Add DestinationStreamMetadata type to pino.d.ts (#1566)

* Add DestinationStreamMetadata type to pino.d.ts

Fixes #1557

* Use symbols.needsMetadataGsym instead

* Improve DestinationStreamWithMetadata type

* Fix tsd weirdness

pino.d.ts

@@ -274,6 +274,17 @@ declare namespace pino {
         write(msg: string): void;
     }
 
+    interface DestinationStreamHasMetadata {
+      [symbols.needsMetadataGsym]: true;
+      lastLevel: number;
+      lastTime: string;
+      lastMsg: string;
+      lastObj: object;
+      lastLogger: pino.Logger;
+    }
+
+    type DestinationStreamWithMetadata = DestinationStream & ({ [symbols.needsMetadataGsym]?: false } | DestinationStreamHasMetadata);
+
     interface StreamEntry {
         stream: DestinationStream
         level?: Level
@@ -795,6 +806,7 @@ export const version: typeof pino.version;
 
 // Types
 export type Bindings = pino.Bindings;
+export type DestinationStreamWithMetadata = pino.DestinationStreamWithMetadata;
 export type Level = pino.Level;
 export type LevelWithSilent = pino.LevelWithSilent;
 export type LevelChangeEventListener = pino.LevelChangeEventListener;

test/types/pino-type-only.test-d.ts

@@ -1,7 +1,7 @@
 import { expectAssignable, expectType } from "tsd";
 
 import pino from "../../";
-import type {LevelWithSilent, Logger, LogFn, P} from "../../pino";
+import type {LevelWithSilent, Logger, LogFn, P, DestinationStreamWithMetadata } from "../../pino";
 
 // NB: can also use `import * as pino`, but that form is callable as `pino()`
 // under `esModuleInterop: false` or `pino.default()` under `esModuleInterop: true`.
@@ -14,3 +14,15 @@ expectType<P.LogFn>(log.info);
 
 const level: LevelWithSilent = 'silent';
 expectAssignable<P.LevelWithSilent>(level);
+
+function createStream(): DestinationStreamWithMetadata {
+    return { write() {} };
+}
+
+const stream = createStream();
+// Argh. TypeScript doesn't seem to narrow unless we assign the symbol like so, and tsd seems to
+// break without annotating the type explicitly
+const needsMetadata: typeof pino.symbols.needsMetadataGsym = pino.symbols.needsMetadataGsym;
+if (stream[needsMetadata]) {
+    expectType<number>(stream.lastLevel);
+}