coc-settings.json

{
    "languageserver": {
        "ccls": {
            "command": "ccls",
            "filetypes": [
                "c",
                "cpp",
                "objc",
                "objcpp"
            ],
            "rootPatterns": [
                ".ccls",
                "compile_commands.json",
                ".vim/",
                ".git/",
                ".hg/"
            ],
            "initializationOptions": {
                "index": {
                    "onChange": true
                },
                "highlight": { "lsRanges" : true },
                "cache": {
                    "directory": "/tmp/ccls"
                },
                "clang": {
                    "extraArgs": [
                        "-isystem/usr/local/include",
                        "-isystem/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1",
                        "-isystem/Library/Developer/CommandLineTools/usr/lib/clang/12.0.0/include",
                        "-isystem/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include",
                        "-isystem/Library/Developer/CommandLineTools/usr/include",
                        "-isystem/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks"
                    ],
                    "resourceDir": "/Library/Developer/CommandLineTools/usr/lib/clang/12.0.0"
                }
            }
        }
    }
}