Custom merge tool like vimdiff1?

[heygarrett]

I'm trying to set up a custom merge tool that works like vimdiff1:

"$merge_tool_path" -f -d \
	-c 'echon "Resolve conflicts leftward then save. Use :cq to abort."' \
	"$LOCAL" "$REMOTE"

The problem is this, from the Jujutsu docs linked above:

$output (REQUIRED) is replaced with the name of the file that the merge tool should output. jj will read this file after the merge tool exits.

But $output contains both sides of the conflict as well as the conflict markers (or is otherwise empty).

Is there a way to do something like this?

[merge-tools.nvim]
program = "nvim"
merge-args = [
	"-f", "-d",
	"$left", "$right",
]

I only want $left and $right when resolving the conflict, and I want the contents of $left to be the file that jj reads after the merge tool exits.

[bnjmnt4n]

You could write a custom shell script wrapper which invokes nvim with only the $left and $right arguments, then copies the contents of the $left file to $output. Perhaps something like the following (untested):

[merge-tools.nvim]
program = "nvim-wrapper.sh"
merge-args = ["$left", "$right", "$out"]

#!/bin/sh
nvim -f -d $1 $2
cp $1 $3

[heygarrett]

Oh, that's what the second part of vimdiff1 is doing. 🤦‍♂️

Okay, this works. I wonder, though, if it would be possible to store this as a jj alias instead of a separate shell script. 🤔

[heygarrett]

Actually, I think I found another, albeit slightly different, way to do this with a Neovim command:

[merge-tools.nvimdiff]
program = "nvim"
merge-args = ["-c", "JJdiff", "-d", "$left", "$output", "$right"]

vim.api.nvim_create_user_command("JJdiff", function()
	local left_contents = vim.api.nvim_buf_get_lines(0, 0, -1, true)
	-- close $left
	vim.cmd.diffoff()
	vim.cmd.close()
	-- put contents of $left into $output
	vim.api.nvim_buf_set_lines(0, 0, -1, true, left_contents)
end, { desc = "jj diff setup" })

[heygarrett]

Thank you for your help, @bnjmnt4n!

[rafikdraoui]

For people looking for a similar workflow, there is the jj-diffconflicts Neovim plugin. It makes use of the materialized conflicts so that in some situations it can automatically resolve parts of the conflicts, leaving only the ambigous parts for the human to resolve.

For example, given the following situation:

Base:

twas bri1lig, and the slithy toves
did gyre and gimble in the wabe
all mimsy were the borogroves
and the m0me raths outgabe.

"Beware the Jabberwock, my son!
The jaws that bite, the claws that catch!
Beware the Jub jub bird, and shun
The frumious bandersnatch!"

Left:

'Twas brillig, and the slithy toves
Did gyre and gimble in the wabe:
All mimsy were the borogroves
And the mome raths outgabe.

"Beware the Jabberwock, my son!
The jaws that bite, the claws that catch!
Beware the Jub jub bird, and shun
The frumious bandersnatch!"

Right:

twas brillig, and the slithy toves
Did gyre and gimble in the wabe:
all mimsy were the borogoves,
And the mome raths outgrabe.

"Beware the Jabberwock, my son!
The jaws that bite, the claws that catch!
Beware the Jubjub bird, and shun
The frumious Bandersnatch!"

The following conflict is generated by Jujutsu:

<<<<<<< Conflict 1 of 1
%%%%%%% Changes from base to side #1
-twas bri1lig, and the slithy toves
-did gyre and gimble in the wabe
-all mimsy were the borogroves
-and the m0me raths outgabe.
+'Twas brillig, and the slithy toves
+Did gyre and gimble in the wabe:
+All mimsy were the borogroves
+And the mome raths outgabe.
+++++++ Contents of side #2
twas brillig, and the slithy toves
Did gyre and gimble in the wabe:
all mimsy were the borogoves,
And the mome raths outgrabe.
>>>>>>> Conflict 1 of 1 ends

"Beware the Jabberwock, my son!
The jaws that bite, the claws that catch!
Beware the Jubjub bird, and shun
The frumious Bandersnatch!"

When using the vimdiff1 tool described in this discussion, the following UI is shown:

When using jj-diffconflicts, the following UI is shown:

Notice that that there is no need to resolve the changes to "Beware the Jubjub bird, and shun" and "The frumious Bandersnatch!", since only one side of the conflict touched those lines, and so Jujutsu already knows how to pick the correct ones.

In addition, jj-diffconflicts can include an "History view" in a new tab that displays both conflict sides in relation to their base, which can sometime help determine how a conflict should be resolved if not already obvious from the two-way diff: