Adding a diff mode to micro

[ilyagr]

I think it would be very useful to have an easy-to-use TUI for viewing and editing diffs, a cross between vimdiff and meld. I am specifically interested in this because of jj-vcs/jj#48, but it would also be very useful for any users of both git and ssh who are unfamiliar with vim.

At a glance, micro seems like a great foundation for a diff tool, and a diff mode would be a nice addition to micro (it was requested in #2510 and #1244). @zyedidia, do you think this is a good idea? Would this be in scope for micro? Would you review pull requests on this topic?

I would probably first work on scroll lock between files based on a diff (micro already seems to understand the concept of diffs for the diff gutters).

Not to raise anybody's hopes too much, I would be working on this in my free time, so there's no guarantee anything would come out of this quickly or at all, even if @zyedidia is willing.

[PThorpe92]

I'm interested in the feature and could contribute, if this is something zyedidia wants to implement.

[ilyagr]

Feel free to take a look at #2759, the first PR in what will hopefully become a series. I also added an outline of a plan below.

[ilyagr]

As a rough outline, my plan is as follows:

1. Next diff / previous diff commands
2. Make micro compute the line correspondence between a buffer and its diffbase
3. A -diff command-line option to open buffers in pairs with each other set up as diffbase. Change the next & previous diff commands to move paired buffers together.
4. Command to synchronize cursor position in paired buffers. Perhaps an option to make them scroll together.

A (very rough) draft of portions of this is in https://github.com/ilyagr/micro/tree/diffdraft2 currently.

A significant obstacle is that there needs to be some way to test all of this functionality.

After that, some additional important steps will be:

5. (help wanted) Highlighting of changed text inside the diff buffer (as opposed to the diff gutter).
6. (help wanted) Improve the diff algorithm. Make it better at matching modified lines. The module micro uses for diffs may well be capable of this, but currently micro uses a only the tiny subset of it necessary to show the diffgutter.
7. Commands to move modified from left to right and vice-versa. Perhaps a separate keyboard scheme for diffing, taking over combinations such as Alt+Down.
8. Better UI for showing which lines correspond to which, like Meld (unless we can think of something better), at least in vertical layout. This will probably require a new UI Node type for files in paired diffs, so that the diffgutter can go on the right in the left file and lines are drawn between the diffgutter of the left file and that of the right file.

And in some uncertain future, we could make it possible to diff more than 2 files at a time (like the 4-pane view for merges in Vim, but hopefully better), but this might be beyond the scope of this feature.

[PThorpe92]

I was just checking out the PR and was just about to ask about your general ideas when you posted this. Let's see what zyedidia thinks about it but it sounds / looks good. Idk maybe 4-pane view seems like that's just asking for headaches when you're dealing with so many environments/OS's and even more terminals/emu's on top but I could be wrong that's just my first impression.

I'm buried in a React project atm 😒 so I don't want to make promises as far as time but if it's greenlighted go ahead a maybe start a project? and I'll start digging through these libraries when I can make time. Go is always a welcome relief and this codebase is well written.

[ilyagr]

What do you mean "start a project"? You like Github's project tab? I can't edit this repo's projects, but I suppose I could make something in my fork.

As for the 4-pane view, it is a very distant consideration, I'm not sure if it's right for micro. I don't think environments and terminals would be a problem there, since micro already implemented all the complicated bits there, but designing it so that it doesn't feel complicated and confusing is hard, and it would require implementing things like moving left/up/right between panes. It's all doable, but I'm not sure it's a good idea.

[PThorpe92]

haha I thought about how little that tab gets used but yeah it would have to be on your fork and that defeats the entire purpose.