From c0ffeeef26050d7b3fc541c0ead18c93a64813f2 Mon Sep 17 00:00:00 2001
From: Thierry Joyal <thierry.joyal@gmail.com>
Date: Mon, 6 Jan 2020 17:17:35 +0000
Subject: [PATCH] [Strainer] Separate factory from template

---
 History.md                                    |   4 +
 lib/liquid.rb                                 |   3 +-
 lib/liquid/context.rb                         |   2 +-
 lib/liquid/strainer_factory.rb                |  36 ++++
 .../{strainer.rb => strainer_template.rb}     |  47 ++---
 lib/liquid/template.rb                        |   2 +-
 test/test_helper.rb                           |  16 +-
 test/unit/strainer_factory_unit_test.rb       |  96 ++++++++++
 test/unit/strainer_template_unit_test.rb      |  82 +++++++++
 test/unit/strainer_unit_test.rb               | 167 ------------------
 10 files changed, 247 insertions(+), 208 deletions(-)
 create mode 100644 lib/liquid/strainer_factory.rb
 rename lib/liquid/{strainer.rb => strainer_template.rb} (50%)
 create mode 100644 test/unit/strainer_factory_unit_test.rb
 create mode 100644 test/unit/strainer_template_unit_test.rb
 delete mode 100644 test/unit/strainer_unit_test.rb

diff --git a/History.md b/History.md
index 9a82faab..b3130f9c 100644
--- a/History.md
+++ b/History.md
@@ -1,5 +1,9 @@
 # Liquid Change Log
 
+### Unreleased
+
+* Split Strainer class as a factory and a template (#1208) [Thierry Joyal]
+
 ## 4.0.3 / 2019-03-12
 
 ### Fixed
diff --git a/lib/liquid.rb b/lib/liquid.rb
index 733fd829..84b11e50 100644
--- a/lib/liquid.rb
+++ b/lib/liquid.rb
@@ -57,7 +57,8 @@ require 'liquid/forloop_drop'
 require 'liquid/extensions'
 require 'liquid/errors'
 require 'liquid/interrupts'
-require 'liquid/strainer'
+require 'liquid/strainer_factory'
+require 'liquid/strainer_template'
 require 'liquid/expression'
 require 'liquid/context'
 require 'liquid/parser_switching'
diff --git a/lib/liquid/context.rb b/lib/liquid/context.rb
index 81bd43d5..0737f744 100644
--- a/lib/liquid/context.rb
+++ b/lib/liquid/context.rb
@@ -52,7 +52,7 @@ module Liquid
     end
 
     def strainer
-      @strainer ||= Strainer.create(self, @filters)
+      @strainer ||= StrainerFactory.create(self, @filters)
     end
 
     # Adds filters to this context.
diff --git a/lib/liquid/strainer_factory.rb b/lib/liquid/strainer_factory.rb
new file mode 100644
index 00000000..7a7bcb8a
--- /dev/null
+++ b/lib/liquid/strainer_factory.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+module Liquid
+  # StrainerFactory is the factory for the filters system.
+  module StrainerFactory
+    extend self
+
+    def add_global_filter(filter)
+      strainer_class_cache.clear
+      global_filters << filter
+    end
+
+    def create(context, filters = [])
+      strainer_from_cache(filters).new(context)
+    end
+
+    private
+
+    def global_filters
+      @global_filters ||= []
+    end
+
+    def strainer_from_cache(filters)
+      strainer_class_cache[filters] ||= begin
+        klass = Class.new(StrainerTemplate)
+        global_filters.each { |f| klass.add_filter(f) }
+        filters.each { |f| klass.add_filter(f) }
+        klass
+      end
+    end
+
+    def strainer_class_cache
+      @strainer_class_cache ||= {}
+    end
+  end
+end
diff --git a/lib/liquid/strainer.rb b/lib/liquid/strainer_template.rb
similarity index 50%
rename from lib/liquid/strainer.rb
rename to lib/liquid/strainer_template.rb
index 3f3417e3..10227c58 100644
--- a/lib/liquid/strainer.rb
+++ b/lib/liquid/strainer_template.rb
@@ -3,54 +3,39 @@
 require 'set'
 
 module Liquid
-  # Strainer is the parent class for the filters system.
+  # StrainerTemplate is the computed class for the filters system.
   # New filters are mixed into the strainer class which is then instantiated for each liquid template render run.
   #
-  # The Strainer only allows method calls defined in filters given to it via Strainer.global_filter,
+  # The Strainer only allows method calls defined in filters given to it via StrainerFactory.add_global_filter,
   # Context#add_filters or Template.register_filter
-  class Strainer #:nodoc:
-    @@global_strainer = Class.new(Strainer) do
-      @filter_methods = Set.new
-    end
-    @@strainer_class_cache = Hash.new do |hash, filters|
-      hash[filters] = Class.new(@@global_strainer) do
-        @filter_methods = @@global_strainer.filter_methods.dup
-        filters.each { |f| add_filter(f) }
-      end
-    end
-
+  class StrainerTemplate
     def initialize(context)
       @context = context
     end
 
     class << self
-      attr_reader :filter_methods
-    end
+      def add_filter(filter)
+        return if include?(filter)
 
-    def self.add_filter(filter)
-      raise ArgumentError, "Expected module but got: #{filter.class}" unless filter.is_a?(Module)
-      unless include?(filter)
         invokable_non_public_methods = (filter.private_instance_methods + filter.protected_instance_methods).select { |m| invokable?(m) }
         if invokable_non_public_methods.any?
           raise MethodOverrideError, "Filter overrides registered public methods as non public: #{invokable_non_public_methods.join(', ')}"
-        else
-          send(:include, filter)
-          @filter_methods.merge(filter.public_instance_methods.map(&:to_s))
         end
+
+        include(filter)
+
+        filter_methods.merge(filter.public_instance_methods.map(&:to_s))
       end
-    end
 
-    def self.global_filter(filter)
-      @@strainer_class_cache.clear
-      @@global_strainer.add_filter(filter)
-    end
+      def invokable?(method)
+        filter_methods.include?(method.to_s)
+      end
 
-    def self.invokable?(method)
-      @filter_methods.include?(method.to_s)
-    end
+      private
 
-    def self.create(context, filters = [])
-      @@strainer_class_cache[filters].new(context)
+      def filter_methods
+        @filter_methods ||= Set.new
+      end
     end
 
     def invoke(method, *args)
diff --git a/lib/liquid/template.rb b/lib/liquid/template.rb
index 228870cf..75b3d2ed 100644
--- a/lib/liquid/template.rb
+++ b/lib/liquid/template.rb
@@ -111,7 +111,7 @@ module Liquid
       # Pass a module with filter methods which should be available
       # to all liquid views. Good for registering the standard library
       def register_filter(mod)
-        Strainer.global_filter(mod)
+        StrainerFactory.add_global_filter(mod)
       end
 
       def default_resource_limits
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 7356a290..7910ec42 100755
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -55,19 +55,21 @@ module Minitest
     end
 
     def with_global_filter(*globals)
-      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
+      original_global_filters = Liquid::StrainerFactory.instance_variable_get(:@global_filters)
+      Liquid::StrainerFactory.instance_variable_set(:@global_filters, [])
+      globals.each do |global|
+        Liquid::StrainerFactory.add_global_filter(global)
+      end
+
+      Liquid::StrainerFactory.send(:strainer_class_cache).clear
 
       globals.each do |global|
         Liquid::Template.register_filter(global)
       end
       yield
     ensure
-      Liquid::Strainer.class_variable_get(:@@strainer_class_cache).clear
-      Liquid::Strainer.class_variable_set(:@@global_strainer, original_global_strainer)
+      Liquid::StrainerFactory.send(:strainer_class_cache).clear
+      Liquid::StrainerFactory.instance_variable_set(:@global_filters, original_global_filters)
     end
 
     def with_taint_mode(mode)
diff --git a/test/unit/strainer_factory_unit_test.rb b/test/unit/strainer_factory_unit_test.rb
new file mode 100644
index 00000000..6d644752
--- /dev/null
+++ b/test/unit/strainer_factory_unit_test.rb
@@ -0,0 +1,96 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class StrainerFactoryUnitTest < Minitest::Test
+  include Liquid
+
+  module AccessScopeFilters
+    def public_filter
+      "public"
+    end
+
+    def private_filter
+      "private"
+    end
+    private :private_filter
+  end
+
+  StrainerFactory.add_global_filter(AccessScopeFilters)
+
+  module LateAddedFilter
+    def late_added_filter(_input)
+      "filtered"
+    end
+  end
+
+  def test_strainer
+    strainer = StrainerFactory.create(nil)
+    assert_equal(5, strainer.invoke('size', 'input'))
+    assert_equal("public", strainer.invoke("public_filter"))
+  end
+
+  def test_stainer_raises_argument_error
+    strainer = StrainerFactory.create(nil)
+    assert_raises(Liquid::ArgumentError) do
+      strainer.invoke("public_filter", 1)
+    end
+  end
+
+  def test_stainer_argument_error_contains_backtrace
+    strainer = StrainerFactory.create(nil)
+
+    exception = assert_raises(Liquid::ArgumentError) do
+      strainer.invoke("public_filter", 1)
+    end
+
+    assert_match(
+      /\ALiquid error: wrong number of arguments \((1 for 0|given 1, expected 0)\)\z/,
+      exception.message
+    )
+    assert_equal(exception.backtrace[0].split(':')[0], __FILE__)
+  end
+
+  def test_strainer_only_invokes_public_filter_methods
+    strainer = StrainerFactory.create(nil)
+    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
+    strainer = StrainerFactory.create(nil)
+    assert_nil(strainer.invoke("private_filter"))
+    assert_nil(strainer.invoke("undef_the_filter"))
+  end
+
+  def test_strainer_returns_first_argument_if_no_method_and_arguments_given
+    strainer = StrainerFactory.create(nil)
+    assert_equal("password", strainer.invoke("undef_the_method", "password"))
+  end
+
+  def test_strainer_only_allows_methods_defined_in_filters
+    strainer = StrainerFactory.create(nil)
+    assert_equal("1 + 1", strainer.invoke("instance_eval", "1 + 1"))
+    assert_equal("puts",  strainer.invoke("__send__", "puts", "Hi Mom"))
+    assert_equal("has_method?", strainer.invoke("invoke", "has_method?", "invoke"))
+  end
+
+  def test_strainer_uses_a_class_cache_to_avoid_method_cache_invalidation
+    a = Module.new
+    b = Module.new
+    strainer = StrainerFactory.create(nil, [a, b])
+    assert_kind_of(StrainerTemplate, strainer)
+    assert_kind_of(a, strainer)
+    assert_kind_of(b, strainer)
+    assert_kind_of(Liquid::StandardFilters, strainer)
+  end
+
+  def test_add_global_filter_clears_cache
+    assert_equal('input', StrainerFactory.create(nil).invoke('late_added_filter', 'input'))
+    StrainerFactory.add_global_filter(LateAddedFilter)
+    assert_equal('filtered', StrainerFactory.create(nil).invoke('late_added_filter', 'input'))
+  end
+end
diff --git a/test/unit/strainer_template_unit_test.rb b/test/unit/strainer_template_unit_test.rb
new file mode 100644
index 00000000..e72ed44d
--- /dev/null
+++ b/test/unit/strainer_template_unit_test.rb
@@ -0,0 +1,82 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class StrainerTemplateUnitTest < Minitest::Test
+  include Liquid
+
+  def test_add_filter_when_wrong_filter_class
+    c = Context.new
+    s = c.strainer
+    wrong_filter = ->(v) { v.reverse }
+
+    exception = assert_raises(TypeError) do
+      s.class.add_filter(wrong_filter)
+    end
+    assert_equal(exception.message, "wrong argument type Proc (expected Module)")
+  end
+
+  module PrivateMethodOverrideFilter
+    private
+
+    def public_filter
+      "overriden as private"
+    end
+  end
+
+  def test_add_filter_raises_when_module_privately_overrides_registered_public_methods
+    strainer = Context.new.strainer
+
+    error = assert_raises(Liquid::MethodOverrideError) do
+      strainer.class.add_filter(PrivateMethodOverrideFilter)
+    end
+    assert_equal('Liquid error: Filter overrides registered public methods as non public: public_filter', error.message)
+  end
+
+  module ProtectedMethodOverrideFilter
+    protected
+
+    def public_filter
+      "overriden as protected"
+    end
+  end
+
+  def test_add_filter_raises_when_module_overrides_registered_public_method_as_protected
+    strainer = Context.new.strainer
+
+    error = assert_raises(Liquid::MethodOverrideError) do
+      strainer.class.add_filter(ProtectedMethodOverrideFilter)
+    end
+    assert_equal('Liquid error: Filter overrides registered public methods as non public: public_filter', error.message)
+  end
+
+  module PublicMethodOverrideFilter
+    def public_filter
+      "public"
+    end
+  end
+
+  def test_add_filter_does_not_raise_when_module_overrides_previously_registered_method
+    strainer = Context.new.strainer
+    with_global_filter do
+      strainer.class.add_filter(PublicMethodOverrideFilter)
+      assert(strainer.class.send(:filter_methods).include?('public_filter'))
+    end
+  end
+
+  def test_add_filter_does_not_include_already_included_module
+    mod = Module.new do
+      class << self
+        attr_accessor :include_count
+        def included(_mod)
+          self.include_count += 1
+        end
+      end
+      self.include_count = 0
+    end
+    strainer = Context.new.strainer
+    strainer.class.add_filter(mod)
+    strainer.class.add_filter(mod)
+    assert_equal(1, mod.include_count)
+  end
+end
diff --git a/test/unit/strainer_unit_test.rb b/test/unit/strainer_unit_test.rb
deleted file mode 100644
index a05f9084..00000000
--- a/test/unit/strainer_unit_test.rb
+++ /dev/null
@@ -1,167 +0,0 @@
-# frozen_string_literal: true
-
-require 'test_helper'
-
-class StrainerUnitTest < Minitest::Test
-  include Liquid
-
-  module AccessScopeFilters
-    def public_filter
-      "public"
-    end
-
-    def private_filter
-      "private"
-    end
-    private :private_filter
-  end
-
-  Strainer.global_filter(AccessScopeFilters)
-
-  def test_strainer
-    strainer = Strainer.create(nil)
-    assert_equal(5, strainer.invoke('size', 'input'))
-    assert_equal("public", strainer.invoke("public_filter"))
-  end
-
-  def test_stainer_raises_argument_error
-    strainer = Strainer.create(nil)
-    assert_raises(Liquid::ArgumentError) do
-      strainer.invoke("public_filter", 1)
-    end
-  end
-
-  def test_stainer_argument_error_contains_backtrace
-    strainer = Strainer.create(nil)
-    begin
-      strainer.invoke("public_filter", 1)
-    rescue Liquid::ArgumentError => e
-      assert_match(
-        /\ALiquid error: wrong number of arguments \((1 for 0|given 1, expected 0)\)\z/,
-        e.message
-      )
-      assert_equal(e.backtrace[0].split(':')[0], __FILE__)
-    end
-  end
-
-  def test_strainer_only_invokes_public_filter_methods
-    strainer = Strainer.create(nil)
-    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
-    strainer = Strainer.create(nil)
-    assert_nil(strainer.invoke("private_filter"))
-    assert_nil(strainer.invoke("undef_the_filter"))
-  end
-
-  def test_strainer_returns_first_argument_if_no_method_and_arguments_given
-    strainer = Strainer.create(nil)
-    assert_equal("password", strainer.invoke("undef_the_method", "password"))
-  end
-
-  def test_strainer_only_allows_methods_defined_in_filters
-    strainer = Strainer.create(nil)
-    assert_equal("1 + 1", strainer.invoke("instance_eval", "1 + 1"))
-    assert_equal("puts",  strainer.invoke("__send__", "puts", "Hi Mom"))
-    assert_equal("has_method?", strainer.invoke("invoke", "has_method?", "invoke"))
-  end
-
-  def test_strainer_uses_a_class_cache_to_avoid_method_cache_invalidation
-    a = Module.new
-    b = Module.new
-    strainer = Strainer.create(nil, [a, b])
-    assert_kind_of(Strainer, strainer)
-    assert_kind_of(a, strainer)
-    assert_kind_of(b, strainer)
-    assert_kind_of(Liquid::StandardFilters, strainer)
-  end
-
-  def test_add_filter_when_wrong_filter_class
-    c = Context.new
-    s = c.strainer
-    wrong_filter = ->(v) { v.reverse }
-
-    assert_raises ArgumentError do
-      s.class.add_filter(wrong_filter)
-    end
-  end
-
-  module PrivateMethodOverrideFilter
-    private
-
-    def public_filter
-      "overriden as private"
-    end
-  end
-
-  def test_add_filter_raises_when_module_privately_overrides_registered_public_methods
-    strainer = Context.new.strainer
-
-    error = assert_raises(Liquid::MethodOverrideError) do
-      strainer.class.add_filter(PrivateMethodOverrideFilter)
-    end
-    assert_equal('Liquid error: Filter overrides registered public methods as non public: public_filter', error.message)
-  end
-
-  module ProtectedMethodOverrideFilter
-    protected
-
-    def public_filter
-      "overriden as protected"
-    end
-  end
-
-  def test_add_filter_raises_when_module_overrides_registered_public_method_as_protected
-    strainer = Context.new.strainer
-
-    error = assert_raises(Liquid::MethodOverrideError) do
-      strainer.class.add_filter(ProtectedMethodOverrideFilter)
-    end
-    assert_equal('Liquid error: Filter overrides registered public methods as non public: public_filter', error.message)
-  end
-
-  module PublicMethodOverrideFilter
-    def public_filter
-      "public"
-    end
-  end
-
-  def test_add_filter_does_not_raise_when_module_overrides_previously_registered_method
-    strainer = Context.new.strainer
-    strainer.class.add_filter(PublicMethodOverrideFilter)
-    assert(strainer.class.filter_methods.include?('public_filter'))
-  end
-
-  module LateAddedFilter
-    def late_added_filter(_input)
-      "filtered"
-    end
-  end
-
-  def test_global_filter_clears_cache
-    assert_equal('input', Strainer.create(nil).invoke('late_added_filter', 'input'))
-    Strainer.global_filter(LateAddedFilter)
-    assert_equal('filtered', Strainer.create(nil).invoke('late_added_filter', 'input'))
-  end
-
-  def test_add_filter_does_not_include_already_included_module
-    mod = Module.new do
-      class << self
-        attr_accessor :include_count
-        def included(_mod)
-          self.include_count += 1
-        end
-      end
-      self.include_count = 0
-    end
-    strainer = Context.new.strainer
-    strainer.class.add_filter(mod)
-    strainer.class.add_filter(mod)
-    assert_equal(1, mod.include_count)
-  end
-end # StrainerTest