Provide better message for barnhc_wiht_tpyo@{u}

Instead of just saying that no upstream exists for such branch,
which is true but not very helpful, check that there's no
refs/heads/barnhc_wiht_tpyo and tell it to the user.

Signed-off-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sha1_name.c

@@ -862,8 +862,11 @@ int interpret_branch_name(const char *name, struct strbuf *buf)
 	 */
 	if (!upstream)
 		return error("HEAD does not point to a branch");
-	if (!upstream->merge || !upstream->merge[0]->dst)
+	if (!upstream->merge || !upstream->merge[0]->dst) {
+		if (!ref_exists(upstream->refname))
+			return error("No such branch: '%s'", cp);
 		return error("No upstream branch found for '%s'", upstream->name);
+	}
 	free(cp);
 	cp = shorten_unambiguous_ref(upstream->merge[0]->dst, 0);
 	strbuf_reset(buf);

t/t1507-rev-parse-upstream.sh

@@ -143,7 +143,7 @@ test_expect_success '@{u} error message when no upstream' '
 
 test_expect_success 'branch@{u} error message with misspelt branch' '
 	cat >expect <<-EOF &&
-	error: No upstream branch found for ${sq}no-such-branch${sq}
+	error: No such branch: ${sq}no-such-branch${sq}
 	fatal: Needed a single revision
 	EOF
 	error_message no-such-branch@{u} 2>actual &&