fix(index.d.ts): allow calling mongoose.model() and Connection#model() with model as generic param

Fix #9678

Author: vkarpov15

index.d.ts

@@ -242,6 +242,12 @@ declare module "mongoose" {
 
     /** Defines or retrieves a model. */
     model<T extends Document>(name: string, schema?: Schema, collection?: string): Model<T>;
+    model<T extends Document, U extends Model<T>>(
+      name: string,
+      schema?: Schema,
+      collection?: string,
+      skipInit?: boolean
+    ): U;
 
     /** Returns an array of model names created on this connection. */
     modelNames(): Array<string>;

test/typescript/models.ts

@@ -23,3 +23,17 @@ const ExpiresSchema = new Schema({
 });
 
 const aggregated: Promise<Document> = Test.aggregate([]).then(res => res[0]);
+
+interface IProject extends Document {
+  name: String;
+}
+
+interface ProjectModel extends Model<IProject> {
+  myStatic(): number;
+}
+
+const projectSchema: Schema = new Schema({ name: String });
+projectSchema.statics.myStatic = () => 42;
+
+const Project = connection.model<IProject, ProjectModel>('Project', projectSchema);
+Project.myStatic();