YouCompleteMe не работает с заголовочными файлами

Можно создать специальный скрипт .ycm_extra_conf.py, который будет выдавать флаги для компиляции для тех файлов, которых нет в базе данных. Конкретных реализаций может быть несколько, но один из вариантов конфигурации, который я использую у себя приведён ниже.

~/.vim/ycm_extra_conf.py

ЕМНИП основан на одном из .ycm_extra_conf.py в самом ycm'е

#
# This is free and unencumbered software released into the public domain.
#
import os
import ycm_core
import re
# 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.
def_flags = [
  '-fexceptions'
]
forse_flags = [
  '-Wall',
  '-Wextra'
]
def Log(msg):
  pass
#  with open("/tmp/ycm_extra_conf.log", "a") as f: 
#    f.write("%s\n" % msg)
Log("loading extraconfig file")
if ( os.path.exists(os.getcwd() + "/compile_commands.json") ):
  compilation_database_folder = os.getcwd()
else:
  compilation_database_folder = ''
if os.path.exists( compilation_database_folder ):
  Log ("Found compilation database")
  database = ycm_core.CompilationDatabase( compilation_database_folder )
else:
  Log ("Compilation database not found")
  database = None
C_SOURCE_EXTENTION = [ '.c' ]
CPP_SOURCE_EXTENTION = [ '.cpp', '.cxx', '.cc' ]
OBJECTIVE_C_SOURCE_EXTENTION = [ '.m', '.mm' ]
SOURCE_EXTENSIONS = C_SOURCE_EXTENTION + CPP_SOURCE_EXTENTION + OBJECTIVE_C_SOURCE_EXTENTION
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 GetExtension( filename ):
    return os.path.splitext( filename )[ 1 ];
def IsHeaderFile( filename ):
  return GetExtension(filename) 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 LangForFile( filename ):
    # determine lang (-x) flag
    lang = None
    extension = GetExtension (filename)
    # set the language according to file extension
    if extension in C_SOURCE_EXTENTION:
        Log("Language determined as C because of extension")
        lang = "c"
    elif extension in CPP_SOURCE_EXTENTION:
        Log("Language determined as C++ because of extension")
        lang = "c++"
    elif IsHeaderFile(filename):
        Log("Determin language for header")
        # .h header might fit both c and c++, if there is a cpp file in the same dir, use C++
        # otherwise use C
        for ext in CPP_SOURCE_EXTENTION:
            if os.path.exists( basename + ext ):
                lang = 'c++'
                break
        if not lang:
            for ext in C_SOURCE_EXTENTION:
                if os.path.exists( basename + ext ):
                    lang = 'c'
                    break
        if not lang:
            # neither c nor cpp file of the same name, lets count which  of them more in the dir
            c_num = 0
            cpp_num = 0
            for f in os.listdir( os.path.dirname(filename) ):
                if os.path.splitext( f )[ 1 ] in C_SOURCE_EXTENTION   : c_num   += 1 
                if os.path.splitext( f )[ 1 ] in CPP_SOURCE_EXTENTION : cpp_num += 1 
            if c_num>cpp_num:
                lang="c"
            else: # even if there is equal count of both, give up it and use c++
                lang = "c++"
    # no fall back... let clang to decide
    return lang

def CustomFlagsForFile( filename ):
    rv = []
    with open(filename) as f:
        for line in f:
            m = re.match (r'\s*//\s*c(xx)?flags:(.*)', line)
            if m:
                rv += m.group(2).split()
            m = re.match (r'\s*//\s*pkg-config cflags:(.*)', line)
            if m:
                for word in m.group(1).split():
                    cmd = "pkg-config --cflags " + word;
                    Log ("Running '" + cmd + "'")
                    rv += os.popen (cmd).read().split()
    return rv

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:
      Log("no compilation info found")
      return None
    final_flags = MakeRelativePathsInFlagsAbsolute(
      compilation_info.compiler_flags_,
      compilation_info.compiler_working_dir_ )
  else:
    Log("Going to use default flags")
    relative_to = os.path.dirname(filename)
    flags = def_flags
    flags += CustomFlagsForFile (filename)
    # set the language if it is determined
    lang = LangForFile( filename )
    if lang:
        Log("Appending language to flags")
        flags += ['-x', lang]
        if lang == "c++":
            flags += ["-std=c++14"]

    final_flags = MakeRelativePathsInFlagsAbsolute( flags, relative_to )
  Log("Compilation flags for file \"" + str(filename) + "\" are:" + str(final_flags))
  return {
    'flags': forse_flags + final_flags,
    'do_cache': True
  }

~/.vimrc

let g:ycm_global_ycm_extra_conf="~/.vim/ycm_extra_conf.py"

Флаги для компиляции хедеров берутся из флагов .c/.cpp файлов с тем же именем. Помимо этого, скрипт дополнительно добавляет -Wall и -Wextra, а если база данных компиляции отсутствует, то угадывает язык и из пытаетсф достать флаги компиляции из файла по шаблонам // cflags: и // pkg-config cflags. Последнее предназначено по большей части для однофайловых тестовых программок.

Само собой, скрипт может потребовать подгонки под свои привычки.