build: require c++17

We don't technically need it yet, but will do so during the 1.7.x series.

configure.ac

@@ -42,15 +42,15 @@ AC_PROG_CC_C99
 AC_PROG_INSTALL
 AC_HEADER_STDC
 
-extra_flags="-Wformat-security                                        \
+extra_flags="-Wformat-security                                    \
          -Wstack-protector                                        \
          -Wstack-protector-all                                    \
          -Wno-cast-function-type                                  \
          -Wno-bad-function-cast"
 
-AX_CXX_COMPILE_STDCXX_14
+AX_CXX_COMPILE_STDCXX_17
 AX_COMPILER_FLAGS_CXXFLAGS([],[],[${extra_cflags}])
-AX_APPEND_COMPILE_FLAGS([-Wno-inline ],[CXXFLAGS])
+AX_APPEND_COMPILE_FLAGS([-Wno-inline],[CXXFLAGS])
 AX_VALGRIND_CHECK
 
 LT_INIT

m4/Makefile.am

@@ -1,4 +1,4 @@
-## Copyright (C) 2008-2020 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+## Copyright (C) 2008-2021 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
 ##
 ## This program is free software; you can redistribute it and/or modify
 ## it under the terms of the GNU General Public License as published by
@@ -36,6 +36,7 @@ EXTRA_DIST=				\
 	ax_compiler_flags_ldflags.m4	\
 	ax_cxx_compile_stdcxx.m4	\
 	ax_cxx_compile_stdcxx_14.m4	\
+	ax_cxx_compile_stdcxx_17.m4	\
 	ax_file_escapes.m4		\
 	ax_is_release.m4		\
 	ax_lib_readline.m4		\

m4/m4_ax_cxx_compile_stdcxx_17.m4

@@ -0,0 +1,35 @@
+# =============================================================================
+#  https://www.gnu.org/software/autoconf-archive/ax_cxx_compile_stdcxx_17.html
+# =============================================================================
+#
+# SYNOPSIS
+#
+#   AX_CXX_COMPILE_STDCXX_17([ext|noext], [mandatory|optional])
+#
+# DESCRIPTION
+#
+#   Check for baseline language coverage in the compiler for the C++17
+#   standard; if necessary, add switches to CXX and CXXCPP to enable
+#   support.
+#
+#   This macro is a convenience alias for calling the AX_CXX_COMPILE_STDCXX
+#   macro with the version set to C++17.  The two optional arguments are
+#   forwarded literally as the second and third argument respectively.
+#   Please see the documentation for the AX_CXX_COMPILE_STDCXX macro for
+#   more information.  If you want to use this macro, you also need to
+#   download the ax_cxx_compile_stdcxx.m4 file.
+#
+# LICENSE
+#
+#   Copyright (c) 2015 Moritz Klammler <moritz@klammler.eu>
+#   Copyright (c) 2016 Krzesimir Nowak <qdlacz@gmail.com>
+#
+#   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 2
+
+AX_REQUIRE_DEFINED([AX_CXX_COMPILE_STDCXX])
+AC_DEFUN([AX_CXX_COMPILE_STDCXX_17], [AX_CXX_COMPILE_STDCXX([17], [$1], [$2])])

meson.build

@@ -25,7 +25,7 @@ project('mu', ['c', 'cpp'],
 	  'buildtype=debugoptimized',
 	  'warning_level=1',
 	  'c_std=c11',
-	  'cpp_std=c++14'
+	  'cpp_std=c++17'
 	]
        )
 
@@ -51,7 +51,6 @@ extra_flags = [
   '-Winit-self',
   '-Wmissing-include-dirs',
   '-Wpointer-arith',
-  #'-Wswitch-enum',
   '-Wswitch-default',
 ]