#serial 15
+#serial 16
 
 dnl  This macro is based on the code from the AX_CXX_COMPILE_STDCXX_11 macro
 dnl  (serial version number 13).
@@ -104,8 +104,9 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
     dnl HP's aCC needs +std=c++11 according to:
     dnl http://h21007.www2.hp.com/portal/download/files/unprot/aCxx/PDF_Release_Notes/769149-001.pdf
     dnl Cray's crayCC needs "-h std=c++11"
+    dnl MSVC needs -std:c++NN for C++17 and later (default is C++14)
     for alternative in ${ax_cxx_compile_alternatives}; do
-      for switch in -std=c++${alternative} +std=c++${alternative} "-h std=c++${alternative}"; do
+      for switch in -std=c++${alternative} +std=c++${alternative} "-h std=c++${alternative}" -std:c++${alternative}; do
         cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
         AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
                        $cachevar,
-- 
cgit v1.2.1


From 3a2674fc7d64171f5cd229590456d106fd4e65d9 Mon Sep 17 00:00:00 2001
From: Olly Betts <olly@survex.com>
Date: Sat, 21 Jan 2023 08:02:16 +1300
Subject: Avoid cache variable name collision

AS_TR_SH maps both `:` and `=` to `_` so -std:c++17 was colliding
with -std=c++17.  Suffix the cache variable name for the former
with _MSVC to avoid this.
---
 m4/ax_cxx_compile_stdcxx.m4 | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

(limited to 'm4')

diff --git a/m4/ax_cxx_compile_stdcxx.m4 b/m4/ax_cxx_compile_stdcxx.m4
index a2e068a..a9c990e 100644
--- a/m4/ax_cxx_compile_stdcxx.m4
+++ b/m4/ax_cxx_compile_stdcxx.m4
@@ -106,8 +106,16 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
     dnl Cray's crayCC needs "-h std=c++11"
     dnl MSVC needs -std:c++NN for C++17 and later (default is C++14)
     for alternative in ${ax_cxx_compile_alternatives}; do
-      for switch in -std=c++${alternative} +std=c++${alternative} "-h std=c++${alternative}" -std:c++${alternative}; do
-        cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
+      for switch in -std=c++${alternative} +std=c++${alternative} "-h std=c++${alternative}" MSVC; do
+        if test x"$switch" = xMSVC; then
+          dnl AS_TR_SH maps both `:` and `=` to `_` so -std:c++17 would collide
+          dnl with -std=c++17.  We suffix the cache variable name with _MSVC to
+          dnl avoid this.
+          switch=-std:c++${alternative}
+          cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_${switch}_MSVC])
+        else
+          cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
+        fi
         AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
                        $cachevar,
           [ac_save_CXX="$CXX"
-- 
cgit v1.2.1