Add multiple selection in diff view

[cruessler]

This is a first attempt at implementing multiple selection in the diff view.
You can use Shift+ArrowUp as well as Shift+ArrowDown to extend the
selection.

Known issue: If the selection spans more than one hunk, only the hunk that
contains the selection’s start is selected. I don’t know a good way to address
that. Preventing the selection from spanning more than hunk seems like an
obvious choice, but then, of course, you could only copy lines out of one hunk
at a time.

Still left to do is the actual copying to clipboard, but that should be fairly
easy once the above issue is resolved.

Closes #229.

[extrawurst]

looks already like a great start. only two minor things:

1. is it intended that when u do both up and down that it simply grows the selection in both directions instead of moving the bottom like usual?
2. similar to 1) I think the scrolling should still work and go with the movable part of the selection
3. I think after stopping to do selection up/down without shift it should land where the movable part of the selection was

[cruessler]

I have updated the PR.

ad 1) I found the initial behavior unexpected, too. I changed it so that Shift+Arrow now only moves the selection’s end which is closer to what you would expect if you come from vim.
ad 2), 3) I have not yet addressed that, but I’ll keep it in mind.

Doing the actual copying seems simple. At least on my machine (Ubuntu 20.04, X11), it worked immediately. Coming from vim, I have bound copy to y, but that can of course easily be changed.

[extrawurst]

@cruessler I checked out the changes. works better now, but I would like to be able to also scroll up beyond the start selection line (basically inverting start/end selection index).
also I can confirm the copy to cb works on Mac too👍

[cruessler]

@extrawurst I just updated the PR with another round of changes! You can now move the end past the start, and the content of the window scrolls, so that the end is always visible.

[extrawurst]

Hey man, this is getting close. Sorry for another round of feedback. Looks pretty good already. Hope those last few are not a big deal anymore. Love to merge this!❤️

[extrawurst]

@cruessler aside the linux question, can you rebase once more onto master, so we see if the windows pipeline (that got fixed now) runs through?

[extrawurst]

Thanks so much @cruessler - great work!

[cruessler]

@extrawurst One addition: I just saw that there are packages for Fedora and Arch. It is possible that they might need to be adapted to support clipboard access, but I am not familiar with building packages, so I don’t know how they work.

[extrawurst]

@ignatenkobrain maintains fedora and @wezm did AUR maybe you guys can chip in before we release this and ruin your day? :)

[wezm]

Looks like there's a couple of new runtime dependencies (xcb and friends). That's no big deal. 👍

[ignatenkobrain]

I think it is fine for Fedora, but right now we are not able to build gitui because there is some bug that makes rustc to segfault on ppc64le.