Workaround for header flags with compilation db

cpp/ycm/.ycm_extra_conf.py

@@ -83,6 +83,7 @@ flags = [
 './tests/gmock/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
@@ -96,6 +97,7 @@ if compilation_database_folder:
 else:
   database = None
 
+SOURCE_EXTENSIONS = [ '.cpp', '.cxx', '.cc', '.c', '.m', '.mm' ]
 
 def DirectoryOfThisScript():
   return os.path.dirname( os.path.abspath( __file__ ) )
@@ -130,11 +132,37 @@ def MakeRelativePathsInFlagsAbsolute( flags, working_directory ):
   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 = database.GetCompilationInfoForFile( filename )
+    compilation_info = GetCompilationInfoForFile( filename )
+    if not compilation_info:
+      return None
+
     final_flags = MakeRelativePathsInFlagsAbsolute(
       compilation_info.compiler_flags_,
       compilation_info.compiler_working_dir_ )

python/ycm/completers/cpp/flags.py

@@ -60,7 +60,7 @@ class Flags( object ):
                                             filename,
                                             client_data )
 
-      if not results.get( 'flags_ready', True ):
+      if not results or not results.get( 'flags_ready', True ):
         return None
 
       flags = list( results[ 'flags' ] )