implement upstream AUR diff

[vn971]

When installing new versions of an already installed package, the user should be able to review changes made upstream. This includes PKGBUILD and other files.

[Morganamilo]

I just pushed this crate https://docs.rs/aur-fetch which may be useful to you. Better error messages is still a todo for me but it should be usable.

One slight problem is that I designed it for batch downloads. As in the helper should resolve all the deps via the RPC ahead of time, then pass all of them to this crate and download them at once. Of course doing it in multiple batches is possible but probably makes it much more annoying to use.

And here's an example binary using this crate: https://asciinema.org/a/MnMRusp1XSRo3ZR5MG7PYqlBh

[vn971]

@Morganamilo interesting. I must note that it's a hard problem though: the ways how you can combine diffing, fetching and asking user questions is pretty broad. I'll take a look at your proposal.

[Morganamilo]

I built this with that in mind. It's a proper library, It never prints anything on it's own. That's up to whoever uses the crate to decide. It does support diffs both as just strings and 'views'.

The view method is pretty much a clone of how aurutils does it if you're familiar with that.

Also this isn't a proposal (otherwise this would be a PR :P) and more hey look at this. But seems as you do want diffs I'd be interested in feedback and if the crate is insufficient in any way for what you want to do.