Implement Slots as potential successor to Content Areas

CHANGELOG.md

@@ -1,5 +1,9 @@
 # master
 
+* Implement Slots as potential successor to Content Areas.
+
+    *Jens Ljungblad, Brian Bugh, Jon Palmer, Joel Hawksley*
+
 # 2.11.1
 
 * Fix kwarg warnings in Ruby 2.7.

README.md

@@ -160,6 +160,133 @@ Returning:
 </div>
 ```
 
+#### Slots (experimental)
+
+_Slots are currently under development as a successor to Content Areas. The Slot APIs should be considered unfinished and subject to breaking changes in non-major releases of ViewComponent._
+
+Slots enable multiple blocks of content to be passed to a single ViewComponent.
+
+Slots exist in two forms: normal slots and collection slots.
+
+Normal slots can be rendered once per component. They expose an accessor with the name of the slot that returns an instance of `BoxComponent::Header`, etc.
+
+Collection slots can be rendered multiple times. They expose an accessor with the pluralized name of the slot (`#rows`), which is an Array of `BoxComponent::Row` instances.
+
+To learn more about the design of the Slots API, see https://github.com/github/view_component/pull/348.
+
+##### Defining Slots
+
+Slots are defined by the `with_slot` macro:
+
+`with_slot :header`
+
+To define a collection slot, add `collection: true`:
+
+`with_slot :row, collection: true`
+
+To define a slot with a custom class, pass `class_name`:
+
+`with_slot :body, class_name: 'BodySlot`
+
+Slot classes should be subclasses of `ViewComponent::Slot`.
+
+##### Example ViewComponent with Slots
+
+`# box_component.rb`
+```ruby
+class BoxComponent < ViewComponent::Base
+  include ViewComponent::Slotable
+
+  with_slot :body, :footer
+  with_slot :header, class_name: "Header"
+  with_slot :row, collection: true, class_name: "Row"
+
+  class Header < ViewComponent::Slot
+    def initialize(class_names: "")
+      @class_names = class_names
+    end
+
+    def class_names
+      "Box-header #{@class_names}"
+    end
+  end
+
+  class Row < ViewComponent::Slot
+    def initialize(theme: :gray)
+      @theme = theme
+    end
+
+    def theme_class_name
+      case @theme
+      when :gray
+        "Box-row--gray"
+      when :hover_gray
+        "Box-row--hover-gray"
+      when :yellow
+        "Box-row--yellow"
+      when :blue
+        "Box-row--blue"
+      when :hover_blue
+        "Box-row--hover-blue"
+      else
+        "Box-row--gray"
+      end
+    end
+  end
+end
+```
+
+`# box_component.html.erb`
+```erb
+<div class="Box">
+  <% if header %>
+    <div class="<%= header.class_names %>">
+      <%= header.content %>
+    </div>
+  <% end %>
+  <% if body %>
+    <div class="Box-body">
+      <%= body.content %>
+    </div>
+  <% end %>
+  <% if rows.any? %>
+    <ul>
+      <% rows.each do |row| %>
+        <li class="Box-row <%= row.theme_class_name %>">
+          <%= row.content %>
+        </li>
+      <% end %>
+    </ul>
+  <% end %>
+  <% if footer %>
+    <div class="Box-footer">
+      <%= footer %>
+    </div>
+  <% end %>
+</div>
+```
+
+`# index.html.erb`
+```erb
+<%= render(BoxComponent.new) do |component| %>
+  <% component.slot(:header, class_names: "my-class-name") do %>
+    This is my header!
+  <% end %>
+  <% component.slot(:body) do %>
+    This is the body.
+  <% end %>
+  <% component.slot(:row) do %>
+    Row one
+  <% end %>
+  <% component.slot(:row, theme: :yellow) do %>
+    Yellow row
+  <% end %>
+  <% component.slot(:footer) do %>
+    This is the footer.
+  <% end %>
+<% end %>
+```
+
 ### Inline Component
 
 ViewComponents can render without a template file, by defining a `call` method:
@@ -785,10 +912,10 @@ ViewComponent is built by:
 |@simonrand|@fugufish|@cover|@franks921|@fsateler|
 |Dublin, Ireland|Salt Lake City, Utah|Barcelona|South Africa|Chile|
 
-|<img src="https://avatars.githubusercontent.com/maxbeizer?s=256" alt="maxbeizer" width="128" />|<img src="https://avatars.githubusercontent.com/franco?s=256" alt="franco" width="128" />|<img src="https://avatars.githubusercontent.com/tbroad-ramsey?s=256" alt="tbroad-ramsey" width="128" />|
-|:---:|:---:|:---:|
-|@maxbeizer|@franco|@tbroad-ramsey|
-|Nashville, TN|Switzerland|Spring Hill, TN|
+|<img src="https://avatars.githubusercontent.com/maxbeizer?s=256" alt="maxbeizer" width="128" />|<img src="https://avatars.githubusercontent.com/franco?s=256" alt="franco" width="128" />|<img src="https://avatars.githubusercontent.com/tbroad-ramsey?s=256" alt="tbroad-ramsey" width="128" />|<img src="https://avatars.githubusercontent.com/jensljungblad?s=256" alt="jensljungblad" width="128" />|<img src="https://avatars.githubusercontent.com/bbugh?s=256" alt="bbugh" width="128" />|
+|:---:|:---:|:---:|:---:|:---:|
+|@maxbeizer|@franco|@tbroad-ramsey|@jensljungblad|@bbugh|
+|Nashville, TN|Switzerland|Spring Hill, TN|New York, NY|Austin, TX|
 
 ## License
 

coverage/coverage.txt

@@ -3,8 +3,8 @@ Incomplete test coverage
 --------------------------------------------------------------------------------
 
 /app/controllers/view_components_controller.rb: 97.22% (missed: 49)
-/lib/view_component/base.rb: 97.8% (missed: 170,253,281,344)
+/lib/view_component/base.rb: 97.85% (missed: 175,262,290,353)
 /lib/view_component/preview.rb: 92.31% (missed: 32,42,78)
 /lib/view_component/render_to_string_monkey_patch.rb: 83.33% (missed: 9)
 /lib/view_component/test_helpers.rb: 95.45% (missed: 17)
-/test/view_component/integration_test.rb: 97.54% (missed: 14,15,16,18,20)
+/test/view_component/integration_test.rb: 97.66% (missed: 14,15,16,18,20)

lib/view_component/base.rb

@@ -5,6 +5,7 @@
 require "view_component/collection"
 require "view_component/compile_cache"
 require "view_component/previewable"
+require "view_component/slotable"
 
 module ViewComponent
   class Base < ActionView::Base
@@ -17,6 +18,10 @@ class Base < ActionView::Base
     class_attribute :content_areas
     self.content_areas = [] # class_attribute:default doesn't work until Rails 5.2
 
+    # Hash of registered Slots
+    class_attribute :slots
+    self.slots = {}
+
     # Entrypoint for rendering components.
     #
     # view_context: ActionView context from calling view
@@ -181,6 +186,10 @@ def inherited(child)
         # has been re-defined by the consuming application, likely in ApplicationComponent.
         child.source_location = caller_locations(1, 10).reject { |l| l.label == "inherited" }[0].absolute_path
 
+        # Clone slot configuration into child class
+        # see #test_slots_pollution
+        child.slots = self.slots.clone
+
         super
       end
 

lib/view_component/slot.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+module ViewComponent
+  class Slot
+    attr_accessor :content
+  end
+end

lib/view_component/slotable.rb

@@ -0,0 +1,121 @@
+# frozen_string_literal: true
+
+require "active_support/concern"
+
+require "view_component/slot"
+
+module ViewComponent
+  module Slotable
+    extend ActiveSupport::Concern
+
+    class_methods do
+      # support initializing slots as:
+      #
+      # with_slot(
+      #   :header,
+      #   collection: true|false,
+      #   class_name: "Header" # class name string, used to instantiate Slot
+      # )
+      def with_slot(*slot_names, collection: false, class_name: nil)
+        slot_names.each do |slot_name|
+          # Ensure slot_name is not already declared
+          if self.slots.key?(slot_name)
+            raise ArgumentError.new("#{slot_name} slot declared multiple times")
+          end
+
+          # Ensure slot name is not :content
+          if slot_name == :content
+            raise ArgumentError.new ":content is a reserved slot name. Please use another name, such as ':body'"
+          end
+
+          # Set the name of the method used to access the Slot(s)
+          accessor_name =
+            if collection
+              # If Slot is a collection, set the accessor
+              # name to the pluralized form of the slot name
+              # For example: :tab => :tabs
+              ActiveSupport::Inflector.pluralize(slot_name)
+            else
+              slot_name
+            end
+
+          instance_variable_name = "@#{accessor_name}"
+
+          # If the slot is a collection, define an accesor that defaults to an empty array
+          if collection
+            class_eval <<-RUBY
+              def #{accessor_name}
+                #{instance_variable_name} ||= []
+              end
+            RUBY
+          else
+            attr_reader accessor_name
+          end
+
+          # Default class_name to ViewComponent::Slot
+          class_name = "ViewComponent::Slot" unless class_name.present?
+
+          # Register the slot on the component
+          self.slots[slot_name] = {
+            class_name: class_name,
+            instance_variable_name: instance_variable_name,
+            collection: collection
+          }
+        end
+      end
+    end
+
+    # Build a Slot instance on a component,
+    # exposing it for use inside the
+    # component template.
+    #
+    # slot: Name of Slot, in symbol form
+    # **args: Arguments to be passed to Slot initializer
+    #
+    # For example:
+    # <%= render(SlotsComponent.new) do |component| %>
+    #   <% component.slot(:footer, class_names: "footer-class") do %>
+    #     <p>This is my footer!</p>
+    #   <% end %>
+    # <% end %>
+    #
+    def slot(slot_name, **args, &block)
+      # Raise ArgumentError if `slot` does not exist
+      unless slots.keys.include?(slot_name)
+        raise ArgumentError.new "Unknown slot '#{slot_name}' - expected one of '#{slots.keys}'"
+      end
+
+      slot = slots[slot_name]
+
+      # The class name of the Slot, such as Header
+      slot_class = self.class.const_get(slot[:class_name])
+
+      unless slot_class <= ViewComponent::Slot
+        raise ArgumentError.new "#{slot[:class_name]} must inherit from ViewComponent::Slot"
+      end
+
+      # Instantiate Slot class, accommodating Slots that don't accept arguments
+      slot_instance = args.present? ? slot_class.new(args) : slot_class.new
+
+      # Capture block and assign to slot_instance#content
+      slot_instance.content = view_context.capture(&block) if block_given?
+
+      if slot[:collection]
+        # Initialize instance variable as an empty array
+        # if slot is a collection and has yet to be initialized
+        unless instance_variable_defined?(slot[:instance_variable_name])
+          instance_variable_set(slot[:instance_variable_name], [])
+        end
+
+        # Append Slot instance to collection accessor Array
+        instance_variable_get(slot[:instance_variable_name]) << slot_instance
+      else
+         # Assign the Slot instance to the slot accessor
+        instance_variable_set(slot[:instance_variable_name], slot_instance)
+      end
+
+      # Return nil, as this method should not output anything to the view itself.
+      nil
+    end
+  end
+end

test/app/components/bad_slot_component.html.erb

@@ -0,0 +1 @@
+<%= title %>

test/app/components/bad_slot_component.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+class BadSlotComponent < ViewComponent::Base
+  include ViewComponent::Slotable
+
+  with_slot :title, class_name: "Title"
+
+  # slots must inherit from ViewComponent::Slot!
+  class Title; end
+end

test/app/components/slots_component.html.erb

@@ -0,0 +1,33 @@
+<div class="card <%= @class_names %>">
+  <div class="title">
+    <%= title.content %>
+  </div>
+  <div class="subtitle">
+    <%= subtitle.content %>
+  </div>
+  <div class="nav">
+    <% if tabs.any? %>
+      <% tabs.each do |tab| %>
+        <div class="tab">
+          <%= tab.content %>
+        </div>
+      <% end %>
+    <% else %>
+      No tabs provided
+    <% end %>
+  </div>
+  <div class="body">
+    <% if items.any? %>
+      <% items.each do |item| %>
+        <div class="item <%= item.class_names %>">
+          <%= item.content %>
+        </div>
+      <% end %>
+    <% else %>
+      No items provided
+    <% end %>
+  </div>
+  <div class="footer <%= footer.class_names %>">
+    <%= footer.content %>
+  </div>
+</div>