Formatter - Keep intentional newlines when formatting comments

This PR improves the HTML formatter so that it keeps at least one line
(which usually are lines we want to keep intentionally) when formatting
comments.

lib/phoenix_live_view/html_algebra.ex

@@ -25,17 +25,37 @@ defmodule Phoenix.LiveView.HTMLAlgebra do
         concat(doc, next_doc)
       end)
 
-    force_unfit? =
-      Enum.any?(block, fn
-        {:text, text, %{newlines: newlines}} -> newlines > 0 or String.contains?(text, "\n")
-        _ -> false
+    {force_unfit?, meta} =
+      Enum.find_value(block, fn
+        {:text, text, meta} ->
+          {String.contains?(text, "\n"), meta}
+
+        _ ->
+          {false, %{}}
       end)
 
-    if force_unfit? do
-      concat |> force_unfit() |> group()
-    else
-      concat |> group()
-    end
+    doc =
+      if force_unfit? do
+        concat |> force_unfit() |> group()
+      else
+        concat |> group()
+      end
+
+    newline_or_empty_before_text =
+      if meta[:newlines_before_text] && meta[:newlines_before_text] > 1 do
+        line()
+      else
+        empty()
+      end
+
+    newline_or_empty_after_text =
+      if meta[:newlines_after_text] && meta[:newlines_after_text] > 1 do
+        line()
+      else
+        empty()
+      end
+
+    concat([newline_or_empty_before_text, doc, newline_or_empty_after_text])
   end
 
   defp block_to_algebra([head | tail], context) do

lib/phoenix_live_view/html_formatter.ex

@@ -446,7 +446,12 @@ defmodule Phoenix.LiveView.HTMLFormatter do
          stack,
          source
        ) do
-    to_tree(tokens, [{:html_comment, [{:text, String.trim(text), %{}}]} | buffer], stack, source)
+    meta = %{
+      newlines_before_text: count_newlines_until_text(text, 0),
+      newlines_after_text: text |> String.reverse() |> count_newlines_until_text(0)
+    }
+
+    to_tree(tokens, [{:html_comment, [{:text, String.trim(text), meta}]} | buffer], stack, source)
   end
 
   defp to_tree([{:text, text, _meta} | tokens], buffer, stack, source) do

test/phoenix_live_view/html_formatter_test.exs

@@ -2100,6 +2100,42 @@ defmodule Phoenix.LiveView.HTMLFormatterTest do
     """)
   end
 
+  test "keep intentional lines breaks from HTML comments" do
+    assert_formatter_doesnt_change("""
+    <h1>Title</h1>
+
+    <!-- comment -->
+    <p>Text</p>
+    """)
+
+    assert_formatter_doesnt_change("""
+    <h1>Title</h1>
+
+    <!-- comment -->
+
+    <p>Text</p>
+    """)
+
+    assert_formatter_output(
+      """
+      <h1>Title</h1>
+
+
+      <!-- comment -->
+
+
+      <p>Text</p>
+      """,
+      """
+      <h1>Title</h1>
+
+      <!-- comment -->
+
+      <p>Text</p>
+      """
+    )
+  end
+
   # TODO: Remove this `if` when we require Elixir 1.14+
   if function_exported?(EEx, :tokenize, 2) do
     test "handle EEx comments" do

test/phoenix_live_view/integrations/html_formatter_test.exs

@@ -95,6 +95,7 @@ defmodule Phoenix.LiveView.Integrations.HTMLFormatterTest do
         </td>
       <% end %>
     </section>
+
     <!-- comment -->
     <div>
       <p>Hello</p>