match-trees: fix leaking prefixes in shift_tree()

In `shift_tree()` we allocate two empty strings that we end up
passing to `match_trees()`. If that function finds a better match it
will update these pointers to point to a newly allocated strings,
freeing the old strings. We never free the final results though, neither
the ones we have allocated ourselves, nor the one that `match_trees()`
might've returned to us.

Fix the resulting memory leaks by creating a common exit path where we
free them.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

match-trees.c

@@ -294,18 +294,22 @@ void shift_tree(struct repository *r,
 		unsigned short mode;
 
 		if (!*del_prefix)
-			return;
+			goto out;
 
 		if (get_tree_entry(r, hash2, del_prefix, shifted, &mode))
 			die("cannot find path %s in tree %s",
 			    del_prefix, oid_to_hex(hash2));
-		return;
+		goto out;
 	}
 
 	if (!*add_prefix)
-		return;
+		goto out;
 
 	splice_tree(hash1, add_prefix, hash2, shifted);
+
+out:
+	free(add_prefix);
+	free(del_prefix);
 }
 
 /*

t/t6409-merge-subtree.sh

@@ -5,6 +5,7 @@ test_description='subtree merge strategy'
 GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 test_expect_success setup '