bug#38044: 27.0.50; There should be an easier way to look at a specific vc commit

[Eli Zaretskii <eliz@gnu.org>]

> Cc: larsi@gnus.org, stephen.berman@gmx.net, 38044@debbugs.gnu.org,
>  juri@linkov.net
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Wed, 20 Nov 2019 01:17:18 +0200
> 
> > That's true, but I'd hesitate to introduce a new class of "show"
> > commands just because Git has it.  I see no problem showing the
> > meta-data with diffs (when Git is the back-end), perhaps with an
> > option to disable that.
> 
> These two sentences seem to contradict each other. To do the latter, we 
> need to "introduce a new class of show commands". Because vc-git-diff 
> won't print any metadata.

I was talking about the VC level, not the vc-git level.  vc-git could
have a show command, but the user of VC would still invoke a variant
of vc-diff.

> > My rationale is that other VCSes have a diff
> > command that shows only the diffs, and that command is used "to show"
> > a revision with those VCSes.
> 
> IMO the log message is more important because it describes and justifies 
> what happened. Showing the diff is good as well.

That's not relevant to the issue at hand.  Like it or not, VCSes other
than Git describe a revision by the diffs alone.

> Maybe the other VCSes don't have a simple command to do the same, but 
> they can either be called twice, or use special formatting. For 
> instance, Hg can use this command:
> 
> hg log -r <REV> -p

IMO, this is over-engineering.  If the VCS developers don't see the
need to have a commands which shows meta-data together with the diffs,
we should not force that on that VCS.  IOW, what Git does is not
necessarily the only game in town.

The VC level should be clean and uniform.  Any VCS-specific mindset
should not enter it too far, or else VC will not do its job of
insulating the user from the VCS differences well.