Re-run diff pager on terminal size change

[snoopdouglas]

Describe the bug

When the terminal is resized, the git diff isn't reproduced. This can mean line breaks don't get updated, eg. when using delta.

To Reproduce

1. Set delta (with colour) as your pager.
2. Open Lazygit to view a diff.
3. Resize the window.

Expected behavior

The pager should be re-run, ideally with an effort made to keep its view scrolled to the same place in the new terminal size.

Screenshots

Before resize:

After:

Version info:

commit=, build date=, build source=voidlinux, version=0.48.0, os=linux, arch=amd64, git version=2.49.0

Additional context

n/a

[stefanhaller]

The problem here is that lazygit can't tell when the user is done resizing the window (i.e. whether the mouse is still down). Ideally we want to rerun the diff only when the resize gesture is done, not again and again with every mouse-move, this would be very inefficient. One ugly way to handle this could be some sort of timer based heuristic to throttle reloads. I'm not excited about adding this.

But I'm also wondering how much of a problem this really is; for diffs of your working files this will fix itself after at most 10 seconds, and for other diffs it is easily fixed by selecting the commit again (e.g. by pressing down-up).

How often do you resize your terminal windows?

ideally with an effort made to keep its view scrolled to the same place in the new terminal size

Now this is an interesting aspect though, one that I have been thinking about in other contexts (e.g. when increasing or decreasing the diff context size using { and }; it's so painful to lose the scroll position there). It's not trivial to do though; when no pager is used it should be possible to parse the diff and work out which line of which source file is at the top of the window (or in the middle?), and then parse the new diff and find the same line again there, or pick the next closest one if it's no longer in the diff. If a pager is used, things get trickier; we'd need some support from the pager for this, see #3986 for some thoughts about that.

[snoopdouglas]

How often do you resize your terminal windows?

I'm using a tiling WM, so it can happen rather often. I know it's a small thing but it'd be a useful fix.

As for waiting until the window has stopped being resized, I guess debouncing would be the solution? eg. only re-run the diff once 0.25s has elapsed since the previous resize.

Am I right in thinking the actual paging/scrolling is done in Lazygit itself (hence the --no-pager suggestion for delta)?

[stefanhaller]

Am I right in thinking the actual paging/scrolling is done in Lazygit itself (hence the --no-pager suggestion for delta)?

Yes.