Add isolated subcontexts

An isolated subcontext inherits the environment, filters,
and static registers of its supercontext, but with a fresh
(isolated) scope.

This will pave the way for adding the `render` tag, which renders
templates in such a subcontext.

lib/liquid/context.rb

@@ -12,13 +12,18 @@ module Liquid
   #
   #   context['bob']  #=> nil  class Context
   class Context
-    attr_reader :scopes, :errors, :registers, :environments, :resource_limits
+    attr_reader :scopes, :errors, :registers, :environments, :resource_limits, :static_registers
     attr_accessor :exception_renderer, :template_name, :partial, :global_filter, :strict_variables, :strict_filters
 
-    def initialize(environments = {}, outer_scope = {}, registers = {}, rethrow_errors = false, resource_limits = nil)
+    def self.build(environments: {}, outer_scope: {}, registers: {}, rethrow_errors: false, resource_limits: nil, static_registers: {})
+      new(environments, outer_scope, registers, rethrow_errors, resource_limits, static_registers)
+    end
+
+    def initialize(environments = {}, outer_scope = {}, registers = {}, rethrow_errors = false, resource_limits = nil, static_registers = {})
       @environments     = [environments].flatten
       @scopes           = [(outer_scope || {})]
       @registers        = registers
+      @static_registers = static_registers.tap(&:freeze)
       @errors           = []
       @partial          = false
       @strict_variables = false
@@ -126,6 +131,19 @@ module Liquid
       @this_stack_used = old_stack_used
     end
 
+    # Creates a new context inheriting resource limits, filters, environment etc.,
+    # but with an isolated scope.
+    def new_isolated_subcontext
+      Context.build(
+        environments: environments,
+        resource_limits: resource_limits,
+        static_registers: static_registers
+      ).tap do |subcontext|
+        subcontext.exception_renderer = exception_renderer
+        subcontext.add_filters(@filters)
+      end
+    end
+
     def clear_instance_assigns
       @scopes[0] = {}
     end

lib/liquid/tags/render.rb

@@ -0,0 +1,89 @@
+module Liquid
+  #
+  # TODO: docs
+  #
+  class Render < Tag
+    Syntax = /(#{QuotedFragment}+)/o
+
+    attr_reader :template_name_expr, :attributes
+
+    def initialize(tag_name, markup, options)
+      super
+
+      if markup =~ Syntax
+        template_name = $1
+
+        @template_name_expr = Expression.parse(template_name)
+
+        @attributes = {}
+        markup.scan(TagAttributes) do |key, value|
+          @attributes[key] = Expression.parse(value)
+        end
+
+      else
+        raise SyntaxError.new(options[:locale].t("errors.syntax.include".freeze))
+      end
+    end
+
+    def parse(_tokens)
+    end
+
+    def render_to_output_buffer(context, output)
+      template_name = context.evaluate(@template_name_expr)
+      raise ArgumentError.new(options[:locale].t("errors.argument.include")) unless template_name
+
+      partial = load_cached_partial(template_name, context)
+
+      inner_context = Context.new
+      inner_context.template_name = template_name
+      inner_context.partial = true
+      @attributes.each do |key, value|
+        inner_context[key] = context.evaluate(value)
+      end
+      partial.render_to_output_buffer(inner_context, output)
+      
+      # TODO: Put into a new #isolated_stack method in Context?
+      inner_context.errors.each { |e| context.errors << e }
+
+      output
+    end
+
+    private
+
+    alias_method :parse_context, :options
+    private :parse_context
+
+    def load_cached_partial(template_name, context)
+      cached_partials = context.registers[:cached_partials] || {}
+
+      if cached = cached_partials[template_name]
+        return cached
+      end
+      source = read_template_from_file_system(context)
+      begin
+        parse_context.partial = true
+        partial = Liquid::Template.parse(source, parse_context)
+      ensure
+        parse_context.partial = false
+      end
+      cached_partials[template_name] = partial
+      context.registers[:cached_partials] = cached_partials
+      partial
+    end
+
+    def read_template_from_file_system(context)
+      file_system = context.registers[:file_system] || Liquid::Template.file_system
+      file_system.read_template_file(context.evaluate(@template_name_expr))
+    end
+
+    class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      def children
+        [
+          @node.template_name_expr,
+        ] + @node.attributes.values
+      end
+    end
+  end
+
+  Template.register_tag('render'.freeze, Render)
+end

test/integration/tags/render_rag_test.rb

@@ -0,0 +1,255 @@
+require 'test_helper'
+
+class TestFileSystem
+  def read_template_file(template_path)
+    case template_path
+    when "product"
+      "Product: {{ product.title }} "
+
+    when "locale_variables"
+      "Locale: {{echo1}} {{echo2}}"
+
+    when "variant"
+      "Variant: {{ variant.title }}"
+
+    when "nested_template"
+      "{% include 'header' %} {% include 'body' %} {% include 'footer' %}"
+
+    when "body"
+      "body {% include 'body_detail' %}"
+
+    when "nested_product_template"
+      "Product: {{ nested_product_template.title }} {%include 'details'%} "
+
+    when "recursively_nested_template"
+      "-{% include 'recursively_nested_template' %}"
+
+    when "pick_a_source"
+      "from TestFileSystem"
+
+    when 'assignments'
+      "{% assign foo = 'bar' %}"
+
+    when 'break'
+      "{% break %}"
+
+    else
+      template_path
+    end
+  end
+end
+
+class OtherFileSystem
+  def read_template_file(template_path)
+    'from OtherFileSystem'
+  end
+end
+
+class CountingFileSystem
+  attr_reader :count
+  def read_template_file(template_path)
+    @count ||= 0
+    @count += 1
+    'from CountingFileSystem'
+  end
+end
+
+class CustomInclude < Liquid::Tag
+  Syntax = /(#{Liquid::QuotedFragment}+)(\s+(?:with|for)\s+(#{Liquid::QuotedFragment}+))?/o
+
+  def initialize(tag_name, markup, tokens)
+    markup =~ Syntax
+    @template_name = $1
+    super
+  end
+
+  def parse(tokens)
+  end
+
+  def render_to_output_buffer(context, output)
+    output << @template_name[1..-2]
+    output
+  end
+end
+
+class IncludeTagTest < Minitest::Test
+  include Liquid
+
+  def setup
+    Liquid::Template.file_system = TestFileSystem.new
+  end
+
+  def test_include_tag_looks_for_file_system_in_registers_first
+    assert_equal 'from OtherFileSystem',
+      Template.parse("{% include 'pick_a_source' %}").render!({}, registers: { file_system: OtherFileSystem.new })
+  end
+
+  def test_include_tag_with
+    assert_template_result "Product: Draft 151cm ",
+      "{% include 'product' with products[0] %}", "products" => [ { 'title' => 'Draft 151cm' }, { 'title' => 'Element 155cm' } ]
+  end
+
+  def test_include_tag_with_default_name
+    assert_template_result "Product: Draft 151cm ",
+      "{% include 'product' %}", "product" => { 'title' => 'Draft 151cm' }
+  end
+
+  def test_include_tag_for
+    assert_template_result "Product: Draft 151cm Product: Element 155cm ",
+      "{% include 'product' for products %}", "products" => [ { 'title' => 'Draft 151cm' }, { 'title' => 'Element 155cm' } ]
+  end
+
+  def test_include_tag_with_local_variables
+    assert_template_result "Locale: test123 ", "{% include 'locale_variables' echo1: 'test123' %}"
+  end
+
+  def test_include_tag_with_multiple_local_variables
+    assert_template_result "Locale: test123 test321",
+      "{% include 'locale_variables' echo1: 'test123', echo2: 'test321' %}"
+  end
+
+  def test_include_tag_with_multiple_local_variables_from_context
+    assert_template_result "Locale: test123 test321",
+      "{% include 'locale_variables' echo1: echo1, echo2: more_echos.echo2 %}",
+      'echo1' => 'test123', 'more_echos' => { "echo2" => 'test321' }
+  end
+
+  def test_included_templates_assigns_variables
+    assert_template_result "bar", "{% include 'assignments' %}{{ foo }}"
+  end
+
+  def test_nested_include_tag
+    assert_template_result "body body_detail", "{% include 'body' %}"
+
+    assert_template_result "header body body_detail footer", "{% include 'nested_template' %}"
+  end
+
+  def test_nested_include_with_variable
+    assert_template_result "Product: Draft 151cm details ",
+      "{% include 'nested_product_template' with product %}", "product" => { "title" => 'Draft 151cm' }
+
+    assert_template_result "Product: Draft 151cm details Product: Element 155cm details ",
+      "{% include 'nested_product_template' for products %}", "products" => [{ "title" => 'Draft 151cm' }, { "title" => 'Element 155cm' }]
+  end
+
+  def test_recursively_included_template_does_not_produce_endless_loop
+    infinite_file_system = Class.new do
+      def read_template_file(template_path)
+        "-{% include 'loop' %}"
+      end
+    end
+
+    Liquid::Template.file_system = infinite_file_system.new
+
+    assert_raises(Liquid::StackLevelError) do
+      Template.parse("{% include 'loop' %}").render!
+    end
+  end
+
+  def test_dynamically_choosen_template
+    assert_template_result "Test123", "{% include template %}", "template" => 'Test123'
+    assert_template_result "Test321", "{% include template %}", "template" => 'Test321'
+
+    assert_template_result "Product: Draft 151cm ", "{% include template for product %}",
+      "template" => 'product', 'product' => { 'title' => 'Draft 151cm' }
+  end
+
+  def test_include_tag_caches_second_read_of_same_partial
+    file_system = CountingFileSystem.new
+    assert_equal 'from CountingFileSystemfrom CountingFileSystem',
+      Template.parse("{% include 'pick_a_source' %}{% include 'pick_a_source' %}").render!({}, registers: { file_system: file_system })
+    assert_equal 1, file_system.count
+  end
+
+  def test_include_tag_doesnt_cache_partials_across_renders
+    file_system = CountingFileSystem.new
+    assert_equal 'from CountingFileSystem',
+      Template.parse("{% include 'pick_a_source' %}").render!({}, registers: { file_system: file_system })
+    assert_equal 1, file_system.count
+
+    assert_equal 'from CountingFileSystem',
+      Template.parse("{% include 'pick_a_source' %}").render!({}, registers: { file_system: file_system })
+    assert_equal 2, file_system.count
+  end
+
+  def test_include_tag_within_if_statement
+    assert_template_result "foo_if_true", "{% if true %}{% include 'foo_if_true' %}{% endif %}"
+  end
+
+  def test_custom_include_tag
+    original_tag = Liquid::Template.tags['include']
+    Liquid::Template.tags['include'] = CustomInclude
+    begin
+      assert_equal "custom_foo",
+        Template.parse("{% include 'custom_foo' %}").render!
+    ensure
+      Liquid::Template.tags['include'] = original_tag
+    end
+  end
+
+  def test_custom_include_tag_within_if_statement
+    original_tag = Liquid::Template.tags['include']
+    Liquid::Template.tags['include'] = CustomInclude
+    begin
+      assert_equal "custom_foo_if_true",
+        Template.parse("{% if true %}{% include 'custom_foo_if_true' %}{% endif %}").render!
+    ensure
+      Liquid::Template.tags['include'] = original_tag
+    end
+  end
+
+  def test_does_not_add_error_in_strict_mode_for_missing_variable
+    Liquid::Template.file_system = TestFileSystem.new
+
+    a = Liquid::Template.parse(' {% include "nested_template" %}')
+    a.render!
+    assert_empty a.errors
+  end
+
+  def test_passing_options_to_included_templates
+    assert_raises(Liquid::SyntaxError) do
+      Template.parse("{% include template %}", error_mode: :strict).render!("template" => '{{ "X" || downcase }}')
+    end
+    with_error_mode(:lax) do
+      assert_equal 'x', Template.parse("{% include template %}", error_mode: :strict, include_options_blacklist: true).render!("template" => '{{ "X" || downcase }}')
+    end
+    assert_raises(Liquid::SyntaxError) do
+      Template.parse("{% include template %}", error_mode: :strict, include_options_blacklist: [:locale]).render!("template" => '{{ "X" || downcase }}')
+    end
+    with_error_mode(:lax) do
+      assert_equal 'x', Template.parse("{% include template %}", error_mode: :strict, include_options_blacklist: [:error_mode]).render!("template" => '{{ "X" || downcase }}')
+    end
+  end
+
+  def test_render_raise_argument_error_when_template_is_undefined
+    assert_raises(Liquid::ArgumentError) do
+      template = Liquid::Template.parse('{% include undefined_variable %}')
+      template.render!
+    end
+    assert_raises(Liquid::ArgumentError) do
+      template = Liquid::Template.parse('{% include nil %}')
+      template.render!
+    end
+  end
+
+  def test_including_via_variable_value
+    assert_template_result "from TestFileSystem", "{% assign page = 'pick_a_source' %}{% include page %}"
+
+    assert_template_result "Product: Draft 151cm ", "{% assign page = 'product' %}{% include page %}", "product" => { 'title' => 'Draft 151cm' }
+
+    assert_template_result "Product: Draft 151cm ", "{% assign page = 'product' %}{% include page for foo %}", "foo" => { 'title' => 'Draft 151cm' }
+  end
+
+  def test_including_with_strict_variables
+    template = Liquid::Template.parse("{% include 'simple' %}", error_mode: :warn)
+    template.render(nil, strict_variables: true)
+
+    assert_equal [], template.errors
+  end
+
+  def test_break_through_include
+    assert_template_result "1", "{% for i in (1..3) %}{{ i }}{% break %}{{ i }}{% endfor %}"
+    assert_template_result "1", "{% for i in (1..3) %}{{ i }}{% include 'break' %}{{ i }}{% endfor %}"
+  end
+end # IncludeTagTest
+

test/integration/tags/render_tag_test.rb

@@ -0,0 +1,230 @@
+require 'test_helper'
+
+class StubFileSystem
+  def initialize(values)
+    @values = values
+  end
+
+  def read_template_file(template_path)
+    @values.fetch(template_path)
+  end
+end
+
+class RenderTagTest < Minitest::Test
+  include Liquid
+
+  def test_render_with_no_arguments
+    Liquid::Template.file_system = StubFileSystem.new('source' => 'rendered content')
+    assert_template_result 'rendered content', "{% render 'source' %}"
+  end
+
+  def test_render_tag_looks_for_file_system_in_registers_first
+    file_system = StubFileSystem.new('pick_a_source' => 'from register file system')
+    assert_equal 'from register file system',
+      Template.parse("{% render 'pick_a_source' %}").render!({}, registers: { file_system: file_system })
+  end
+
+  def test_render_passes_named_arguments_into_inner_scope
+    Liquid::Template.file_system = StubFileSystem.new('product' => '{{ inner_product.title }}')
+    assert_template_result 'My Product', "{% render 'product', inner_product: outer_product %}",
+      'outer_product' => { 'title' => 'My Product' }
+  end
+
+  def test_render_accepts_literals_as_arguments
+    Liquid::Template.file_system = StubFileSystem.new('snippet' => '{{ price }}')
+    assert_template_result '123', "{% render 'snippet', price: 123 %}"
+  end
+
+  def test_render_accepts_multiple_named_arguments
+    Liquid::Template.file_system = StubFileSystem.new('snippet' => '{{ one }} {{ two }}')
+    assert_template_result '1 2', "{% render 'snippet', one: 1, two: 2 %}"
+  end
+
+  def test_render_does_inherit_parent_scope_variables
+    Liquid::Template.file_system = StubFileSystem.new('snippet' => '{{ outer_variable }}')
+    assert_template_result '', "{% render 'snippet' %}", 'outer_variable' => 'should not be visible'
+  end
+
+  def test_render_does_not_inherit_variable_with_same_name_as_snippet
+    Liquid::Template.file_system = StubFileSystem.new('snippet' => '{{ snippet }}')
+    assert_template_result '', "{% render 'snippet' %}", 'snippet' => 'should not be visible'
+  end
+
+  def test_render_sets_the_correct_template_name_for_errors
+    Liquid::Template.file_system = StubFileSystem.new('snippet' => '{{ unsafe }}')
+    Liquid::Template.taint_mode = :error
+
+    template = Liquid::Template.parse("{% render 'snippet', unsafe: unsafe %}")
+    template.render('unsafe' => String.new('unsafe').tap(&:taint))
+    refute_empty template.errors
+
+    assert_equal 'snippet', template.errors.first.template_name
+  end
+
+  def test_render_sets_the_correct_template_name_for_warnings
+    Liquid::Template.file_system = StubFileSystem.new('snippet' => '{{ unsafe }}')
+    Liquid::Template.taint_mode = :warn
+
+    template = Liquid::Template.parse("{% render 'snippet', unsafe: unsafe %}")
+    template.render('unsafe' => String.new('unsafe').tap(&:taint))
+    refute_empty template.warnings
+
+    assert_equal 'snippet', template.errors.first.template_name
+  end
+
+  def test_render_does_not_mutate_parent_scope
+    Liquid::Template.file_system = StubFileSystem.new('snippet' => '{% assign inner = 1 %}')
+    assert_template_result '', "{% render 'snippet' %}{{ inner }}"
+  end
+
+  def test_nested_render_tag
+    Liquid::Template.file_system = StubFileSystem.new(
+      'one' => "one {{ render 'two' }}",
+      'two' => 'two'
+    )
+    assert_template_result 'one two', "{% include 'one' %}"
+  end
+
+  def test_nested_include_with_variable
+    skip 'To be implemented'
+    assert_template_result "Product: Draft 151cm details ",
+      "{% include 'nested_product_template' with product %}", "product" => { "title" => 'Draft 151cm' }
+
+    assert_template_result "Product: Draft 151cm details Product: Element 155cm details ",
+      "{% include 'nested_product_template' for products %}", "products" => [{ "title" => 'Draft 151cm' }, { "title" => 'Element 155cm' }]
+  end
+
+  def test_recursively_included_template_does_not_produce_endless_loop
+    skip 'To be implemented'
+    infinite_file_system = Class.new do
+      def read_template_file(template_path)
+        "-{% include 'loop' %}"
+      end
+    end
+
+    Liquid::Template.file_system = infinite_file_system.new
+
+    assert_raises(Liquid::StackLevelError) do
+      Template.parse("{% include 'loop' %}").render!
+    end
+  end
+
+  def test_dynamically_choosen_template
+    skip 'To be implemented'
+    assert_template_result "Test123", "{% include template %}", "template" => 'Test123'
+    assert_template_result "Test321", "{% include template %}", "template" => 'Test321'
+
+    assert_template_result "Product: Draft 151cm ", "{% include template for product %}",
+      "template" => 'product', 'product' => { 'title' => 'Draft 151cm' }
+  end
+
+  def test_include_tag_caches_second_read_of_same_partial
+    skip 'To be implemented'
+    file_system = CountingFileSystem.new
+    assert_equal 'from CountingFileSystemfrom CountingFileSystem',
+      Template.parse("{% include 'pick_a_source' %}{% include 'pick_a_source' %}").render!({}, registers: { file_system: file_system })
+    assert_equal 1, file_system.count
+  end
+
+  def test_include_tag_doesnt_cache_partials_across_renders
+    skip 'To be implemented'
+    file_system = CountingFileSystem.new
+    assert_equal 'from CountingFileSystem',
+      Template.parse("{% include 'pick_a_source' %}").render!({}, registers: { file_system: file_system })
+    assert_equal 1, file_system.count
+
+    assert_equal 'from CountingFileSystem',
+      Template.parse("{% include 'pick_a_source' %}").render!({}, registers: { file_system: file_system })
+    assert_equal 2, file_system.count
+  end
+
+  def test_include_tag_within_if_statement
+    skip 'To be implemented'
+    assert_template_result "foo_if_true", "{% if true %}{% include 'foo_if_true' %}{% endif %}"
+  end
+
+  def test_custom_include_tag
+    skip 'To be implemented'
+    original_tag = Liquid::Template.tags['include']
+    Liquid::Template.tags['include'] = CustomInclude
+    begin
+      assert_equal "custom_foo",
+        Template.parse("{% include 'custom_foo' %}").render!
+    ensure
+      Liquid::Template.tags['include'] = original_tag
+    end
+  end
+
+  def test_custom_include_tag_within_if_statement
+    skip 'To be implemented'
+    original_tag = Liquid::Template.tags['include']
+    Liquid::Template.tags['include'] = CustomInclude
+    begin
+      assert_equal "custom_foo_if_true",
+        Template.parse("{% if true %}{% include 'custom_foo_if_true' %}{% endif %}").render!
+    ensure
+      Liquid::Template.tags['include'] = original_tag
+    end
+  end
+
+  def test_does_not_add_error_in_strict_mode_for_missing_variable
+    skip 'To be implemented'
+    Liquid::Template.file_system = TestFileSystem.new
+
+    a = Liquid::Template.parse(' {% include "nested_template" %}')
+    a.render!
+    assert_empty a.errors
+  end
+
+  def test_passing_options_to_included_templates
+    skip 'To be implemented'
+    assert_raises(Liquid::SyntaxError) do
+      Template.parse("{% include template %}", error_mode: :strict).render!("template" => '{{ "X" || downcase }}')
+    end
+    with_error_mode(:lax) do
+      assert_equal 'x', Template.parse("{% include template %}", error_mode: :strict, include_options_blacklist: true).render!("template" => '{{ "X" || downcase }}')
+    end
+    assert_raises(Liquid::SyntaxError) do
+      Template.parse("{% include template %}", error_mode: :strict, include_options_blacklist: [:locale]).render!("template" => '{{ "X" || downcase }}')
+    end
+    with_error_mode(:lax) do
+      assert_equal 'x', Template.parse("{% include template %}", error_mode: :strict, include_options_blacklist: [:error_mode]).render!("template" => '{{ "X" || downcase }}')
+    end
+  end
+
+  def test_render_raise_argument_error_when_template_is_undefined
+    skip 'To be implemented'
+    assert_raises(Liquid::ArgumentError) do
+      template = Liquid::Template.parse('{% include undefined_variable %}')
+      template.render!
+    end
+    assert_raises(Liquid::ArgumentError) do
+      template = Liquid::Template.parse('{% include nil %}')
+      template.render!
+    end
+  end
+
+  def test_including_via_variable_value
+    skip 'To be implemented'
+    assert_template_result "from TestFileSystem", "{% assign page = 'pick_a_source' %}{% include page %}"
+
+    assert_template_result "Product: Draft 151cm ", "{% assign page = 'product' %}{% include page %}", "product" => { 'title' => 'Draft 151cm' }
+
+    assert_template_result "Product: Draft 151cm ", "{% assign page = 'product' %}{% include page for foo %}", "foo" => { 'title' => 'Draft 151cm' }
+  end
+
+  def test_including_with_strict_variables
+    skip 'To be implemented'
+    template = Liquid::Template.parse("{% include 'simple' %}", error_mode: :warn)
+    template.render(nil, strict_variables: true)
+
+    assert_equal [], template.errors
+  end
+
+  def test_break_through_include
+    skip 'To be implemented'
+    assert_template_result "1", "{% for i in (1..3) %}{{ i }}{% break %}{{ i }}{% endfor %}"
+    assert_template_result "1", "{% for i in (1..3) %}{{ i }}{% include 'break' %}{{ i }}{% endfor %}"
+  end
+end # IncludeTagTest
+

test/unit/context_unit_test.rb

@@ -473,6 +473,64 @@ class ContextUnitTest < Minitest::Test
     assert_equal 'hi', context.apply_global_filter('hi')
   end
 
+  def test_new_isolated_subcontext_does_not_inherit_variables
+    super_context = Context.new
+    super_context['my_variable'] = 'some value'
+    subcontext = super_context.new_isolated_subcontext
+
+    assert_nil subcontext['my_variable']
+  end
+
+  def test_new_isolated_subcontext_inherits_environment
+    super_context = Context.new('my_environment_value' => 'my value')
+    subcontext = super_context.new_isolated_subcontext
+
+    assert_equal 'my value',subcontext['my_environment_value']
+  end
+
+  def test_new_isolated_subcontext_inherits_resource_limits
+    resource_limits = ResourceLimits.new({})
+    super_context = Context.new({}, {}, {}, false, resource_limits)
+    subcontext = super_context.new_isolated_subcontext
+    assert_equal resource_limits, subcontext.resource_limits
+  end
+
+  def test_new_isolated_subcontext_inherits_exception_renderer
+    super_context = Context.new
+    super_context.exception_renderer = -> (_e) { 'my exception message' }
+    subcontext = super_context.new_isolated_subcontext
+    assert_equal 'my exception message', subcontext.handle_error(Liquid::Error.new)
+  end
+
+  def test_new_isolated_subcontext_does_not_inherit_non_static_registers
+    registers = {
+      my_register: :my_value
+    }
+    super_context = Context.new({}, {}, registers)
+    subcontext = super_context.new_isolated_subcontext
+    assert_nil subcontext.registers[:my_register]
+  end
+
+  def test_new_isolated_subcontext_inherits_static_registers
+    super_context = Context.build(static_registers: { my_register: :my_value })
+    subcontext = super_context.new_isolated_subcontext
+    assert_equal :my_value, subcontext.static_registers[:my_register]
+  end
+
+  def test_new_isolated_subcontext_inherits_filters
+    my_filter = Module.new do
+      def my_filter(*)
+        'my filter result'
+      end
+    end
+
+    super_context = Context.new
+    super_context.add_filters([my_filter])
+    subcontext = super_context.new_isolated_subcontext
+    template = Template.parse('{{ 123 | my_filter }}')
+    assert_equal 'my filter result', template.render(subcontext)
+  end
+
   private
 
   def assert_no_object_allocations