Re: `.git` symlink makes `git submodule add` fail

From: Jeff King <peff@peff.net>
Date: Feb 13, 2016, 18:52 UTC
Message-ID: <20160213185252.GA10063@sigill.intra.peff.net>
In-Reply-To: <20160213042008.GA26677@witiko>

On Sat, Feb 13, 2016 at 05:20:09AM +0100, Vít Novotný wrote:

Show 20 quoted lines

> On Fri, Feb 12, 2016 at 01:27:33PM -0500, Jeff King wrote:
> > On Fri, Feb 12, 2016 at 10:19:38AM -0800, Junio C Hamano wrote:
> > 
> > > >> Is this a bug, or is the ability to symlink `.git` just a happy coincidence?
> > > >
> > > > It has never been supported.
> > > 
> > > Oops, hit "send" too early.
> > > 
> > > We have support for a "gitdir:" facility that would work even on a
> > > filesystem that cannot do symlinks (see gitrepository-layout(5)),
> > > and both the higher-level submodule Porcelain and the more recent
> > > "worktree" experimental code do use it.
> > 
> > And the way to convince git to make the link for you is with clone's
> > "--separate-git-dir" option.
> 
> What's curious is that this doesn't really work either, so the issue
> doesn't seem to be the lack of symlink support, but rather the lack of
> willingness on the part of Git to resolve a path recursively.

Right. The fundamental problem is that if git needs to construct a related path, symlinks mean it cannot do so textually. I'm sure there are spots where we use real_path() to get a canonical path for a particular $GIT_DIR, but from your results, it's clear we don't do so consistently.

So you can call that "git doesn't support symlinks", or you can call it "git supports symlinks, but needs to do so more consistently". :) I am not sure whether the existing uses of real_path() are there intentionally to support the kind of path-munging that submodules do or not. But either way, canonicalizing the paths before creating relative ones is probably going to be the solution.

I say all of that without having really looked at the code. You asked earlier if there would be any objects to a patch to implement better symlink support. That is hard to answer without somebody digging in to see what the fix would look like, and whether there would be any tradeoffs.

-Peff