feat: Diff source autodetection and caching

[poliorcetics]

Following discussions in both #9892 and #8056, this PR adds diff source autodetection and caching.

Supported diff sources

• None
• Git (when the relevant feature is active)

Work left for another PR because it would clutter this one (it's possible not all of this will be implemented, those are ideas):

• Adding "File" Diff source
• Adding command to select diff source
• Adding config for diff source detection order
• Adding a statusline element to show the currently active diff source
• Adding support for JJ as an example of another vcs based diff source (see feat: vcs: support Jujutsu as a diff-provider #12022)

I did not find any issue about diff source autodetection, if there is one I missed tell me or edit the PR desc to mark it as closing the issue if relevant :)

[pascalkuthe]

if I see this right this does "autodetection" per document and turns diff provider into a per-document thing right?

I want this to be a config option in the future that can be set for the document with :set buffer::diff_source git for the buffer and :set diff.provider git globally.

All this is part of the config refactor I am working on. I also want to add an :unset option so you could do :unset buffer diff.provider to reset to the global diff source (otherwise if you change the global setting the global setting doesn't change).

If no explicit value is provided autodetection would be used.

This would be particularly relevant to this PR because I don't want the file diff source to be enabled by default. It's a neat feature but should be opt-in. That would mean its precluded from the auto-detection.

I was only thinking of VCS with the autodection. I thought that there would usually only be one vcs per workspace (we use .git for root detection anyway) so we would just do the autodetection once at startup/when changing directories.

[poliorcetics]

That's a lot of ideas in one comment :) !

This would be particularly relevant to this PR because I don't want the file diff source to be enabled by default. It's a neat feature but should be opt-in. That would mean its precluded from the auto-detection.

Sure I can do that easily, I don't have a strong opinion and copied the previous MR (1)

I thought that there would usually only be one vcs per workspace (we use .git for root detection anyway) so we would just do the autodetection once at startup/when changing directories.

I thought about that but for now I find it useless since the git repo is not kept open between diff calls. Ideally we would do it yes but I'm unsure it should be done in this MR just yet

There are also issues with updating this from external events and even just removing the git dir for example, but I think the proper solution will be to tell people to reload the diffs

I want this to be a config option in the future that can be set for the document with :set buffer::diff_source git for the buffer and :set diff.provider git globally.

that can be done in another MR without issues I feel

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I'll do (1) today, for the rest, especially keeping track of workspaces will need more work

[pascalkuthe]

I thought about that but for now I find it useless since the git repo is not kept open between diff calls. Ideally we would do it yes but I'm unsure it should be done in this MR just yet

I originally was thinking in the direction of just having a global config option that would be controlled by autodetection by default. I was hoping to go that direction since I wanted to avoid adding :diffsource (since it would be covered by :set buffer diff.source in the future) But on second thought I like having a typable command for this from a ui standpoint. We can alias that to :set buffer diff source in the future (I will probably do the same for other commands which set stuff per document right now which will become proper config options in the future).

There are also issues with updating this from external events and even just removing the git dir for example, but I think the proper solution will be to tell people to reload the diff

Yeah I think this should only update if people reload. Maybe something fancier once we have a filewatcher But that is still in the more distant future.

[poliorcetics]

I changed the approach completely:

• Removed the "File" diff source, I'll do it in a subsequent PR
• Removed the "diffsource" command since it's now useless
• Added diff provider caching, to avoid recomputing a git repo on each diff-related data gathering

[poliorcetics]

I'll add the "File" diff source and the "diffsource" command in a PR on top when this one is merged since it's an orthogonal issue and would make reviewing this harder