Add getDeprecationReason.js

Author: migueloller

src/build/__tests__/getDeprecationReason-test.js

@@ -0,0 +1,21 @@
+/* @flow */
+
+import { parse } from 'graphql/language';
+import getDeprecationReason from '../getDeprecationReason';
+
+describe('getDeprecationReason()', () => {
+  const generateNode = reason => (parse(`
+    type Type {
+      deprecatedInt: Int ${reason === undefined ? '' : `@deprecated(reason: "${reason}")`}
+    }
+  `).definitions[0]: Object).fields[0].directives;
+
+  test('gets deprecation reason', () => {
+    const reason = 'A reason.';
+    expect(getDeprecationReason(generateNode(reason))).toBe(reason);
+  });
+
+  test('returns undefined if there\'s no deprecation reason', () => {
+    expect(getDeprecationReason(generateNode())).toBeUndefined();
+  });
+});

src/build/getDeprecationReason.js

@@ -0,0 +1,19 @@
+/* @flow */
+
+import type { DirectiveNode } from 'graphql/language';
+import { GraphQLDeprecatedDirective } from 'graphql/type';
+import { getArgumentValues } from 'graphql/execution/values';
+
+/**
+ * Retrieves the deprecation reason given the directives of an AST.
+ *
+ * Mirror of [getDeprecationReason]{@link https://github.com/graphql/graphql-js/blob/master/src/utilities/buildASTSchema.js#L468}.
+ */
+export default function getDeprecationReason(directives: ?Array<DirectiveNode>): ?string {
+  const deprecatedNode = directives && directives
+    .find(directive => directive.name.value === GraphQLDeprecatedDirective.name);
+
+  if (!deprecatedNode) return undefined;
+
+  return (getArgumentValues(GraphQLDeprecatedDirective, deprecatedNode).reason: any);
+}