research: configure eslint to prefer return next() when no await is needed

[gao-sun]

No description provided.

[wangsijie]

Koa's middleware uses ctx instead of return value, is not "pure function", so return value may not be important.

[gao-sun]

yes, just wanna align our code style.

[gao-sun]

agreed with you that return value doesn't matter.

[wangsijie]

disallow return has an adventage: prevent treating the return value as useful staff by mistake

[gao-sun]

agreed, so i added the following type in packages/core/src/include.d/koa.d.ts:

export type KoaMiddleware<T, R> = (context: T, next: KoaNext<R>) => Promise<void>;

this makes sure that middleware is a void promise which means nothing. plus, return can enable eslint check for unreachable code and save 1 LOC for every middleware that doesn't need operations after next.

also check out the official example of using return next().

[gao-sun]

tracked in https://linear.app/silverhand/issue/LOG-37/configure-eslint-to-prefer-return-next-when-no-await-is-needed