Replace Promise with PromiseLike in resolver types

[qsona]

Is your feature request related to a problem? Please describe.

When using non-native Promise library like Bluebird, the return type of resolvers will often be PromiseLike, but it doesn't adapt with generated resolver-types because the generated code is using native Promise type.

graphql-code-generator/packages/plugins/typescript/resolvers/src/index.ts

Line 138 in 8e4d582

) => Promise<TResult> | TResult;`;

sample code:

const resolvers: Resolvers = {
  Query: {
    name: () => { // string field
      return Promise.resolve('1') as PromiseLike<string>
    }
  }
}

error message:

(...omitted)
    Type 'PromiseLike<string>' is not assignable to type 'ResolverTypeWrapper<string> | Promise<ResolverTypeWrapper<string>>'.
      Type 'PromiseLike<string>' is missing the following properties from type 'Promise<ResolverTypeWrapper<string>>': catch, finally, [Symbol.toStringTag]

Describe the solution you'd like

Can Promise be just replaced with PromiseLike?

📝 https://github.com/graphql/graphql-js/blob/0fef3c49907b63b1ea5a4ff1da7011775f465fc2/src/execution/execute.ts#L505-L506

Describe alternatives you've considered

We can customize it by using customResolverFn.

So this feature request is not mandatory, but I feel it's better if I don't have to customize and manage it in our code.

Additional context

[dotansimha]

Hi @qsona ! This is a great idea. What do you think about creating a PR for this? :)

[qsona]

Yes, I'd like to try this :)

[qsona]

I realized it's necessary to clarify if graphql-js expects PromiseLike value as resolver's return value. I'm waiting and seeing the discussion on graphql-js.
graphql/graphql-js#3243 (review)

[qsona]

Hi, I'm sorry for not updating this long time. My idea was simply replacing Promise with PromiseLike (firstly in graphql-js firstly, then this repository) but it seems it needs some works to be accepted in graphql-js. Actually I'm not so enthusiastic for this issue (because casting PromiseLike to Promise is easy by using async-await) so please feel free to close this issue and PR.