Checkin even stale connections from reap

Previously when we reaped connections, we checked if they were inactive
(connected and responding to ping in most adapters) and if so we would
remove the connection instead of checking it back in.

Removing the connection would not wake a thread waiting on the queue for
a connection. This commit changes that to always re-check in the
connection.

activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb

@@ -432,12 +432,8 @@ def reap
         end
 
         stale_connections.each do |conn|
-          if conn.active?
-            conn.reset!
-            checkin conn
-          else
-            remove conn
-          end
+          conn.reset!
+          checkin conn
         end
       end
 

activerecord/test/cases/connection_pool_test.rb

@@ -215,6 +215,30 @@ def test_reap_inactive
         @pool.connections.each { |conn| conn.close if conn.in_use? }
       end
 
+      def test_inactive_are_returned_from_dead_thread
+        ready = Concurrent::CountDownLatch.new
+        @pool.instance_variable_set(:@size, 1)
+
+        child = new_thread do
+          @pool.checkout
+          ready.count_down
+          stop_thread
+        end
+
+        pass_to(child) until ready.wait(0)
+
+        assert_equal 1, active_connections(@pool).size
+
+        child.terminate
+        child.join
+
+        @pool.checkout
+
+        assert_equal 1, active_connections(@pool).size
+      ensure
+        @pool.connections.each { |conn| conn.close if conn.in_use? }
+      end
+
       def test_idle_timeout_configuration
         @pool.disconnect!