Re: Git merge should report an actual syntax error when a semicolon is used instead of space for specifying multiple branches

From: Junio C Hamano <gitster@pobox.com>
Date: Apr 12, 2019, 15:21 UTC
Message-ID: <xmqqd0lrxn9i.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <NVqJoDneX4bKnXsESFmcKt_7jDQE8Wk9l_F9rkNcnplXgV8TVjfbaMIhKfZ2v9BwJrJ2QJYcq-E6UdshPdhKttO4bIUGdsbs0zZUPNwQvUY=@protonmail.com>

Ron <ronazek@protonmail.com> writes:

>> I do not know what "git fetch" uses semicolon for here. Care to
>> elaborate?
>
> Those were all typos, I meant colon, two dots. Sorry.

Do you mean to say that because you can say

	$ git fetch origin +master:refs/remotes/origin/master

you expected that you can say this?

	$ git merge +master:refs/remotes/origin/master

The "git merge" command takes one or more commit-ishes to be merged to the current branch on its command line, and the above command line is correct at the syntax level.

But because 'master:refs/remotes/origin/master' does not name a commit-ish, it is the right thing to barf, saying that it is not something the command can merge.

If you replace the colon with space, that would mean an entirely different thing, i.e.

	$ git merge master refs/remotes/origin/master

would mean "I want two commit-ishes, the tip of my 'master' branch, and the last observed commit at the tip of the 'master' branch at the 'origin' repository, merged into the branch that is currently checked out, making an octopus merge". It also is syntactically correct, but it may not be what you wanted to do. Most likely, you would have rather wanted to do one of these:

	$ git merge refs/remotes/origin/master
	$ git merge origin/master
	$ git merge origin

In any case, because the "what to fetch, followed by where to store it, separated by a colon, with how to store it optionally signalled by a leading plus sign" argument syntax used by "git fetch" must convey a lot more (and different kind of) information than "which commit to merge to the currently checked-out branch" argument syntax used by "git merge", these two commands have to take quite different kind of information and use quite different ways to express these two kinds of information at the syntax level. The 'master' on the left-hand-side of the colon used by "git fetch" does not even name the 'master' branch _you_ have, while "git merge" that is a totally local operation only can name a commit-ish object that is locally available (e.g. a request to merge the 'master' branch you have would say "git merge master").