Fix EventedFileUpdateChecker through a symlink

On MacOS, Dir.tmpdir gives me a folder inside "/var/folders/". However,
/var is a symlink to /private/var.

Previously, the nonexistent directory test would fail because it was
initialized with /var/folders/... but the filenames from listen would be
the realpaths.

This commit normalizes the dirs by calling realpath on them if they
exist. This is done on boot!, so it will work with newly directories
through the symlink.

2 files changed, 25 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/evented_file_update_checker.rb b/activesupport/lib/active_support/evented_file_update_checker.rb
index 3893b0de0e..15b84537cc 100644
--- a/activesupport/lib/active_support/evented_file_update_checker.rb
+++ b/activesupport/lib/active_support/evented_file_update_checker.rb
@@ -107,6 +107,7 @@ module ActiveSupport
 
     private
       def boot!
+        normalize_dirs!
         Listen.to(*@dtw, &method(:changed)).start
       end
 
@@ -114,6 +115,12 @@ module ActiveSupport
         Listen.stop
       end
 
+      def normalize_dirs!
+        @dirs.transform_keys! do |dir|
+          dir.exist? ? dir.realpath : dir
+        end
+      end
+
       def changed(modified, added, removed)
         unless updated?
           @updated.make_true if (modified + added + removed).any? { |f| watching?(f) }
diff --git a/activesupport/test/evented_file_update_checker_test.rb b/activesupport/test/evented_file_update_checker_test.rb
index ce09fa1586..bec2643b45 100644
--- a/activesupport/test/evented_file_update_checker_test.rb
+++ b/activesupport/test/evented_file_update_checker_test.rb
@@ -77,6 +77,24 @@ class EventedFileUpdateCheckerTest < ActiveSupport::TestCase
     Process.wait(pid)
   end
 
+  test "should detect changes through symlink" do
+    actual_dir = File.join(tmpdir, "actual")
+    linked_dir = File.join(tmpdir, "linked")
+
+    Dir.mkdir(actual_dir)
+    FileUtils.ln_s(actual_dir, linked_dir)
+
+    checker = new_checker([], linked_dir => ".rb") { }
+
+    assert_not_predicate checker, :updated?
+
+    FileUtils.touch(File.join(actual_dir, "a.rb"))
+    wait
+
+    assert_predicate checker, :updated?
+    assert checker.execute_if_updated
+  end
+
   test "updated should become true when nonexistent directory is added later" do
     watched_dir = File.join(tmpdir, "app")
     unwatched_dir = File.join(tmpdir, "node_modules")