Add polyfill for 'flatMap' (#1686)

src/polyfills/flatMap.js

@@ -0,0 +1,34 @@
+/**
+ * Copyright (c) 2019-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 strict
+ */
+
+declare function flatMap<T, U>(
+  list: $ReadOnlyArray<T>,
+  fn: (item: T, index: number) => $ReadOnlyArray<U> | U,
+): Array<U>;
+
+/* eslint-disable no-redeclare */
+// $FlowFixMe
+const flatMap = Array.prototype.flatMap
+  ? function(list, fn) {
+      // $FlowFixMe
+      return Array.prototype.flatMap.call(list, fn);
+    }
+  : function(list, fn) {
+      let result = [];
+      for (let i = 0; i < list.length; i++) {
+        const value = fn(list[i]);
+        if (Array.isArray(value)) {
+          result = result.concat(value);
+        } else {
+          result.push(value);
+        }
+      }
+      return result;
+    };
+export default flatMap;

src/type/validate.js

@@ -8,6 +8,7 @@
  */
 
 import find from '../polyfills/find';
+import flatMap from '../polyfills/flatMap';
 import objectValues from '../polyfills/objectValues';
 import objectEntries from '../polyfills/objectEntries';
 import {
@@ -548,14 +549,7 @@ function getAllSubNodes<T: ASTNode, K: ASTNode, L: ASTNode>(
   object: SDLDefinedObject<T, K>,
   getter: (T | K) => ?(L | $ReadOnlyArray<L>),
 ): $ReadOnlyArray<L> {
-  let result = [];
-  for (const astNode of getAllNodes(object)) {
-    const subNodes = getter(astNode);
-    if (subNodes) {
-      result = result.concat(subNodes);
-    }
-  }
-  return result;
+  return flatMap(getAllNodes(object), item => getter(item) || []);
 }
 
 function getImplementsInterfaceNode(

src/utilities/concatAST.js

@@ -7,6 +7,7 @@
  * @flow strict
  */
 
+import flatMap from '../polyfills/flatMap';
 import type { DocumentNode } from '../language/ast';
 
 /**
@@ -15,15 +16,8 @@ import type { DocumentNode } from '../language/ast';
  * GraphQL source files which together represent one conceptual application.
  */
 export function concatAST(asts: $ReadOnlyArray<DocumentNode>): DocumentNode {
-  const 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,
+    definitions: flatMap(asts, ast => ast.definitions),
   };
 }

src/utilities/extendSchema.js

@@ -7,6 +7,7 @@
  * @flow strict
  */
 
+import flatMap from '../polyfills/flatMap';
 import objectValues from '../polyfills/objectValues';
 import invariant from '../jsutils/invariant';
 import mapValue from '../jsutils/mapValue';
@@ -410,14 +411,3 @@ export function extendSchema(
     return extendNamedType(typeDef);
   }
 }
-
-function flatMap<T, U>(
-  list: $ReadOnlyArray<T>,
-  mapFn: T => $ReadOnlyArray<U>,
-): Array<U> {
-  let result = [];
-  for (const item of list) {
-    result = result.concat(mapFn(item));
-  }
-  return result;
-}

src/utilities/schemaPrinter.js

@@ -7,6 +7,7 @@
  * @flow strict
  */
 
+import flatMap from '../polyfills/flatMap';
 import objectValues from '../polyfills/objectValues';
 import isNullish from '../jsutils/isNullish';
 import isInvalid from '../jsutils/isInvalid';
@@ -392,27 +393,18 @@ function printDescriptionWithComments(lines, indentation, firstInBlock) {
 }
 
 function descriptionLines(description: string, maxLen: number): Array<string> {
-  const lines = [];
   const rawLines = description.split('\n');
-  for (let i = 0; i < rawLines.length; i++) {
-    if (rawLines[i] === '') {
-      lines.push(rawLines[i]);
-    } else {
-      // For > 120 character long lines, cut at space boundaries into sublines
-      // of ~80 chars.
-      const sublines = breakLine(rawLines[i], maxLen);
-      for (let j = 0; j < sublines.length; j++) {
-        lines.push(sublines[j]);
-      }
+  return flatMap(rawLines, line => {
+    if (line.length < maxLen + 5) {
+      return line;
     }
-  }
-  return lines;
+    // For > 120 character long lines, cut at space boundaries into sublines
+    // of ~80 chars.
+    return breakLine(line, maxLen);
+  });
 }
 
 function breakLine(line: string, maxLen: number): Array<string> {
-  if (line.length < maxLen + 5) {
-    return [line];
-  }
   const parts = line.split(new RegExp(`((?: |^).{15,${maxLen - 40}}(?= |$))`));
   if (parts.length < 4) {
     return [line];