branch --set-upstream considered harmful

[Jay Soffian <jaysoffian@gmail.com>]

Say I have an existing branch and it doesn't have a tracking config.
(My local users often just do "checkout -b topic" instead of "checkout
-b topic origin/master".)

I would naively expect this to work, while on that branch:

  (topic)$ git branch --set-upstream origin/master

But, um no:

  (topic)$ git branch --set-upstream origin/master
  Branch origin/master set up to track local branch topic.

Doh!

Well, maybe this works:

  (topic)$ git branch --set-upstream origin/master topic
  Branch origin/master set up to track local branch topic.

Doh!^2

Well, maybe we can say "HEAD" since that seems to mean "the current
branch" everywhere else in gitland:

  (topic)$ git branch --set-upstream HEAD origin/master
  Branch HEAD set up to track remote branch master from origin.

(Aside, being able to create a branch named HEAD is surely a bug, right?)

Finally after exhausting all other possibilities (or finally making
sense of --set-upstream in the man page), we realize:

  (topic)$ git branch --set-upstream topic origin/master
  Branch topic set up to track remote branch master from origin.

Trying to make myself feel better, I realize that this works:

  (topic)$ git branch topic --set-upstream origin/master

So here's how I'm thinking about fixing it, but maybe I'm just making
it even more confusing. What say you:

  (topic)$ git branch --set-upstream=origin/master
  Branch topic set up to track remote branch master from origin.

--track would be similarly enhanced, which allows a little more
flexibility in creating a branch thusly:

  $ git branch --track=origin/master topic

Which creates topic, starting from HEAD, but tracking origin/master.
(And I'd do the same for checkout's --track option.)

I recognize that having both positional and non-positional forms of
--track/--set-upstream  may be confusing, but I think it's less
confusing than set-upstream's current semantics, I'm loathe to
introduce yet another option, and I don't want to break backward
compatibility.

Flames?

j.