Clear level overrides in #dup and #clone

Cloning loggers can be used, for example, to create different loggers
for different classes/components/subsystems that share the same log_dev
and other configuration (possibly a subclass of Logger), but with
different verbosity levels, formatters, etc.

But, that doesn't work if they share `@level_override`.  Rather than
use OverrideMap.new, the existing `@level_override` is cloned and
cleared, to preserve `@level_override`'s class.

Author: nevans

lib/logger.rb

@@ -380,7 +380,7 @@ class Logger
   include Severity
 
   # Must respond to .new and return a Hash-like object.
-  # The returned object must respond to #[], #[]=, #delete.
+  # The returned object must respond to #[], #[]=, #delete, #dup, and #clear.
   #
   # ObjectSpace::WeakKeyMap when supported.
   OverrideMap =
@@ -800,6 +800,11 @@ def level_override
     @level_override ||= OverrideMap.new
   end
 
+  def initialize_copy(other)
+    super
+    @level_override = @level_override&.clone&.clear
+  end
+
   def level_key
     Fiber.current
   end

test/logger/test_severity.rb

@@ -36,6 +36,11 @@ def test_fiber_local_level
     logger.with_level(:WARN) do
       assert_equal(other.level, ERROR)
       assert_equal(logger.level, WARN)
+      assert_equal(logger.dup.level, INFO)
+      assert_equal(logger.clone.level, INFO)
+      logger.clone.with_level(:FATAL) do
+        assert_equal(logger.level, WARN)
+      end
 
       logger.with_level(DEBUG) do # verify reentrancy
         assert_equal(logger.level, DEBUG)
@@ -45,6 +50,8 @@ def test_fiber_local_level
           logger.with_level(:WARN) do
             assert_equal(other.level, ERROR)
             assert_equal(logger.level, WARN)
+            assert_equal(logger.dup.level, INFO)
+            assert_equal(logger.clone.level, INFO)
           end
           assert_equal(logger.level, INFO)
         end.resume
@@ -72,6 +79,11 @@ def level_key
     logger.with_level(:WARN) do
       assert_equal(other.level, ERROR)
       assert_equal(logger.level, WARN)
+      assert_equal(logger.dup.level, INFO)
+      assert_equal(logger.clone.level, INFO)
+      logger.clone.with_level(:FATAL) do
+        assert_equal(logger.level, WARN)
+      end
 
       logger.with_level(DEBUG) do # verify reentrancy
         assert_equal(logger.level, DEBUG)
@@ -81,6 +93,8 @@ def level_key
           logger.with_level(:WARN) do
             assert_equal(other.level, ERROR)
             assert_equal(logger.level, WARN)
+            assert_equal(logger.dup.level, INFO)
+            assert_equal(logger.clone.level, INFO)
           end
           assert_equal(logger.level, DEBUG)
         end.resume