Re: [PATCH 14/33] refs: extract a function peel_entry()

Michael Haggerty [off-list ref] writes:

 	if (read_ref_full(refname, base, 1, &flag))
 		return -1;
 
-	if ((flag & REF_ISPACKED)) {
+	/*
+	 * If the reference is packed, read its ref_entry from the
+	 * cache in the hope that we already know its peeled value.
+	 * We only try this optimization on packed references because
+	 * (a) forcing the filling of the loose reference cache could
+	 * be expensive and (b) loose references anyway usually do not
+	 * have REF_KNOWS_PEELED.
+	 */
+	if (flag & REF_ISPACKED) {
 		struct ref_entry *r = get_packed_ref(refname);

This code makes the reader wonder what happens when a new loose ref
masks a stale packed ref, but the worry is unfounded because the
read_ref_full() wouldn't have gave us REF_ISPACKED in the flag in
such a case.

But somehow the calling sequence looks like such a mistake waiting
to happen.  It would be much more clear if a function that returns a
"struct ref_entry *" is used instead of read_ref_full() above, and
we checked (r->flag & REF_ISPACKED) in the conditional, without a
separate get_packed_ref(refname).

-
-		if (r && (r->flag & REF_KNOWS_PEELED)) {
-			if (is_null_sha1(r->u.value.peeled))
-			    return -1;
+		if (r) {
+			if (peel_entry(r))
+				return -1;
 			hashcpy(sha1, r->u.value.peeled);
 			return 0;
 		}