make typesafe custom level loggers great again

pass in logger's generic based on value of customLevels and/or logger.customLevels option

TS does not like what I did here so I added a ts-expect-error to silence it
but it does work as expected, this is covered in the tests

fixes #317 and supersedes #318 if merged

index.d.ts

@@ -12,13 +12,17 @@ import { IncomingMessage, ServerResponse } from 'http';
 import pino from 'pino';
 import { err, req, res, SerializedError, SerializedRequest, SerializedResponse } from 'pino-std-serializers';
 
-declare function PinoHttp<IM = IncomingMessage, SR = ServerResponse, CustomLevels extends string = never>(opts?: Options<IM, SR>, stream?: pino.DestinationStream): HttpLogger<IM, SR, CustomLevels>;
+declare function PinoHttp< IM = IncomingMessage, SR = ServerResponse, Opts = Options<IM, SR>>(opts?: Opts, stream?: pino.DestinationStream): HttpLogger<IM, SR, Opts>;
 
 declare function PinoHttp<IM = IncomingMessage, SR = ServerResponse>(stream?: pino.DestinationStream): HttpLogger<IM, SR>;
 
-export interface HttpLogger<IM = IncomingMessage, SR = ServerResponse, CustomLevels extends string = never> {
-    (req: IM, res: SR, next?: () => void): void;
-    logger: pino.Logger<CustomLevels>;
+export interface HttpLogger<IM = IncomingMessage, SR = ServerResponse, Opts = Options<IM, SR>> {
+  (req: IM, res: SR, next?: () => void): void;
+  logger: pino.Logger<
+    // this makes custom level loggers typesafe, but TS complains
+    // @ts-expect-error
+    keyof Opts["customLevels"] | keyof Opts["logger"]["customLevels"]
+  >;
 }
 export type ReqId = number | string | object;
 

index.test-d.ts

@@ -206,10 +206,21 @@ const httpServerListener: RequestListener = (request, response) => {
   response.end("Hello world");
 };
 
-// custom levels added in the options should be available
+// custom levels added in the options should be available/typesafe
 // on the logger returned by pino-http
-pinoHttp<IncomingMessage, ServerResponse, 'bark'>({
-    customLevels: {
-        bark: 25,
-    }
-}).logger.bark("arf arf");
+pinoHttp({ customLevels: { bark: 25 } }).logger.bark("arf arf");
+
+// custom levels added to the logger passed in the options should be available/typesafe
+pinoHttp({ logger: pino({ customLevels: { bark: 35 } }) }).logger.bark(
+  "arf arf"
+);
+
+// if custom levels are passed in both the customLevels option and via the logger
+// all the levels should be available/typesafe
+const { logger: customLevelsLogger } = pinoHttp({
+  logger: pino({ customLevels: { meow: 35 } }),
+  customLevels: { bark: 25 },
+});
+
+customLevelsLogger.meow("meow meow");
+customLevelsLogger.bark("arf arf");