chore(index.d.ts): exclude methods defined in interface from lean doc…

…uments

Address some feedback from @taxilian

Re: #8108

index.d.ts

@@ -1704,7 +1704,10 @@ declare module "mongoose" {
 
   export type DocumentDefinition<T> = Omit<T, Exclude<keyof Document, '_id'>>;
 
-  export type LeanDocument<T> = Omit<T, Exclude<keyof Document, '_id'>>;
+  type FunctionPropertyNames<T> = { 
+    [K in keyof T]: T[K] extends Function ? K : never 
+  }[keyof T];
+  export type LeanDocument<T> = Omit<Omit<T, Exclude<keyof Document, '_id'>>, FunctionPropertyNames<T>>;
 
   class QueryCursor<DocType extends Document> extends stream.Readable {
     /**

test/typescript/leanDocuments.ts

@@ -5,19 +5,26 @@ const schema: Schema = new Schema({ name: { type: 'String' } });
 interface ITest extends Document {
   _id?: Types.ObjectId,
   name?: string;
+  testMethod: () => number;
 }
 
+schema.method('testMethod', () => 42);
+
 const Test = model<ITest>('Test', schema);
 
 void async function main() {
   const doc: ITest = await Test.findOne();
 
+  doc.testMethod();
+
   const pojo = doc.toObject();
   await pojo.save();
 
   const _doc = await Test.findOne().lean();
   await _doc.save();
 
+  _doc.testMethod();
+
   const hydrated = Test.hydrate(_doc);
   await hydrated.save();
 }();

test/typescript/main.test.js

@@ -125,9 +125,10 @@ describe('typescript syntax', function() {
     if (process.env.D && errors.length) {
       console.log(errors);
     }
-    assert.equal(errors.length, 2);
+    assert.equal(errors.length, 3);
     assert.ok(errors[0].messageText.includes('Property \'save\' does not exist'), errors[0].messageText);
     assert.ok(errors[1].messageText.includes('Property \'save\' does not exist'), errors[0].messageText);
+    assert.ok(errors[2].messageText.includes('Property \'testMethod\' does not exist'), errors[0].messageText);
   });
 });