[bug#50359] [PATCH 3/3] import: Add 'generic-git' updater.

[Sarah Morgensen <iskarian@mgsn.dev>]

Hi,

Xinglu Chen <public@yoctocell.xyz> writes:

> On Wed, Sep 15 2021, iskarian@mgsn.dev wrote:
>
>> Hi,
>>
>> September 10, 2021 9:21 AM, "Xinglu Chen" <public@yoctocell.xyz> wrote:
>>
>>> * guix/git.scm (ls-remote-refs): New procedure.
>>> * tests/git.scm ("remote-refs" "remote-refs: only tags"): New tests.
>>> * guix/import/git.scm: New file.
>>> * doc/guix.texi (Invoking guix refresh): Document it.
>>> * tests/import-git.scm: New test file.
>>> * Makefile.am (MODULES, SCM_TESTS): Register the new files.
>>> 
>>> Co-authored-by: Sarah Morgensen <iskarian@mgsn.dev>
>>
>> Overall this is looking good.  Thank you for adding tests (for
>> remote-refs as well!), much appreciated.  It looks like you've done
>> some good polishing.  I see a few nits, which I'll point out in a
>> separate email when I'm not on mobile.  I'll also give it a good test.
>>
>> But... I've been thinking about the overall approach for a couple
>> days, because I'm not very happy with the complexity of my heuristic.
>>
>> There can be a lot of weird tags in a repository--look at the one for
>> xf86-video-intel for example.  My heuristic attempts to capture the
>> assumption that repostories tend to move from using "_" or "-" to "."
>> but it does fail to account for moving to or from dates (because dates
>> don't compare with normal versions).
>
> But if a repo moved from using versions to tags, or vice-versa, we still
> wouldn’t know if say “3.0.1” is newer than “2021.03.02”.  We would have
> to know when the “3.0.1” tag was created.

You're right; I thought of that afterwards.

> Maybe we could have a ‘release-tag-date-scheme?’ property, that way we
> could just try to match dates?

That seems like it might be the only way to handle it in some cases (if
they have both versions and dates with a "." delimiter).  (Though, we
are actually interested in the *lack* of a date scheme.  If they use a
date scheme now, other versions will be disregarded, so we're fine; but
if they use versions now and used a date scheme before, the versions
will be discarded.)

>> I also realized that we are not using a very useful piece of
>> information--the previous version/tag combo.  I expect that in the
>> vast majority of cases, the version delimiter for the newest version
>> will be the same as the version delimiter for the last known version.
>> (Perhaps the prefix as well?)  Can we use this information to make our
>> guesses better?  What do you think?
>
> That sounds like a good idea.  What should happen if the delimiter from
> the previous version/tag combo is different from the one that the
> ‘guess-delimiter’ procedure returns?  Should the one from the previous
> version/tag combo take precedence.

Consider:

  prefix := 'tag-prefix or guess-prefix-from-current-version+tag or default
  delim := 'tag-delim or guess-delim-from-current-version+tag or guess-delimiter
  suffix := 'tag-suffix or default

This should cover:

  1. Format stayed the same (including date formats)
  2. Format changed from (git-version ...) to proper version

This does not otherwise cover a complete change in format, such as "_"
-> ".", date(-) -> version, or version -> date(.), for which I could
argue requiring a manual update is reasonable.  It also does not cover
when the tags have both versions and dates with the same delimiter.

Though it would be nice to see when such updates are available, is it
worth some bogus results?  Are false positives better or false negatives
better?

Unless you/we want to pursue one or both of the above changes now, the
latest patch LGTM (modulo my nits).

Thanks for your work,
--
Sarah