Merge pull request #583 from Shopify/slice-nil-offset

Raise a Liquid::ArgumentError in slice filter for invalid integers.

lib/liquid/standardfilters.rb

@@ -46,8 +46,8 @@ module Liquid
     end
 
     def slice(input, offset, length = nil)
-      offset = Integer(offset)
+      offset = to_integer(offset)
-      length = length ? Integer(length) : 1
+      length = length ? to_integer(length) : 1
 
       if input.is_a?(Array)
         input.slice(offset, length) || []
@@ -317,6 +317,16 @@ module Liquid
 
     private
 
+    def to_integer(num)
+      return num if num.is_a?(Integer)
+      num = num.to_s
+      begin
+        Integer(num)
+      rescue ::ArgumentError
+        raise Liquid::ArgumentError, "invalid integer"
+      end
+    end
+
     def to_number(obj)
       case obj
       when Float

test/integration/standard_filter_test.rb

@@ -76,6 +76,13 @@ class StandardFiltersTest < Minitest::Test
     assert_equal '', @filters.slice(nil, 0)
     assert_equal '', @filters.slice('foobar', 100, 10)
     assert_equal '', @filters.slice('foobar', -100, 10)
+    assert_equal 'oob', @filters.slice('foobar', '1', '3')
+    assert_raises(Liquid::ArgumentError) do
+      @filters.slice('foobar', nil)
+    end
+    assert_raises(Liquid::ArgumentError) do
+      @filters.slice('foobar', 0, "")
+    end
   end
 
   def test_slice_on_arrays