For those using YCM

.gitignore

@@ -5,3 +5,4 @@ bin/
 cmake_install.cmake
 lib/
 tags
+.ycm_extra_conf.pyc

.ycm_extra_conf.py

+import os
+import ycm_core
+
+# These are the compilation flags that will be used in case there's no
+# compilation database set (by default, one is not set).
+# CHANGE THIS LIST OF FLAGS. YES, THIS IS THE DROID YOU HAVE BEEN LOOKING FOR.
+flags = [
+'-Wall',
+'-Werror',
+'-pendantic-errors',
+'-std=c++0x',
+'-fno-strict-aliasing',
+'-O3',
+'-DNDEBUG',
+# ...and the same thing goes for the magic -x option which specifies the
+# language that the files to be compiled are written in. This is mostly
+# relevant for c++ headers.
+# For a C project, you would set this to 'c' instead of 'c++'.
+'-x',
+'c++',
+'-I',
+'.',
+'-isystem',
+'/usr/include',
+'-isystem',
+'/usr/local/include',
+]
+
+
+# Set this to the absolute path to the folder (NOT the file!) containing the
+# compile_commands.json file to use that instead of 'flags'. See here for
+# more details: http://clang.llvm.org/docs/JSONCompilationDatabase.html
+#
+# Most projects will NOT need to set this to anything; you can just change the
+# 'flags' list of compilation flags. Notice that YCM itself uses that approach.
+compilation_database_folder = ''
+
+if os.path.exists( compilation_database_folder ):
+  database = ycm_core.CompilationDatabase( compilation_database_folder )
+else:
+  database = None
+
+SOURCE_EXTENSIONS = [ '.cc' ]
+
+def DirectoryOfThisScript():
+  return os.path.dirname( os.path.abspath( __file__ ) )
+
+
+def MakeRelativePathsInFlagsAbsolute( flags, working_directory ):
+  if not working_directory:
+    return list( flags )
+  new_flags = []
+  make_next_absolute = False
+  path_flags = [ '-isystem', '-I', '-iquote', '--sysroot=' ]
+  for flag in flags:
+    new_flag = flag
+
+    if make_next_absolute:
+      make_next_absolute = False
+      if not flag.startswith( '/' ):
+        new_flag = os.path.join( working_directory, flag )
+
+    for path_flag in path_flags:
+      if flag == path_flag:
+        make_next_absolute = True
+        break
+
+      if flag.startswith( path_flag ):
+        path = flag[ len( path_flag ): ]
+        new_flag = path_flag + os.path.join( working_directory, path )
+        break
+
+    if new_flag:
+      new_flags.append( new_flag )
+  return new_flags
+
+
+def IsHeaderFile( filename ):
+  extension = os.path.splitext( filename )[ 1 ]
+  return extension in [ '.h', '.hxx', '.hpp', '.hh' ]
+
+
+def GetCompilationInfoForFile( filename ):
+  # The compilation_commands.json file generated by CMake does not have entries
+  # for header files. So we do our best by asking the db for flags for a
+  # corresponding source file, if any. If one exists, the flags for that file
+  # should be good enough.
+  if IsHeaderFile( filename ):
+    basename = os.path.splitext( filename )[ 0 ]
+    for extension in SOURCE_EXTENSIONS:
+      replacement_file = basename + extension
+      if os.path.exists( replacement_file ):
+        compilation_info = database.GetCompilationInfoForFile(
+          replacement_file )
+        if compilation_info.compiler_flags_:
+          return compilation_info
+    return None
+  return database.GetCompilationInfoForFile( filename )
+
+
+def FlagsForFile( filename, **kwargs ):
+  if database:
+    # Bear in mind that compilation_info.compiler_flags_ does NOT return a
+    # python list, but a "list-like" StringVec object
+    compilation_info = GetCompilationInfoForFile( filename )
+    if not compilation_info:
+      return None
+
+    final_flags = MakeRelativePathsInFlagsAbsolute(
+      compilation_info.compiler_flags_,
+      compilation_info.compiler_working_dir_ )
+  else:
+    relative_to = DirectoryOfThisScript()
+    final_flags = MakeRelativePathsInFlagsAbsolute( flags, relative_to )
+
+  return {
+    'flags': final_flags,
+    'do_cache': True
+  }