feat: add focus-column-or-monitor-left, focus-column-or-monitor-right

[lpnh]

Partially addresses: #296

This is a preliminary sketch for implementing focus-column-or-monitor-left and focus-column-or-monitor-right, which expand the default left and and right focus behaviors. If a window is available in the target direction, it receives focus; otherwise, the focus shifts to the corresponding monitor.

Current state: it kinda works, but there are cases that still need to be fixed. I will try to provide a better description soon.

To be completely honest, I'm new to the Niri codebase, so there's a lot I'm still unsure about. I was hoping to provide a good starting point for this PR, but it seems like I still have a lot to learn.

Any feedback would be greatly appreciated.

[lpnh]

Well, it seems both focus-window-or-monitor-left and focus-window-or-monitor-right are now working as expected.

A couple of things about the implementation:

maybe_focus_window_or_monitor_*

• I'm not entirely sure if using a boolean here is the most idiomatic approach, but it seems like a reasonable solution to avoid adding further complexity.
• The "maybe" prefix try to suggest that this function depends on the availability of the output and that it's not solely responsible for handling the focus.

FocusWindowOrMonitor*

• Given the need to manage the output and handle three different possible cases, the structure ended up quite clear.
• The main challenge seems to be handling both focus and cursor at the same time.

Now, about the test... I'm not quite sure how to write it properly. I attempted to provide some, but I am unsure if they make any sense.

This was very fun, so I wouldn't mind rewriting anything you think could be improved. Also, feel free to take it from here.

[YaLTeR]

Sorry for taking so long to review, just some minor changes needed.

I'm not entirely sure if using a boolean here is the most idiomatic approach

It's alright.

Now, about the test... I'm not quite sure how to write it properly. I attempted to provide some, but I am unsure if they make any sense.

Seems correct. Just random index should be from 1 because the output random indices are 1 to 5.

[YaLTeR]

Looks good.

[YaLTeR]

Wait, I just realized. Could you rename Window to Column throughout? Left-Right focus goes by columns, not by windows, and other actions are also focus-column-left, etc.

[lpnh]

Wait, I just realized. Could you rename Window to Column throughout? Left-Right focus goes by columns, not by windows, and other actions are also focus-column-left, etc.

Sure! I had the same thought initially. We might have been influenced by the initial request. Thanks for catching this.

[lpnh]

May I move them next to the other Column variables?

[YaLTeR]

Yeah

[YaLTeR]

Thanks!