build system: look for & use system-wide version of nlohmann json-cpp

If one is found, it will be used. Otherwise the included version in
lib/nlohmann-json will be used.

Implements #1858.

NEWS.md

@@ -48,6 +48,9 @@
 
 ## Build system changes
 
+* nlohman json-cpp: configure now looks for a system-wide installed version of
+  the nlohmann json-cpp header-only library. If one is found, it is used;
+  otherwise the included version will be used. Implements #1858.
 * If MKVToolNix is built with rake v10.0.0 or newer, its "multitask" feature
   will be turned on allowing automatic parallel builds.
 * CURL is no longer used by MKVToolNix and is therefore not required

ac/nlohmann_jsoncpp.m4

@@ -0,0 +1,32 @@
+dnl
+dnl Check for nlohmann's json-cpp library
+dnl
+
+
+AC_CACHE_CHECK([nlohmann's json-cpp],[ac_cv_nlohmann_jsoncpp],[
+  AC_LANG_PUSH(C++)
+
+  AC_TRY_COMPILE([
+    #include <cstdint>
+    #include <iostream>
+    #include <limits>
+
+    #include <json.hpp>
+  ],[
+    nlohmann::json json{
+      { "unsigned_64bit_integer", std::numeric_limits<std::uint64_t>::max() },
+      { "signed_64bit_integer",   std::numeric_limits<std::int64_t>::min()  },
+    };
+
+    std::cout << json.dump();
+  ],[ac_cv_nlohmann_jsoncpp=yes],[ac_cv_nlohmann_jsoncpp=no])
+
+  AC_LANG_POP
+])
+
+if test x"$ac_cv_nlohmann_jsoncpp" = xyes; then
+  AC_MSG_NOTICE([Using the system version of nlohmann json-cpp])
+  AC_DEFINE([HAVE_NLOHMANN_JSONCPP],[1],[Define if nlohmann's json-cpp is available.])
+else
+  AC_MSG_NOTICE([Using the internal version of nlohmann json-cpp])
+fi

configure.ac

@@ -29,6 +29,7 @@ m4_include(ac/vorbis.m4)
 m4_include(ac/flac.m4)
 m4_include(ac/matroska.m4)
 m4_include(ac/pugixml.m4)
+m4_include(ac/nlohmann_jsoncpp.m4)
 m4_include(ac/utf8cpp.m4)
 m4_include(ac/zlib.m4)
 m4_include(ac/qt5.m4)

debian-upstream/control

@@ -12,6 +12,7 @@ Build-Depends:
  libboost-dev (>= 1.46), libboost-filesystem-dev (>= 1.46),
  libboost-regex-dev (>= 1.46), libboost-date-time-dev (>= 1.46),
  libboost-system-dev (>= 1.46), qtbase5-dev, qtbase5-dev-tools,
+ base-files (< 9.6) | nlohmann-json-dev (>= 2),
  pkg-config
 
 Package: mkvtoolnix

mkvtoolnix.spec

@@ -26,7 +26,7 @@ BuildRequires: gcc5-c++
 %endif
 
 %if 0%{?fedora}
-BuildRequires: gcc-c++ >= 4.9.0, rubypick, pugixml-devel, rubygem-rake
+BuildRequires: gcc-c++ >= 4.9.0, rubypick, pugixml-devel, rubygem-rake, json-devel >= 2
 %endif
 
 %if 0%{?suse_version}

src/common/id_info.h

@@ -14,8 +14,8 @@
 
 #include "common/common_pch.h"
 
+#include "common/json.h"
 #include "common/strings/editing.h"
-#include "nlohmann-json/src/json.hpp"
 
 namespace mtx { namespace id {
 

src/common/json.h

@@ -16,7 +16,11 @@
 
 #include "common/common_pch.h"
 
-#include "nlohmann-json/src/json.hpp"
+#if defined(HAVE_NLOHMANN_JSONCPP)
+# include <json.hpp>
+#else
+# include "nlohmann-json/src/json.hpp"
+#endif // HAVE_NLOHMANN_JSONCPP
 
 namespace mtx { namespace json {
 

src/common/output.h

@@ -20,9 +20,9 @@
 
 #include <ebml/EbmlElement.h>
 
+#include "common/json.h"
 #include "common/locale.h"
 #include "common/mm_io.h"
-#include "nlohmann-json/src/json.hpp"
 
 using namespace libebml;
 

src/merge/generic_reader.cpp

@@ -19,7 +19,6 @@
 #include "merge/generic_reader.h"
 #include "merge/input_x.h"
 #include "merge/output_control.h"
-#include "nlohmann-json/src/json.hpp"
 
 static int64_rational_c s_probe_range_percentage{3, 10}; // 0.3%
 

src/mkvtoolnix-gui/util/json.h

@@ -3,7 +3,7 @@
 
 #include "common/common_pch.h"
 
-#include "nlohmann-json/src/json.hpp"
+#include "common/json.h"
 
 class QVariant;