test.ts.lint

[typescript]: <= 3.6.0

// in TS 3.6 and later, the type checker infers this anonymous function as returning 'unknown'
declare function f<T>(action: () => T | undefined): void;
f(() => { return undefined; });
          ~~~~~~~~~~~~~~~~~ [VOID]

[VOID]: `void` function should use `return;`, not `return undefined;`.
[UNDEFINED]: Value-returning function should use `return undefined;`, not just `return;`.