Added support for annotate_rendered_view_with_filenames

ActionView's erb template handler can annotate html with comments to indicate which file any given snippet of html comes from. This is very useful in development, but it isn't supported by better-html.

This adds equivalent support to better-html, using the same approach that ActionView takes, so it should work automatically for anyone switching from rails' default erb handler.

lib/better_html/better_erb.rb

@@ -52,10 +52,20 @@ def generate(template, source)
         klass ||= self.class.erb_implementation
 
         escape = self.class.escape_ignore_list.include?(template.type)
+
+        options = {
+          escape: escape,
+          trim: (self.class.erb_trim_mode == "-"),
+        }
+        if BetterHtml.config.annotate_rendered_view_with_filenames && template.format == :html
+          options[:preamble] = "@output_buffer.safe_append='<!-- BEGIN #{template.short_identifier} -->';"
+          options[:postamble] = "@output_buffer.safe_append='<!-- END #{template.short_identifier} -->';" +
+            "@output_buffer.to_s"
+        end
+
         generator = klass.new(
           erb,
-          escape: escape,
-          trim: (self.class.erb_trim_mode == "-")
+          **options
         )
         generator.validate! if generator.respond_to?(:validate!)
         generator.src

lib/better_html/config.rb

@@ -15,6 +15,7 @@ class Config
     property :template_exclusion_filter
     property :lodash_safe_javascript_expression, default: -> { [/\AJSON\.stringify\(/] }
     property :disable_parser_validation, default: false
+    property :annotate_rendered_view_with_filenames, default: false
 
     def javascript_attribute_name?(name)
       javascript_attribute_names.any? { |other| other === name.to_s } # rubocop:disable Style/CaseEquality

lib/better_html/railtie.rb

@@ -7,5 +7,11 @@ class Railtie < Rails::Railtie
     initializer "better_html.better_erb.initialization" do
       BetterHtml::BetterErb.prepend!
     end
+
+    config.after_initialize do |app|
+      ActiveSupport.on_load(:action_view) do
+        BetterHtml.config.annotate_rendered_view_with_filenames = ActionView::Base.annotate_rendered_view_with_filenames
+      end
+    end
   end
 end

test/better_html/better_erb/implementation_test.rb

@@ -366,6 +366,14 @@ class ImplementationTest < ActiveSupport::TestCase
         end
       end
 
+      if ActionView.version >= Gem::Version.new("6.1")
+        test "comments are added to show the filename when annotate_rendered_view_with_filenames=true" do
+          config = build_config(annotate_rendered_view_with_filenames: true)
+          assert_equal "<!-- BEGIN _better_test.html.erb --><foo>bar<foo><!-- END _better_test.html.erb -->",
+            render("<foo>bar<foo>", config: config, filename: "_better_test.html.erb")
+        end
+      end
+
       test "capture works as intended" do
         output = render(<<-HTML)
       <%- foo = capture do -%>
@@ -420,13 +428,13 @@ def build_config(**options)
         BetterHtml::Config.new(**options)
       end
 
-      def render(source, config: build_config, locals: {})
+      def render(source, config: build_config, locals: {}, filename: "test.html.erb")
         old_config = BetterHtml.config
         BetterHtml.config = config
 
         ActionView::Template.new(
           source,
-          "test.html.erb",
+          filename,
           ActionView::Template::Handlers::ERB.new,
           virtual_path: "partial",
           format: :html,