Subject: Re: [PATCH/RFC] WIP: log: allow "-" as a short-hand for "previous branch"

From: Matthieu Moy <[email-masked]>
Date: Wed, 08 Feb 2017 15:40:28 +0100

Siddharth Kannan <[email-masked]> writes:

> Making a change in sha1_name.c will touch a lot of commands
> (setup_revisions is called from everywhere in the codebase), so, I am
> still trying to figure out how to do this such that the rest of the
> codepath remains unchanged.

Changing sha1_name.c is the way to go *if* we want all commands to
support this. Just like other ways to name a revision...

> I hope that you do not mind this side-effect, but rather, you intended
> for this to happen, right? More commands will start supporting this
> shorthand, suddenly.  (such as format-patch, whatchanged, diff to name
> a very few).

... but: the initial implementation of this '-' shorthand was
special-casing a single command (IIRC, "git checkout") for which the
shorthand was useful.

In a previous discussion, I made an analogy with "cd -" (which is the
source of inspiration of this shorthand AFAIK): "-" did not magically
become "the last visited directory" for all Unix commands, just for
"cd". And in this case, I'm happy with it. For example, I never need
"mkdir -", and I'm happy I can't "rm -fr -" by mistake.

So, it's debatable whether it's a good thing to have all commands
support "-". For example, forcing users to explicitly type "git branch
-d @{1}" and not providing them with a shortcut might be a good thing.

I don't have strong opinion on this: I tend to favor consistency and
supporting "-" everywhere goes in this direction, but I think the
downsides should be considered too. A large part of the exercice here is
to write a good commit message!

Another issue with this is: - is also a common way to say "use stdin
instead of a file", so before enabling - for "previous branch", we need
to make sure it does not introduce any ambiguity. Git does not seem to
use "- for stdin" much (most commands able to read from stdin have an
explicit --stdin option for that), a quick grep in the docs shows only
"git blame --contents -" which is OK because a revision wouldn't make
sense here anyway.

-- 
Matthieu Moy
http://www-verimag.imag.fr/~moy/