[Sass] [Convert] Fix a rare bug with multiline selectors getting cut off.

doc-src/SASS_CHANGELOG.md

@@ -50,6 +50,9 @@ this won't cause any backwards-incompatibilities.
 * Perform all conversions to rules within directive blocks
   when converting CSS.
 
+* Prevent multiline CSS selectors from getting cut off
+  in certain rare cases.
+
 ### `@import` in Sass
 
 The Sass `@import` statement now allows non-CSS files to be specified with quotes,

lib/sass/css.rb

@@ -134,7 +134,7 @@ module Sass
           next child
         end
 
-        first, rest = child.rule.first.scan(/^(&?(?: .|[^ ])[^.#: \[]*)([.#: \[].*)?$/).first
+        first, rest = child.rule.first.scan(/\A(&?(?: .|[^ ])[^.#: \[]*)([.#: \[].*)?\Z/m).first
 
         if current_rule.nil? || current_rule.rule.first != first
           current_rule = Tree::RuleNode.new([first])

test/sass/css2sass_test.rb

@@ -253,6 +253,21 @@ SASS
 CSS
   end
 
+  def test_multiline_selector_within_media_and_with_child_selector
+    assert_equal(<<SASS, css2sass(<<CSS))
+@media all
+  foo bar, baz
+    padding-left: 0
+    padding-right: 0
+SASS
+@media all {
+  foo bar,
+  baz {
+    padding-left: 0;
+    padding-right: 0; } }
+CSS
+  end
+
   # Error reporting
 
   def test_error_reporting