Re: Confusion about diffing branches

From: Junio C Hamano <gitster@pobox.com>
Date: Aug 27, 2007, 07:07 UTC
Message-ID: <7vlkbxmp50.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <20070827014056.GB7422@mediacenter.austin.rr.com>

Shawn Bohrer <shawn.bohrer@gmail.com> writes:

> So if I understand you correctly people in the git world are simply more
> used to typing two dots (instead of three) so that is why the two dot
> notation shows the more common use case (show me the difference between
> the tip of the master branch and the tip of the topic branch).

No, what I said was that two dot form is merely there to avoid saying 'if you want to diff two trees, do not say "diff a..b" but say "diff a b", dummy!'. Instead of giving such an error message, we just say "oh, you want difference between a and b? here it is".

As to which is common between "diff a..b" and "diff a...b", that really depends. You seem to be hinting that you think a...b is more useful but that is not always the case. Comparing two arbitrary trees _is_ the base form of diff, and that is what "diff a b" gives you. It does not require two trees to be related in ancestry relationships in _any_ way. For example, you can say "git diff v2.6.20 v2.6.21" or "git diff v2.6.20.4 v2.6.21.2".

On the other hand, when you are into topic branch development workflow, "diff a...b" is often useful but that does not mean people using topic branch development does not need "diff a b" form. You can say either "diff a b" if you want straight diff between two trees, or "diff a...b" if you want "what happened in b, since it forked from the history leading to a"; if the two-dot form confuses you, you do not have to use that synonym.

Both semantics of two-dot form and three-dot form are useful, and choice between the two depends on what you want out of the command. You just need to know which one you want.