Re: [PATCH 5/7] shortlog: implement `--group=author` in terms of `--group=<format>`

> Instead of handling SHORTLOG_GROUP_AUTHOR separately, reimplement it as
> a special case of the new `--group=<format>` mode, where the author mode
> is a shorthand for `--group='%aN <%aE>'.
>
> Note that we still need to keep the SHORTLOG_GROUP_AUTHOR enum since it
> has a different meaning in `read_from_stdin()`, where it is still used
> for a different purpose.
>
> Signed-off-by: Taylor Blau <me@ttaylorr.com>
> ---
>  builtin/log.c      |  1 +
>  builtin/shortlog.c | 23 ++++++++++++-----------
>  shortlog.h         |  1 +
>  3 files changed, 14 insertions(+), 11 deletions(-)
>
> diff --git a/builtin/log.c b/builtin/log.c
> index ee19dc5d45..6b77e520b5 100644
> --- a/builtin/log.c
> +++ b/builtin/log.c
> @@ -1334,6 +1334,7 @@ static void make_cover_letter(struct rev_info *rev, int use_separate_file,
>  	log.in2 = 4;
>  	log.file = rev->diffopt.file;
>  	log.groups = SHORTLOG_GROUP_AUTHOR;
> +	shortlog_init_group(&log);
>  	for (i = 0; i < nr; i++)
>  		shortlog_add_commit(&log, list[i]);
>  
> diff --git a/builtin/shortlog.c b/builtin/shortlog.c
> index f708d96558..aac8c7afa4 100644
> --- a/builtin/shortlog.c
> +++ b/builtin/shortlog.c
> @@ -245,15 +245,6 @@ void shortlog_add_commit(struct shortlog *log, struct commit *commit)
>  	}
>  	oneline_str = oneline.len ? oneline.buf : "<none>";
>  
> -	if (log->groups & SHORTLOG_GROUP_AUTHOR) {
> -		strbuf_reset(&ident);
> -		format_commit_message(commit,
> -				      log->email ? "%aN <%aE>" : "%aN",
> -				      &ident, &ctx);
> -		if (!HAS_MULTI_BITS(log->groups) ||
> -		    strset_add(&dups, ident.buf))
> -			insert_one_record(log, ident.buf, oneline_str);
> -	}
>  	if (log->groups & SHORTLOG_GROUP_COMMITTER) {
>  		strbuf_reset(&ident);
>  		format_commit_message(commit,
> @@ -372,6 +363,16 @@ void shortlog_init(struct shortlog *log)
>  	log->format.strdup_strings = 1;
>  }
>  
> +void shortlog_init_group(struct shortlog *log)
> +{
> +	if (!log->groups)
> +		log->groups = SHORTLOG_GROUP_AUTHOR;
> +
> +	if (log->groups & SHORTLOG_GROUP_AUTHOR)