General mechanism to supply "rich history" to git-ubuntu

[Robie Basak]

On Wed, Feb 03, 2021 at 10:23:37AM +0100, Julian Andres Klode wrote:
> On Tue, Feb 02, 2021 at 01:03:23PM +0000, Robie Basak wrote:
> > We need the Refs field because git is designed not to be able to fetch a
> > commit by hash, but by a ref that can reach it only. So Vcs-Git-Refs
> > must specify what ref(s), when fetched will make the commit given to be
> > reachable. In practice this could just be the branch name prefixed by
> > 'refs/heads/' as in this example.
> 
> I don't buy this argument. A ref is just a file containing the commit
> name, it doesn't matter to git.

It's more complicated than this. See uploadpack.allowReachableSHA1InWant
in git-config(1). It defaults to false because of the computational
complexity. Your example probably works because it's local. Try it with
a remote (eg. Launchpad) and with a commit hash that isn't the tip of
any branch (or tag), and you get, for example:

error: Server does not allow request for unadvertised object 28a1d92b5823a971399dc275683c4ece1c7ebc86

In the general case, it doesn't work. I suppose one could specify that
the hash specified in Vcs-Git-Commit must be fetchable as a bare hash,
but I don't think that would be useful. Better to require a ref, and
it's clearer for everyone.

Robie
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