feat: types to infer middleware params

[luixo]

Describe the feature you'd like to request

Hi,
I have a procedure (technically, it's called procedure builder as an internal type) that is updating context. I want to reuse object of this context in an external function, but I have hard time extracting it.
E.g.:

import { initTRPC, TRPCError } from "@trpc/server";

type UnauthorizedContext = {
  req: NextApiRequest;
  res: NextApiResponse;
};

const { router, procedure, middleware } = initTRPC.context<UnauthorizedContext>().create();

const authProcedure = t.procedure.use(
  t.middleware(async ({ ctx, next }) => {
    const authObject = getAuthObject(ctx.req);
    if (!authObject) {
      throw new TRPCError({
        code: "UNAUTHORIZED",
        message: "Not authorized",
      });
    }
    return next({
      ctx: { ...ctx, auth: authObject, },
    });
  }),
);

type Auth = {
  // this is type I want to infer
}
const getDataByAuth = (auth: Auth) => {
  // do stuff
}

const procedure = authProcedure
  .mutation(async ({ ctx }) => {
    const data = getDataByAuth(ctx.auth);
    return data;
  });

export const appRouter = t.router({ procedure });

Currently I infer type like that:

type ProcedureParams<P extends ProcedureBuilder<any>> = P extends ProcedureBuilder<infer X> ? X : never;
type ProcedureContext<P extends ProcedureBuilder<any>> = ProcedureParams<P>["_ctx_out"];
type Auth = ProcedureContext<typeof authProcedure>

I believe this might be extract as a helper.

Describe the solution you'd like to see

type ProcedureParams<P extends ProcedureBuilder<any>> = P extends ProcedureBuilder<infer X> ? X : never;
export type inferProcedureContext<P extends ProcedureBuilder<any>> = ProcedureParams<P>["_ctx_out"];
// This might be useful to someone as well though I don't have a use case
export type inferProcedureMeta<P extends ProcedureBuilder<any>> = ProcedureParams<P>["_meta"];

Describe alternate solutions

Bring your own type inferrers

Additional information

No response

👨‍👧‍👦 Contributing

• 🙋‍♂️ Yes, I'd be down to file a PR implementing this feature!

Funding

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