Neovim LSP (ccls) and coc settings for AVR development

This is a short guide to getting AVR header completion on a Linux system. Note that I have never tried to compile using clang (I use avr-gcc in a separate Makefile).

Minimal Neovim LSP configuration

lua << EOF
require "lspconfig".ccls.setup {
    init_options = {documentFormatting = true},
    settings = {
        rootMarkers = {".ccls",".git/"},
        languages = {
            lua = {
                {formatCommand = "lua-format -i", formatStdin = true}
            }
        }
    }
}
EOF

If using coc, it can be provided with include paths as extra arguments. The coc config file is easiest found by typing :CocConfig in Neovim.

{
    "languageserver": {
        "ccls": {
            "command": "ccls",
            "filetypes": ["c", "cpp", "objc", "objcpp"],
            "rootPatterns": [".ccls", "compile_commands.json", ".vim/", ".git/", ".hg/"],
            "initializationOptions": {
                "cache": {
                    "directory": "/tmp/ccls" 
                },
                "clang": {
                    "extraArgs": [
                        "-isystem/usr/lib/clang/13.0.0/include",
                        "-isystem/usr/local/include",
                        "-isystem/usr/include"
                    ],
                    "resourceDir": "/usr/lib/clang/13.0.0"
                }
            }
        }
    }
}

One problem with this configuration on my machine is that the LSP crashes when displaying -Wall. This is my .ccls file in the project root, in this case using an ATMega328p

clang
-target
avr
-mmcu=atmega328p
-nostdinc
-ffreestanding
-isystem/usr/avr/include
%h -x
%h c-header

Some versions of ccls does not load this file properly if there are trailing spaces or an empty line at EOF.