Re: [RFC PATCH] diff: only prefetch for certain output formats

[Jonathan Tan <jonathantanmy@google.com>]

> Ah, true, "options->detect_rename" would be overly broad.
> 
> I actually don't think it would be that bad to put the logic in
> diffcore_rename(). If we wait until the right moment (after inexact
> renames have been resolved, and when we see if there are any candidates
> left), it should just be a matter of walking over the candidate lists.
> 
> Something like this (it would need the add_if_missing() helper from
> diffcore_std()):

[snip]

> @@ -538,6 +539,25 @@ void diffcore_rename(struct diff_options *options)
>  		break;
>  	}
>  
> +	/*
> +	 * At this point we know there's actual work to do: we have rename
> +	 * destinations that didn't find an exact match, and we have potential
> +	 * sources. So we'll have to do inexact rename detection, which
> +	 * requires looking at the blobs. It's worth pre-fetching them as a
> +	 * group now.
> +	 */
> +	for (i = 0; i < rename_dst_nr; i++) {
> +		if (rename_dst[i].pair)
> +			continue; /* already found exact match */
> +		add_if_missing(options->repo, &to_fetch, rename_dst[i].two);
> +	}
> +	for (i = 0; i < rename_src_nr; i++) {
> +		add_if_missing(options->repo, &to_fetch, rename_src[i].p->one);
> +	}
> +	if (to_fetch.nr)
> +		promisor_remote_get_direct(options->repo,
> +					   to_fetch.oid, to_fetch.nr);
> +
>  	if (options->show_rename_progress) {
>  		progress = start_delayed_progress(
>  				_("Performing inexact rename detection"),

And also the equivalent code in diffcore_break() and in diffcore_std()
after both these functions are invoked (in case nothing got prefetched,
but the diff still requires blobs).