Add 'introspectionFromSchema' utility function

src/index.js

@@ -309,6 +309,8 @@ export {
   introspectionQuery,
   // Gets the target Operation from a Document
   getOperationAST,
+  // Convert a GraphQLSchema to an IntrospectionQuery
+  introspectionFromSchema,
   // Build a GraphQLSchema from an introspection result.
   buildClientSchema,
   // Build a GraphQLSchema from a parsed GraphQL Schema language AST.

src/utilities/__tests__/introspectionFromSchema-test.js

@@ -0,0 +1,66 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import { describe, it } from 'mocha';
+import { expect } from 'chai';
+
+import dedent from '../../jsutils/dedent';
+import { GraphQLSchema, GraphQLObjectType, GraphQLString } from '../../type';
+import { printSchema } from '../schemaPrinter';
+import { buildClientSchema } from '../buildClientSchema';
+import { introspectionFromSchema } from '../introspectionFromSchema';
+
+function introspectionToSDL(introspection) {
+  return printSchema(buildClientSchema(introspection));
+}
+
+describe('introspectionFromSchema', () => {
+  const schema = new GraphQLSchema({
+    query: new GraphQLObjectType({
+      name: 'Simple',
+      description: 'This is a simple type',
+      fields: {
+        string: {
+          type: GraphQLString,
+          description: 'This is a string field',
+        },
+      },
+    }),
+  });
+
+  it('converts a simple schema', () => {
+    const introspection = introspectionFromSchema(schema);
+
+    expect(introspectionToSDL(introspection)).to.deep.equal(dedent`
+      schema {
+        query: Simple
+      }
+
+      """This is a simple type"""
+      type Simple {
+        """This is a string field"""
+        string: String
+      }
+    `);
+  });
+
+  it('converts a simple schema without descriptions', () => {
+    const introspection = introspectionFromSchema(schema, {
+      descriptions: false,
+    });
+
+    expect(introspectionToSDL(introspection)).to.deep.equal(dedent`
+      schema {
+        query: Simple
+      }
+
+      type Simple {
+        string: String
+      }
+    `);
+  });
+});

src/utilities/index.js

@@ -41,6 +41,9 @@ export type {
 // Gets the target Operation from a Document
 export { getOperationAST } from './getOperationAST';
 
+// Convert a GraphQLSchema to an IntrospectionQuery
+export { introspectionFromSchema } from './introspectionFromSchema';
+
 // Build a GraphQLSchema from an introspection result.
 export { buildClientSchema } from './buildClientSchema';
 

src/utilities/introspectionFromSchema.js

@@ -0,0 +1,37 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+import invariant from '../jsutils/invariant';
+import { getIntrospectionQuery } from './introspectionQuery';
+import { GraphQLSchema } from '../type/schema';
+import { execute } from '../execution/execute';
+import { parse } from '../language/parser';
+import type {
+  IntrospectionQuery,
+  IntrospectionOptions,
+} from './introspectionQuery';
+
+/**
+ * Build an IntrospectionQuery from a GraphQLSchema
+ *
+ * IntrospectionQuery is useful for utilities that care about type and field
+ * relationships, but do not need to traverse through those relationships.
+ *
+ * This is the inverse of buildClientSchema. The primary use case is outside
+ * of the server context, for instance when doing schema comparisons.
+ */
+export function introspectionFromSchema(
+  schema: GraphQLSchema,
+  options: IntrospectionOptions,
+): IntrospectionQuery {
+  const queryAST = parse(getIntrospectionQuery(options));
+  const result = execute(schema, queryAST);
+  invariant(!result.then && !result.errors && result.data);
+  return (result.data: any);
+}