types: Fixes and improves Query.projection method signature

index.d.ts

@@ -2125,6 +2125,8 @@ declare module 'mongoose' {
 
   type UnpackedIntersection<T, U> = T extends (infer V)[] ? (V & U)[] : T & U;
 
+  type ProjectionFields<DocType> = {[Key in keyof Omit<LeanDocument<DocType>, '__v'>]?: any} & Record<string, any>;
+
   class Query<ResultType, DocType, THelpers = {}, RawDocType = DocType> {
     _mongooseOptions: MongooseQueryOptions;
 
@@ -2411,7 +2413,9 @@ declare module 'mongoose' {
     populate<Paths = {}>(options: PopulateOptions | Array<PopulateOptions>): QueryWithHelpers<UnpackedIntersection<ResultType, Paths>, DocType, THelpers, RawDocType>;
 
     /** Get/set the current projection (AKA fields). Pass `null` to remove the current projection. */
-    projection(fields?: any | null): this;
+    projection(): ProjectionFields<DocType> | null;
+    projection(fields: null): null;
+    projection(fields?: ProjectionFields<DocType> | string): ProjectionFields<DocType>;
 
     /** Determines the MongoDB nodes from which to read. */
     read(pref: string | mongodb.ReadPreferenceMode, tags?: any[]): this;

test/typescript/queries.ts

@@ -116,6 +116,17 @@ query instanceof Query;
 Test.findOne().where({ name: 'test' });
 Test.where().find({ name: 'test' });
 
+// Projection
+const p0: Record<string, number> = Test.find().projection({
+  age: true,
+  parent: 1,
+  'docs.id': 1
+});
+const p1: Record<string, number> = Test.find().projection('age docs.id');
+const p2: Record<string, number> | null = Test.find().projection();
+const p3: null = Test.find().projection(null);
+
+
 // Super generic query
 function testGenericQuery(): void {
   interface CommonInterface<T> extends Document {
@@ -200,4 +211,4 @@ async function gh11156(): Promise<void> {
   const User: Model<User> = model<User>('User', schema);
 
   const overwritten: User = await User.findOne<Pick<User, 'name'>>({}).orFail();
-}
+}