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Re: [PATCH v4 4/4] sha1_name: minimize OID comparisons during disambiguation




On 10/9/2017 9:49 AM, Jeff King wrote:
On Sun, Oct 08, 2017 at 02:49:42PM -0400, Derrick Stolee wrote:

@@ -505,6 +506,65 @@ static int extend_abbrev_len(const struct object_id *oid, void *cb_data)
  	return 0;
  }
+static void find_abbrev_len_for_pack(struct packed_git *p,
+				     struct min_abbrev_data *mad)
+{
+	int match = 0;
+	uint32_t num, last, first = 0;
+	struct object_id oid;
+
+	open_pack_index(p);
+	num = p->num_objects;
+	last = num;
+	while (first < last) {
[...]
Your cover letter lists:

   * Silently skip packfiles that fail to open with open_pack_index()

as a change from the previous version. But this looks the same as the
last round. I think this _does_ end up skipping such packfiles because
p->num_objects will be zero. Is it worth having a comment to that
effect (or even just an early return) to make it clear that the
situation is intentional?

Although...

+	/*
+	 * first is now the position in the packfile where we would insert
+	 * mad->hash if it does not exist (or the position of mad->hash if
+	 * it does exist). Hence, we consider a maximum of three objects
+	 * nearby for the abbreviation length.
+	 */
+	mad->init_len = 0;
+	if (!match) {
+		nth_packed_object_oid(&oid, p, first);
+		extend_abbrev_len(&oid, mad);
If we have zero objects in the pack, what would nth_packed_object_oid()
be returning here?

So I actually think we do want an early return, not just when
open_packed_index() fails, but also when p->num_objects is zero.

-Peff

Sorry about this. I caught this while I was writing my cover letter and amended my last commit to include the following:

    if (open_pack_index(p))
        return;

After I amended the commit, I forgot to 'format-patch' again. I can send a diff between the commits after review has calmed.

Thanks,
-Stolee