Add ObjectScalar custom-scalar fixtures from zth#583

ValdemarGr's stale PR zth#583 added a schema input shape, two custom
scalar modules, and a relay-config registration to reproduce issue
zth#582 (encoding doesn't always apply scalar encoders). This commit
lifts those fixtures in preparation for a full integration test for
zth#582 and broader regression coverage in this PR. ValdemarGr's
ObjectScalar serializers and parsers also log to the console, which
the harness in a later commit uses to assert which converters
actually ran for a given operation.

The Datetime and Number serializers in TestsUtils gain similar
console.log lines (matching the existing pattern in IntString) so a
follow-up zth#407 regression test can verify that a non-array custom
scalar variable still has its serializer run when it follows an
array-backed scalar variable in the same operation.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: drewwestphal

packages/rescript-relay/__tests__/TestsUtils.res

@@ -10,11 +10,11 @@ module Datetime = {
     | None => throw(Malformed_date)
     | Some(dateStr) => dateStr->Date.fromString
     }
-  let serialize = t =>
-    t
-    ->Date.toJSON
-    ->Option.getOr("-")
-    ->JSON.Encode.string
+  let serialize = t => {
+    // This log is used for testing purposes - do not remove
+    Console.log("Datetime.serialize")
+    t->Date.toJSON->Option.getOr("-")->JSON.Encode.string
+  }
 }
 
 module IntString = {
@@ -32,11 +32,54 @@ type number = array<int>
 
 module Number = {
   type t = number
-  let serialize = t => JSON.Encode.float(Float.fromInt(t->Array.reduce(0, (x, y) => y + x)))
+  let serialize = t => {
+    // This log is used for testing purposes - do not remove
+    Console.log("Number.serialize")
+    JSON.Encode.float(Float.fromInt(t->Array.reduce(0, (x, y) => y + x)))
+  }
 
   let parse = t =>
     switch t->JSON.Decode.float {
     | None => throw(Malformed_number)
     | Some(_) => []
     }
 }
+
+type objectScalarPayload = {
+  a: string,
+  b?: string,
+  c?: string,
+}
+
+// Custom-scalar shapes used by the regression tests for issues #582 and
+// #631. The serializers log so a Jest harness can assert which converters
+// actually ran for a given operation — the bug in those issues was that
+// converters silently DIDN'T run for fields placed after a custom-scalar
+// array in the same selection set.
+module ObjectScalar1 = {
+  type t = objectScalarPayload
+  let serialize = (_: t) => {
+    // This log is used for testing purposes - do not remove
+    Console.log("ObjectScalar1.serialize")
+    JSON.Encode.string("serialized1")
+  }
+  let parse = (_: JSON.t): t => {
+    // This log is used for testing purposes - do not remove
+    Console.log("ObjectScalar1.parse")
+    {a: "parsed1"}
+  }
+}
+
+module ObjectScalar2 = {
+  type t = objectScalarPayload
+  let serialize = (_: t) => {
+    // This log is used for testing purposes - do not remove
+    Console.log("ObjectScalar2.serialize")
+    JSON.Encode.string("serialized2")
+  }
+  let parse = (_: JSON.t): t => {
+    // This log is used for testing purposes - do not remove
+    Console.log("ObjectScalar2.parse")
+    {a: "parsed2"}
+  }
+}

packages/rescript-relay/__tests__/__generated__/RelaySchemaAssets_graphql.res

@@ -258,6 +258,9 @@ type Mutation {
   serializeCustomScalarArray(
     input: [IntString!]!
   ): SerializeCustomScalarArrayPayload
+  serializeMultipleCustomScalars(
+    input: SerializeMultipleCustomScalars!
+  ): Boolean
 }
 
 type Subscription {
@@ -277,3 +280,11 @@ input Location @oneOf {
   byLoc: ByLoc
   byId: ID
 }
+
+scalar ObjectScalar1
+scalar ObjectScalar2
+
+input SerializeMultipleCustomScalars {
+  os1s: [ObjectScalar1!]!
+  os2: ObjectScalar2
+}

packages/rescript-relay/__tests__/schema.graphql

@@ -13,6 +13,8 @@ module.exports = {
     IntString: "TestsUtils.IntString",
     JSON: "JSON.t",
     Number: "TestsUtils.Number",
+    ObjectScalar1: "TestsUtils.ObjectScalar1",
+    ObjectScalar2: "TestsUtils.ObjectScalar2",
   },
   persistConfig: PERSISTING
     ? {