Re: [PATCH 04/23] remember commit/tag parse failures

[Jeff King <peff@peff.net>]

On Thu, Oct 24, 2019 at 04:25:46PM -0700, Jonathan Tan wrote:

> Firstly, this patch is not about remembering, but about not setting
> anything, so I think that the title should be something like:
> 
>   commit, tag: set parsed only if no parsing error

True. I had also played with actually remembering via a bit, which I
think is how I ended up thinking about it that way. You could argue that
it is "not forgetting", which is remembering. :) But I think your
suggested title is better.

> Incidentally, the check that you mentioned in PATCH 02 is probably no
> longer necessary. The tests all pass even with the following diff:
> 
> diff --git a/commit.c b/commit.c
> index e12e7998ad..086011d944 100644
> --- a/commit.c
> +++ b/commit.c
> @@ -359,7 +359,7 @@ struct tree *repo_get_commit_tree(struct repository *r,
>  struct object_id *get_commit_tree_oid(const struct commit *commit)
>  {
>         struct tree *tree = get_commit_tree(commit);
> -       return tree ? &tree->object.oid : NULL;
> +       return &tree->object.oid;
>  }

Ah, I see the confusion you had earlier. The check I meant in patch 2
(and here) was the one in write_graph_chunk_data(), which checks for a
non-NULL tree even after we just saw a successful parse.

I agree that getting rid of the check in get_commit_tree_oid() is
unlikely to cause any bugs, but there are still cases where it could
help. Namely if I choose to ignore the parse failure (because I want to
see the parts of the commit struct that we did manage to get), then I'd
like to be able to ask whether we have a valid tree, like:

  oid = get_commit_tree_oid(commit);
  if (!oid)
	do something...

With the revert you showed above, that's dangerous, because we'd get a
bogus value like "8" (because the oid is offset 8 bytes in the struct
which we've dereferenced as NULL).

You could obviously use "get_commit_tree()" instead, which would let you
compare to NULL. But it seemed simpler to leave the extra safety in
place.

-Peff