[PATCH] remote: prefer exact matches when using refspecs

[Jonathan Tan <jonathantanmy@google.com>]

When matching a non-wildcard LHS of a refspec against a list of refs,
find_ref_by_name_abbrev() returns the first ref that matches using the
DWIM rules used by refname_match() in refs.c, even if an exact match
occurs later in the list of refs.

This causes unexpected behavior when (for example) fetching using the
refspec "refs/heads/s:<something>" from a remote with both
"refs/heads/refs/heads/s" and "refs/heads/s". (Even if the former was
inadvertently created, one would still expect the latter to be fetched.)

This problem has only been observed when the desired ref comes after the
undesired ref in alphabetical order. However, for completeness, the test
in this patch also checks what happens when the desired ref comes first
alphabetically.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
---
 remote.c         |  7 +++++--
 t/t5510-fetch.sh | 28 ++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/remote.c b/remote.c
index 3fd43453f..eeffe3488 100644
--- a/remote.c
+++ b/remote.c
@@ -1687,12 +1687,15 @@ static struct ref *get_expanded_map(const struct ref *remote_refs,
 
 static const struct ref *find_ref_by_name_abbrev(const struct ref *refs, const char *name)
 {
+	const struct ref *best_match = NULL;
 	const struct ref *ref;
 	for (ref = refs; ref; ref = ref->next) {
-		if (refname_match(name, ref->name))
+		if (!strcmp(name, ref->name))
 			return ref;
+		if (refname_match(name, ref->name))
+			best_match = ref;
 	}
-	return NULL;
+	return best_match;
 }
 
 struct ref *get_remote_ref(const struct ref *remote_refs, const char *name)
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index e402aee6a..da88f35f0 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -535,6 +535,34 @@ test_expect_success "should be able to fetch with duplicate refspecs" '
 	)
 '
 
+test_expect_success 'LHS of refspec prefers exact matches' '
+	mkdir lhs-exact &&
+	(
+		cd lhs-exact &&
+		git init server &&
+		test_commit -C server unwanted &&
+		test_commit -C server wanted &&
+
+		git init client &&
+
+		# Check a name coming after "refs" alphabetically ...
+		git -C server update-ref refs/heads/s wanted &&
+		git -C server update-ref refs/heads/refs/heads/s unwanted &&
+		git -C client fetch ../server refs/heads/s:refs/heads/checkthis &&
+		git -C server rev-parse wanted >expect &&
+		git -C client rev-parse checkthis >actual &&
+		test_cmp expect actual &&
+
+		# ... and one before.
+		git -C server update-ref refs/heads/q wanted &&
+		git -C server update-ref refs/heads/refs/heads/q unwanted &&
+		git -C client fetch ../server refs/heads/q:refs/heads/checkthis &&
+		git -C server rev-parse wanted >expect &&
+		git -C client rev-parse checkthis >actual &&
+		test_cmp expect actual
+	)
+'
+
 # configured prune tests
 
 set_config_tristate () {
-- 
2.18.0.345.g5c9ce644c3-goog