Closest equivalent for git describe --tags?

[BatmanAoD]

I really like using git describe --tags as an easy way to generate a version string. It has the following advantages:

• Extremely simple
• Always uniquely identifies the state of the code (as long as versions are not reassigned)
• If the current HEAD is on a commit corresponding to a release tag, you get that release version
• The commit-info is formatted as a valid semver prerelease tag; thus, if the version tags used are semver-compatible, the generated string is always semver-compatible

Is there anything like this in jj? For collocated repos git describe --tags works, but I think it would be good to have a native command that behaves similarly.

[moderation]

I had a similar question and just found https://github.com/hymkor/jjtagdesc. It doesn't look like it works anymore probably due to output changes in jj but it might provide some ideas

[shanesveller]

Loosely borrowed a few small particulars from this, and I came up with:

jj log -r 'latest(tags())::@- ~ empty()' --no-graph --reversed -T 'commit_id.short(10) ++ " " ++ tags ++ "\n"' \
| awk '{latest = $1; count++}; $2 != "" && tag == "" { tag = $2 } END {print tag "-" count "-" latest}'

My awk skill level is atrocious, so it can probably be golfed down some more. Tested with jj 0.25.0.

[lgarron]

@shanesveller: Thanks, that was very helpful! I found three discrepancies:

• Git includes a g at the beggining of the hash.
• Git includes 8 characters of the hash.
• This snippet counts an empty working commit, so the count is off. It's possible to use (count - 1), but that will presumably be off if you haven't done jj new on a commit.

Fixing the first two gives me:

jj log -r 'latest(tags())::@- ~ empty()' --no-graph --reversed -T 'commit_id.short(8) ++ " " ++ tags ++ "\n"' \
  | awk '{latest = $1; count++}; $2 != "" && tag == "" { tag = $2 } END {print tag "-" count "-g" latest}'

[moderation]

This is awesome. Thanks for sharing. I converted to a Fish shell function which is working well:

# https://github.com/jj-vcs/jj/discussions/2563
function jj_describe --description 'replicate git describe --tags for jj'
    
    set count 0
    set tag ""
    set latest_commit ""

    set jj_output (jj log -r 'latest(tags())::@- ~ empty()' --no-graph --reversed -T 'commit_id.short(10) ++ " " ++ tags ++ "\n"')

    for line in $jj_output
        set count (math $count + 1)
        set -l parts (string split " " $line)
        set latest_commit $parts[1]

        if test (count $parts) -gt 1; and test -z "$tag"
            set tag (string sub --start 2 $parts[2])
        end
    end

    printf "%s-%d-%s\n" $tag $count $latest_commit

end

[lgarron]

I have a program that helps me implement common operations across repositories, across both git and jj: https://github.com/lgarron/repo

Matching git describe --tags is really not very simple.

• When the latest commit is a tag, the count and the hash should not be printed. Not too hard.
• I only just learned about git_head(). No one's mentioned it here yet!
• Counting commits must be done manually, with a chance for an off-by-one error depending on the implementation.
• https://git-scm.com/docs/git-describe says the number of hex digits in the hash "(will vary according to the number of objects in the repository with a default of 7) … or as many digits as needed to form a unique object name". It's not yet clear to me if .short() implements the latter.
• When the minimum distance to each of multiple commits is the same, jj's selection of the latest() is incorrect. https://git-scm.com/docs/git-describe states:

If multiple tags were found during the walk then the tag which has the fewest commits different from the input commit-ish will be selected and output. Here fewest commits different is defined as the number of commits which would be shown by git log tag..input will be the smallest number of commits possible.

I don't see a way to do this with jj without listing all the closest tags and calculating the range for each. This seems silly and error-prone.¹ Something like a nearest() function to match git would be useful here.

And that's all not even mentioning other flags for git describe, or even the functionality when --tags is not passed (which only considers annotated tags).

Footnotes

1. In fact, I haven't even figured out how to list all closest tags. heads(tags()) only returns a single result even if there are multiple tags at the same distance. Enumerating all tags would be unacceptably inefficient. I probably need something like tags() & ~(tags()+..), except that doesn't work. ↩

[jkuebart]

I know this is lame, but given the original motivation

For collocated repos git describe --tags works

this worked for me as a very quick hack both for colocated and non-colocated repos:

git -C "$(jj git root)" \
    describe --tags \
    "$(jj log --limit 1 --no-graph --template commit_id)"

[bnjmnt4n]

You might want to use jj git root, in case the internal repository format changes.

[jkuebart]

Thanks! Great suggestion, updated.