Add optional compatibility module for capture/form/turbo compatibility fixes (ViewComponent#1650)

This adds an optional module, `CaptureCompatibility` which is meant to
monkey patch `ActionView::Base` so that forms, turbo frames, and
content_for, and other common Rails code works as-expected.

Author: BlakeWilliams

.github/workflows/ci.yml

@@ -29,14 +29,34 @@ jobs:
         include:
           - rails_version: "5.2.6"
             ruby_version: "2.7"
+            mode: "capture_patch_enabled"
           - rails_version: "6.0.4.4"
             ruby_version: "2.7"
+            mode: "capture_patch_enabled"
           - rails_version: "6.1.4.4"
             ruby_version: "2.7"
+            mode: "capture_patch_enabled"
           - rails_version: "7.0.2.3"
             ruby_version: "3.0"
+            mode: "capture_patch_enabled"
           - rails_version: "main"
             ruby_version: "3.1"
+            mode: "capture_patch_enabled"
+          - rails_version: "5.2.6"
+            ruby_version: "2.7"
+            mode: "capture_patch_disabled"
+          - rails_version: "6.0.4.4"
+            ruby_version: "2.7"
+            mode: "capture_patch_disabled"
+          - rails_version: "6.1.4.4"
+            ruby_version: "2.7"
+            mode: "capture_patch_disabled"
+          - rails_version: "7.0.2.3"
+            ruby_version: "3.0"
+            mode: "capture_patch_disabled"
+          - rails_version: "main"
+            ruby_version: "3.1"
+            mode: "capture_patch_disabled"
     steps:
     - uses: actions/checkout@master
     - name: Setup Ruby
@@ -56,6 +76,7 @@ jobs:
         RAISE_ON_WARNING: 1
         MEASURE_COVERAGE: true
         RAILS_VERSION: ${{ matrix.rails_version }}
+        CAPTURE_PATCH_ENABLED: ${{ matrix.mode == 'capture_patch_enabled' && 'true' || 'false' }}
     - name: Upload coverage results
       uses: actions/upload-artifact@master
       if: always()

docs/CHANGELOG.md

@@ -10,6 +10,10 @@ nav_order: 5
 
 ## main
 
+* Add experimental `config.view_component.capture_compatibility_patch_enabled` option resolving rendering issues related to forms, capture, turbo frames, etc.
+
+    *Blake Williams*
+
 * Add `#content?` method that indicates if content has been passed to component.
 
     *Joel Hawksley*

lib/view_component.rb

@@ -7,6 +7,7 @@ module ViewComponent
   extend ActiveSupport::Autoload
 
   autoload :Base
+  autoload :CaptureCompatibility
   autoload :Compiler
   autoload :CompileCache
   autoload :ComponentError

lib/view_component/capture_compatibility.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+module ViewComponent
+  # CaptureCompatibility is a module that patches #capture to fix issues
+  # related to ViewComponent and functionality that relies on `capture`
+  # like forms, capture itself, turbo frames, etc.
+  #
+  # This underlying incompatibility with ViewComponent and capture is
+  # that several features like forms keep a reference to the primary
+  # `ActionView::Base` instance which has its own @output_buffer. When
+  # `#capture` is called on the original `ActionView::Base` instance while
+  # evaluating a block from a ViewComponent the @output_buffer is overridden
+  # in the ActionView::Base instance, and *not* the component. This results
+  # in a double render due to `#capture` implementation details.
+  #
+  # To resolve the issue, we override `#capture` so that we can delegate
+  # the `capture` logic to the ViewComponent that created the block.
+  module CaptureCompatibility
+    def self.included(base)
+      base.class_eval do
+        alias_method :original_capture, :capture
+      end
+
+      base.prepend(InstanceMethods)
+    end
+
+    module InstanceMethods
+      def capture(*args, &block)
+        # Handle blocks that originate from C code and raise, such as `&:method`
+        return original_capture(*args, &block) if block.source_location.nil?
+
+        block_context = block.binding.receiver
+
+        if block_context != self && block_context.class < ActionView::Base
+          block_context.original_capture(*args, &block)
+        else
+          original_capture(*args, &block)
+        end
+      end
+    end
+  end
+end

lib/view_component/config.rb

@@ -23,7 +23,8 @@ def defaults
           show_previews: Rails.env.development? || Rails.env.test?,
           preview_paths: default_preview_paths,
           test_controller: "ApplicationController",
-          default_preview_layout: nil
+          default_preview_layout: nil,
+          capture_compatibility_patch_enabled: false
         })
       end
 
@@ -137,6 +138,13 @@ def defaults
       # A custom default layout used for the previews index page and individual
       # previews.
       # Defaults to `nil`. If this is falsy, `"component_preview"` is used.
+      #
+      # @!attribute capture_compatibility_patch_enabled
+      # @return [Boolean]
+      # Enables the experimental capture compatibility patch that makes ViewComponent
+      # compatible with forms, capture, and other built-ins.
+      # previews.
+      # Defaults to `false`.
 
       def default_preview_paths
         return [] unless defined?(Rails.root) && Dir.exist?("#{Rails.root}/test/components/previews")

lib/view_component/engine.rb

@@ -47,6 +47,14 @@ class Engine < Rails::Engine # :nodoc:
       end
     end
 
+    # :nocov:
+    initializer "view_component.enable_capture_patch" do |app|
+      ActiveSupport.on_load(:view_component) do
+        ActionView::Base.include(ViewComponent::CaptureCompatibility) if app.config.view_component.capture_compatibility_patch_enabled
+      end
+    end
+    # :nocov:
+
     initializer "view_component.set_autoload_paths" do |app|
       options = app.config.view_component
 

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

@@ -0,0 +1,3 @@
+<%= form_for Post.new, url: "/" do |form| %>
+  <%= render "forms/label", form: form %>
+<% end %>

test/sandbox/app/components/form_partial_component.rb

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

test/sandbox/app/views/forms/_label.html.erb

@@ -0,0 +1,3 @@
+<%= form.label :published do %>
+  <%= form.check_box :published %>
+<% end %>

test/sandbox/config/environments/test.rb

@@ -25,6 +25,7 @@
   config.view_component.render_monkey_patch_enabled = true
   config.view_component.show_previews_source = true
   config.view_component.test_controller = "IntegrationExamplesController"
+  config.view_component.capture_compatibility_patch_enabled = ENV["CAPTURE_PATCH_ENABLED"] == "true"
 
   # Tell Action Mailer not to deliver emails to the real world.
   # The :test delivery method accumulates sent emails in the

test/sandbox/test/action_view_compatibility_test.rb

@@ -4,35 +4,39 @@
 
 class ViewComponent::ActionViewCompatibilityTest < ViewComponent::TestCase
   def test_renders_form_for_labels_with_block_correctly
-    skip
-
+    skip unless ENV["CAPTURE_PATCH_ENABLED"] == "true"
     render_inline(FormForComponent.new)
 
     assert_selector("form > div > label > input")
     refute_selector("form > div > input")
   end
 
   def test_renders_form_with_labels_with_block_correctly
-    skip
-
+    skip unless ENV["CAPTURE_PATCH_ENABLED"] == "true"
     render_inline(FormWithComponent.new)
 
     assert_selector("form > div > label > input")
     refute_selector("form > div > input")
   end
 
   def test_form_without_compatibility_does_not_raise
-    skip
-
+    skip unless ENV["CAPTURE_PATCH_ENABLED"] == "true"
     render_inline(IncompatibleFormComponent.new)
 
     # Bad selector should be present, at least until fixed upstream or included by default
     refute_selector("form > div > input")
   end
 
-  def test_helper_with_content_tag
-    skip
+  def test_form_with_partial_render_works
+    skip unless ENV["CAPTURE_PATCH_ENABLED"] == "true"
+    render_inline(FormPartialComponent.new)
 
+    # Bad selector should be present, at least until fixed upstream or included by default
+    refute_selector("form > div > input")
+  end
+
+  def test_helper_with_content_tag
+    skip unless ENV["CAPTURE_PATCH_ENABLED"] == "true"
     render_inline(ContentTagComponent.new)
     assert_selector("div > p")
   end

test/sandbox/test/config_test.rb

@@ -37,5 +37,13 @@ def test_all_methods_are_documented
       assert configuration_methods_to_document.map(&:docstring).all?(&:present?),
         "Configuration options are missing docstrings."
     end
+
+    def test_compatibility_module_included
+      if ENV["CAPTURE_PATCH_ENABLED"] == "true"
+        assert ActionView::Base < ViewComponent::CaptureCompatibility
+      else
+        refute ActionView::Base < ViewComponent::CaptureCompatibility
+      end
+    end
   end
 end