Allow Attachables to override default template when attachment is missing

actiontext/CHANGELOG.md

@@ -1,3 +1,12 @@
+*   Attachables now can override default attachment missing template.
+
+    When rendering ActionText attachments where the underlying attachable model has
+    been removed, a fallback template is used. You now can override this template on
+    a per-model basis. For example, you could render a placeholder image for a file
+    attachment or the text "Deleted User" for a User attachment.
+
+    *Matt Swanson*, *Joel Drapper*
+
 *   Update bundled Trix version from `1.3.1` to `2.0.4`.
 
     *Sean Doyle*

actiontext/lib/action_text/attachable.rb

@@ -15,7 +15,7 @@ def from_node(node)
         elsif attachable = ActionText::Attachables::RemoteImage.from_node(node)
           attachable
         else
-          ActionText::Attachables::MissingAttachable
+          ActionText::Attachables::MissingAttachable.new(node["sgid"])
         end
       end
 
@@ -37,6 +37,10 @@ def attachable_from_sgid(sgid)
       def from_attachable_sgid(sgid)
         ActionText::Attachable.from_attachable_sgid(sgid, only: self)
       end
+
+      def to_missing_attachable_partial_path
+        ActionText::Attachables::MissingAttachable::DEFAULT_PARTIAL_PATH
+      end
     end
 
     def attachable_sgid

actiontext/lib/action_text/attachables/missing_attachable.rb

@@ -2,11 +2,25 @@
 
 module ActionText
   module Attachables
-    module MissingAttachable
+    class MissingAttachable
       extend ActiveModel::Naming
 
-      def self.to_partial_path
-        "action_text/attachables/missing_attachable"
+      DEFAULT_PARTIAL_PATH = "action_text/attachables/missing_attachable"
+
+      def initialize(sgid)
+        @sgid = SignedGlobalID.parse(sgid, for: ActionText::Attachable::LOCATOR_NAME)
+      end
+
+      def to_partial_path
+        if model
+          model.to_missing_attachable_partial_path
+        else
+          DEFAULT_PARTIAL_PATH
+        end
+      end
+
+      def model
+        @sgid&.model_name.to_s.safe_constantize
       end
     end
   end

actiontext/test/dummy/app/models/person.rb

@@ -1,6 +1,10 @@
 class Person < ApplicationRecord
   include ActionText::Attachable
 
+  def self.to_missing_attachable_partial_path
+    "people/missing_attachable"
+  end
+
   def to_trix_content_attachment_partial_path
     "people/trix_content_attachment"
   end

actiontext/test/dummy/app/views/people/_missing_attachable.html.erb

@@ -0,0 +1 @@
+<span class="missing-attachable">Missing person</span>

actiontext/test/integration/controller_render_test.rb

@@ -48,4 +48,13 @@ class ActionText::ControllerRenderTest < ActionDispatch::IntegrationTest
 
     assert_select ".mentioned-person", text: alice.name
   end
+
+  test "resolves missing ActionText::Attachable based on their to_missing_attachable_partial_path" do
+    alice = people(:alice)
+    alice.destroy!
+
+    get messages_path
+
+    assert_select ".missing-attachable", text: "Missing person"
+  end
 end

actiontext/test/unit/content_test.rb

@@ -56,19 +56,26 @@ class ActionText::ContentTest < ActiveSupport::TestCase
   end
 
   test "identifies destroyed attachables as missing" do
-    attachable = create_file_blob(filename: "racecar.jpg", content_type: "image/jpeg")
-    html = %Q(<action-text-attachment sgid="#{attachable.attachable_sgid}"></action-text-attachment>)
-    attachable.destroy!
+    file = create_file_blob(filename: "racecar.jpg", content_type: "image/jpeg")
+    html = %Q(<action-text-attachment sgid="#{file.attachable_sgid}"></action-text-attachment>)
+    file.destroy!
     content = content_from_html(html)
     assert_equal 1, content.attachments.size
-    assert_equal ActionText::Attachables::MissingAttachable, content.attachments.first.attachable
+
+    attachable = content.attachments.first.attachable
+    assert_kind_of ActionText::Attachables::MissingAttachable, attachable
+    assert_equal file.class, attachable.model
+    assert_equal ActionText::Attachables::MissingAttachable::DEFAULT_PARTIAL_PATH, attachable.to_partial_path
   end
 
   test "extracts missing attachables" do
     html = '<action-text-attachment sgid="missing"></action-text-attachment>'
     content = content_from_html(html)
     assert_equal 1, content.attachments.size
-    assert_equal ActionText::Attachables::MissingAttachable, content.attachments.first.attachable
+
+    attachable = content.attachments.first.attachable
+    assert_kind_of ActionText::Attachables::MissingAttachable, attachable
+    assert_nil attachable.model
   end
 
   test "converts Trix-formatted attachments" do

guides/source/action_text_overview.md

@@ -205,12 +205,38 @@ partial-local variable:
 <span><%= image_tag user.avatar %> <%= user.name %></span>
 ```
 
+If Action Text is unable to resolve the `User` instance (for example, if the
+record has been deleted), then a default fallback partial will be rendered.
+
+Rails provides a global partial for missing attachments. This partial is installed
+in your application at `views/action_text/attachables/missing_attachable` and can
+be modified if you want to render different HTML.
+
+To render a different missing attachment partial, define a class-level
+`to_missing_attachable_partial_path` method:
+
+```ruby
+class User < ApplicationRecord
+  def self.to_missing_attachable_partial_path
+    "users/missing_attachable"
+  end
+end
+```
+
+Then declare that partial.
+
+```html+erb
+<%# app/views/users/missing_attachable.html.erb %>
+<span>Deleted user</span>
+```
+
 To integrate with Action Text `<action-text-attachment>` element rendering, a
 class must:
 
 * include the `ActionText::Attachable` module
 * implement `#to_sgid(**options)` (made available through the [`GlobalID::Identification` concern][global-id])
 * (optional) declare `#to_attachable_partial_path`
+* (optional) declare a class-level method `#to_missing_attachable_partial_path` for handling missing records
 
 By default, all `ActiveRecord::Base` descendants mix-in
 [`GlobalID::Identification` concern][global-id], and are therefore