neovim/runtime/lua/vim/lsp/log.lua

-- Logger for language client plugin.

local log = {}

-- FIXME: DOC
-- Should be exposed in the vim docs.
--
-- Log level dictionary with reverse lookup as well.
--
-- Can be used to lookup the number from the name or the name from the number.
-- Levels by name: "TRACE", "DEBUG", "INFO", "WARN", "ERROR"
-- Level numbers begin with "TRACE" at 0
log.levels = vim.deepcopy(vim.log.levels)

-- Default log level is warn.
local current_log_level = log.levels.WARN
local log_date_format = "%F %H:%M:%S"
local format_func = function(arg) return vim.inspect(arg, {newline=''}) end

do
  local path_sep = vim.loop.os_uname().version:match("Windows") and "\\" or "/"
  ---@private
  local function path_join(...)
    return table.concat(vim.tbl_flatten{...}, path_sep)
  end
  local logfilename = path_join(vim.fn.stdpath('cache'), 'lsp.log')

  --- Returns the log filename.
  ---@returns (string) log filename
  function log.get_filename()
    return logfilename
  end

  vim.fn.mkdir(vim.fn.stdpath('cache'), "p")
  local logfile = assert(io.open(logfilename, "a+"))

  local log_info = vim.loop.fs_stat(logfilename)
  if log_info and log_info.size > 1e9 then
    local warn_msg = string.format(
      "LSP client log is large (%d MB): %s",
      log_info.size / (1000 * 1000),
      logfilename
    )
    vim.notify(warn_msg)
  end

  -- Start message for logging
  logfile:write(string.format("[START][%s] LSP logging initiated\n", os.date(log_date_format)))
  for level, levelnr in pairs(log.levels) do
    -- Also export the log level on the root object.
    log[level] = levelnr
    -- FIXME: DOC
    -- Should be exposed in the vim docs.
    --
    -- Set the lowercase name as the main use function.
    -- If called without arguments, it will check whether the log level is
    -- greater than or equal to this one. When called with arguments, it will
    -- log at that level (if applicable, it is checked either way).
    --
    -- Recommended usage:
    -- ```
    -- local _ = log.warn() and log.warn("123")
    -- ```
    --
    -- This way you can avoid string allocations if the log level isn't high enough.
    log[level:lower()] = function(...)
      local argc = select("#", ...)
      if levelnr < current_log_level then return false end
      if argc == 0 then return true end
      local info = debug.getinfo(2, "Sl")
      local header = string.format("[%s][%s] ...%s:%s", level, os.date(log_date_format), string.sub(info.short_src, #info.short_src - 15), info.currentline)
      local parts = { header }
      for i = 1, argc do
        local arg = select(i, ...)
        if arg == nil then
          table.insert(parts, "nil")
        else
          table.insert(parts, format_func(arg))
        end
      end
      logfile:write(table.concat(parts, '\t'), "\n")
      logfile:flush()
    end
  end
end

-- This is put here on purpose after the loop above so that it doesn't
-- interfere with iterating the levels
vim.tbl_add_reverse_lookup(log.levels)

--- Sets the current log level.
---@param level (string or number) One of `vim.lsp.log.levels`
function log.set_level(level)
  if type(level) == 'string' then
    current_log_level = assert(log.levels[level:upper()], string.format("Invalid log level: %q", level))
  else
    assert(type(level) == 'number', "level must be a number or string")
    assert(log.levels[level], string.format("Invalid log level: %d", level))
    current_log_level = level
  end
end

--- Gets the current log level.
---@return string current log level
function log.get_level()
  return current_log_level
end

--- Sets formatting function used to format logs
---@param handle function function to apply to logging arguments, pass vim.inspect for multi-line formatting
function log.set_format_func(handle)
  assert(handle == vim.inspect or type(handle) == 'function', "handle must be a function")
  format_func = handle
end

--- Checks whether the level is sufficient for logging.
---@param level number log level
---@returns (bool) true if would log, false if not
function log.should_log(level)
  return level >= current_log_level
end

return log
-- vim:sw=2 ts=2 et