eslint react-hooks/rulesOfHooks: add rule to check for non-function return from useEffect about react

[noahtallen]

I opened a related issue in the DT repo, for reference: DefinitelyTyped/DefinitelyTyped#65890. Unfortunately, the types as they exist aren't strong enough to prevent crashes.

[vkurchatkin]

This has nothing to do with rules of hooks. What you want is type checking, that is what TypeScript is for

[jlbooker]

@vkurchatkin Yes, a realize a full and complete solution to this requires a type checking system to fully evaluate the return type. However, it seems there are at least a few cases we could check for with lint rules, and that would handle 95% of the basic cases. For example, I came upon uses return "none"; and return null;, which are clearly not allowed and easily caught by a lint rule. Anything other than a bare return, undefined, or an arrow function is probably an error.

[noahtallen]

Looks like it is simply impossible to catch this type of issue with TS, which is suuuper unfortunate.

Honestly, I really wish that React didn't crash here. IMO, it's unlikely that most expect a return value to do anything at all. For example, inline callbacks:

// returns whatever `doSomething` returns, or false, but I wouldn't expect the return value to do anything

useEffect( () => checkSomething && doSomething() );

[maximejen]

Any update on this issue ?
With React 18 it looks like return undefined; or doing a return ; is also crashing, which was not the case in React 17.
We have a huge code base, and there is no way I can do a regexp that complicated, and a global search of all useEffects is not even an option.