FR: git commit --verbose equivalent for jj describe

[sullyj3]

Often when writing a commit message, it's useful to be able to see the diff at a glance. Git has git commit --verbose, which displays the diff inline in your editor while you're writing the message. This saves having to try to remember what changes you made.
I personally use this all the time. I have

alias gca='git commit --all --verbose'

which I use for committing almost exclusively.

It would be cool if jj supported this as well! I'm not wedded to the name --verbose, which I think could be clearer (and in fact looking at the help it conflicts with an existing flag with different functionality). Maybe --show-diff?

[ilyagr]

This could apply to quite a few commands (describe, split, squash, etc)

[martinvonz]

Maybe we can have a configurable template for producing that. We currently include something like this:

JJ: This commit contains the following changes:
JJ:     M lib/src/working_copy.rs
JJ:     M lib/tests/test_working_copy.rs

Maybe that could be replaced by a template like "This commit contains the following changes:\n" ++ indent(" ", diffsummary), and you could replace the diffsummary by diff (or gitdiff, perhaps) to get the full diff.

We don't yet have support for including a diff in templates, so we'd need to implement that first.

#1354 is slightly related.

[9999years]

I went looking for this feature, remembered jj has templates, and was a little surprised that jj describe didn't have a --template option for this yet, so I think templates would be a natural place to implement this. (Although I suspect this is a common enough use-case that a dedicated flag might be worthwhile, even if it's just an alias for --template=commit-with-diff or something.)

[Cretezy]

Looking for consensus before implementing this:

1. Should we use --show-diff for diff/squash/split?
2. Should we instead use a template feature for this?
3. If using template, how will this be used? Will jj ship with a built-in template for this?

[yuja]

1. Should we use --show-diff for diff/squash/split?

I think config knob is better. It was discussed previously in
#3470 (comment)

2. Should we instead use a template feature for this?

Template is preferred because it can solve other problems (such as #1354 and #3385), but it's not easy. I think adding a diff formatting option is also good as a short-term workaround.

3. If using template, how will this be used? Will jj ship with a built-in template for this?

Yeah. Perhaps, the default ui.default-description will be a template like

concat(
  description,
  "\n",
  "JJ: This commit contains the following changes:\n",
  indent("JJ:     ", format_diff_in_commit_description(diff)),
)

and format_diff_in_commit_description() will be customized by user.

[yuja]

Template is preferred because it can solve other problems (such as #1354 and #3385), but it's not easy.

FWIW, I'm working on commit.diff([paths]) template function, and I think a basic version can be added soon.

[lukerandall]

For those who stumble upon this; the nearest equivalent (since #4153) is to add something like this to your config file:

[templates]
draft_commit_description = '''
concat(
  description,
  surround(
    "\nJJ: This commit contains the following changes:\n", "",
    indent("JJ:     ", diff.stat(72)),
  ),
  surround(
    "\nJJ: Diff:\n", "",
    indent("JJ:     ", diff.git(3)),
  ),
)
'''

or if you don't want it all the time add an alias using --config-toml (in this example I use a template-alias to make the alias easier to read):

[aliases]
diffscribe = [
  "describe",
  "--config-toml=templates.draft_commit_description=\"commit_description_with_diff\"",
]

[template-aliases]
commit_description_with_diff = '''
concat(
  description,
  surround(
    "\nJJ: This commit contains the following changes:\n", "",
    indent("JJ:     ", diff.stat(72)),
  ),
  surround(
    "\nJJ: Diff:\n", "",
    indent("JJ:     ", diff.git()),
  ),
)
'''

The most notable deficiency is that you don't get diff highlighting in your text editor like you would with a git commit diff because of the prefixed JJ:.

Edited to fix git(72) → git() as noted by @tbodt below.

[tbodt]

 surround(
   "\nJJ: Diff:\n", "",
   indent("JJ:     ", diff.git(72)),
 ),

Important note - you almost certainly don't want diff.git(72), because the 72 becomes the number of lines of diff context! diff.git() appears to default to 3 lines of context which is fine.

[bryceberger]

Since #5155, you can now do something like:

[template-aliases]
commit_description_verbose = '''
concat(
  description,
  "\n",
  "JJ: This commit contains the following changes:\n",
  indent("JJ:    ", diff.stat(72)),
  "JJ: ignore-rest\n",
  diff.git(),
)
'''

[aliases]
dv = ["--config=templates.draft_commit_description=commit_description_verbose", "describe"]

[yuja]

Thanks. I think we can now close this issue?