Adds support for empty per spec

lib/solid/expression.ex

@@ -79,6 +79,10 @@ defmodule Solid.Expression do
   def eval({v1, :<, nil}) when is_number(v1), do: false
   def eval({nil, :>=, v2}) when is_number(v2), do: false
   def eval({nil, :>, v2}) when is_number(v2), do: false
+  def eval({v1, :==, :empty}) when is_list(v1), do: v1 == []
+  def eval({v1, :!=, :empty}) when is_list(v1), do: v1 != []
+  def eval({v1, :==, :empty}) when is_binary(v1), do: v1 == ""
+  def eval({v1, :!=, :empty}) when is_binary(v1), do: v1 != ""
   def eval({v1, op, v2}), do: apply(Kernel, op, [v1, v2])
 
   def eval(value) do

lib/solid/parser/literal.ex

@@ -50,6 +50,10 @@ defmodule Solid.Parser.Literal do
       string("nil")
       |> replace(nil)
 
+    empty =
+      string("empty")
+      |> replace(:empty)
+
     frac =
       string(".")
       |> concat(integer(min: 1))
@@ -72,6 +76,7 @@ defmodule Solid.Parser.Literal do
       true_value,
       false_value,
       null,
+      empty,
       single_quoted_string(),
       double_quoted_string()
     ])

test/cases/if/input.json

@@ -18,5 +18,6 @@
     }
   },
  "enabled?" : true,
-  "enabled2?" : false
+  "enabled2?" : false,
+  "var4": ""
 }

test/cases/if/input.liquid

@@ -27,6 +27,12 @@
 
 {% if array contains 1 %} true {% else %} false {% endif %}
 
+
+{% if array == empty %} true {% else %} false {% endif %}
+{% if array != empty %} true {% else %} false {% endif %}
+{% if var4 == empty %} true {% else %} false {% endif %}
+{% if var4 != empty %} true {% else %} false {% endif %}
+
 {% if string-array[1] == "b" %}
   letter b
 {% endif %}

test/cases/object/input.liquid

@@ -9,9 +9,9 @@
 {{ multiarray[12] }}
 {{ multiarray[-1][1] }}
 
-{{ empty[0][1] }}
-{{ empty[1][1] }}
-{{ empty[12] }}
+{{ nullobj[0][1] }}
+{{ nullobj[1][1] }}
+{{ nullobj[12] }}
 
 {{ string[0][1] }}
 {{ string[1][1] }}