peel_ref(): fix return value for non-peelable, not-current reference

The old version was inconsistent: when a reference was
REF_KNOWS_PEELED but with a null peeled value, it returned non-zero
for the current reference but zero for other references.  Change the
behavior for non-current references to match that of current_ref,
which is what callers expect.  Document the behavior.

Current callers only call peel_ref() from within a for_each_ref-style
iteration and only for the current ref; therefore, the buggy code path
was never reached.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/refs.c b/refs.c
index 7405d1c..787db21 100644
--- a/refs.c
+++ b/refs.c
@@ -119,7 +119,8 @@ struct ref_value {
 	/*
 	 * If REF_KNOWS_PEELED, then this field holds the peeled value
 	 * of this reference, or null if the reference is known not to
-	 * be peelable.
+	 * be peelable.  See the documentation for peel_ref() for an
+	 * exact definition of "peelable".
 	 */
 	unsigned char peeled[20];
 };
@@ -1340,6 +1341,8 @@ int peel_ref(const char *refname, unsigned char *sha1)
 		struct ref_entry *r = get_packed_ref(refname);
 
 		if (r && (r->flag & REF_KNOWS_PEELED)) {
+			if (is_null_sha1(r->u.value.peeled))
+			    return -1;
 			hashcpy(sha1, r->u.value.peeled);
 			return 0;
 		}