Handle max_time edge cases for epoch times and add test

2 files changed, 29 insertions, 3 deletions

diff --git a/activesupport/lib/active_support/file_update_checker.rb b/activesupport/lib/active_support/file_update_checker.rb
index 4f0a2dedc5..d1eb410c85 100644
--- a/activesupport/lib/active_support/file_update_checker.rb
+++ b/activesupport/lib/active_support/file_update_checker.rb
@@ -111,13 +111,22 @@ module ActiveSupport
     # healthy to consider this edge case because with mtimes in the future
     # reloading is not triggered.
     def max_mtime(paths)
+      return nil if paths.empty?
+
       time_now = Time.now
-      time_at_zero = Time.at(0)
-      max_time = time_at_zero
+      max_time = nil
 
       paths.each do |path|
         time = File.mtime(path)
 
+        if max_time.nil?
+          if time.compare_without_coercion(time_now) < 0
+            max_time = time
+          end
+
+          next
+        end
+
         # This avoids ActiveSupport::CoreExt::Time#time_with_coercion
         # which is super slow when comparing two Time objects
         #
@@ -128,7 +137,7 @@ module ActiveSupport
         end
       end
 
-      max_time.object_id == time_at_zero.object_id ? nil : max_time
+      max_time
     end
 
     def compile_glob(hash)
diff --git a/activesupport/test/file_update_checker_shared_tests.rb b/activesupport/test/file_update_checker_shared_tests.rb
index 5207860a0e..a78c3a67b6 100644
--- a/activesupport/test/file_update_checker_shared_tests.rb
+++ b/activesupport/test/file_update_checker_shared_tests.rb
@@ -134,6 +134,23 @@ module FileUpdateCheckerSharedTests
     assert_equal 1, i
   end
 
+  test 'should return max_time for files with mtime = Time.at(0)' do
+    i = 0
+
+    FileUtils.touch(tmpfiles)
+
+    now  = Time.now
+    time = Time.at(0) # wrong mtime from the future
+    File.utime(time, time, tmpfiles[0])
+
+    checker = new_checker(tmpfiles) { i += 1 }
+
+    touch(tmpfiles[1..-1])
+
+    assert checker.execute_if_updated
+    assert_equal 1, i
+  end
+
   test 'should cache updated result until execute' do
     i = 0