fix: corner case for concat filter without argument, #481

test/e2e/issues.ts

@@ -217,8 +217,14 @@ describe('Issues', function () {
       {{ foo | newline_to_br }}
       {{ foo | strip_html }}
       {{ foo | truncatewords }}
+      {{ foo | concat | json }}
     `)
     const html = await engine.render(tpl, { foo: undefined })
-    expect(html.trim()).to.equal('')
+    expect(html.trim()).to.equal('[]')
+  })
+  it('#481 concat should always return an array', async () => {
+    const engine = new Liquid()
+    const html = await engine.parseAndRender(`{{ foo | concat | json }}`)
+    expect(html).to.equal('[]')
   })
 })

test/integration/builtin/filters/array.ts

@@ -75,11 +75,24 @@ describe('filters/array', function () {
   })
 
   describe('concat', () => {
+    it('should concat args value', async () => {
+      const scope = { val: ['hey'], arr: ['foo', 'bar'] }
+      await test('{{ val | concat: arr | join: "," }}', scope, 'hey,foo,bar')
+    })
+    it('should support undefined left value', async () => {
+      const scope = { arr: ['foo', 'bar'] }
+      await test('{{ notDefined | concat: arr | join: "," }}', scope, 'foo,bar')
+    })
     it('should ignore nil left value', async () => {
       const scope = { undefinedValue: undefined, nullValue: null, arr: ['foo', 'bar'] }
       await test('{{ undefinedValue | concat: arr | join: "," }}', scope, 'foo,bar')
       await test('{{ nullValue | concat: arr | join: "," }}', scope, 'foo,bar')
     })
+    it('should ignore nil right value', async () => {
+      const scope = { nullValue: null }
+      await test('{{ nullValue | concat | join: "," }}', scope, '')
+      await test('{{ nullValue | concat: nil | join: "," }}', scope, '')
+    })
   })
 
   describe('reverse', function () {