awful.screen.focus moves mouse to incorrect position after chaning re-enabling monitors with xrandr

[MaciekChudek]

Output of awesome --version:

awesome v4.3 (Too long)
 • Compiled against Lua 5.3.6 (running with Lua 5.3)
 • D-Bus support: ✔
 • execinfo support: ✔
 • xcb-randr version: 1.6
 • LGI version: 0.9.2

Output of xrandr -v:

xrandr program version       1.5.1
Server reports RandR version 1.6

How to reproduce the issue:

• connect and enable multiple monitors
• define shortcut to focus screens using awful.screen.focus()

    awful.key({ modkey,}, "w", function () awful.screen.focus(1) end, {description="Focus left screen", group="Focus"}),
    awful.key({ modkey,}, "e", function () awful.screen.focus(2) end, {description="Focus middle screen", group="Focus"}),
    awful.key({ modkey,}, "r", function () awful.screen.focus(3) end, {description="Focus right screen", group="Focus"}),

• ensure screen ordering with screen[i]:swap()
• shortcuts correctly shift focus and mouse cursor to last position on screen
• disable some screens with xrandr

xrandr --output $LEFT --off --output $MIDDLE --off

• enable those screens with xrandr

xrandr --output $MIDDLE --left-of $RIGHT --output $LEFT --left-of $MIDDLE

• shortcuts now position mouse in between monitors, though keyboard focus still correctly shifts to selected screen
  Actual result:

awful.screen.focus positions mouse between screens

Expected result:

awful.screen.focus continues to position mouse in last known position, even after adding/removing screens with xrandr

Suggested solution:

Reset last known mouse position on screens when added/removed. For example screen.mouse_per_screen = false, but this property is encapsulated and not accessible to users. Alternatively, provide a parameter that allows users to choose whether to restore mouse position on screen focus (screen.lua line 105: if not _screen.mouse_per_screen and not restore_mouse_position then)

[MaciekChudek]

After more digging, it looks like the cause is the mouse moving to screen edge automatically when monitors are added/removed, and this position being remembered and restored by awful.screen.focus. This can be solved by giving users the option to not return the mouse to its former position, which currently is mandatory.

I created a pull request with this functionality: #3517