Fix overloading of functions with unnamed arguments (specifically for prefer params=single-object)

test/Feature/RpcSpec.hs

@@ -284,6 +284,19 @@ spec actualPgVersion =
           [json|null|]
           { matchHeaders = [matchContentTypeJson] }
 
+      context "different types when overloaded" $ do
+        it "returns composite type" $
+          post "/rpc/ret_point_overloaded" [json|{"x": 1, "y": 2}|] `shouldRespondWith`
+            [json|[{"x": 1, "y": 2}]|]
+            { matchHeaders = [matchContentTypeJson] }
+
+        it "returns json scalar with prefer single object" $
+          request methodPost "/rpc/ret_point_overloaded" [("Prefer","params=single-object")]
+            [json|{"x": 1, "y": 2}|]
+            `shouldRespondWith`
+            [json|{"x": 1, "y": 2}|]
+            { matchHeaders = [matchContentTypeJson] }
+
     context "proc argument types" $ do
       -- different syntax for array needed for pg<10
       when (actualPgVersion < pgVersion100) $

test/fixtures/schema.sql

@@ -983,6 +983,14 @@ create function test.ret_point_2d() returns test.point_2d as $$
   select row(10, 5)::test.point_2d;
 $$ language sql;
 
+create function test.ret_point_overloaded(x int, y int) returns test.point_2d as $$
+  select row(x, y)::test.point_2d;
+$$ language sql;
+
+create function test.ret_point_overloaded(json) returns json as $$
+  select $1;
+$$ language sql;
+
 -- domains on composite types are only supported from pg 11 on
 do $do$begin
   if (SELECT current_setting('server_version_num')::int >= 110000) then