Re: git-fetch: default globally to --no-tags

From: Jeff King <peff@peff.net>
Date: Nov 19, 2014, 18:57 UTC
Message-ID: <20141119185708.GA9908@peff.net>
In-Reply-To: <xmqqr3wzrpur.fsf@gitster.dls.corp.google.com>

On Wed, Nov 19, 2014 at 10:45:48AM -0800, Junio C Hamano wrote:

Show 25 quoted lines

> > My email boils down to two questions:
> >
> >   (A) Has there been progress on implementing a proposal like in [2]?
> 
> I do not think so, and also I do not agree that "mirror everybody
> else's ref hierarchy into separate namespaces" is necessarily a good
> idea, especially for tags, whose reason of existence is to give
> people a way to have anchoring points they agree on to have a shared
> world view necessary to move things forward.
> 
> In other words, talks in [2] are attempting to solve a wrong
> problem.  The problem people want to solve is to have a mechanism to
> keep private anchoring points that are not necessarily shared
> project wide, which tags in refs/tags hierarchy is *not*.
> 
> Like it or not, tags are meant to be used for globally shared
> anchoring points and the whole machinery (e.g. "fetch" that
> auto-follows tags, "clone" that gives refs/tags*:refs/tags/*
> refspec) is geared towards supporting that use pattern, which will
> be broken by moving tags to per-remote namespace.
> 
> I can see "git tag --local foo" that creates refs/local-tags/foo
> and also adding a mechanism to propagate local-tags/ hierarchy just
> like heads/ hierarchy is propagated per-remote as a solution to that
> problem that does not break the "release tags" use case, though.

I am not sure I agree here that the discussions in [2] were not handling this case. Here you are arguing for the tag-writer to distinguish between two separate namespaces: global and local.

But I think the proposals in [2] were about pushing that logic into the lookup phase. That is, pulling in all of the remote's tags as "refs/remotes/origin/tags/*", and then at lookup time checking multiple locations for tags (and preferring your local "refs/tags" to what is pulled from a remote).

I think that system is better because it gives flexibility in resolution to the viewer of the tags, not the writer. E.g., consider a project that is merging two different sub-projects, project1 and project2. Each of the sub-projects has their own global namespace with v1.0, v2.0, etc. They would never use local-tags; these are meant to be in a per-project global namespace.

But the superproject is pulling them both together; if it uses refs/tags, the global namespaces will clash. Instead, it would be more convenitn to have refs/remotes/project1/tags and so on. And then a lookup of "v1.0" can either prefer project1 to project2, vice-versa, or even respect neither. But the point is that the desired outcome is in the eye of the beholder, not the writer.

> This is a tangent, but it is an important one because we are talking
> about "tagopt" specifically.  I think we should start deprecating
> "*.tagopt --[no-]tags".

Thanks for writing this out. I touched on it in the other email I sent, but did not explain it very well. The transition you mentioned here is exactly what I was thinking of.

-Peff