Accessing a Signal value from a preact PureComponent should error in development mode

[DanielHeath]

Describe the feature you'd love to see

If you access a signal from a PureComponent, it does not re-render when the signal value changes.

That makes sense to me - the component claims to be a pure function of its state/props - but it's easy to accidentally introduce a signal dependency to a pure component without changing its definition to impure, and the result looks like a bug in signals.

Would it be worth logging an error (at least in development mode) in this case?

Alternatively, should pure components also be able to subscribe to signal updates?

[JoviDeCroock]

Hey,

This is indeed a footgun but there are "reasons" for this, by default signals already consider each component memoized.

• A component with signals will update depending on whether or not they contain an update signal
• A component with class-state will always update
• A component with hook state will defer the update to the hooks to decide

This means that both class and function components work by default, PureComponent does not because it overrides the shouldComponentUpdate of the inner component. memo does work because it wraps the inner component with a new shouldComponentUpdate.

Making this work would be quite complex and because it's a "react" feature (it lives in compat) I doubt it's worth it. Historically we've refrained from adding debug hints for the react/preact intersection.