Fix hidden field validation

lib/src/main/java/graphql/nadel/validation/NadelFieldValidation.kt

@@ -37,9 +37,10 @@ class NadelFieldValidation internal constructor(
         parent: NadelServiceSchemaElement.FieldsContainer,
         overallFields: List<GraphQLFieldDefinition>,
     ): NadelSchemaValidationResult {
-        if(areAllFieldsHidden(overallFields)) {
+        if (isTypeBrokenByHiddenFields(parent, overallFields)) {
             return NadelSchemaValidationError.AllFieldsUsingHiddenDirective(parent)
         }
+
         return overallFields
             .asSequence()
             .let { fieldSequence ->
@@ -57,8 +58,19 @@ class NadelFieldValidation internal constructor(
             .toResult()
     }
 
-    private fun areAllFieldsHidden(overallFields: List<GraphQLFieldDefinition>): Boolean {
-        return overallFields.all { it.hasAppliedDirective(NadelDirectives.hiddenDirectiveDefinition.name) };
+    context(NadelValidationContext)
+    private fun isTypeBrokenByHiddenFields(
+        parent: NadelServiceSchemaElement.FieldsContainer,
+        overallFields: List<GraphQLFieldDefinition>,
+    ): Boolean {
+        // Means type is deleted, so we're fine
+        if (hiddenTypeNames.contains(parent.overall.name)) {
+            return false
+        }
+
+        return overallFields.all {
+            it.hasAppliedDirective(NadelDirectives.hiddenDirectiveDefinition.name)
+        }
     }
 
     context(NadelValidationContext)

lib/src/main/java/graphql/nadel/validation/NadelSchemaValidation.kt

@@ -49,6 +49,7 @@ class NadelSchemaValidation internal constructor(
 
         val operationTypes = getOperationTypeNames(engineSchema)
         val namespaceTypes = getNamespaceOperationTypes(engineSchema)
+        val hiddenTypeNames = getHiddenTypeNames(engineSchema)
 
         val definitions = definitionParser.parse(engineSchema)
             .onError { return it }
@@ -60,6 +61,7 @@ class NadelSchemaValidation internal constructor(
             hydrationUnions = getHydrationUnions(engineSchema),
             namespaceTypeNames = namespaceTypes,
             combinedTypeNames = namespaceTypes + operationTypes.map { it.name },
+            hiddenTypeNames = hiddenTypeNames,
             definitions = definitions,
             hook = hook,
         )
@@ -208,6 +210,37 @@ private fun makeFieldContributorMap(services: List<Service>): Map<FieldCoordinat
         .toMapStrictly()
 }
 
+/**
+ * Gets the types that will be removed by the `@hidden` directive.
+ *
+ * i.e. all fields that reference this type are `@hidden`
+ */
+private fun getHiddenTypeNames(engineSchema: GraphQLSchema): Set<String> {
+    val hiddenTypeNames = HashMap<String, Boolean>(engineSchema.typeMap.size)
+
+    engineSchema
+        .typeMap
+        .values
+        .asSequence()
+        .filterIsInstance<GraphQLFieldsContainer>()
+        .forEach { type ->
+            type.fields.forEach { field ->
+                val outputTypeName = field.type.unwrapAll().name
+
+                if (field.hasAppliedDirective(NadelDirectives.hiddenDirectiveDefinition.name)) {
+                    val existing = hiddenTypeNames[outputTypeName]
+                    if (existing == null) {
+                        hiddenTypeNames[outputTypeName] = true
+                    }
+                } else {
+                    hiddenTypeNames[outputTypeName] = false
+                }
+            }
+        }
+
+    return hiddenTypeNames.keys
+}
+
 private fun getOperationTypeNames(engineSchema: GraphQLSchema): List<GraphQLObjectType> {
     return listOfNotNull(
         engineSchema.queryType,

lib/src/main/java/graphql/nadel/validation/NadelValidationContext.kt

@@ -20,6 +20,7 @@ data class NadelValidationContext internal constructor(
     val hydrationUnions: Set<String>,
     val namespaceTypeNames: Set<String>,
     val combinedTypeNames: Set<String>,
+    val hiddenTypeNames: Set<String>,
     val definitions: Map<NadelSchemaMemberCoordinates, List<NadelDefinition>>,
     val hook: NadelSchemaValidationHook,
 ) {