Fix empty list parameters.

lib/runtime/ppx_pgsql_runtime.ml

@@ -45,8 +45,11 @@ let rebuild_query_with_placeholders query_fragments params =
       | `Variable (_name, true (* is_list *), _) ->
         let list_param = List.nth params !param_idx in
         let list_placeholders = List.map mkplaceholder list_param in
+        let expr = match list_placeholders with
+          | [] -> "NULL"
+          | _ -> String.concat "," list_placeholders in
         incr param_idx;
-        "(" ^ String.concat "," list_placeholders ^ ")"
+        "(" ^ expr ^ ")"
     ) query_fragments in
   String.concat "" fragments
 

tests/test_ppx.ml

@@ -1,3 +1,45 @@
 let test1 = [%sqlf "SELECT 1"]
 
 let test2 = [%sqlf "SELECT hasindexes FROM pg_catalog.pg_tables WHERE hasrules = $hasrules"]
+
+let test_list = [%sqlf {|
+  SELECT true WHERE $?needle::integer IN $@haystack
+|}]
+
+let check msg f =
+  print_string @@ msg ^ "... " ;
+  try
+    assert (f ());
+    print_endline "OK"
+  with e ->
+    print_endline "FAIL";
+    raise e
+
+let () =
+  let dbh = PGOCaml.connect () in
+  check "test 1" (fun () ->
+      let res = test1 dbh in
+      res = [Some 1l]);
+
+  check "test 2" (fun () ->
+      let _res = test2 ~hasrules:true dbh in
+      (* TODO: fixme *)
+      true);
+
+  check "test list param positive" (fun () ->
+      let res = test_list ~needle:1l ~haystack:[1l;2l;3l] dbh in
+      res = [Some true]);
+
+  check "test list param negative" (fun () ->
+      let res = test_list ~needle:4l ~haystack:[1l;2l;3l] dbh in
+      res = []);
+
+  check "test list param with NULL" (fun () ->
+      let res = test_list ?needle:None ~haystack:[1l;2l;3l] dbh in
+      res = []);
+
+  check "test list param with empty list" (fun () ->
+      let res = test_list ~needle:1l ~haystack:[] dbh in
+      res = []);
+
+  PGOCaml.close dbh