[@grpc/grpc-js] Broken ClientOptions types

[smolijar]

Problem description

ClientOptions type is intersection of its definition and Partial<ChannelOptions>. Partial<ChannelOptions> defines constants and index signature [key: string]: string | number | undefined;, which contradicts with ClientOptions defintions: Since intersection is used, all string attributes of ClientOptions are required to be string | number | undefined, which contradicts for example ClientOptions's interceptors, which is array of functions.

This issue makes the new interceptor unusable with TS without force-casting.

Reproduction steps

import { Interceptor, Client, ChannelCredentials } from "@grpc/grpc-js";

const interceptor = (null as any) as Interceptor; // just type demonstration
new Client("", ChannelCredentials.createInsecure(), {
  interceptors: [interceptor], // triggers error, whole options object
});

Argument of type '{ interceptors: Interceptor[]; }' is not assignable to parameter of type 'ClientOptions'.
  Type '{ interceptors: Interceptor[]; }' is not assignable to type 'Partial<ChannelOptions>'.
    Property 'interceptors' is incompatible with index signature.
      Type 'Interceptor[]' is not assignable to type 'string | number'.
        Type 'Interceptor[]' is not assignable to type 'string'.

Environment

• @grpc/js 1.1.5
• Tested on TS 4.0.2 and 3.9.7

Additional context

We could solve this either by removing the index signature or removing it before the type intersection, which is a bit hard on eyes with generics. Will try to post a PR soon.