Merge branch 'jk/help-unknown-ref-fix'

Improve the code to show args with potential typo that cannot be
interpreted as a commit-ish.

* jk/help-unknown-ref-fix:
  help_unknown_ref(): check for refname ambiguity
  help_unknown_ref(): duplicate collected refnames

help.c

@@ -754,19 +754,19 @@ static int append_similar_ref(const char *refname, const struct object_id *oid,
 {
 	struct similar_ref_cb *cb = (struct similar_ref_cb *)(cb_data);
 	char *branch = strrchr(refname, '/') + 1;
-	const char *remote;
 
 	/* A remote branch of the same name is deemed similar */
-	if (skip_prefix(refname, "refs/remotes/", &remote) &&
+	if (starts_with(refname, "refs/remotes/") &&
 	    !strcmp(branch, cb->base_ref))
-		string_list_append(cb->similar_refs, remote);
+		string_list_append_nodup(cb->similar_refs,
+					 shorten_unambiguous_ref(refname, 1));
 	return 0;
 }
 
 static struct string_list guess_refs(const char *ref)
 {
 	struct similar_ref_cb ref_cb;
-	struct string_list similar_refs = STRING_LIST_INIT_NODUP;
+	struct string_list similar_refs = STRING_LIST_INIT_DUP;
 
 	ref_cb.base_ref = ref;
 	ref_cb.similar_refs = &similar_refs;

t/t7600-merge.sh

@@ -893,4 +893,24 @@ test_expect_success 'merge --quit' '
 	)
 '
 
+test_expect_success 'merge suggests matching remote refname' '
+	git commit --allow-empty -m not-local &&
+	git update-ref refs/remotes/origin/not-local HEAD &&
+	git reset --hard HEAD^ &&
+
+	# This is white-box testing hackery; we happen to know
+	# that reading packed refs is more picky about the memory
+	# ownership of strings we pass to for_each_ref() callbacks.
+	git pack-refs --all --prune &&
+
+	test_must_fail git merge not-local 2>stderr &&
+	grep origin/not-local stderr
+'
+
+test_expect_success 'suggested names are not ambiguous' '
+	git update-ref refs/heads/origin/not-local HEAD &&
+	test_must_fail git merge not-local 2>stderr &&
+	grep remotes/origin/not-local stderr
+'
+
 test_done