[cmake] only add format target if clang format 3.7 is found

clang format discovery is improved a lot by using cmake
builtins, allowing us to very easily target a specific
version only.

This is one half of #10

cmake/modules/DuneXtCommonMacros.cmake

@@ -46,9 +46,9 @@ macro(add_analyze)
     endif(EXISTS ${ANALYZER})
 endmacro(add_analyze)
 
-find_package(ClangFormat 3.7)
+find_package(ClangFormat 3.7 EXACT)
 macro(add_format)
-  if(CLANG_FORMAT_FOUND)
+  if(ClangFormat_FOUND)
     message(STATUS "adding format target")
     if (NOT TARGET format)
       add_custom_target( format SOURCES ${ARGN} )
@@ -59,12 +59,13 @@ macro(add_format)
           # 'fix' relative source defs
         set(_file ${CMAKE_CURRENT_SOURCE_DIR}/${_file})
       endif(NOT EXISTS ${_file})
-      add_custom_target("format_${fn}" ${CLANG_FORMAT_BINARY} -i -style=file ${_file} )
+      add_custom_target("format_${fn}" ${ClangFormat_EXECUTABLE} -i -style=file ${_file} )
       add_dependencies( format "format_${fn}" )
     endforeach(_file )
   else()
-    message(WARNING "not adding format target because clang-format is missing")
-  endif(CLANG_FORMAT_FOUND)
+    message(WARNING "not adding format target because clang-format is missing or" 
+                "wrong version: ${ClangFormat_EXECUTABLE} ${ClangFormat_VERSION}")
+  endif(ClangFormat_FOUND)
 endmacro(add_format)
 
 macro(add_forced_doxygen_target)

cmake/modules/FindClangFormat.cmake

@@ -5,25 +5,18 @@
 #     )                      
 #
 #   optionally pass the minimal version you require like so find_package(ClangFormat 3.7) 
-#   this module set CLANG_FORMAT_EXECUTABLE, CLANG_FORMAT_VERSION
-#   and CLANG_FORMAT_FOUND accordingly
+#   this module set ClangFormat_EXECUTABLE, ClangFormat_VERSION
+#   and ClangFormat_FOUND accordingly
 #
-set(CLANG_FORMAT_FOUND 0)
-find_program(format_binary NAMES clang-format clang-format-3.6 clang-format-3.7 clang-format-3.8 clang-format-3.9 clang-format-4.0)
-if(EXISTS ${format_binary})
-  execute_process(COMMAND ${format_binary} -version OUTPUT_VARIABLE clang_out )
-  message("clang verison out" ${clang_out})
-  string(REGEX REPLACE ".*clang-format version ([0-9]+\\.[0-9]+).*"  "\\1" CLANG_FORMAT_VERSION ${clang_out})
-  set(CLANG_FORMAT_FOUND 1)
-  set(CLANG_FORMAT_EXECUTABLE ${format_binary})
-  if(optional argument passed)
-    check match with CLANG_FORMAT_VERSION
-    if(not matched)
-      message(INFO "Requested clang-format >= arg_passed, found ${CLANG_FORMAT_VERSION}"
-      set(CLANG_FORMAT_FOUND 0)
-    endif()
-  endif()
-  #message("clang-format executable: ${CLANG_FORMAT_EXECUTABLE}")
-  #message("clang-format version: ${CLANG_FORMAT_VERSION}")
+find_program(ClangFormat_EXECUTABLE NAMES clang-format clang-format-3.6 clang-format-3.7 clang-format-3.8 clang-format-3.9 clang-format-4.0)
+if(EXISTS ${ClangFormat_EXECUTABLE})
+  execute_process(COMMAND ${ClangFormat_EXECUTABLE} -version OUTPUT_VARIABLE clang_out )
+  string(REGEX REPLACE ".*clang-format version ([0-9]+\\.[0-9]+).*"  "\\1" ClangFormat_VERSION ${clang_out})
 endif()
 
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(ClangFormat 
+    REQUIRED_VARS ClangFormat_EXECUTABLE
+    VERSION_VAR ClangFormat_VERSION
+    )
+