Merge pull request #272 from ojwb/fix-AX_CXX_COMPILE_STDCXX-for-MSVC-C++17

AX_CXX_COMPILE_STDCXX: Fix MSVC with C++17 or later

1 files changed, 12 insertions, 3 deletions

diff --git a/m4/ax_cxx_compile_stdcxx.m4 b/m4/ax_cxx_compile_stdcxx.m4
index a3d964c..a9c990e 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).
@@ -104,9 +104,18 @@ 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
-        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"