require that promise-returning functions that could throw are async

[turadg]

What is the Problem Being Solved?

When a sync function returns a Promise, it could throw before the promise is returned. That forces complexity on the caller to handle both exceptions and rejected promises.

Description of the Design

https://typescript-eslint.io/rules/promise-function-async/ is close but has some unnecessary ugliness,

  return E.when(
    E(recoveryPurse).deposit(srcPayment, optAmountShape),
-    amount => E(recoveryPurse).withdraw(amount),
+    async amount => E(recoveryPurse).withdraw(amount),

-  return Promise.all(amounts.map(amount => E(recoveryPurse).withdraw(amount)));
+  return Promise.all(
+   amounts.map(async amount => E(recoveryPurse).withdraw(amount)),
+  );

-  await t.throwsAsync(() => brand.isMyIssuer('not an issuer'), {
+  await t.throwsAsync(async () => brand.isMyIssuer('not an issuer'), {

-export const delay = ms => new Promise(resolve => setTimeout(resolve, ms));
+export const delay = async ms =>
  new Promise(resolve => setTimeout(resolve, ms));

-  return Promise.all(amounts.map(amount => E(recoveryPurse).withdraw(amount)));
+  return Promise.all(
+    amounts.map(async amount => E(recoveryPurse).withdraw(amount)),
+  );

Take their rule and put it into an Agoric eslint plugin (#10665), adding new config options. It should be backwards compatible with typescript-eslint so we can propose adding the features upstream.

A new option like allowBlockless should not flag:

• a block-less arrow function
• which only contains expressions that cannot throw
  • calling a promise returning function is assumed to not throw
  • E(foo).bar is known to not throw

We might also need a safePromisNames option to express that EGetters can't throw.

If it's too difficult to generalize for typescript-eslint it could migrate to Endo instead.

Security Considerations

Scaling Considerations

Test Plan

Upgrade Considerations