Re: [PATCH JGIT] Circular references shouldn't be created

From: Avery Pennarun <apenwarr@gmail.com>
Date: Sep 17, 2009, 21:40 UTC
Message-ID: <32541b130909171440w1a6d2394t4acc6a2f791c143@mail.gmail.com>
In-Reply-To: <C89280B882467443A695734861B942B28759DB95@DEWDFECCR09.wdf.sap.corp>

On Thu, Sep 17, 2009 at 3:23 PM, Sohn, Matthias <matthias.sohn@sap.com> wrote:

Show 5 quoted lines

>        void link(final String name, final String target) throws IOException {
> +               if (name.equals(target))
> +                       throw new IllegalArgumentException(
> +                                       "illegal circular reference : symref " + name
> +                                                       + " cannot refer to " + target);

This isn't a very thorough fix.  It doesn't catch longer loops, like

    HEAD -> chicken -> HEAD

or

   a -> b -> c -> d -> a

Experimenting with original git.git's implementation, I see that this is allowed:

   git symbolic-ref refs/heads/boink refs/heads/boink

It succeeds and creates a file that looks like this:

   ref: refs/heads/boink

And "git show-ref refs/heads/boink" says: nothing (but returns an error code).

And "git log refs/heads/boink" says:

   warning: ignoring dangling symref refs/heads/boink.
   fatal: ambiguous argument 'refs/heads/boink': unknown revision or
path not in the working tree.
   Use '--' to separate paths from revisions

Clearly, in git.git, symref loops are caught at ref read time, not write time. This makes sense, since someone might foolishly twiddle the repository by hand and you don't want to get into an infinite loop in that case. Also, it's potentially useful to allow people to set invalid symrefs *temporarily*, as part of a multi step process.

Have fun,

Avery