Re: [PATCH] repository.c: always allocate 'index' at repo init time

From: Duy Nguyen <pclouds@gmail.com>
To: Jeff King <peff@peff.net>
Cc: Junio C Hamano <gitster@pobox.com>, Antonio Ospite <ao2@ao2.it>,
	Eric Wong <e@80x24.org>, Git Mailing List <git@vger.kernel.org>
Subject: Re: [PATCH] repository.c: always allocate 'index' at repo init time
Date: Tue, 21 May 2019 17:34:02 +0700	[thread overview]
Message-ID: <CACsJy8CoauTdJ1huU=w2YNbw53iea5U304yAu2oCUuTvFRaV7w@mail.gmail.com> (raw)
In-Reply-To: <20190520131702.GB13474@sigill.intra.peff.net>

On Mon, May 20, 2019 at 8:17 PM Jeff King <peff@peff.net> wrote:
> The patch looks good, though I wonder if we could simplify even further
> by just embedding an index into the repository object. The purpose of
> having it as a pointer, I think, is so that the_repository can point to
> the_index. But we could possibly hide the latter behind some macro
> trickery like:
>
>   #define the_index (the_repository->index)
>
> I spent a few minutes on a proof of concept patch, but it gets a bit
> hairy:
>
>   1. There are some circular dependencies in the header files. We'd need
>      repository.h to depend on cache.h to get the definition of
>      index_state, but the latter includes repository.h. We'd need to
>      break the index bits out of cache.h into index.h, which in turn
>      requires breaking out some other parts. I did a sloppy job of it in
>      the patch below.
>
>   2. There are hundreds of spots that need to swap out "repo->index" for
>      "&repo->index". In the patch below I just did enough to compile
>      archive-zip.o, to illustrate. :)

You are more thorough than me. I saw #2 first and immediately backed
off (partly for a selfish reason: I have plenty of the_repo conversion
patches in queue and anything touching "repo" may delay those patches
even more).

There's also #3 but this one is minor. So far 'struct repo' is more of
a glue of things. Embedding index_state in it while leaving
object_store, ref_store... pointers feels inconsistent and a bit
weird. It's not a strong reason for making index_state a pointer too,
but if we have to deal with pointers anyway...

> So it's definitely non-trivial to go that way. I'm not sure if it's
> worth the effort to switch at this point, but even if it is, your patch
> seems like a good thing to do in the meantime.
>
> Either way, I think we could probably revert the non-test portion of my
> 581d2fd9f2 (get_oid: handle NULL repo->index, 2019-05-14) after this.

Yeah. I'm thinking of doing that after, scanning for similar lines
too. But it looks like it's the only one. Will fix in v2.
-- 
Duy