[Utility] concatAST()

This accepts an array of AST documents and returns a single AST document which is the concatenation of all definitions within those documents.

This is useful for retaining accurate source:line statements when GraphQL source material is spread across multiple files.

src/utilities/__tests__/concatAST.js

@@ -0,0 +1,46 @@
+/**
+ *  Copyright (c) 2015, Facebook, Inc.
+ *  All rights reserved.
+ *
+ *  This source code is licensed under the BSD-style license found in the
+ *  LICENSE file in the root directory of this source tree. An additional grant
+ *  of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+import { describe, it } from 'mocha';
+import { expect } from 'chai';
+import { concatAST } from '../concatAST';
+import { Source, parse, print } from '../../language';
+
+
+describe('concatAST', () => {
+
+  it('concats two ASTs together', () => {
+    const sourceA = new Source(`
+      { a, b, ...Frag }
+    `);
+
+    const sourceB = new Source(`
+      fragment Frag on T {
+        c
+      }
+    `);
+
+    const astA = parse(sourceA);
+    const astB = parse(sourceB);
+    const astC = concatAST([ astA, astB ]);
+
+    expect(print(astC)).to.equal(
+`{
+  a
+  b
+  ...Frag
+}
+
+fragment Frag on T {
+  c
+}
+`);
+  });
+
+});

src/utilities/concatAST.js

@@ -0,0 +1,31 @@
+/* @flow */
+/**
+ *  Copyright (c) 2015, Facebook, Inc.
+ *  All rights reserved.
+ *
+ *  This source code is licensed under the BSD-style license found in the
+ *  LICENSE file in the root directory of this source tree. An additional grant
+ *  of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+import type { Document } from '../language/ast';
+
+
+/**
+ * Provided a collection of ASTs, presumably each from different files,
+ * concatenate the ASTs together into batched AST, useful for validating many
+ * GraphQL source files which together represent one conceptual application.
+ */
+export function concatAST(asts: Array<Document>): Document {
+  let batchDefinitions = [];
+  for (let i = 0; i < asts.length; i++) {
+    const definitions = asts[i].definitions;
+    for (let j = 0; j < definitions.length; j++) {
+      batchDefinitions.push(definitions[j]);
+    }
+  }
+  return {
+    kind: 'Document',
+    definitions: batchDefinitions,
+  };
+}

src/utilities/index.js

@@ -41,3 +41,6 @@ export { isValidJSValue } from './isValidJSValue';
 
 // Determine if AST values adhere to a GraphQL type.
 export { isValidLiteralValue } from './isValidLiteralValue';
+
+// Concatenates multiple AST together.
+export { concatAST } from './concatAST';