Merge branch 'maint'

Author: sverker

erts/configure

@@ -26388,6 +26388,8 @@ ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
 
           old_CXXFLAGS=$CXXFLAGS
           CXXFLAGS="$CXXFLAGS -std=c++17"
+          { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for C++17 support" >&5
+printf %s "checking for C++17 support... " >&6; }
           cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -26397,24 +26399,68 @@ main (void)
 #if __cplusplus < 201703L
                 #error "Needs C++17 compiler"
                 #endif
+
   ;
   return 0;
 }
+
 _ACEOF
 if ac_fn_cxx_try_compile "$LINENO"
 then :
-  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for C++17 support" >&5
-printf %s "checking for C++17 support... " >&6; }
+
                { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
 printf "%s\n" "yes" >&6; }
                HAVE_CXX17=true
+
+               if test "$builtin_ryu" = "no"
+then :
+
+                   { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for C++ std::to_chars" >&5
+printf %s "checking for C++ std::to_chars... " >&6; }
+                   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+                          #include <charconv>
+
+int
+main (void)
+{
+
+                          char fbuf[20];
+                          std::to_chars(fbuf, fbuf + sizeof(fbuf), 3.14);
+
+  ;
+  return 0;
+}
+
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"
+then :
+
+                       { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+printf "%s\n" "yes" >&6; }
+
 else case e in #(
-  e) { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for C++17 support" >&5
-printf %s "checking for C++17 support... " >&6; }
+  e)
+                       { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
+printf "%s\n" "no" >&6; }
+                       { printf "%s\n" "$as_me:${as_lineno-$LINENO}: WARNING: C++17 support found but no std::to_chars for floating point" >&5
+printf "%s\n" "$as_me: WARNING: C++17 support found but no std::to_chars for floating point" >&2;}
+                       as_fn_error $? "Alternative to builtin ryu needs C++17 with std::to_chars" "$LINENO" 5
+                      ;;
+esac
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext
+
+fi
+
+else case e in #(
+  e)
                { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
 printf "%s\n" "no" >&6; }
                CXXFLAGS=$old_CXXFLAGS
-               HAVE_CXX17=false ;;
+               HAVE_CXX17=false
+               ;;
 esac
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext

erts/configure.ac

@@ -3099,18 +3099,42 @@ AS_IF([test ${enable_jit} != no -o "$builtin_ryu" = "no"],
           AC_LANG_PUSH(C++)
           old_CXXFLAGS=$CXXFLAGS
           CXXFLAGS="$CXXFLAGS -std=c++17"
+          AC_MSG_CHECKING([for C++17 support])
           AC_COMPILE_IFELSE(
               [AC_LANG_PROGRAM([[]],
                [[#if __cplusplus < 201703L
                 #error "Needs C++17 compiler"
-                #endif]])],
-              [AC_MSG_CHECKING([for C++17 support])
+                #endif
+                ]])
+              ],[
                AC_MSG_RESULT([yes])
-               HAVE_CXX17=true],
-              [AC_MSG_CHECKING([for C++17 support])
+               HAVE_CXX17=true
+
+               AS_IF([test "$builtin_ryu" = "no"],
+                 [
+                   AC_MSG_CHECKING([for C++ std::to_chars])
+                   AC_COMPILE_IFELSE(
+                     [AC_LANG_PROGRAM(
+                        [[
+                          #include <charconv>
+                        ]],
+                        [[
+                          char fbuf[20];
+                          std::to_chars(fbuf, fbuf + sizeof(fbuf), 3.14);
+                        ]])
+                     ],[
+                       AC_MSG_RESULT([yes])
+                     ],[
+                       AC_MSG_RESULT([no])
+                       AC_MSG_WARN([C++17 support found but no std::to_chars for floating point])
+                       AC_MSG_ERROR([Alternative to builtin ryu needs C++17 with std::to_chars])
+                     ])
+                 ])
+              ],[
                AC_MSG_RESULT([no])
                CXXFLAGS=$old_CXXFLAGS
-               HAVE_CXX17=false])
+               HAVE_CXX17=false
+              ])
           AC_LANG_POP()
          ])
        if test "$CXX" = false -o "$HAVE_CXX17" = false; then