From d846c37bfac98c77a984011b8ceb4a269ba033ec Mon Sep 17 00:00:00 2001
From: Teus Benschop <teusjannette@gmail.com>
Date: Sun, 15 Oct 2023 14:19:00 +0200
Subject: [PATCH] Switch to C++20

https://github.com/bibledit/cloud/issues/907
---
 Makefile.in  |  2 +-
 config.h     |  4 ++--
 config.h.in  |  4 ++--
 configure    | 52 +++++++++++++++++++++++++++++++++++++++-------------
 configure.ac |  2 +-
 5 files changed, 45 insertions(+), 19 deletions(-)

diff --git a/Makefile.in b/Makefile.in
index c934e3142..9442e4c65 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -942,7 +942,7 @@ GUMBO_CFLAGS = @GUMBO_CFLAGS@
 GUMBO_LIBS = @GUMBO_LIBS@
 GUNZIP_PATH = @GUNZIP_PATH@
 GZIP_PATH = @GZIP_PATH@
-HAVE_CXX17 = @HAVE_CXX17@
+HAVE_CXX20 = @HAVE_CXX20@
 ICU_CFLAGS = @ICU_CFLAGS@
 ICU_LIBS = @ICU_LIBS@
 INSTALL = @INSTALL@
diff --git a/config.h b/config.h
index 8df8d6c89..ebbd5cb94 100644
--- a/config.h
+++ b/config.h
@@ -4,8 +4,8 @@
 /* Define whether to compile for Android */
 /* #undef HAVE_ANDROID */
 
-/* define if the compiler supports basic C++17 syntax */
-#define HAVE_CXX17 1
+/* define if the compiler supports basic C++20 syntax */
+#define HAVE_CXX20 1
 
 /* Define whether execinfo.h is present */
 #define HAVE_EXECINFO 1
diff --git a/config.h.in b/config.h.in
index 5f3831846..950dc7a53 100644
--- a/config.h.in
+++ b/config.h.in
@@ -3,8 +3,8 @@
 /* Define whether to compile for Android */
 #undef HAVE_ANDROID
 
-/* define if the compiler supports basic C++17 syntax */
-#undef HAVE_CXX17
+/* define if the compiler supports basic C++20 syntax */
+#undef HAVE_CXX20
 
 /* Define whether execinfo.h is present */
 #undef HAVE_EXECINFO
diff --git a/configure b/configure
index 5cf24f6de..a12300cd8 100755
--- a/configure
+++ b/configure
@@ -686,7 +686,7 @@ FIND_TAR
 GUNZIP_PATH
 GZIP_PATH
 RANLIB
-HAVE_CXX17
+HAVE_CXX20
 am__fastdepCXX_FALSE
 am__fastdepCXX_TRUE
 CXXDEPMODE
@@ -5274,7 +5274,7 @@ ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ex
 ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
 
 
-  ax_cxx_compile_alternatives="17 1z"    ax_cxx_compile_cxx17_required=true
+  ax_cxx_compile_alternatives="20"    ax_cxx_compile_cxx20_required=true
   ac_ext=cpp
 ac_cpp='$CXXCPP $CPPFLAGS'
 ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
@@ -5291,12 +5291,12 @@ ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
       for switch in -std=c++${alternative} +std=c++${alternative} "-h std=c++${alternative}" MSVC; do
         if test x"$switch" = xMSVC; then
                                         switch=-std:c++${alternative}
-          cachevar=`printf "%s\n" "ax_cv_cxx_compile_cxx17_${switch}_MSVC" | $as_tr_sh`
+          cachevar=`printf "%s\n" "ax_cv_cxx_compile_cxx20_${switch}_MSVC" | $as_tr_sh`
         else
-          cachevar=`printf "%s\n" "ax_cv_cxx_compile_cxx17_$switch" | $as_tr_sh`
+          cachevar=`printf "%s\n" "ax_cv_cxx_compile_cxx20_$switch" | $as_tr_sh`
         fi
-        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether $CXX supports C++17 features with $switch" >&5
-printf %s "checking whether $CXX supports C++17 features with $switch... " >&6; }
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether $CXX supports C++20 features with $switch" >&5
+printf %s "checking whether $CXX supports C++20 features with $switch... " >&6; }
 if eval test \${$cachevar+y}
 then :
   printf %s "(cached) " >&6
@@ -6095,6 +6095,32 @@ namespace cxx17
 
 
 
+
+#ifndef __cplusplus
+
+#error "This is not a C++ compiler"
+
+#elif __cplusplus < 202002L && !defined _MSC_VER
+
+#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 && !defined _MSC_VER
+
+
+
 _ACEOF
 if ac_fn_cxx_try_compile "$LINENO"
 then :
@@ -6128,19 +6154,19 @@ ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
 ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
 ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
 
-  if test x$ax_cxx_compile_cxx17_required = xtrue; then
+  if test x$ax_cxx_compile_cxx20_required = xtrue; then
     if test x$ac_success = xno; then
-      as_fn_error $? "*** A compiler with support for C++17 language features is required." "$LINENO" 5
+      as_fn_error $? "*** A compiler with support for C++20 language features is required." "$LINENO" 5
     fi
   fi
   if test x$ac_success = xno; then
-    HAVE_CXX17=0
-    { printf "%s\n" "$as_me:${as_lineno-$LINENO}: No compiler with C++17 support was found" >&5
-printf "%s\n" "$as_me: No compiler with C++17 support was found" >&6;}
+    HAVE_CXX20=0
+    { printf "%s\n" "$as_me:${as_lineno-$LINENO}: No compiler with C++20 support was found" >&5
+printf "%s\n" "$as_me: No compiler with C++20 support was found" >&6;}
   else
-    HAVE_CXX17=1
+    HAVE_CXX20=1
 
-printf "%s\n" "#define HAVE_CXX17 1" >>confdefs.h
+printf "%s\n" "#define HAVE_CXX20 1" >>confdefs.h
 
   fi
 
diff --git a/configure.ac b/configure.ac
index cc3ba01f2..2495304f8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -6,7 +6,7 @@ ac_default_prefix=/usr
 AC_PROG_CC
 AC_PROG_CXX
 AC_LANG([C++])
-AX_CXX_COMPILE_STDCXX(17,[noext],[mandatory])
+AX_CXX_COMPILE_STDCXX(20,[noext],[mandatory])
 AC_PROG_RANLIB
 AC_CONFIG_HEADERS([config.h])