Omit redundant slice in join method of diffArrays

Author: pedrottimark

src/diff/array.js

@@ -1,10 +1,10 @@
 import Diff from './base';
 
 export const arrayDiff = new Diff();
-arrayDiff.tokenize = arrayDiff.join = function(value) {
+arrayDiff.tokenize = function(value) {
   return value.slice();
 };
-arrayDiff.removeEmpty = function(value) {
+arrayDiff.join = arrayDiff.removeEmpty = function(value) {
   return value;
 };
 

test/diff/array.js

@@ -33,7 +33,35 @@ describe('diff/array', function() {
         {count: 1, value: [c], removed: true, added: undefined}
       ]);
     });
+    describe('anti-aliasing', function() {
+      // Test apparent contract that no chunk value is ever an input argument.
+      const value = [0, 1, 2];
+      const expected = [
+        {count: value.length, value: value}
+      ];
 
+      const input = value.slice();
+      const diffResult = diffArrays(input, input);
+      it('returns correct deep result for identical inputs', function() {
+        expect(diffResult).to.deep.equals(expected);
+      });
+      it('does not return the input array', function() {
+        expect(diffResult[0].value).to.not.equal(input);
+      });
+
+      const input1 = value.slice();
+      const input2 = value.slice();
+      const diffResult2 = diffArrays(input1, input2);
+      it('returns correct deep result for equivalent inputs', function() {
+        expect(diffResult2).to.deep.equals(expected);
+      });
+      it('does not return the first input array', function() {
+        expect(diffResult2[0].value).to.not.equal(input1);
+      });
+      it('does not return the second input array', function() {
+        expect(diffResult2[0].value).to.not.equal(input2);
+      });
+    });
     it('Should diff arrays with comparator', function() {
       const a = {a: 0}, b = {a: 1}, c = {a: 2}, d = {a: 3};
       function comparator(left, right) {