Run clang-format to format a buffer and keep the cursor location intact

clang-format.lua

local clang_format_bin = "clang-format"

local function run_clang(args, input, on_done)
    local uv = vim.uv

    local stdin = uv.new_pipe(false)
    local stdout = uv.new_pipe(false)

    local chunks = {}

    local function on_read(err, data)
        assert(not err, err)
        if data then
            table.insert(chunks, data)
        end
    end

    local handle
    handle, _ = uv.spawn(clang_format_bin, {
        args = args,
        stdio = { stdin, stdout, nil },
    },
    vim.schedule_wrap(function(code, signal)
        stdout:read_stop()
        stdout:close()
        handle:close()

        local output = table.concat(chunks)
        on_done(output)
    end))

    uv.write(stdin, input)
    stdin:close()

    uv.read_start(stdout, on_read)

    uv.run('once')
end

local function clang_format()
    local lines = vim.api.nvim_buf_get_lines(0, 0, -1, false)
    local input = table.concat(lines, "\n")
    local cursor = vim.api.nvim_win_get_cursor(0)

    local function on_done(output)
        local new_lines = vim.split(output, "\n", { plain = true })
        local json_message = table.remove(new_lines, 1)
        local json_decoded = vim.json.decode(json_message)
        vim.api.nvim_buf_set_lines(0, 0, -1, false, new_lines)

        local new_cursor = json_decoded["Cursor"]
        local row = 0
        while row < #new_lines and new_cursor > vim.api.nvim_buf_get_offset(0, row + 1) do
            row = row + 1
        end
        local col = new_cursor - vim.api.nvim_buf_get_offset(0, row)

        vim.api.nvim_win_set_cursor(0, { row + 1, col })
    end

    local offset = cursor[2] + vim.api.nvim_buf_get_offset(0, cursor[1] - 1)
    run_clang({ "--cursor=" .. tostring(offset), }, input, on_done)
end

vim.api.nvim_create_user_command("CF", clang_format, {})