Pass all compact filter golden tests.

spec/integration/golden_liquid.pending

@@ -41,8 +41,6 @@ liquid.golden.base64_url_safe_encode_filter from string
 liquid.golden.base64_url_safe_encode_filter from string with URL unsafe
 liquid.golden.base64_url_safe_encode_filter not a string
 liquid.golden.base64_url_safe_encode_filter unexpected argument
-liquid.golden.compact_filter array of objects with key property
-liquid.golden.compact_filter too many arguments
 liquid.golden.concat_filter left value contains non string
 liquid.golden.concat_filter left value is not array-like
 liquid.golden.concat_filter missing argument is an error

src/liquid/drop.cr

@@ -31,6 +31,11 @@ module Liquid
     def call(method : String) : Liquid::Any
       raise Liquid::InvalidExpression.new("Method #{method} not found for #{self.class.name}.")
     end
+
+    # Alias to `#call`.
+    def [](method : String) : Liquid::Any
+      call(method)
+    end
   end
 end
 

src/liquid/filters/compact.cr

@@ -5,11 +5,24 @@ module Liquid::Filters
     extend Filter
 
     def self.filter(data : Any, args : Array(Any), options : Hash(String, Any)) : Any
-      if d = data.as_a?
-        Any.new(d.reject(&.raw.nil?))
-      else
-        data
+      raise FilterArgumentException.new("compact filter expects at most 1 argument.") if args.size > 1
+
+      array = data.as_a?
+      return data if array.nil?
+
+      key = args.first?
+      return Any.new(array.reject(&.raw.nil?)) if key.nil? || !key.as_s?
+
+      key = key.as_s
+      result = array.reject do |item|
+        raw_item = item.raw
+        if raw_item.is_a?(Drop) || raw_item.is_a?(Hash)
+          raw_item[key].raw.nil?
+        else
+          raw_item.nil?
+        end
       end
+      Any.new(result)
     end
   end