[Fix] shallow: .equals(): flatten children when comparing

Fixes #1347

packages/enzyme-test-suite/test/ShallowWrapper-spec.jsx

@@ -425,6 +425,35 @@ describe('shallow', () => {
         expect(shallow(<Foo />).equals(<Foo />)).to.equal(false);
       });
     });
+
+    it('flattens arrays of children to compare', () => {
+      class TwoChildren extends React.Component {
+        render() {
+          return (
+            <div className="parent-component-class">
+              <div key="a" className="asd" />
+              <div key="b" className="fgh" />
+            </div>
+          );
+        }
+      }
+
+      class TwoChildrenOneArrayed extends React.Component {
+        render() {
+          return (
+            <div className="parent-component-class">
+              <div key="a" className="asd" />
+              {[<div key="b" className="fgh" />]}
+            </div>
+          );
+        }
+      }
+      const twoChildren = shallow(<TwoChildren />);
+      const twoChildrenOneArrayed = shallow(<TwoChildrenOneArrayed />);
+
+      expect(twoChildren.equals(twoChildrenOneArrayed.getElement())).to.equal(true);
+      expect(twoChildrenOneArrayed.equals(twoChildren.getElement())).to.equal(true);
+    });
   });
 
   describe('.hostNodes()', () => {

packages/enzyme/package.json

@@ -34,6 +34,7 @@
   "author": "Leland Richardson <leland.richardson@airbnb.com>",
   "license": "MIT",
   "dependencies": {
+    "array.prototype.flat": "^1.2.1",
     "cheerio": "^1.0.0-rc.2",
     "function.prototype.name": "^1.0.3",
     "has": "^1.0.1",

packages/enzyme/src/Utils.js

@@ -4,6 +4,8 @@ import is from 'object-is';
 import entries from 'object.entries';
 import functionName from 'function.prototype.name';
 import has from 'has';
+import flat from 'array.prototype.flat';
+
 import configuration from './configuration';
 import validateAdapter from './validateAdapter';
 import { childrenOfNode } from './RSTTraversal';
@@ -72,11 +74,12 @@ function internalChildrenCompare(a, b, lenComp, isLoose) {
   if (!Array.isArray(a) && !Array.isArray(b)) {
     return nodeCompare(a, b, lenComp);
   }
-  if (!a && !b) return true;
-  if (a.length !== b.length) return false;
-  if (a.length === 0 && b.length === 0) return true;
-  for (let i = 0; i < a.length; i += 1) {
-    if (!nodeCompare(a[i], b[i], lenComp)) return false;
+  const flatA = flat(a, Infinity);
+  const flatB = flat(b, Infinity);
+  if (flatA.length !== flatB.length) return false;
+  if (flatA.length === 0 && flatB.length === 0) return true;
+  for (let i = 0; i < flatA.length; i += 1) {
+    if (!nodeCompare(flatA[i], flatB[i], lenComp)) return false;
   }
   return true;
 }