From 4e29c6e32b5463bc637862b3ccc11ffd0de35d44 Mon Sep 17 00:00:00 2001
From: Jeremy Daer <jeremy@37signals.com>
Date: Thu, 15 Oct 2026 16:59:25 -0700
Subject: [PATCH] Keep a code block's leading newline when linking a message's
 text

A <pre> whose text starts with a newline needs one more written out to
survive being parsed again, as the html5 serializer does with
preserve_newline. Without it, linking text dropped one more of a code
block's leading blank lines than rendering did before.
---
 app/helpers/messages_helper.rb       | 3 ++-
 test/helpers/messages_helper_test.rb | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/app/helpers/messages_helper.rb b/app/helpers/messages_helper.rb
index 2b3faf6..687d9a4 100644
--- a/app/helpers/messages_helper.rb
+++ b/app/helpers/messages_helper.rb
@@ -130,7 +130,8 @@ module MessagesHelper
         end
       end
 
-      fragment.to_html.html_safe
+      # A <pre> starting with a newline needs an extra one written out to survive the next parse
+      fragment.to_html(preserve_newline: true).html_safe
     end
 
     def messages_actions
diff --git a/test/helpers/messages_helper_test.rb b/test/helpers/messages_helper_test.rb
index 65830f1..911317a 100644
--- a/test/helpers/messages_helper_test.rb
+++ b/test/helpers/messages_helper_test.rb
@@ -58,6 +58,12 @@ class MessagesHelperTest < ActionView::TestCase
     end
   end
 
+  test "linking text doesn't eat a code block's leading blank line" do
+    linked = view.send(:auto_link_text, "<pre>\n\n\nfirst https://example.com</pre>".html_safe)
+
+    assert_equal "\nfirst https://example.com", Nokogiri::HTML5.fragment(linked).at_css("pre").text
+  end
+
   test "message_presentation leaves an existing link's text alone" do
     message = Message.create! room: rooms(:pets), body: '<div><a href="https://example.com/">https://example.org/</a></div>', client_message_id: "0015", creator: users(:jason)