From 05f8333e7693c70cd4891c2f34005eb3651be07a Mon Sep 17 00:00:00 2001
From: Maximilien Colange <colange@lrde.epita.fr>
Date: Tue, 13 Dec 2016 17:42:07 +0100
Subject: [PATCH] Add an option to enable C++14.

* configure.ac: add an option --enable-c++14.
* NEWS: mention the new option.
---
 NEWS         |  5 ++++
 configure.ac | 77 +++++++++++++++++++++++++++++++++++++++++++++-------
 2 files changed, 72 insertions(+), 10 deletions(-)

diff --git a/NEWS b/NEWS
index f2de77c6f..6755d07e6 100644
--- a/NEWS
+++ b/NEWS
@@ -19,6 +19,11 @@ New in spot 2.2.1.dev (Not yet released)
   * If the system has an installed libltdl library, use it instead of
     the one we distribute.
 
+  * The configure script has a new option --enable-c++14, to compile in
+    C++14 mode. Obviously you need a compiler that supports it. This allows
+    to check that nothing breaks when we will switch to C++14. This option
+    is also available in the configure script of buddy.
+
   Bug fixes:
 
   * scc_filter() had a left-over print statement that would print
diff --git a/configure.ac b/configure.ac
index c82cd40e9..b49250f08 100644
--- a/configure.ac
+++ b/configure.ac
@@ -44,8 +44,18 @@ AC_PROG_CXX
 AM_PROG_LEX
 adl_CHECK_BISON
 
+# Option to activate C/C++14
+AC_ARG_ENABLE([c++14],
+              [AC_HELP_STRING([--enable-c++14],
+                              [Use C++14.])],
+              [enable_14=yes], [enable_14=no])
+
 # Activate at C11 for gnulib tests
-AX_CHECK_COMPILE_FLAG([-std=c11], [CFLAGS="$CFLAGS -std=c11"])
+if test x"${enable_14}" = xyes; then
+  AX_CHECK_COMPILE_FLAG([-std=c14], [CFLAGS="$CFLAGS -std=c14"])
+else
+  AX_CHECK_COMPILE_FLAG([-std=c11], [CFLAGS="$CFLAGS -std=c11"])
+fi
 
 gl_INIT
 
@@ -67,7 +77,7 @@ m4_define([_AX_CXX_COMPILE_STDCXX_11_testbody],
 #include <chrono>  // fails with some installation of clang
 #include <map>
 
-   template <typename T>
+    template <typename T>
     struct check
     {
       static_assert(sizeof(int) <= sizeof(T), "not big enough");
@@ -93,14 +103,61 @@ m4_define([_AX_CXX_COMPILE_STDCXX_11_testbody],
     }
 ])])
 
-for f in -std=c++11 '-std=c++11 -stdlib=libc++' -std=c++0x
-do
-  AX_CHECK_COMPILE_FLAG([$f], [CXXFLAGS="$CXXFLAGS $f" stdpass=true], [], [],
-                        [_AX_CXX_COMPILE_STDCXX_11_testbody])
-  ${stdpass-false} && break
-done
-if ! "${stdpass-false}"; then
-  AC_ERROR([unable to turn on C++11 mode with this compiler])
+# Turn on C++14 support
+# This is currently a copy of the above code for C++11, feel free to add
+# further tests here when necessary.
+m4_define([_AX_CXX_COMPILE_STDCXX_14_testbody],
+[AC_LANG_SOURCE([#include <memory>
+#include <string>
+#include <chrono>  // fails with some installation of clang
+#include <map>
+
+    template <typename T>
+    struct check
+    {
+      static_assert(sizeof(int) <= sizeof(T), "not big enough");
+    };
+
+    typedef check<check<bool>> right_angle_brackets;
+
+    auto f = std::make_shared<std::string>("shared_ptr");
+
+    int a;
+    decltype(a) b;
+
+    typedef check<int> check_type;
+    check_type c;
+    check_type&& cr = static_cast<check_type&&>(c);
+
+    auto d = a;
+
+    void test_emplace()
+    {
+       std::map<int, int> m;
+       m.emplace(1, 2); // fails with g++ 4.6
+    }
+])])
+
+if test x"${enable_14}" = xyes; then
+  for f in -std=c++14 '-std=c++14 -stdlib=libc++' -std=c++1y
+  do
+    AX_CHECK_COMPILE_FLAG([$f], [CXXFLAGS="$CXXFLAGS $f" stdpass=true], [], [],
+                          [_AX_CXX_COMPILE_STDCXX_14_testbody])
+    ${stdpass-false} && break
+  done
+  if ! "${stdpass-false}"; then
+    AC_ERROR([unable to turn on C++14 mode with this compiler])
+  fi
+else
+  for f in -std=c++11 '-std=c++11 -stdlib=libc++' -std=c++0x
+  do
+    AX_CHECK_COMPILE_FLAG([$f], [CXXFLAGS="$CXXFLAGS $f" stdpass=true], [], [],
+                          [_AX_CXX_COMPILE_STDCXX_11_testbody])
+    ${stdpass-false} && break
+  done
+  if ! "${stdpass-false}"; then
+    AC_ERROR([unable to turn on C++11 mode with this compiler])
+  fi
 fi
 
 AX_CHECK_BUDDY