Note: This PR is stacked on top of #452 (adds $width variable for preview commands). Please merge #452 first.

fyi the issue with delta side-by-side has a workaround as discussed in #314 (comment)

linting is failing, please run go fmt

Thank! Let me explain a bit better what is the problem. When pressing d on a file in jjui, the built-in diff view runs the diff command inside the TUI. With delta's --side-by-side, two issues occur:

1. Width detection fails - Delta can't detect the terminal width when running inside jjui's TUI, so side-by-side columns render incorrectly
2. Pager doesn't work - Delta's pager (less) needs an interactive terminal, which isn't available in the embedded view

The workaround in #314 avoids the problem by disabling side-by-side mode entirely (side-by-side = false). That works, but you lose the side-by-side feature.

This PR solves it properly by:

• Adding $width so delta knows the exact terminal width
• Adding show = "interactive" to open the diff in a real terminal where the pager works

This lets you use delta with --side-by-side as intended, without compromises.

Hey thanks,

This side by side diff issue when using delta is coming up regularly and at this point I am just ignoring it. I don't feel comfortable adding a configuration block just to enable integration one of the tools out there.

My take on this is that;

If you want to use a custom pager for diffs, you can unbind the d from the internal diff view and define a custom command that binds to d and invokes the external diff viewer in an interactive session. You already have the command for that. I understand delta doesn't read the width of the terminal and defaults to 50 and it is the root cause here. I would instead have a look at why that's the case, because it should be able to query the terminal dimensions itself. Maybe our interactive session is missing some env variables for it to be able to do that or maybe that feature doesn't exists at all. In either case, I don't think the solution is to customise jjui to patch that gap.

avoids the problem by disabling side-by-side mode entirely (side-by-side = false). That works, but you lose the side-by-side feature.

hey @pablospe , i'm using delta side-by-side with no issue at all, using the config suggested in #314 ,

.gitconfig

[delta "split-view"]
    side-by-side = true

[delta "non-split-view"]
    side-by-side = false

[delta]
    features = split-view
    navigate = true
    line-numbers = true

jj/config.toml:

[ui]
diff-formatter = [
    "bash",
    "-c",
    "delta --width $width $left $right --features=split-view || true",
]
pager = "delta"

@baggiiiie Thanks! One question. Is this working for you when you enter to delta from jjui (when opened from the file list l shortcut)?
navigate = true # use n and N to move between diff sections

Is this working for you when you enter to delta from jjui (when opened from the file list l shortcut)?

display works fine when showing diff from file list, tho it's only display, losing pager's other functionalities (regarding pager, related discussion see #366 )

losing pager's other functionalities

Yes, exactly, thanks for the video and the confirmation. I thought I was missing something. This is exactly what I noticed and wanted to solve with this PR, which allow me to have the full delta experience with n/N navigation (pager functionalities).

you can unbind the d from the internal diff view and define a custom command that binds to d and invokes the external diff viewer in an interactive session

@idursun
Before we abandon this PR. How would you do that? I mean, unbind and bind again? I tried with this configuration:

  [keys]
  diff = []

  [keys.details]
  diff = []

  [custom_commands.deltadiff]
  key = ["d"]
  args = ["util", "exec", "--", "bash", "-c", "jj diff --git --color always -r $change_id $file | delta --pager 'less -R +g'"]
  show = "interactive"

but it doesn't seem to be working:

• d is only working in the revision list
• d is not working In the details view (after pressing l) → how do I re-bind d to shows diff for a specific file with a custom command?

@idursun ignore my previous message. I found a solution for what I wanted to achieve with this PR, I think the inline format made the difference (somehow).

In jjui config file:

# Unbind built-in diff key to allow custom command to handle it
[keys]
diff = []

# Interactive diff with delta (works in both revision list and details view)
# - $change_id: replaced with selected revision
# - $file: replaced with selected file (in details view) or empty (in revision view)
# - show = "interactive": opens real terminal so delta's pager/navigation works
[custom_commands]
"deltadiff" = { key = ["d"], args = ["util", "exec", "--", "bash", "-c", "jj diff --git --color always -r $change_id $file | delta --pager 'less -R +g'"], show = "interactive" }

@baggiiiie Could you give a try to this? It will give you the pager's functionalities. And you don't need to touch .gitconfig and jj/config anymore, only jjui/config.

@pablospe nice thanks, your custom command works!

Ok, we can close this PR. Thanks for the help both and the very useful tool, @idursun and @baggiiiie.