fix: reverse filter not pure, see #126

src/builtin/filters/array.ts

@@ -6,7 +6,7 @@ export default {
   'last': <T>(v: T[]): T => last(v),
   'first': <T>(v: T[]): T => v[0],
   'map': <T1, T2>(arr: {[key: string]: T1}[], arg: string): T1[] => arr.map(v => v[arg]),
-  'reverse': (v: any[]) => v.reverse(),
+  'reverse': (v: any[]) => [...v].reverse(),
   'sort': <T>(v: T[], arg: (lhs: T, rhs: T) => number) => v.sort(arg),
   'size': (v: string | any[]) => v.length,
   'concat': <T1, T2>(v: T1[], arg: T2[] | T2): Array<T1 | T2> => Array.prototype.concat.call(v, arg),

test/integration/builtin/filters/array.ts

@@ -1,6 +1,12 @@
 import { test } from '../../../stub/render'
+import Liquid from '../../../../src/liquid'
+import {expect} from 'chai'
 
 describe('filters/array', function () {
+  let liquid: Liquid
+  beforeEach(function () {
+    liquid = new Liquid()
+  })
   describe('join', function () {
     it('should support join', function () {
       const src = '{% assign beatles = "John, Paul, George, Ringo" | split: ", " %}' +
@@ -21,9 +27,17 @@ describe('filters/array', function () {
   it('should support map', function () {
     return test('{{posts | map: "category"}}', 'foo,bar')
   })
-  it('should support reverse', function () {
-    return test('{{ "Ground control to Major Tom." | split: "" | reverse | join: "" }}',
-      '.moT rojaM ot lortnoc dnuorG')
+  describe('reverse', function () {
+    it('should support reverse', async function () {
+      const html = await liquid.parseAndRender('{{ "Ground control to Major Tom." | split: "" | reverse | join: "" }}')
+      expect(html).to.equal('.moT rojaM ot lortnoc dnuorG')
+    })
+    it('should be pure', async function () {
+      const scope = {arr: ['a', 'b', 'c']}
+      await liquid.parseAndRender('{{ arr | reverse | join: "" }}', scope)
+      const html = await liquid.parseAndRender('{{ arr | join: "" }}', scope)
+      expect(html).to.equal('abc')
+    })
   })
   describe('size', function () {
     it('should return string length',