On Tue, May 28, 2019 at 08:19:07AM -0700, Derrick Stolee via GitGitGadget wrote:
> From: Derrick Stolee <dsto...@microsoft.com>
>
> The OBJECT_INFO_FOR_PREFETCH bitflag was added to sha1-file.c in 0f4a4fb1
> (sha1-file: support OBJECT_INFO_FOR_PREFETCH, 2019-03-29) and is used to
> prevent the fetch_objects() method when enabled.
>
> However, there is a problem with the current use. The definition of
> OBJECT_INFO_FOR_PREFETCH is given by adding 32 to OBJECT_INFO_QUICK. This is
> clearly stated above the definition (in a comment) that this is so
> OBJECT_INFO_FOR_PREFETCH implies OBJECT_INFO_QUICK. The problem is that using
> "flag & OBJECT_INFO_FOR_PREFETCH" means that OBJECT_INFO_QUICK also implies
> OBJECT_INFO_FOR_PREFETCH.
>
> Split out the single bit from OBJECT_INFO_FOR_PREFETCH into a new
> OBJECT_INFO_SKIP_FETCH_OBJECT as the single bit and keep
> OBJECT_INFO_FOR_PREFETCH as the union of two flags. This allows a clearer use
> of flag checking while also keeping the implication of OBJECT_INFO_QUICK.
Oof. I actually suggested splitting these up for review, but thought it
was only a clarity/flexibility issue, and completely missed the
correctness aspect of checking when the bit is set.
I agree with Junio's other response that using "==" would be the right
way for a multi-bit check, in general. But I like the split here,
because I think the result is more clear to read and harder to get
wrong for future checks.
I'd even go so far as to say...
> + * This is meant for bulk prefetching of missing blobs in a partial
> + * clone. Implies OBJECT_INFO_SKIP_FETCH_OBJECT and OBJECT_INFO_QUICK
> + */
> +#define OBJECT_INFO_FOR_PREFETCH (OBJECT_INFO_SKIP_FETCH_OBJECT |
> OBJECT_INFO_QUICK)
we could dump this, and callers should just say what they mean (i.e.,
specify both flags).
There are only two of them, and I think both would be more readable with
a helper more like:
int should_prefetch_object(struct repository *r,
const struct object_id *oid) {
return !oid_object_info_extended(r, oid, NULL,
OBJECT_INFO_SKIP_FETCH_OBJECT |
OBJECT_INFO_QUICK);
}
but unless everybody is immediately on-board with "yes, that is much
nicer", I don't want bikeshedding to hold up your important and
obviously-correct fix.
-Peff
