Re: [RFC] Submodules in GIT

From: Shawn Pearce <spearce@spearce.org>
Date: Nov 25, 2006, 06:53 UTC
Message-ID: <20061125065338.GC4528@spearce.org>
In-Reply-To: <20061123232313.GB24909@nan92-1-81-57-214-146.fbx.proxad.net>

Yann Dirson <ydirson@altern.org> wrote:

Show 13 quoted lines

> On Tue, Nov 21, 2006 at 10:40:56PM -0500, Shawn Pearce wrote:
> > Yet we still want to be able to efficiently perform operations like
> > "git bisect" within the scope of that submodule, to help narrow down
> > a particular bug that is within that submodule.  To do that we need
> > the commit chain (all 10,000 of those commits) in the submodule.
> > To get those we really need a commit-ish and not a tree-ish, as
> > going from a tree-ish to a commit-ish is not only not unique but
> > is also pretty infeasible to do (you need to scan *every* commit).
> 
> We don't need to have commits in the tree for this.  We'll just have
> submodule commits which are not attached to a supermodule commit, and we
> can access the whole submodule history through the submodule .git/HEAD,
> just like we do for a standard git project.

No.  You cannot do that.

How do we setup .git/HEAD when bisecting the supermodule? Or merging it? Or doing anything else with it?

Ideally the .git/HEAD of every submodule should seek to the commit that points at the tree of the submodule which the supermodule is referencing. This lets you then perform a bisect within the submodule when you identify the supermodule commit which caused the breakage.

We need the submodule commits to do this. Doing it without is too expensive.