Remove extra advisory lock connection

In #38235 I moved advisory locks to their own named connections, then
in #39758 the advisory lock was left on Base.connection but then moved
it it's own connection handler. I believe with #45450 that this change
was made obsolete and can be returned to the prior behavior without
having to open an additional connection. The tests added pass and I also
tested this in my local demo to ensure that this is working correctly.

When I originally changed the behavior here Matthew noted that this
could be surprising for some setups that expect only one connection for
a running migration. I thought there was an issue related to this but I
can't find it.

activerecord/lib/active_record/migration.rb

@@ -1466,29 +1466,18 @@ def use_advisory_lock?
 
       def with_advisory_lock
         lock_id = generate_migrator_advisory_lock_id
+        connection = ActiveRecord::Base.connection
 
-        with_advisory_lock_connection do |connection|
+        got_lock = connection.get_advisory_lock(lock_id)
-          got_lock = connection.get_advisory_lock(lock_id)
+        raise ConcurrentMigrationError unless got_lock
-          raise ConcurrentMigrationError unless got_lock
+        load_migrated # reload schema_migrations to be sure it wasn't changed by another process before we got the lock
-          load_migrated # reload schema_migrations to be sure it wasn't changed by another process before we got the lock
+        yield
-          yield
-        ensure
-          if got_lock && !connection.release_advisory_lock(lock_id)
-            raise ConcurrentMigrationError.new(
-              ConcurrentMigrationError::RELEASE_LOCK_FAILED_MESSAGE
-            )
-          end
-        end
-      end
-
-      def with_advisory_lock_connection(&block)
-        pool = ActiveRecord::ConnectionAdapters::ConnectionHandler.new.establish_connection(
-          ActiveRecord::Base.connection_db_config
-        )
-
-        pool.with_connection(&block)
       ensure
-        pool&.disconnect!
+        if got_lock && !connection.release_advisory_lock(lock_id)
+          raise ConcurrentMigrationError.new(
+            ConcurrentMigrationError::RELEASE_LOCK_FAILED_MESSAGE
+          )
+        end
       end
 
       MIGRATOR_SALT = 2053462845

activerecord/test/cases/migration_test.rb

@@ -1095,6 +1095,9 @@ def migrate(x)
     end
 
     def test_with_advisory_lock_doesnt_release_closed_connections
+      # make sure we have a connection
+      ActiveRecord::Base.establish_connection :arunit
+
       migration = Class.new(ActiveRecord::Migration::Current).new
       migrator = ActiveRecord::Migrator.new(:up, [migration], @schema_migration, @internal_metadata, 100)
 
@@ -1137,10 +1140,8 @@ def test_with_advisory_lock_raises_the_right_error_when_it_fails_to_release_lock
 
       e = assert_raises(ActiveRecord::ConcurrentMigrationError) do
         silence_stream($stderr) do
-          migrator.stub(:with_advisory_lock_connection, ->(&block) { block.call(ActiveRecord::Base.connection) }) do
+          migrator.send(:with_advisory_lock) do
-            migrator.send(:with_advisory_lock) do
+            ActiveRecord::Base.connection.release_advisory_lock(lock_id)
-              ActiveRecord::Base.connection.release_advisory_lock(lock_id)
-            end
           end
         end
       end