Re: [PATCHv2] grep: use slash for path delimiter, not colon

[Jeff King <peff@peff.net>]

On Mon, Aug 26, 2013 at 10:46:12AM -0400, Phil Hord wrote:

> This version is a bit more deterministic and also adds a test.
> 
> It accepts the expense of examining the path argument again to 
> determine if it is a tree-ish + path rather than just a tree (commit).
> The get_sha1 call occurs one extra time for each tree-ish argument,
> so it's not expensive.

I don't like this approach in general because it lacks atomicity. IOW,
the thing you are looking up may change between the two get_sha1 calls.
You're _almost_ good here because you don't actually care what the
second call returns, but only which features it _would_ have used. But
you may see the second call fail because the ref doesn't exist anymore,
or points to a different tree, and you will erroneously use ":" instead
of "/".

I admit this is not that likely, but I'd really rather avoid introducing
such races if we can.

> We avoid mucking with the object_array API this way, and also do not
> rely on the object-type to tell us anything about the way the object
> name was spelled.

Changing the object_array API would be hard, but I don't think we need
to do it here. Can we simply stop using object_array to pass the list,
and instead just have a custom list?

I'll see how painful that is.

-Peff