Subject: Re: idea: git "came from" tags

From: Michael J Gruber <[email-masked]>
Date: Mon, 18 Jan 2010 10:49:38 +0100

D Herring venit, vidit, dixit 18.01.2010 05:22:
> Actors:
> - public "upstream" repository
> - public "local" repository
> - end users tracking both
> 
> Situation:
> - local starts by tracking upstream
> - local makes changes, commits, and sends upstream
> - users now tracking local ahead of upstream

Here I have to ask why. If users choose to track a volatile branch then
they have to live with rebasing or hard resets. If they want something
stable then they should track upstream.

> - upstream makes modified commits
> - local satisfied, wants to reset master to upstream/master
> 
> Problem:
> - A merge will perpetually leave two parallel branches.  Even though
> there are no longer any diffs, local/master cannot use the same
> objects as upstream/master.

If there are no diffs then, in fact, it can share most objects since
most trees will be the same, only a few commit objects will differ.

> - A hard reset lets local/master return to sharing objects with
> upstream/master; but this may break pulls or cause other problems for
> users.
> 
> Proposed solution:
> - Local adds a "came from" tag to upstream/master, leaves a tag on the
> head of local/master, and does a hard reset from local/master to
> upstream/master.  When a user tracking local/master does a pull, their
> client detects a non-fast-forward, finds the came-from tag, and treats
> it as a fast-forward.
> 
> Basically, this is a protocol to glue a "strategy ours" merge onto an
> existing tree.  This way local can cleanly track upstream, with no
> added complexity in the nominal (no local changes) case.

But doesn't that mean that users completely trust you about what they
should consider a fast forward, i.e. when they should do a hard reset?
So, this is completely equivalent to following one of your branches with
+f, i.e. having a public a branch which they pull from no matter what,
and having a private branch which pushes to the public one in case of
fast-forwards as well as in the case when you would use your special tag.

Michael