2 files changed, 50 insertions, 2 deletions
diff --git a/activesupport/lib/active_support/evented_file_update_checker.rb b/activesupport/lib/active_support/evented_file_update_checker.rb
index 97e982eb05..1ef8584c52 100644
--- a/activesupport/lib/active_support/evented_file_update_checker.rb
+++ b/activesupport/lib/active_support/evented_file_update_checker.rb
@@ -52,7 +52,10 @@ module ActiveSupport
       @pid        = Process.pid
       @boot_mutex = Mutex.new
 
-      if (@dtw = directories_to_watch).any?
+      dtw = directories_to_watch
+      @dtw, @missing = dtw.partition(&:exist?)
+
+      if @dtw.any?
         # Loading listen triggers warnings. These are originated by a legit
         # usage of attr_* macros for private attributes, but adds a lot of noise
         # to our test suite. Thus, we lazy load it and disable warnings locally.
@@ -75,6 +78,19 @@ module ActiveSupport
           @updated.make_true
         end
       end
+
+      if @missing.any?(&:exist?)
+        @boot_mutex.synchronize do
+          appeared, @missing = @missing.partition(&:exist?)
+          shutdown!
+
+          @dtw += appeared
+          boot!
+
+          @updated.make_true
+        end
+      end
+
       @updated.true?
     end
 
@@ -96,6 +112,10 @@ module ActiveSupport
         Listen.to(*@dtw, &method(:changed)).start
       end
 
+      def shutdown!
+        Listen.stop
+      end
+
       def changed(modified, added, removed)
         unless updated?
           @updated.make_true if (modified + added + removed).any? { |f| watching?(f) }
@@ -123,7 +143,7 @@ module ActiveSupport
       end
 
       def directories_to_watch
-        dtw = (@files + @dirs.keys).map { |f| @ph.existing_parent(f) }
+        dtw = @files.map(&:dirname) + @dirs.keys
         dtw.compact!
         dtw.uniq!
 
diff --git a/activesupport/test/evented_file_update_checker_test.rb b/activesupport/test/evented_file_update_checker_test.rb
index a557608986..b2d5eb94c2 100644
--- a/activesupport/test/evented_file_update_checker_test.rb
+++ b/activesupport/test/evented_file_update_checker_test.rb
@@ -76,6 +76,34 @@ class EventedFileUpdateCheckerTest < ActiveSupport::TestCase
 
     Process.wait(pid)
   end
+
+  test "updated should become true when nonexistent directory is added later" do
+    Dir.mktmpdir do |dir|
+      watched_dir = File.join(dir, "app")
+      unwatched_dir = File.join(dir, "node_modules")
+      not_exist_watched_dir = File.join(dir, "test")
+
+      Dir.mkdir(watched_dir)
+      Dir.mkdir(unwatched_dir)
+
+      checker = new_checker([], watched_dir => ".rb", not_exist_watched_dir => ".rb") { }
+
+      FileUtils.touch(File.join(watched_dir, "a.rb"))
+      wait
+      assert_predicate checker, :updated?
+      assert checker.execute_if_updated
+
+      Dir.mkdir(not_exist_watched_dir)
+      wait
+      assert_predicate checker, :updated?
+      assert checker.execute_if_updated
+
+      FileUtils.touch(File.join(unwatched_dir, "a.rb"))
+      wait
+      assert_not_predicate checker, :updated?
+      assert_not checker.execute_if_updated
+    end
+  end
 end
 
 class EventedFileUpdateCheckerPathHelperTest < ActiveSupport::TestCase