useSafeSetState incompatible with @types/react@16.14 and later

[bayareacoder]

What you were expecting:
react-admin should compile in Typescript when using @types/react@16.14 or @types/react@17

What happened instead:
Throws an error at compile time due to the return type from the returned destructor from useSafeSetState in file ra_core/src/util/hooks.ts

   const mountedRef = useRef(false);
  > 12 |     useEffect(() => {
       |               ^
    13 |         mountedRef.current = true;
    14 |         return () => (mountedRef.current = false);
    15 |     }, []);

Type 'boolean' is not assignable to type 'void | { [UNDEFINED_VOID_ONLY]: never; }'

Root cause:
Type definitions for EffectCallback changed to explicitly disallow to return anything else than void from the Destructor

From @types/react@16.9

  type EffectCallback = () => (void | (() => void | undefined));

To @types/react@16.14 (maybe already from earlier version but not tested)

type EffectCallback = () => (void | Destructor);
type Destructor = () => void | { [UNDEFINED_VOID_ONLY]: never };
declare const UNDEFINED_VOID_ONLY: unique symbol;

Fix
2 character fix: replace () by {}

Environment

• React-admin version: 3.12.5

[fzaninotto]

Thanks for the detailed description and root cause analysis. The fix is simple indeed.