ref should not provide element when disconnected

[sorvell]

Which package(s) are affected?

Lit Core (lit / lit-html / lit-element / reactive-element)

Description

The ref directive supplies an element when it runs update and it is in a disconnected state. This does not make sense since ref supplies undefined when disconnected and the element again when reconnected. Since this behavior implies that ref is intended to supply undefined when disconnected, it's incorrect for this to change while it is disconnected.

This can cause practical problems if code depends on installing/removing behavior based on connection state. See discord discussion.

Note also that checking refElement.isConnected is not a workaround since directives are run in a connected state regardless of whether or not the host context is connected.

Reproduction

In the repro example here https://lit.dev/playground/#gist=fe6d7deeba80b76873eb057819ed2bc4

1. open the console
2. click the remove button
3. click the increment button
4. click the add button

Note that:
A. After (3) the ref callback is supplied when an element. This is unexpected.
B. After (4) the ref callback gets undefined and then the element. This is unexpected.

Workaround

Gate behavior on the host's connection state.

Is this a regression?

No or unsure. This never worked, or I haven't tried before.

Affected versions

3.x

Browser/OS/Node environment

All