Updater form of setters throw when current value is loading or in an error state.

[wojtekmaj]

I have selector that asynchronously loads data and atom that uses it as its default value:

export const asyncDefaultAccounts = selector({
  key: 'asyncAccountsState',
  async get() {
    const response = await get('/api/accounts');
    return response;
  };
});

export const accountsState = atom({
  key: 'accountsState',
  default: asyncDefaultAccounts,
});

So far, so good. Works flawlessly.

But I also have a form that adds account and, on success, appends newly created account to the list:

const setAccounts = useSetRecoilState(accountsState);

function onSubmit() {
  const response = await post('/api/accounts', body);

  setAccounts((oldAccounts) => [
    ... oldAccounts,
    response,
  ]);
}

This forks good enough. UNLESS... I've never been to account list page and consequently have never subscribed to accountsState. In such case, the following error appears:

Tried to set the value of Recoil selector accountsState__withFallback using an updater function, but it is an async selector in a pending or error state; this is not supported.

An obvious fix would be to subscribe to Recoil state:

-const setAccounts = useSetRecoilState(accountsState);
+const [accounts, setAccounts] = useRecoilState(accountsState);

but this causes unnecessary GET from /api/accounts. Is there a way I could tell Recoil to set Recoil state, but only if said state has already been fetched, without subscribing to it?

[drarmstr]

Yeah, we're currently discussing the semantics of asynchronous atom states and how to manage the updater form. Considering API tradeoffs now...

[drarmstr]

Related to #237, #762

[jh0l]

any updates?