Re: error with $ git push origin HEAD:newbranch

[Jeff King <peff@peff.net>]

On Fri, May 06, 2011 at 02:16:03AM +0000, chris wrote:

> Jeff King <peff <at> peff.net> writes:
> > 
> > On Thu, May 05, 2011 at 10:06:21AM +0000, chris wrote:
> > 
> > > It is slightly surprising that git-push doesn't default to assuming 
> > > one means refs/heads/newbranch in this case.  I don't see a reason 
> > > not to?
> > 
> > Consider something like:
> > 
> >   $ git checkout v1.5
> >   $ git push origin HEAD:foo
> > 
> > Would you want "foo" to be a branch or a tag? I can see arguments for
> > either.
> 
> If the above command wanted to produce a tag, just provide 'v1.5' as the source 
> ref.  It seems to me that first checking out the tag then pushing from HEAD is 
> extra steps in order to push a branch ref without having to be explicit about 
> it.  $ git push origin v1.5:foo would have been simpler if intending to push a 
> tag ref.

Sure, but that was just a small example. It could just as easily have
been:

  $ git checkout v1.5
  ... look look look ...
  ... hmm, this one doesn't have the bug or feature I'm looking for ...
  $ git checkout v1.5.1
  ... look look look ...
  ... nor this one ...
  $ git checkout v1.5.2
  ... look look look ...
  ... oh, this one has it, let's push it upstream to communicate to
      somebody ...
  $ git push origin HEAD:foo

Sure, I _could_ say "git push origin v1.5.2:foo" in the final step. But
my mental model is "I have found the thing I am looking for, now push
it", which means HEAD is more natural.  This is more obvious to see when
you start leaving refs, like:

  $ git checkout HEAD^
  ... look look look; nope ...
  $ git checkout HEAD^
  ... look look look; nope ...
  $ git checkout HEAD^
  ... yep, found it ...
  $ git push origin HEAD:foo

So in both of those cases, what should be pushed? A tag or a branch? My
argument is that git would have to guess. Rather than guess, we come
back to the user and say "please be more specific".

> Given that git-push has specific syntax for pushing a tag, and git-push makes 
> other assumptions that give the perception it is generally used for branches 
> unless told otherwise also makes me expect that "foo" to be a branch.

That tag syntax is antique and predates most of the nice DWIM behavior
of refspecs. Nowadays you can just say "git push <remote> v1.5" and it
will do the same thing without the "tag" modifier. So I doubt anyone
uses it.

I wonder if we should more clearly mark it as useless in the
documentation.

> The following is provided for specifically calling out a tag:
> 
>   $ git push origin tag <refspec>
> 
> However, that syntax as far as I can tell is pretty worthless anyway, as the 
> following will not work:
> 
>   $ git push origin tag HEAD:newtag
>   error: src refspec refs/tags/HEAD does not match any.
> 
>   $ git push origin tag 183c65e:newtag
>   error: src refspec refs/tags/183c65e does not match any.

Right. It's literally about expanding "tag foo" into
"refs/tags/foo:refs/tags/foo". So it only works for a tag ref.

For both of those, you would need:

  git push origin HEAD:refs/tags/newtag

  git push origin 183c65e:refs/tags/newtag

> But both the following are successful, which makes me ask why the 'tag' option 
> exists if the above doesn't work.
> 
>   $ git push tag existingtag:newtag1
> 
>   $ git push existingtag:newtag2
> 
> So I see little purpose in the $ git push tag <refspec> syntax, as the source 
> must already be a tag anyway.

Right. Once upon a time, that didn't Just Work. These days we see that
the LHS of the refspec is a tag, and infer that the RHS should be, as
well (in the absence of anything more specific).

> Personally, I would prefer that git-push work on branches by default[1], 
> providing shortcuts for pushing tag[2] refs and remote branch[3] refs, while all 
> other ref types must be called out explicitly.  Creating new refs isn't 
> destructive, so it seems these could be supported without concern.
> 
> 1. $ git push origin SHA1:branch1
>   => $ git push origin SHA1:refs/heads/branch1
> 
> 2. $ git push origin tag SHA1:tagname
>   => $ git push origin SHA1:refs/tags/tagname
> 
> 3. $ git push origin SHA1:upstream/branch2
>   => $ git push origin SHA1:refs/remotes/upstream/branch2

In (3), how do you differentiate between the branch
"refs/heads/upstream/branch2" and the remote tracking branch
"refs/remotes/upstream/branches"?

-Peff