Fs widget issue on callback (missing "function" type check)

[Sébastien Le Corre]

Install information

Running on Archlinux

$ awesome -v
awesome v4.3 (Too long)
 • Compiled against Lua 5.3.5 (running with Lua 5.3)
 • D-Bus support: ✔
 • execinfo support: ✔
 • xcb-randr version: 1.6
 • LGI version: 0.9.2
$ lua5.3 -v
Lua 5.3.6  Copyright (C) 1994-2020 Lua.org, PUC-Rio

First observed on lain version 6b3bdca (but same content observed on master latest commit)

Expected behaviour

No silent error (none displayed in the usual red popup, but present in X logs).

Steps to reproduce the problem

Use the following rc.lua (no other configuration required)

local awful = require("awful")
local wibox = require("wibox")
local lain  = require("lain")

local fsroothome = lain.widget.fs({
    partition = "/home",
    settings  = function()
        widget:set_markup(" " .. fs_now["/home"].percentage .. "% ")
    end,
    followtag = true,
})

awful.screen.connect_for_each_screen(function(s)
    s.mylayoutbox = awful.widget.layoutbox(s)
    s.mywibox = awful.wibar({ position = "top", screen = s, height = 18 })
    s.mywibox:setup {
        layout = wibox.layout.align.horizontal,
        {
            layout = wibox.layout.fixed.horizontal,
            fsroothome,
        },
    }
end)

X error log

Obtained through awmtt, a script around Xephyr, results in

$ awmtt start -C rc.lua 
2021-01-13 03:50:41 E: awesome: Error during a protected call: /usr/share/lua/5.3/lain/widget/fs.lua:141: attempt to call a table value (upvalue 'callback')
stack traceback:
	/usr/share/lua/5.3/lain/widget/fs.lua:141: in function </usr/share/lua/5.3/lain/widget/fs.lua:138>
	[C]: in function 'xpcall'
	/usr/share/awesome/lib/gears/protected_call.lua:36: in function </usr/share/awesome/lib/gears/protected_call.lua:35>
	(...tail calls...)
Caution: NOT using a test file (rc.lua)
Display: 1, Awesome PID: 84384, Xephyr PID: 84368

Possible fix

From what I could gather, it comes from the test performed on the callback in the update function (l.137) :

    function fs.update(callback)
        Gio.Async.start(gears.protected_call.call)(function()
            update_synced()
            if callback then
                callback()
            end
        end)
    end

Possible fix

The following type check seems to solve it , but considering I'm not a LUA developer (besides a couple of Nmap NSE scripts), I'd like your opinion if I'm missing something elsewhere, or if introspection is not the way to go here before opening a PR.

    function fs.update(callback)
        Gio.Async.start(gears.protected_call.call)(function()
            update_synced()
            if type(callback) == "function" then callback()
        end)
    end

Edit

I found the two other widgets that use a callback in their update function, alsabar and pulsebar, and both implement the same type check before calling :

if type(callback) == "function" then callback() end