2 files changed, 37 insertions, 1 deletions
diff --git a/activesupport/lib/active_support/file_evented_update_checker.rb b/activesupport/lib/active_support/file_evented_update_checker.rb
index ae500d697f..9c66363e9f 100644
--- a/activesupport/lib/active_support/file_evented_update_checker.rb
+++ b/activesupport/lib/active_support/file_evented_update_checker.rb
@@ -79,7 +79,14 @@ module ActiveSupport
       using Module.new {
         refine Pathname do
           def ascendant_of?(other)
-            other.to_s =~ /\A#{Regexp.quote(to_s)}#{Pathname::SEPARATOR_PAT}?/
+            if self != other && other.to_s.start_with?(to_s)
+              # On Windows each_filename does not include the drive letter,
+              # but the test above already detects if they differ.
+              parts = each_filename.to_a
+              other_parts = other.each_filename.to_a
+
+              other_parts[0, parts.length] == parts
+            end
           end
         end
       }
diff --git a/activesupport/test/file_evented_update_checker_test.rb b/activesupport/test/file_evented_update_checker_test.rb
index 9d09cbca8f..071449d399 100644
--- a/activesupport/test/file_evented_update_checker_test.rb
+++ b/activesupport/test/file_evented_update_checker_test.rb
@@ -118,4 +118,33 @@ class FileEventedUpdateCheckerPathHelperTest < ActiveSupport::TestCase
 
     assert_equal paths.values_at(0, 2, 4), @ph.filter_out_descendants(paths)
   end
+
+  test '#filter_out_descendants works on path units' do
+    paths = %w(
+      /foo/bar
+      /foo/barrrr
+    ).map { |path| pn(path) }
+
+    assert_equal paths, @ph.filter_out_descendants(paths)
+  end
+
+  test '#filter_out_descendants deals correctly with the root directory' do
+    paths = %w(
+      /
+      /foo
+      /foo/bar
+    ).map { |path| pn(path) }
+
+    assert_equal paths.values_at(0), @ph.filter_out_descendants(paths)
+  end
+
+  test '#filter_out_descendants preserves duplicates' do
+    paths = %w(
+      /foo
+      /foo/bar
+      /foo
+    ).map { |path| pn(path) }
+
+    assert_equal paths.values_at(0, 2), @ph.filter_out_descendants(paths)
+  end
 end