Re: [RFC PATCH v2] shortlog: add group-by options for year and month

[Jeff King <peff@peff.net>]

On Wed, Oct 05, 2022 at 05:43:20PM -0400, Taylor Blau wrote:

> > Heh, I was about to make the exact same suggestion. The existing
> > "--group=author" could really just be "--group='%an <%ae>'" (or variants
> > depending on the "-e" flag).
> 
> This caught my attention, so I wanted to see how hard it would be to
> implement. It actually is quite straightforward, and gets us most of the
> way to being able to get the same functionality as in Jacob's patch
> (minus being able to do the for-each-ref-style sub-selectors, like
> `%(authordate:format=%Y-%m)`).

Yeah, your patch is about what I'd expect.

The date thing I think can be done with --date; I just sent a sketch in
another part of the thread.

> +static void insert_record_from_pretty(struct shortlog *log,
> +				      struct strset *dups,
> +				      struct commit *commit,
> +				      struct pretty_print_context *ctx,
> +				      const char *oneline)
> +{
> +	struct strbuf ident = STRBUF_INIT;
> +	size_t i;
> +
> +	for (i = 0; i < log->pretty.nr; i++) {
> +		if (i)
> +			strbuf_addch(&ident, ' ');
> +
> +		format_commit_message(commit, log->pretty.items[i].string,
> +				      &ident, ctx);
> +	}

So here you're allowing multiple pretty options. But really, once we
allow the user an arbitrary format, is there any reason for them to do:

  git shortlog --group=%an --group=%ad

versus just:

  git shortlog --group='%an %ad'

?

>  void shortlog_add_commit(struct shortlog *log, struct commit *commit)
>  {
>  	struct strbuf ident = STRBUF_INIT;
> @@ -243,6 +266,8 @@ void shortlog_add_commit(struct shortlog *log, struct commit *commit)
>  	if (log->groups & SHORTLOG_GROUP_TRAILER) {
>  		insert_records_from_trailers(log, &dups, commit, &ctx, oneline_str);
>  	}
> +	if (log->groups & SHORTLOG_GROUP_PRETTY)
> +		insert_record_from_pretty(log, &dups, commit, &ctx, oneline_str);

I was puzzled at first that this was a bitwise check. But I forgot that
we added support for --group options already, in 63d24fa0b0 (shortlog:
allow multiple groups to be specified, 2020-09-27).

So a plan like:

  git shortlog --group=author --group=date

(as in the original patch in this thread) doesn't quite work, I think.
Because the semantics for multiple --group lines are that the commit is
credited individually to each ident. That's what lets you do:

  git shortlog -ns --group=author --group=trailer:co-authored-by

and credit authors and co-authors equally. So likewise, I think multiple
group-format options don't really make sense (or at least, do not make
sense to concatenate; you'd put each key in its own single format).

> @@ -321,8 +346,10 @@ static int parse_group_option(const struct option *opt, const char *arg, int uns
>  	else if (skip_prefix(arg, "trailer:", &field)) {
>  		log->groups |= SHORTLOG_GROUP_TRAILER;
>  		string_list_append(&log->trailers, field);
> -	} else
> -		return error(_("unknown group type: %s"), arg);
> +	} else {
> +		log->groups |= SHORTLOG_GROUP_PRETTY;
> +		string_list_append(&log->pretty, arg);
> +	}

We probably want to insist that the format contains a "%" sign, and/or
git it a keyword like "format:". Otherwise a typo like:

  git shortlog --format=autor

stops being an error we detect, and just returns nonsense results
(every commit has the same ident).

I think you'd want to detect SHORTLOG_GROUP_PRETTY in the
read_from_stdin() path, too. And probably just die() with "not
supported", like we do for trailers.

> I think you could also do some cleanup on top, like replacing the
> SHORTLOG_GROUP_AUTHOR mode with adding either "%aN <%aE>" (or "%aN",
> without --email) as an entry in the `pretty` string_list.

Yeah, that would be a nice cleanup. I think might even be a good idea to
explain the various options to the users in terms of "--author is
equivalent to %aN <%aE>". It may help them understand how the tool
works.

-Peff