Bug: act warning misleading if an effect wasn't run

[eps1lon]

React version: 16.13.1 and next

Steps To Reproduce

1. Re-render a component where an effect wasn't run because dependencies didn't change
2. Receive missing act warning

Link to code example: https://codesandbox.io/s/missing-act-on-every-effect-ldy3b?file=/src/index.test.js

The current behavior

React creates warnings for each call of React.useEffect regardless of whether an effect was actually scheduled i.e. the effect was run.

The expected behavior

If it is impossible for an effect to be run I shouldn't have to wrap it in act. Changing the behavior would help identifying what effects were unexpectedly scheduled. Right now we receive warnings for effects that are unrelated to a specific update.

I consider the current warning misleading and unnecessary because the documentation talks about "all updates related to these “units”" which is not the case here in my opinion. The act warning says "When testing, code that causes React state updates should be wrapped into act(...):" which also doesn't apply here: The code in question could not cause a state update from an effect.

[stale]

This issue has been automatically marked as stale. If this issue is still affecting you, please leave any comment (for example, "bump"), and we'll keep it open. We are sorry that we haven't been able to prioritize it yet. If you have any new additional information, please include it with your comment!

[eps1lon]

Bump

[eps1lon]

Will no longer be relevant for React 18 where even a render needs to be wrapped in act. See reactwg/react-18#23 (reply in thread)