remove comment, add tests

src/hooks/op_rewrite.c

@@ -235,8 +235,6 @@ static Node *operator_rewriting_mutator(Node *node, void *ctx)
         return (Node *)seqscan;
     }
 
-    // todo:: there is a function called query_or_expression_tree_mutator that might be able to replace the custom plan
-    // tree handling
     if(is_plan_node(node)) {
         return (Node *)plan_tree_mutator((Plan *)node, ctx);
     } else {

test/expected/hnsw_select.out

@@ -204,5 +204,45 @@ SELECT has_index_scan('EXPLAIN WITH t AS (SELECT id FROM test1 ORDER BY v <-> ''
  t
 (1 row)
 
+-- Validate <-> is replaced with the matching function when an index is present
+set enable_seqscan = true;
+EXPLAIN (COSTS false) SELECT * from small_world ORDER BY v <-> '{1,1,1}';
+                  QUERY PLAN                   
+-----------------------------------------------
+ Sort
+   Sort Key: (l2sq_dist(v, '{1,1,1}'::real[]))
+   ->  Seq Scan on small_world
+(3 rows)
+
+SELECT * from small_world ORDER BY v <-> '{1,1,1}';
+ id  | b |    v    
+-----+---+---------
+ 111 | t | {1,1,1}
+ 101 | f | {1,0,1}
+ 110 | f | {1,1,0}
+ 011 | t | {0,1,1}
+ 100 | f | {1,0,0}
+ 001 | t | {0,0,1}
+ 010 | f | {0,1,0}
+ 000 | t | {0,0,0}
+(8 rows)
+
+begin;
+INSERT INTO test2 (v) VALUES ('{1,4}');
+INSERT INTO test2 (v) VALUES ('{2,4}');
+CREATE INDEX test2_cos ON test2 USING hnsw(v dist_cos_ops);
+INFO:  done init usearch index
+INFO:  inserted 3 elements
+INFO:  done saving 3 vectors
+EXPLAIN (COSTS false) SELECT * from test2 ORDER BY v <-> '{1,4}';
+                 QUERY PLAN                 
+--------------------------------------------
+ Sort
+   Sort Key: (cos_dist(v, '{1,4}'::real[]))
+   ->  Seq Scan on test2
+(3 rows)
+
+rollback;
+set enable_seqscan = false;
 -- todo:: Verify joins work and still use index
 -- todo:: Verify incremental sorts work

test/sql/hnsw_select.sql

@@ -71,5 +71,17 @@ SELECT has_index_scan('EXPLAIN (SELECT id FROM test1 ORDER BY v <-> ''{1,4}'') U
 -- Validate CTEs work and still use index
 SELECT has_index_scan('EXPLAIN WITH t AS (SELECT id FROM test1 ORDER BY v <-> ''{1,4}'') SELECT id FROM t UNION SELECT id FROM t');
 
+-- Validate <-> is replaced with the matching function when an index is present
+set enable_seqscan = true;
+EXPLAIN (COSTS false) SELECT * from small_world ORDER BY v <-> '{1,1,1}';
+SELECT * from small_world ORDER BY v <-> '{1,1,1}';
+begin;
+INSERT INTO test2 (v) VALUES ('{1,4}');
+INSERT INTO test2 (v) VALUES ('{2,4}');
+CREATE INDEX test2_cos ON test2 USING hnsw(v dist_cos_ops);
+EXPLAIN (COSTS false) SELECT * from test2 ORDER BY v <-> '{1,4}';
+rollback;
+set enable_seqscan = false;
+
 -- todo:: Verify joins work and still use index
 -- todo:: Verify incremental sorts work