Add option to build CMake against a system jsoncpp

Create a CMAKE_USE_SYSTEM_JSONCPP option.

CMakeLists.txt

@@ -65,7 +65,7 @@ macro(CMAKE_HANDLE_SYSTEM_LIBRARIES)
 
   # Allow the user to enable/disable all system utility library options by
   # defining CMAKE_USE_SYSTEM_LIBRARIES or CMAKE_USE_SYSTEM_LIBRARY_${util}.
-  set(UTILITIES BZIP2 CURL EXPAT FORM LIBARCHIVE LIBLZMA ZLIB)
+  set(UTILITIES BZIP2 CURL EXPAT FORM JSONCPP LIBARCHIVE LIBLZMA ZLIB)
   foreach(util ${UTILITIES})
     if(NOT DEFINED CMAKE_USE_SYSTEM_LIBRARY_${util}
         AND DEFINED CMAKE_USE_SYSTEM_LIBRARIES)
@@ -104,6 +104,7 @@ macro(CMAKE_HANDLE_SYSTEM_LIBRARIES)
   CMAKE_DEPENDENT_OPTION(CMAKE_USE_SYSTEM_LIBLZMA "Use system-installed liblzma"
     "${CMAKE_USE_SYSTEM_LIBRARY_LIBLZMA}" "NOT CMAKE_USE_SYSTEM_LIBARCHIVE" ON)
   option(CMAKE_USE_SYSTEM_FORM "Use system-installed libform" "${CMAKE_USE_SYSTEM_LIBRARY_FORM}")
+  option(CMAKE_USE_SYSTEM_JSONCPP "Use system-installed jsoncpp" "${CMAKE_USE_SYSTEM_LIBRARY_JSONCPP}")
 
   # Mention to the user what system libraries are being used.
   foreach(util ${UTILITIES})
@@ -373,8 +374,24 @@ macro (CMAKE_BUILD_UTILITIES)
 
   #---------------------------------------------------------------------
   # Build jsoncpp library.
-  add_subdirectory(Utilities/cmjsoncpp)
-  CMAKE_SET_TARGET_FOLDER(cmjsoncpp "Utilities/3rdParty")
+  if(CMAKE_USE_SYSTEM_JSONCPP)
+    if(EXISTS ${CMAKE_ROOT}/Modules/FindJsonCpp.cmake)
+      find_package(JsonCpp)
+    elseif(NOT CMAKE_VERSION VERSION_LESS 3.0)
+      include(${CMake_SOURCE_DIR}/Modules/FindJsonCpp.cmake)
+    else()
+      message(FATAL_ERROR "CMAKE_USE_SYSTEM_JSONCPP requires CMake >= 3.0")
+    endif()
+    if(NOT JsonCpp_FOUND)
+      message(FATAL_ERROR
+        "CMAKE_USE_SYSTEM_JSONCPP is ON but a JsonCpp is not found!")
+    endif()
+    set(CMAKE_JSONCPP_LIBRARIES JsonCpp::JsonCpp)
+  else()
+    set(CMAKE_JSONCPP_LIBRARIES cmjsoncpp)
+    add_subdirectory(Utilities/cmjsoncpp)
+    CMAKE_SET_TARGET_FOLDER(cmjsoncpp "Utilities/3rdParty")
+  endif()
 
   #---------------------------------------------------------------------
   # Build XMLRPC library for CMake and CTest.

Source/CMakeLists.txt

@@ -503,7 +503,7 @@ target_link_libraries(CMakeLib cmsys
   ${CMAKE_EXPAT_LIBRARIES} ${CMAKE_ZLIB_LIBRARIES}
   ${CMAKE_TAR_LIBRARIES} ${CMAKE_COMPRESS_LIBRARIES}
   ${CMAKE_CURL_LIBRARIES}
-  cmjsoncpp
+  ${CMAKE_JSONCPP_LIBRARIES}
   )
 
 # On Apple we need CoreFoundation

Utilities/cmThirdParty.h.in

@@ -20,6 +20,7 @@
 #cmakedefine CMAKE_USE_SYSTEM_LIBARCHIVE
 #cmakedefine CMAKE_USE_SYSTEM_LIBLZMA
 #cmakedefine CMAKE_USE_SYSTEM_FORM
+#cmakedefine CMAKE_USE_SYSTEM_JSONCPP
 #cmakedefine CTEST_USE_XMLRPC
 
 #endif

Utilities/cm_jsoncpp_reader.h

@@ -13,6 +13,11 @@
 #define cm_jsoncpp_reader_h
 
 /* Use the jsoncpp library configured for CMake.  */
-#include <cmjsoncpp/include/json/reader.h>
+#include "cmThirdParty.h"
+#ifdef CMAKE_USE_SYSTEM_JSONCPP
+# include <json/reader.h>
+#else
+# include <cmjsoncpp/include/json/reader.h>
+#endif
 
 #endif

Utilities/cm_jsoncpp_value.h

@@ -13,6 +13,11 @@
 #define cm_jsoncpp_value_h
 
 /* Use the jsoncpp library configured for CMake.  */
-#include <cmjsoncpp/include/json/value.h>
+#include "cmThirdParty.h"
+#ifdef CMAKE_USE_SYSTEM_JSONCPP
+# include <json/value.h>
+#else
+# include <cmjsoncpp/include/json/value.h>
+#endif
 
 #endif

Utilities/cm_jsoncpp_writer.h

@@ -13,6 +13,11 @@
 #define cm_jsoncpp_writer_h
 
 /* Use the jsoncpp library configured for CMake.  */
-#include <cmjsoncpp/include/json/writer.h>
+#include "cmThirdParty.h"
+#ifdef CMAKE_USE_SYSTEM_JSONCPP
+# include <json/writer.h>
+#else
+# include <cmjsoncpp/include/json/writer.h>
+#endif
 
 #endif