Re: [1.8.0] Provide proper remote ref namespaces

[Johan Herland <johan@herland.net>]

On Wednesday 02 February 2011, Santi Béjar wrote:
> On Wednesday 02 February 2011, Johan Herland wrote:
> > Proposal:
> >
> > Currently, git stores remote refs in the local repo by default as
> > follows:
> >
> >  Remote repo    ->   Local repo
> >  ---------------------------------------------------------
> >  HEAD                refs/remotes/$remote/HEAD  (implicit)
> >  refs/heads/*        refs/remotes/$remote/*
> >  refs/tags/*         refs/tags/*         (implicit, autofollow)
> >  refs/replace/*      (TBD) 
> >  refs/notes/*        (TBD)
> >
> > Instead, we should change the default ref mappings into the
> > following:
> >
> >  Remote repo    ->   Local repo
> >  --------------------------------------------------
> >  HEAD                refs/remotes/$remote/HEAD
> >  refs/heads/*        refs/remotes/$remote/heads/*
> >  refs/tags/*         refs/remotes/$remote/tags/*
> >  refs/replace/*      refs/remotes/$remote/replace/*
> >  refs/notes/*        refs/remotes/$remote/notes/*
>
> [...]
>
> > - We might want to generalize the handling of "$remote/$head" into
> > allowing shorthands like "$remote/$tag", "$remote/$replace" and
> > "$remote/$note" as well (provided, of course, that they match
> > unambiguously).
>
> [...]
>
> > [2]: When looking up a shorthand tag name (e.g. v1.7.4): If a local
> > tag (refs/tags/v1.7.4) is found, then we have an unambiguous match.
> > If no local tag is found, we look up the tag name in all configured
> > remotes (using the method described in [1]). If the tag name exists
> > in one or more remotes, and those remotes all agree on its ultimate
> > object name (after applying e.g. ^{commit} or whatever is
> > appropriate in the context of the lookup), then we also have an
> > unambiguous match. However, if the tag name exists in multiple
> > remotes, and they do NOT all agree on its ultimate object name,
> > then the shorthand tag name is ambiguous and the lookup fails. The
> > user can always resolve this ambiguity by creating a local tag
> > (refs/tags/v1.7.4) pointing to the desired object.
>
> And the other way around. What would be the output of "git name-rev"
> , "git describe", "--decorate", and such? $remote/tags/$tag?
> $remote/$tag? $tag?
>
> I would say $remote/$tag for "git name-rev" and "--decorate" but $tag
> for "git describe" as it is usually used to create files, i.e.
> git-1.7.4.261.g705f.tar.gz. And I think many people, me included, do
> not expect to have an / in the "git describe" output, at least in the
> default output (in contrast with the --all flag).

Thanks for raising an important point.

I don't buy the file name creation argument, as 'describe' is used from 
many different contexts, and file name creation is nowhere documented 
as one of its primary objectives.

Still, the objective of 'describe' is to create a human-readable string 
that tries to say something meaningful about a commit in relation to 
its preceding history, while at the same time uniquely identifying the 
commit. The "uniquely identifying" part is taken care of by 
the "-g<SHA1>" part of the output, while the initial "<tagname>-<n>" 
part makes it human-friendly. Therefore, we only care that the 
<tagname> is fairly unambiguous in the mind of the reader. From this 
perspective, which of the alternatives makes more sense? I would 
disqualify "$remote/$tag" and "$remote/tags/$tag", since the $remote 
name is repo-specific, and 'describe' output is often passed around 
between multiple developers/repos. Hence, I think that "$tag" is a good 
choice for 'describe'. If "$tag" is ambiguous in the current repo, then 
an "ambiguous tag" tag warning can be printed, but I would still 
use "$tag".

When it comes to 'name-rev' and '--decorate', those are (AFAICS) much 
more repo-specific, and seldom passed between users. Also, they don't 
have the "-g<SHA1>" part from the 'describe' output. Hence, in this 
case, I consider unique identification (unambiguity) much more 
important than not displaying $remote names. Therefore, I'd propose 
using the shortest unambiguous alternative.

> Another point to consider is if we want a default remote for tags, a
> config tags.defaultRemote (TBD), defaulting to origin, specifying the
> default remote for tags. There would be a hierarchy: local tags,
> default remote tags, remote tags. With this if one tag is on multiple
> remote the tag from the default remote always wins.
>
> In this way all the tag related input/output would no change much.
> For example all the decoration would be $tag instead of origin/tag.

Agreed, tags.defaultRemote (or tags.preferredRemote if I'm allowed to 
bikeshed) may be a valuable addition. Another way to achieve this would 
be to explicitly copy tags from the preferred remote (e.g. origin) 
directly into refs/tags. I.e. in addition to the (new) default tag 
refspec

	+refs/tags/*:refs/remotes/origin/tags/*

you could add an _additional_ refspec

	refs/tags/*:refs/tags/*

that would also copy all of origin's tags directly into your local tag 
namespace.


Thanks for the feedback! :)

...Johan

-- 
Johan Herland, <johan@herland.net>
www.herland.net