Allow filters to redefine Object methods to make them invokable.

lib/liquid/context.rb

@@ -44,21 +44,8 @@ module Liquid
     # for that
     def add_filters(filters)
       filters = [filters].flatten.compact
-      filters.each do |f|
-        raise ArgumentError, "Expected module but got: #{f.class}" unless f.is_a?(Module)
-        Strainer.add_known_filter(f)
-      end
-
-      # If strainer is already setup then there's no choice but to use a runtime
-      # extend call. If strainer is not yet created, we can utilize strainers
-      # cached class based API, which avoids busting the method cache.
-      if @strainer
-        filters.each do |f|
-          strainer.extend(f)
-        end
-      else
-        @filters.concat filters
-      end
+      @filters += filters
+      @strainer = nil
     end
 
     # are there any not handled interrupts?

lib/liquid/strainer.rb

@@ -8,12 +8,13 @@ module Liquid
   # The Strainer only allows method calls defined in filters given to it via Strainer.global_filter,
   # Context#add_filters or Template.register_filter
   class Strainer #:nodoc:
-    @@filters = []
-    @@known_filters = Set.new
-    @@known_methods = Set.new
+    @@global_strainer = Class.new(Strainer) do
+      @filter_methods = Set.new
+    end
     @@strainer_class_cache = Hash.new do |hash, filters|
-      hash[filters] = Class.new(Strainer) do
-        filters.each { |f| include f }
+      hash[filters] = Class.new(@@global_strainer) do
+        @filter_methods = @@global_strainer.filter_methods.dup
+        filters.each { |f| add_filter(f) }
       end
     end
 
@@ -21,33 +22,32 @@ module Liquid
       @context = context
     end
 
-    def self.global_filter(filter)
-      raise ArgumentError, "Passed filter is not a module" unless filter.is_a?(Module)
-      add_known_filter(filter)
-      @@filters << filter unless @@filters.include?(filter)
+    def self.filter_methods
+      @filter_methods
     end
 
-    def self.add_known_filter(filter)
-      unless @@known_filters.include?(filter)
-        @@method_blacklist ||= Set.new(Strainer.instance_methods.map(&:to_s))
-        new_methods = filter.instance_methods.map(&:to_s)
-        new_methods.reject!{ |m| @@method_blacklist.include?(m) }
-        @@known_methods.merge(new_methods)
-        @@known_filters.add(filter)
+    def self.add_filter(filter)
+      raise ArgumentError, "Expected module but got: #{f.class}" unless filter.is_a?(Module)
+      unless self.class.include?(filter)
+        self.send(:include, filter)
+        @filter_methods.merge(filter.public_instance_methods.map(&:to_s))
       end
     end
 
-    def self.strainer_class_cache
-      @@strainer_class_cache
+    def self.global_filter(filter)
+      @@global_strainer.add_filter(filter)
+    end
+
+    def self.invokable?(method)
+      @filter_methods.include?(method.to_s)
     end
 
     def self.create(context, filters = [])
-      filters = @@filters + filters
-      strainer_class_cache[filters].new(context)
+      @@strainer_class_cache[filters].new(context)
     end
 
     def invoke(method, *args)
-      if invokable?(method)
+      if self.class.invokable?(method)
         send(method, *args)
       else
         args.first
@@ -55,9 +55,5 @@ module Liquid
     rescue ::ArgumentError => e
       raise Liquid::ArgumentError.new(e.message)
     end
-
-    def invokable?(method)
-      @@known_methods.include?(method.to_s) && respond_to?(method)
-    end
   end
 end

test/integration/filter_test.rb

@@ -25,6 +25,12 @@ end
 class FiltersTest < Minitest::Test
   include Liquid
 
+  module OverrideObjectMethodFilter
+    def tap(input)
+      "tap overridden"
+    end
+  end
+
   def setup
     @context = Context.new
   end
@@ -105,6 +111,13 @@ class FiltersTest < Minitest::Test
     output = Variable.new(%! 'hello %{first_name}, %{last_name}' | substitute: first_name: surname, last_name: 'doe' !).render(@context)
     assert_equal 'hello john, doe', output
   end
+
+  def test_override_object_method_in_filter
+    assert_equal "tap overridden", Template.parse("{{var | tap}}").render!({ 'var' => 1000 }, :filters => [OverrideObjectMethodFilter])
+
+    # tap still treated as a non-existent filter
+    assert_equal "1000", Template.parse("{{var | tap}}").render!({ 'var' => 1000 })
+  end
 end
 
 class FiltersInTemplate < Minitest::Test

test/test_helper.rb

@@ -49,13 +49,19 @@ module Minitest
     end
 
     def with_global_filter(*globals)
-      original_filters = Array.new(Liquid::Strainer.class_variable_get(:@@filters))
+      original_global_strainer = Liquid::Strainer.class_variable_get(:@@global_strainer)
+      Liquid::Strainer.class_variable_set(:@@global_strainer, Class.new(Liquid::Strainer) do
+        @filter_methods = Set.new
+      end)
+      Liquid::Strainer.class_variable_get(:@@strainer_class_cache).clear
+
       globals.each do |global|
         Liquid::Template.register_filter(global)
       end
       yield
     ensure
-      Liquid::Strainer.class_variable_set(:@@filters, original_filters)
+      Liquid::Strainer.class_variable_get(:@@strainer_class_cache).clear
+      Liquid::Strainer.class_variable_set(:@@global_strainer, original_global_strainer)
     end
 
     def with_taint_mode(mode)

test/unit/strainer_unit_test.rb

@@ -31,11 +31,11 @@ class StrainerUnitTest < Minitest::Test
 
   def test_strainer_only_invokes_public_filter_methods
     strainer = Strainer.create(nil)
-    assert_equal false, strainer.invokable?('__test__')
-    assert_equal false, strainer.invokable?('test')
-    assert_equal false, strainer.invokable?('instance_eval')
-    assert_equal false, strainer.invokable?('__send__')
-    assert_equal true, strainer.invokable?('size') # from the standard lib
+    assert_equal false, strainer.class.invokable?('__test__')
+    assert_equal false, strainer.class.invokable?('test')
+    assert_equal false, strainer.class.invokable?('instance_eval')
+    assert_equal false, strainer.class.invokable?('__send__')
+    assert_equal true, strainer.class.invokable?('size') # from the standard lib
   end
 
   def test_strainer_returns_nil_if_no_filter_method_found
@@ -63,9 +63,7 @@ class StrainerUnitTest < Minitest::Test
     assert_kind_of Strainer, strainer
     assert_kind_of a, strainer
     assert_kind_of b, strainer
-    Strainer.class_variable_get(:@@filters).each do |m|
-      assert_kind_of m, strainer
-    end
+    assert_kind_of Liquid::StandardFilters, strainer
   end
 
 end # StrainerTest