Add feature flag for new batch hydrator (#470)

lib/src/main/java/graphql/nadel/NadelExecutionHints.kt

@@ -2,12 +2,14 @@ package graphql.nadel
 
 import graphql.nadel.hints.AllDocumentVariablesHint
 import graphql.nadel.hints.LegacyOperationNamesHint
+import graphql.nadel.hints.NewBatchHydrationGroupingHint
 import graphql.nadel.hints.NewResultMergerAndNamespacedTypename
 
-data class NadelExecutionHints constructor(
+data class NadelExecutionHints(
     val legacyOperationNames: LegacyOperationNamesHint,
     val allDocumentVariablesHint: AllDocumentVariablesHint,
     val newResultMergerAndNamespacedTypename: NewResultMergerAndNamespacedTypename,
+    val newBatchHydrationGrouping: NewBatchHydrationGroupingHint,
 ) {
     /**
      * Returns a builder with the same field values as this object.
@@ -20,9 +22,10 @@ data class NadelExecutionHints constructor(
     }
 
     class Builder {
-        private var legacyOperationNames: LegacyOperationNamesHint = LegacyOperationNamesHint { false }
-        private var allDocumentVariablesHint: AllDocumentVariablesHint = AllDocumentVariablesHint { false }
-        private var newResultMergerAndNamespacedTypename: NewResultMergerAndNamespacedTypename = NewResultMergerAndNamespacedTypename { false }
+        private var legacyOperationNames = LegacyOperationNamesHint { false }
+        private var allDocumentVariablesHint = AllDocumentVariablesHint { false }
+        private var newResultMergerAndNamespacedTypename = NewResultMergerAndNamespacedTypename { false }
+        private var newBatchHydrationGrouping = NewBatchHydrationGroupingHint { false }
 
         constructor()
 
@@ -47,11 +50,17 @@ data class NadelExecutionHints constructor(
             return this
         }
 
+        fun newBatchHydrationGrouping(flag: NewBatchHydrationGroupingHint): Builder {
+            newBatchHydrationGrouping = flag
+            return this
+        }
+
         fun build(): NadelExecutionHints {
             return NadelExecutionHints(
                 legacyOperationNames,
                 allDocumentVariablesHint,
                 newResultMergerAndNamespacedTypename,
+                newBatchHydrationGrouping,
             )
         }
     }

lib/src/main/java/graphql/nadel/engine/transform/hydration/batch/NadelBatchHydrationTransform.kt

@@ -27,6 +27,7 @@ internal class NadelBatchHydrationTransform(
     engine: NextgenEngine,
 ) : NadelTransform<State> {
     private val hydrator = NadelBatchHydrator(engine)
+    private val newHydrator = NadelNewBatchHydrator(engine)
 
     data class State(
         val executionBlueprint: NadelOverallExecutionBlueprint,
@@ -115,7 +116,11 @@ internal class NadelBatchHydrationTransform(
             flatten = true,
         )
 
-        return hydrator.hydrate(state, executionBlueprint, parentNodes)
+        if (executionContext.hints.newBatchHydrationGrouping()) {
+            return newHydrator.hydrate(state, executionBlueprint, parentNodes)
+        } else {
+            return hydrator.hydrate(state, executionBlueprint, parentNodes)
+        }
     }
 
     private fun makeTypeNameField(

lib/src/main/java/graphql/nadel/engine/transform/hydration/batch/NadelNewBatchHydrator.kt

@@ -0,0 +1,19 @@
+package graphql.nadel.engine.transform.hydration.batch
+
+import graphql.nadel.NextgenEngine
+import graphql.nadel.engine.blueprint.NadelOverallExecutionBlueprint
+import graphql.nadel.engine.transform.hydration.batch.NadelBatchHydrationTransform.State
+import graphql.nadel.engine.transform.result.NadelResultInstruction
+import graphql.nadel.engine.transform.result.json.JsonNode
+
+internal class NadelNewBatchHydrator(
+    private val engine: NextgenEngine,
+) {
+    fun hydrate(
+        state: State,
+        executionBlueprint: NadelOverallExecutionBlueprint,
+        parentNodes: List<JsonNode>,
+    ): List<NadelResultInstruction> {
+        throw UnsupportedOperationException()
+    }
+}

lib/src/main/java/graphql/nadel/hints/NewBatchHydrationGroupingHint.kt

@@ -0,0 +1,8 @@
+package graphql.nadel.hints
+
+fun interface NewBatchHydrationGroupingHint {
+    /**
+     * Uses new grouping algorithm for batched hydrations.
+     */
+    operator fun invoke(): Boolean
+}