[Haml] Don't remove \n in filters with interpolation.

doc-src/HAML_CHANGELOG.md

@@ -8,6 +8,8 @@
 * Don't crash when `rake gems` is run in Rails with Haml installed.
   Thanks to [Florian Frank](http://github.com/flori).
 
+* Don't remove `\n` in filters with interpolation.
+
 ## 2.2.22
 
 [Tagged on GitHub](http://github.com/nex3/haml/commit/2.2.22).

lib/haml/filters.rb

@@ -100,7 +100,11 @@ module Haml
           if contains_interpolation?(text)
             return if options[:suppress_eval]
 
-            text = unescape_interpolation(text).gsub("\\n", "\n")
+            text = unescape_interpolation(text).gsub(/(\\+)n/) do |s|
+              escapes = $1.size
+              next s if escapes % 2 == 0
+              ("\\" * (escapes - 1)) + "\n"
+            end
             newline if text.gsub!(/\n"\Z/, "\\n\"")
             push_script <<RUBY.strip, :escape_html => false
 find_and_preserve(#{filter.inspect}.render_with_options(#{text}, _hamlout.options))

test/haml/engine_test.rb

@@ -629,6 +629,15 @@ HAML
     assert_equal("<a href='#\"'></a>\n", render('%a(href="#\\"")'))
   end
 
+  def test_filter_with_newline_and_interp
+    assert_equal(<<HTML, render(<<HAML))
+\\n
+HTML
+:plain
+  \\n\#{""}
+HAML
+  end
+
   # HTML escaping tests
 
   def test_ampersand_equals_should_escape