refactor: Validate existing @defer directive

apollo-ios-codegen/Sources/GraphQLCompiler/JavaScript/src/index.ts

@@ -10,13 +10,19 @@ import {
   buildASTSchema,
   printSchema,
   extendSchema,
+  Kind,
+  GraphQLDeferDirective,
+  GraphQLDirective,
+  DirectiveDefinitionNode,
+  ASTNode,
 } from "graphql";
 import { defaultValidationRules, ValidationOptions } from "./validationRules";
 import { compileToIR, CompilationResult } from "./compiler";
 import { assertValidSchema, assertValidSDL } from "./utilities/graphql";
 import {
   addApolloCodegenSchemaExtensionToDocument,
 } from "./utilities/apolloCodegenSchemaExtension";
+import { definitionNode } from "./utilities";
 
 // We need to export all the classes we want to map to native objects,
 // so we have access to the constructor functions for type checks.
@@ -51,6 +57,7 @@ export function loadSchemaFromSources(sources: Source[]): GraphQLSchema {
   }
 
   var document = addApolloCodegenSchemaExtensionToDocument(concatAST(documents))
+  document = validateOrAddExperimentalDeferDirectiveToDocument(document)
 
   if (!introspectionJSONResult) { assertValidSDL(document) }
 
@@ -105,3 +112,51 @@ export function compileDocument(
 ): CompilationResult {
   return compileToIR(schema, document, legacySafelistingCompatibleOperations, validationOptions);
 }
+
+// While @defer is experimental the directive needs to be manually added to the list of available 
+// directives for the schema document. If the directive is already in the document it must be 
+// validated to ensure it matches the directive definition that Apollo iOS defer support was
+// built to support.
+//
+// Once defer is part of the GraphQL spec and the directive is no longer considered experimental
+// this check can be removed.
+function validateOrAddExperimentalDeferDirectiveToDocument(document: DocumentNode): DocumentNode {
+  const definition = document.definitions.find(isDeferDirectiveDefinitionNode)
+
+  if (definition === undefined) {
+    return concatAST([document, experimentalDeferDirectiveDocumentNode()])
+  }
+
+  if (!match(definition, GraphQLDeferDirective)) {
+    throw new Error(
+      `Mismatched ${GraphQLDeferDirective.toString()} directive found.`,
+    );
+  }
+
+  return document
+}
+
+// Returns whether the current node is a defer directive definition node.
+function isDeferDirectiveDefinitionNode(node: ASTNode): node is DirectiveDefinitionNode {
+  return (
+    node.kind === Kind.DIRECTIVE_DEFINITION && 
+    node.name.value === GraphQLDeferDirective.name
+  )
+}
+
+// Checks whether the supplied directive definition node matches against important properties
+// of the experimentally defined defer directive that Apollo iOS expects.
+function match(definition: DirectiveDefinitionNode, target: GraphQLDirective): Boolean {
+  return(
+    definition.repeatable === target.isRepeatable &&
+    definition.locations.map((node) => node.value).sort().toString() === target.locations.slice(0).sort().toString() &&
+    definition.arguments?.map((value) => value.name.value).sort().toString() === target.args.map((value) => value.name).sort().toString()
+  )
+}
+
+function experimentalDeferDirectiveDocumentNode(): DocumentNode {
+  return {
+    kind: Kind.DOCUMENT,
+    definitions: [definitionNode(GraphQLDeferDirective)]
+  }
+}