fix: Parsing of preamble with escaped content in runkit tags (#11466)

app/views/liquids/_runkit.html.erb

@@ -1,6 +1,6 @@
 <div class="runkit-element">
   <code style="display: none">
-    <%= preamble %>
+    <%= CGI.unescapeHTML preamble %>
   </code>
   <code style="display: none;">
     <%= parsed_content %>

spec/fixtures/files/article_with_runkit_tag_with_preamble.txt

@@ -0,0 +1,45 @@
+---
+title: Sample Article
+published: true
+description: this is a sample article
+tags: test
+---
+
+Suspendisse ac lobortis velit, a feugiat sapien. Aenean condimentum, nulla at fermentum sagittis, tellus nisi suscipit velit, vel sollicitudin odio ligula a odio. Integer eget efficitur massa, in sodales velit. Nunc fermentum consequat scelerisque. Morbi elementum tristique faucibus. Nulla vel lectus non justo euismod varius. Vivamus id nisl sit amet odio tincidunt fringilla. Pellentesque odio odio, vulputate in risus eu, lacinia porttitor lorem. Nunc posuere tempus est, imperdiet suscipit odio maximus id. Nam eget feugiat magna.
+
+{% runkit %}
+const node = data => next => callback => callback (data) (next)
+//           ----    ----    --------              ----   ----
+//             \       |        /                 /      /
+//           parameters are curried        -------------
+//                                       /    
+// closures make data and next available
+// to callback when it is finally called.
+
+// I can use bind to store my data and next values.
+const head = node ('data') (null)
+//                 ------   ----
+//                  /        /
+//           We can partially apply the arguments `data` and null.
+
+// Use a callback to read the values from head.
+head (data => next => {
+  return { data, next }
+})
+{% endrunkit %}
+
+
+{% runkit
+const V = a => b => c => c (a) (b)
+%}
+const node = V
+
+const leftRight = node ('Left') ('Right')
+
+// TODO: modify callback so the code returns 'Left'
+const callback = a => b => {}
+
+leftRight (callback) //=> 'Left'
+{% endrunkit %} 
+
+

spec/system/articles/user_creates_an_article_spec.rb

@@ -8,6 +8,9 @@ RSpec.describe "Creating an article with the editor", type: :system do
   let!(:template_with_runkit_tag) do
     file_fixture("article_with_runkit_tag.txt").read
   end
+  let!(:template_with_runkit_tag_with_preamble) do
+    file_fixture("article_with_runkit_tag_with_preamble.txt").read
+  end
 
   before do
     sign_in user
@@ -44,6 +47,15 @@ RSpec.describe "Creating an article with the editor", type: :system do
       expect_runkit_tag_to_be_active
     end
 
+    it "creates a new article with a Runkit tag with complex preamble" do
+      visit new_path
+      fill_in "article_body_markdown", with: ""
+      fill_in "article_body_markdown", with: template_with_runkit_tag_with_preamble
+      click_button "Save changes"
+
+      expect_runkit_tag_to_be_active(count: 2)
+    end
+
     # TODO: [@forem/sre] figure out why this fails intermittently :-|
     xit "previews article with a Runkit tag and creates it" do
       visit new_path