Add configuration and support for freezing string literals in compiled templates

docs/CHANGELOG.md

@@ -66,6 +66,10 @@ nav_order: 5
 
     *Cameron Dutro*
 
+* Add configuration and support for compiling templates with `frozen_string_literal` magic comment.
+
+    *Mitchell Henke*
+
 ## 3.8.0
 
 * Use correct value for the `config.action_dispatch.show_exceptions` config option for edge Rails.

lib/view_component/base.rb

@@ -68,7 +68,7 @@ def set_original_view_context(view_context)
     #
     # @return [String]
     def render_in(view_context, &block)
-      self.class.compile(raise_errors: true)
+      self.class.compile(raise_errors: true, frozen_string_literal: ViewComponent::Base.config.frozen_string_literal)
 
       @view_context = view_context
       self.__vc_original_view_context ||= view_context
@@ -509,7 +509,7 @@ def short_identifier
       def inherited(child)
         # Compile so child will inherit compiled `call_*` template methods that
         # `compile` defines
-        compile
+        compile(frozen_string_literal: ViewComponent::Base.config.frozen_string_literal)
 
         # Give the child its own personal #render_template_for to protect against the case when
         # eager loading is disabled and the parent component is rendered before the child. In
@@ -520,7 +520,7 @@ def inherited(child)
             def render_template_for(variant = nil)
               # Force compilation here so the compiler always redefines render_template_for.
               # This is mostly a safeguard to prevent infinite recursion.
-              self.class.compile(raise_errors: true, force: true)
+              self.class.compile(raise_errors: true, force: true, frozen_string_literal: #{ViewComponent::Base.config.frozen_string_literal})
               # .compile replaces this method; call the new one
               render_template_for(variant)
             end
@@ -573,8 +573,8 @@ def ensure_compiled
       # Do as much work as possible in this step, as doing so reduces the amount
       # of work done each time a component is rendered.
       # @private
-      def compile(raise_errors: false, force: false)
-        compiler.compile(raise_errors: raise_errors, force: force)
+      def compile(raise_errors: false, force: false, frozen_string_literal: false)
+        compiler.compile(raise_errors: raise_errors, force: force, frozen_string_literal: frozen_string_literal)
       end
 
       # @private

lib/view_component/compiler.rb

@@ -27,7 +27,7 @@ def development?
       self.class.mode == DEVELOPMENT_MODE
     end
 
-    def compile(raise_errors: false, force: false)
+    def compile(raise_errors: false, force: false, frozen_string_literal: false)
       return if compiled? && !force
       return if component_class == ViewComponent::Base
 
@@ -49,12 +49,17 @@ def compile(raise_errors: false, force: false)
 
         redefinition_lock.synchronize do
           component_class.silence_redefinition_of_method("call")
-          # rubocop:disable Style/EvalWithLocation
-          component_class.class_eval <<-RUBY, template.path, template.lineno
+          source = <<-SOURCE
           def call
             #{compiled_inline_template(template)}
           end
-          RUBY
+          SOURCE
+          # rubocop:disable Style/EvalWithLocation
+          if frozen_string_literal
+            component_class.class_eval(source.prepend("# frozen_string_literal: true\n"), template.path, template.lineno - 1)
+          else
+            component_class.class_eval(source, template.path, template.lineno)
+          end
           # rubocop:enable Style/EvalWithLocation
 
           component_class.define_method(:"_call_#{safe_class_name}", component_class.instance_method(:call))
@@ -73,12 +78,17 @@ def render_template_for(variant = nil)
 
           redefinition_lock.synchronize do
             component_class.silence_redefinition_of_method(method_name)
+            source = <<-SOURCE
+              def #{method_name}
+                #{compiled_template(template[:path])}
+              end
+            SOURCE
             # rubocop:disable Style/EvalWithLocation
-            component_class.class_eval <<-RUBY, template[:path], 0
-            def #{method_name}
-              #{compiled_template(template[:path])}
+            if frozen_string_literal
+              component_class.class_eval(source.prepend("# frozen_string_literal: true\n"), template[:path], -1)
+            else
+              component_class.class_eval(source, template[:path], 0)
             end
-            RUBY
             # rubocop:enable Style/EvalWithLocation
           end
         end

lib/view_component/config.rb

@@ -25,7 +25,8 @@ def defaults
           preview_paths: default_preview_paths,
           test_controller: "ApplicationController",
           default_preview_layout: nil,
-          capture_compatibility_patch_enabled: false
+          capture_compatibility_patch_enabled: false,
+          frozen_string_literal: :inherit_from_rails
         })
       end
 
@@ -154,6 +155,16 @@ def defaults
       # previews.
       # Defaults to `false`.
 
+      # @!attribute frozen_string_literal
+      # @return [Boolean]
+      # Enables compiling templates with the frozen_string_literal magic
+      # comment, which prevents modification of string objects by
+      # assuming they are frozen on initialize. Has performance
+      # benefits. This configuration will default to inheriting from
+      # `Rails.application.config.action_view.frozen_string_literal`, but can be
+      # overridden.
+      # Defaults to `:inherit_from_rails`.
+
       def default_preview_paths
         return [] unless defined?(Rails.root) && Dir.exist?("#{Rails.root}/test/components/previews")
 

lib/view_component/engine.rb

@@ -13,6 +13,9 @@ class Engine < Rails::Engine # :nodoc:
     end
 
     initializer "view_component.set_configs" do |app|
+      if app.config.view_component.frozen_string_literal == :inherit_from_rails
+        app.config.view_component.frozen_string_literal = !!app.config.action_view.frozen_string_literal
+      end
       options = app.config.view_component
 
       %i[generate preview_controller preview_route show_previews_source].each do |config_option|
@@ -71,9 +74,13 @@ class Engine < Rails::Engine # :nodoc:
       end
     end
 
-    initializer "view_component.eager_load_actions" do
+    initializer "view_component.eager_load_actions" do |app|
       ActiveSupport.on_load(:after_initialize) do
-        ViewComponent::Base.descendants.each(&:compile) if Rails.application.config.eager_load
+        if Rails.application.config.eager_load
+          ViewComponent::Base.descendants.each do |descendant|
+            descendant.compile(frozen_string_literal: app.config.view_component.frozen_string_literal)
+          end
+        end
       end
     end
 

test/sandbox/app/components/mutated_string_component.html.erb

@@ -0,0 +1 @@
+<%= "a" << "b" %>

test/sandbox/app/components/mutated_string_component.rb

@@ -0,0 +1,4 @@
+# frozen_string_literal: true
+
+class MutatedStringComponent < ViewComponent::Base
+end

test/sandbox/app/components/mutated_string_inline_component.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class MutatedStringInlineComponent < ViewComponent::Base
+  erb_template <<~ERB
+    <%= "a" << "b" %>
+  ERB
+end

test/sandbox/test/config_test.rb

@@ -18,6 +18,7 @@ def test_defaults_are_correct
       assert_equal @config.render_monkey_patch_enabled, true
       assert_equal @config.show_previews, true
       assert_equal @config.preview_paths, ["#{Rails.root}/test/components/previews"]
+      assert_equal @config.frozen_string_literal, :inherit_from_rails
     end
 
     def test_all_methods_are_documented

test/sandbox/test/integration_test.rb

@@ -670,6 +670,38 @@ def test_sets_the_compiler_mode_in_development_mode
     end
   end
 
+  def test_default_sets_frozen_string_literal_to_rails_action_view_frozen_string_literal_value_true
+    fake_application = OpenStruct.new(config: OpenStruct.new(view_component: ViewComponent::Config.new, action_view: OpenStruct.new(frozen_string_literal: true)))
+    ViewComponent::Engine.initializers.find { |i| i.name == "view_component.set_configs" }.run(fake_application)
+    assert_equal fake_application.config.view_component.frozen_string_literal, true
+  end
+
+  def test_default_sets_frozen_string_literal_to_rails_action_view_frozen_string_literal_value_false
+    fake_application = OpenStruct.new(config: OpenStruct.new(view_component: ViewComponent::Config.new, action_view: OpenStruct.new(frozen_string_literal: false)))
+    ViewComponent::Engine.initializers.find { |i| i.name == "view_component.set_configs" }.run(fake_application)
+    assert_equal fake_application.config.view_component.frozen_string_literal, false
+  end
+
+  def test_default_sets_frozen_string_literal_to_rails_action_view_frozen_string_literal_value_nil
+    fake_application = OpenStruct.new(config: OpenStruct.new(view_component: ViewComponent::Config.new, action_view: OpenStruct.new(frozen_string_literal: nil)))
+    ViewComponent::Engine.initializers.find { |i| i.name == "view_component.set_configs" }.run(fake_application)
+    assert_equal fake_application.config.view_component.frozen_string_literal, false
+  end
+
+  def test_override_true_does_not_set_frozen_string_literal_to_rails_action_view_frozen_string_literal_value_false
+    fake_application = OpenStruct.new(config: OpenStruct.new(view_component: ViewComponent::Config.new, action_view: OpenStruct.new(frozen_string_literal: false)))
+    fake_application.config.view_component.frozen_string_literal = true
+    ViewComponent::Engine.initializers.find { |i| i.name == "view_component.set_configs" }.run(fake_application)
+    assert_equal fake_application.config.view_component.frozen_string_literal, true
+  end
+
+  def test_override_false_does_not_set_frozen_string_literal_to_rails_action_view_frozen_string_literal_value_true
+    fake_application = OpenStruct.new(config: OpenStruct.new(view_component: ViewComponent::Config.new, action_view: OpenStruct.new(frozen_string_literal: true)))
+    fake_application.config.view_component.frozen_string_literal = false
+    ViewComponent::Engine.initializers.find { |i| i.name == "view_component.set_configs" }.run(fake_application)
+    assert_equal fake_application.config.view_component.frozen_string_literal, false
+  end
+
   def test_link_to_helper
     get "/link_to_helper"
     assert_select "a > i,span"

test/sandbox/test/rendering_test.rb

@@ -1113,4 +1113,52 @@ def test_use_helper
     render_inline(UseHelpersComponent.new)
     assert_selector ".helper__message", text: "Hello helper method"
   end
+
+  def test_frozen_string_literal_disabled
+    old_value = ViewComponent::Base.config.frozen_string_literal
+    ViewComponent::Base.config.frozen_string_literal = false
+
+    with_new_cache do
+      render_inline(MutatedStringComponent.new)
+      assert_includes rendered_content, "ab"
+    end
+  ensure
+    ViewComponent::Base.config.frozen_string_literal = old_value
+  end
+
+  def test_frozen_string_literal_enabled
+    old_value = ViewComponent::Base.config.frozen_string_literal
+    ViewComponent::Base.config.frozen_string_literal = true
+    with_new_cache do
+      assert_raises FrozenError do
+        render_inline(MutatedStringComponent.new)
+      end
+    end
+  ensure
+    ViewComponent::Base.config.frozen_string_literal = old_value
+  end
+
+  def test_inline_frozen_string_literal_disabled
+    old_value = ViewComponent::Base.config.frozen_string_literal
+    ViewComponent::Base.config.frozen_string_literal = false
+
+    with_new_cache do
+      render_inline(MutatedStringInlineComponent.new)
+      assert_includes rendered_content, "ab"
+    end
+  ensure
+    ViewComponent::Base.config.frozen_string_literal = old_value
+  end
+
+  def test_inline_frozen_string_literal_enabled
+    old_value = ViewComponent::Base.config.frozen_string_literal
+    ViewComponent::Base.config.frozen_string_literal = true
+    with_new_cache do
+      assert_raises FrozenError do
+        render_inline(MutatedStringInlineComponent.new)
+      end
+    end
+  ensure
+    ViewComponent::Base.config.frozen_string_literal = old_value
+  end
 end