Linematch, diffopt, and diffget/put not working as expected.

[SeniorMars]

Problem

Linematch and diffget do not work correctly together. I use diffget to resolve merge conflicts, and with this new diffopt option, I'm not getting the expected behavior.

Since merging is a complicated mess, I tried to record what I mean in a 17second gif:

Steps to reproduce

Generally:

1. Have a merge conflict and start with nvim -d
2. Set diffopt+=linematch:50
3. Try to use :diffget <buffer num/name>

I see that diffget does not resolve a merge conflict as I expected.

Expected behavior

With the default options of diffopt, using diffget with nvim -d, I can resolve merge conflicts, but not with linematch appened to diffopt.

Neovim version (nvim -v)

NVIM v0.9.0-dev-2446+g995196c61-dirty

Vim (not Nvim) behaves the same?

No, as linematch is not implmented yet: vim/vim#9661

Operating system/version

macOS 13.2.1

Terminal name/version

kitty

$TERM environment variable

xterm-kitty

Installation

brew

related to #14537 and perhaps #20931

[lewis6991]

@jwhite510. Do you know why this might be?

[jwhite510]

@SeniorMars
@lewis6991
Sorry, I did not see this until now

linematch with diffget looks like it's working as I'd expect.

As the differences are more granular, the 'diffget' and 'diffput' operations
behave accordingly.

The difference when it comes to 'diffget' and 'diffput' operations is that this
conflict is no longer treated as a single diff, it is now 6 diffs, stacked on
top of each other

  BUFFER 1   BUFFER 2   BUFFER 3  BUFFER 4
----------------------------------------------
           |           |       |<<<<<< HEAD     DIFF 1
-----------|-----------|-------|--------------
rabbits    |           |       |rabbits         DIFF 2
lions      |           |       |lions
-----------|-----------|-------|--------------
salamanders|salamanders|       |salamanders     DIFF 3
-----------|-----------|-------|--------------
           |           |       |======          DIFF 4
-----------|-----------|-------|--------------
           |           |Monkeys|Monkeys         DIFF 5
-----------|-----------|-------|--------------
	   |           |       | >>>>>> monkey  DIFF 6
----------------------------------------------

when you have the cursor in buffer 4 and call a :diffget from buffer 3, it is getting
it, and it is non existent, so you see that just the '<<<<< HEAD' is erased.

I believe the behaviour you are looking for can be obtained by first visually
selecting the entire conflict (buffer 4 in my diagram), and then typing
:diffget buffer 3

like this:

:'<,'>diffget ...

so that diffget will be applied to each diff (all 6) in the visual selection

when you disable linematch, the entire thing is one diff, and diffget will get
the whole content because it is just one diff, you don't have to visually
select it