Add hooks to integrate with Action Text

One major challenge that applications face when integrating with
morphing-powered Page Refreshes involves `<trix-editor>` elements
rendered by Action Text.

The emergent guidance instructs applications to skip morphing by
marking the `<trix-editor>` as permanent. This guidance, while correct,
does not encapsulate the entire story. In the case of Action
Text-rendered `<trix-editor>` elements, applications might invoke
`form.rich_text_area` with `data: {turbo_permanent: true}`, expecting
for the presence of `trix-editor[data-turbo-permanent]` to be
sufficient.

However, to achieve the intended behavior, applications must *nest*
their `<trix-editor>` elements *within* an element with
`[data-turbo-permanent]` (a `<div>`, a `<fieldset>`, etc.). This
provides a container for the `trix-editor` to inject its associated
`<input>` and `<trix-toolbar>` elements. A `<trix-editor>` element will
insert an `<input type="hidden">` element and a `<trix-toolbar>` element
when they are absent on connect.

Applications can skip a Trix-manage injection by rendering those
either (or both) elements ahead of time, then associating them to the
`trix-editor` through `[input]` and `[toolbar]` attributes
(respectively).

Action Text skips the `<input>` injection step by rendering and
associating an Action View-rendered `<input type="hidden">` attribute
with the appropriate attributes.

No matter how the `<input>` connects to the document, it's important for
it to keep its `[data-turbo-permanent]` synchronized with the
`trix-editor`'s attribute in order to tolerate a morph.

Since Page Refreshes, Morphing, and permanence are all Turbo concepts,
and Action Text is a Rails framework, `turbo-rails` feels like the most
appropriate codebase (out of `rails`, `trix`, `turbo`, and
`turbo-rails`) to house the integration.

app/assets/javascripts/turbo.js

@@ -5430,10 +5430,35 @@ function isBodyInit(body) {
   return body instanceof FormData || body instanceof URLSearchParams;
 }
 
+function observeAttributes(element, attributeFilter, callback) {
+  const observer = new MutationObserver((mutations => {
+    mutations.forEach((({attributeName: attributeName, target: target}) => {
+      callback(target.getAttribute(attributeName), attributeName);
+    }));
+  }));
+  observer.observe(element, {
+    attributeFilter: attributeFilter
+  });
+  attributeFilter.forEach((attributeName => {
+    callback(element.getAttribute(attributeName), attributeName);
+  }));
+  return observer;
+}
+
+function observeTurboAttributes({target: target}) {
+  observeAttributes(target, [ "data-turbo-permanent" ], (value => {
+    if (target.inputElement) {
+      target.inputElement.toggleAttribute("data-turbo-permanent", value ?? false);
+    }
+  }));
+}
+
 window.Turbo = Turbo$1;
 
 addEventListener("turbo:before-fetch-request", encodeMethodIntoRequestBody);
 
+addEventListener("trix-initialize", observeTurboAttributes);
+
 var adapters = {
   logger: self.console,
   WebSocket: self.WebSocket

app/javascript/turbo/actiontext.js

@@ -0,0 +1,9 @@
+import { observeAttributes } from "./util"
+
+export function observeTurboAttributes({ target }) {
+  observeAttributes(target, ["data-turbo-permanent"], (value) => {
+    if (target.inputElement) {
+      target.inputElement.toggleAttribute("data-turbo-permanent", value ?? false)
+    }
+  })
+}

app/javascript/turbo/index.js

@@ -7,7 +7,9 @@ import * as cable from "./cable"
 export { cable }
 
 import { encodeMethodIntoRequestBody } from "./fetch_requests"
+import { observeTurboAttributes } from "./actiontext"
 
 window.Turbo = Turbo
 
 addEventListener("turbo:before-fetch-request", encodeMethodIntoRequestBody)
+addEventListener("trix-initialize", observeTurboAttributes)

app/javascript/turbo/util.js

@@ -0,0 +1,14 @@
+export function observeAttributes(element, attributeFilter, callback) {
+  const observer = new MutationObserver((mutations) => {
+    mutations.forEach(({ attributeName, target }) => {
+      callback(target.getAttribute(attributeName), attributeName)
+    })
+  })
+  observer.observe(element, { attributeFilter })
+
+  attributeFilter.forEach((attributeName) => {
+    callback(element.getAttribute(attributeName), attributeName)
+  })
+
+  return observer
+}

test/dummy/app/controllers/messages_controller.rb

@@ -1,4 +1,8 @@
 class MessagesController < ApplicationController
+  def new
+    @message = Message.new
+  end
+
   def show
     @message = Message.find(params[:id])
 

test/dummy/app/javascript/application.js

@@ -1,2 +1,3 @@
 // Configure your import map in config/importmap.rb. Read more: https://github.com/rails/importmap-rails
 import "@hotwired/turbo-rails"
+import "trix"

test/dummy/app/views/messages/new.html.erb

@@ -0,0 +1,9 @@
+<% if params[:method] == "morph" %>
+  <% turbo_refreshes_with method: :morph %>
+<% end %>
+
+<%= form_with model: @message do |form| %>
+  <%= form.rich_text_area :content, data: {turbo_permanent: true} %>
+<% end %>
+
+<%= link_to "Page Refresh", {}, data: {turbo_action: "replace"} %>

test/dummy/config/application.rb

@@ -2,6 +2,7 @@
 
 require "action_controller/railtie"
 require "action_cable/engine"
+require "action_text/engine"
 require "active_job/railtie"
 require "active_model/railtie"
 require "active_record/railtie"

test/dummy/config/importmap.rb

@@ -6,3 +6,4 @@
 pin "application"
 pin "@hotwired/turbo-rails", to: "turbo.js"
 pin "@rails/actioncable", to: "actioncable.esm.js"
+pin "trix", to: "trix.js"

test/system/actiontext_test.rb

@@ -0,0 +1,36 @@
+require "application_system_test_case"
+
+class ActionTextTest < ApplicationSystemTestCase
+  test "forwards [data-turbo-permanent] from trix-editor to its input and trix-toolbar" do
+    visit new_message_path
+
+    assert_trix_editor name: "message[content]", "data-turbo-permanent": true
+
+    find(:rich_text_area).execute_script <<~JS
+      this.removeAttribute("data-turbo-permanent")
+    JS
+
+    assert_trix_editor name: "message[content]", "data-turbo-permanent": false
+  end
+
+  test "keeps a trix-editor[data-turbo-permanent] interactive through a Page Refresh" do
+    visit new_message_path(method: "morph")
+    fill_in_rich_text_area with: "Hello"
+    click_link "Page Refresh"
+
+    assert_trix_editor name: "message[content]", with: /Hello/
+
+    fill_in_rich_text_area with: "Hello world"
+
+    assert_trix_editor name: "message[content]", with: /Hello world/
+  end
+
+  def assert_trix_editor(name: nil, with: nil, **options, &block)
+    trix_editor = find(:element, "trix-editor", **options, &block)
+
+    assert_field name, type: "hidden", with: with do |input|
+      assert_equal trix_editor.evaluate_script("this.inputElement"), input
+      assert_matches_selector input, :element, **options
+    end
+  end
+end