fix: comparison for empty/nil, fixes #321

src/drop/empty-drop.ts

@@ -1,9 +1,11 @@
 import { Drop } from './drop'
 import { Comparable } from './comparable'
-import { isObject, isString, isArray } from '../util/underscore'
+import { isObject, isString, isArray, toValue } from '../util/underscore'
 
 export class EmptyDrop extends Drop implements Comparable {
   public equals (value: any) {
+    if (value instanceof EmptyDrop) return false
+    value = toValue(value)
     if (isString(value) || isArray(value)) return value.length === 0
     if (isObject(value)) return Object.keys(value).length === 0
     return false

src/drop/null-drop.ts

@@ -1,11 +1,10 @@
 import { Drop } from './drop'
 import { Comparable } from './comparable'
 import { isNil, toValue } from '../util/underscore'
-import { BlankDrop } from '../drop/blank-drop'
 
 export class NullDrop extends Drop implements Comparable {
   public equals (value: any) {
-    return isNil(toValue(value)) || value instanceof BlankDrop
+    return isNil(toValue(value))
   }
   public gt () {
     return false

src/util/literal.ts

@@ -2,11 +2,12 @@ import { NullDrop } from '../drop/null-drop'
 import { EmptyDrop } from '../drop/empty-drop'
 import { BlankDrop } from '../drop/blank-drop'
 
+const nil = new NullDrop()
 export const literalValues = {
   'true': true,
   'false': false,
-  'nil': new NullDrop(),
-  'null': new NullDrop(),
+  'nil': nil,
+  'null': nil,
   'empty': new EmptyDrop(),
   'blank': new BlankDrop()
 }

test/e2e/issues.ts

@@ -87,4 +87,12 @@ describe('Issues', function () {
     const html = await engine.parseAndRender(`{{ name | default: "default name" }}`)
     expect(html).to.equal('default name')
   })
+  it('#321 comparison for empty/nil', async () => {
+    const engine = new Liquid()
+    const html = await engine.parseAndRender(
+      '{% if empty == nil %}true{%else%}false{%endif%}' +
+      '{% if nil == empty %}true{%else%}false{%endif%}'
+    )
+    expect(html).to.equal('falsefalse')
+  })
 })

test/integration/drop/empty-drop.ts

@@ -79,4 +79,14 @@ describe('drop/empty-drop', function () {
     const html = await liquid.parseAndRender(src)
     expect(html).to.equal('true')
   })
+  it('empty != empty', async function () {
+    const src = '{%if empty == empty %}true{%else%}false{% endif %}'
+    const html = await liquid.parseAndRender(src)
+    expect(html).to.equal('false')
+  })
+  it('empty != nil', async function () {
+    const src = '{%if empty == nil %}true{%else%}false{% endif %}'
+    const html = await liquid.parseAndRender(src)
+    expect(html).to.equal('false')
+  })
 })

test/integration/drop/null-drop.ts

@@ -13,22 +13,27 @@ describe('drop/null-drop', function () {
     const html = await liquid.parseAndRender('{{null}}')
     expect(html).to.equal('')
   })
-  it('undefined variable should equal to null', async function () {
+  it('undefined == null', async function () {
     const src = '{%if foo == nil %}foo == nil{%else%}foo != nil{% endif %}'
     const html = await liquid.parseAndRender(src)
     expect(html).to.equal('foo == nil')
   })
-  it('nil equals blank', async function () {
-    const src = '{%if nil == blank %}nil == blank{%else%}nil != blank{% endif %}'
+  it('nil != blank', async function () {
+    const src = '{%if nil == blank %}eq{%else%}neq{% endif %}'
     const html = await liquid.parseAndRender(src)
-    expect(html).to.equal('nil == blank')
+    expect(html).to.equal('neq')
   })
-  it('0 should not equal to null', async function () {
+  it('nil != empty', async function () {
+    const src = '{%if nil == empty %}eq{%else%}neq{% endif %}'
+    const html = await liquid.parseAndRender(src)
+    expect(html).to.equal('neq')
+  })
+  it('0 != null', async function () {
     const src = '{%if 0 == null %}0 == null{%else%}0 != null{% endif %}'
     const html = await liquid.parseAndRender(src)
     expect(html).to.equal('0 != null')
   })
-  it('nil should equal to null', async function () {
+  it('nil == null', async function () {
     const src = '{%if nil == null %}nil == null{%else%}nil != null{% endif %}'
     const html = await liquid.parseAndRender(src)
     expect(html).to.equal('nil == null')