perf: escape token values with a single binary scan

lib/makeup/formatters/html/html_formatter.ex

@@ -53,9 +53,28 @@ defmodule Makeup.Formatters.HTML.HTMLFormatter do
   defp escape_for(c) when is_integer(c) and c >= 128, do: << c :: utf8 >>
 
   defp escape_for(string) when is_binary(string) do
-    string
-    |> to_charlist()
-    |> Enum.map(&escape_for/1)
+    escape_binary(string, string, 0, 0, [])
+  end
+
+  for {char, replacement} <- [
+        {?&, "&amp;"},
+        {?<, "&lt;"},
+        {?>, "&gt;"},
+        {?", "&quot;"},
+        {?', "&#39;"}
+      ] do
+    defp escape_binary(<<unquote(char), rest::binary>>, original, skip, len, acc) do
+      part = binary_part(original, skip, len)
+      escape_binary(rest, original, skip + len + 1, 0, [acc, part, unquote(replacement)])
+    end
+  end
+
+  defp escape_binary(<<_char, rest::binary>>, original, skip, len, acc) do
+    escape_binary(rest, original, skip, len + 1, acc)
+  end
+
+  defp escape_binary(<<>>, original, skip, len, acc) do
+    [acc | binary_part(original, skip, len)]
   end
 
   defp escape(iodata) when is_list(iodata) do

test/html_formatter_test.exs

@@ -74,6 +74,17 @@ defmodule MakeupTest.Lexer.HTMLFormatterTest do
     end
   end
 
+  test "a binary value is escaped, preserving safe characters and utf8" do
+    value = "a < b & \"c\" é 日"
+
+    assert HTMLFormatter.format_as_binary([{:string, %{}, value}]) ==
+             ~S[<pre class="highlight"><code>] <>
+             ~S[<span class="s">] <>
+             ~S[a &lt; b &amp; &quot;c&quot; é 日] <>
+             ~S[</span>] <>
+             ~S[</code></pre>]
+  end
+
   test "group ids are encoded before being written to data attributes" do
     html =
       HTMLFormatter.format_as_binary([