From 4315ff5c4d1facf7c069bb227e1d779e6d3e33dc Mon Sep 17 00:00:00 2001
From: mohammad0-0ahmad <kurtular.vadisi@gmail.com>
Date: Wed, 23 Mar 2022 23:02:17 +0100
Subject: [PATCH 1/2] Improve RawDocType returned by calling populate FN

---
 test/types/populate.test.ts | 25 +++++++++++++++++++++++++
 types/index.d.ts            |  4 ++--
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/test/types/populate.test.ts b/test/types/populate.test.ts
index 6933eff6f63..12336248857 100644
--- a/test/types/populate.test.ts
+++ b/test/types/populate.test.ts
@@ -197,4 +197,29 @@ function gh11544() {
   User.findOne({}).populate({ path: 'friends', strictPopulate: false });
   User.findOne({}).populate({ path: 'friends', strictPopulate: true });
   User.findOne({}).populate({ path: 'friends', populate: { path: 'someNestedPath', strictPopulate: false } });
+}
+
+async function _11532() {
+  interface IParent {
+    name: string;
+    child: Types.ObjectId;
+  }
+  interface IChild {
+    name: string;
+  }
+
+  const parentSchema = new Schema(
+    {
+      name: { type: String, required: true },
+      child: { type: Schema.Types.ObjectId, ref: 'Child', required: true }
+    });
+
+  const parent = model<IParent>('Parent', parentSchema);
+
+  const populateQuery = parent.findOne().populate<{ child: IChild }>('child');
+  const populateResult = await populateQuery;
+  const leanResult = await populateQuery.lean();
+
+  expectType<string>(populateResult.child.name);
+  expectType<string>(leanResult.child.name);
 }
\ No newline at end of file
diff --git a/types/index.d.ts b/types/index.d.ts
index 6a5d4db9cac..951a79f6759 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -1774,8 +1774,8 @@ declare module 'mongoose' {
     polygon(path: string, ...coordinatePairs: number[][]): this;
 
     /** Specifies paths which should be populated with other documents. */
-    populate<Paths = {}>(path: string | string[], select?: string | any, model?: string | Model<any, THelpers>, match?: any): QueryWithHelpers<UnpackedIntersection<ResultType, Paths>, DocType, THelpers, RawDocType>;
-    populate<Paths = {}>(options: PopulateOptions | (PopulateOptions | string)[]): QueryWithHelpers<UnpackedIntersection<ResultType, Paths>, DocType, THelpers, RawDocType>;
+    populate<Paths = {}, TRawDocType = UnpackedIntersection<ResultType, Paths>>(path: string | string[], select?: string | any, model?: string | Model<any, THelpers>, match?: any): QueryWithHelpers<TRawDocType, DocType, THelpers, TRawDocType>;
+    populate<Paths = {}, TRawDocType = UnpackedIntersection<ResultType, Paths>>(options: PopulateOptions | (PopulateOptions | string)[]): QueryWithHelpers<TRawDocType, DocType, THelpers, TRawDocType>;
 
     /** Get/set the current projection (AKA fields). Pass `null` to remove the current projection. */
     projection(): ProjectionFields<DocType> | null;

From f28627369aa9a6a96ebe3ee5b3000db2e9a5e9b4 Mon Sep 17 00:00:00 2001
From: mohammad0-0ahmad <kurtular.vadisi@gmail.com>
Date: Sun, 27 Mar 2022 14:35:01 +0200
Subject: [PATCH 2/2] Refactor UnpackedIntersection type & some tests related
 to populate FN

---
 test/types/populate.test.ts | 9 +++++++--
 types/index.d.ts            | 2 +-
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/test/types/populate.test.ts b/test/types/populate.test.ts
index 12336248857..748434ff8e0 100644
--- a/test/types/populate.test.ts
+++ b/test/types/populate.test.ts
@@ -170,12 +170,14 @@ function gh11503() {
   const User = model<User>('friends', userSchema);
 
   User.findOne({}).populate('friends').then(user => {
-    expectType<Types.ObjectId | undefined>(user?.friends[0]);
+    if (!user) return;
+    expectType<Types.ObjectId>(user?.friends[0]);
     expectError(user?.friends[0].blocked);
     expectError(user?.friends.map(friend => friend.blocked));
   });
 
-  User.findOne({}).populate<{friends: Friend[]}>('friends').then(user => {
+  User.findOne({}).populate<{ friends: Friend[] }>('friends').then(user => {
+    if (!user) return;
     expectAssignable<Friend>(user?.friends[0]);
     expectType<boolean>(user?.friends[0].blocked);
     const firstFriendBlockedValue = user?.friends.map(friend => friend)[0];
@@ -220,6 +222,9 @@ async function _11532() {
   const populateResult = await populateQuery;
   const leanResult = await populateQuery.lean();
 
+  if (!populateResult) return;
   expectType<string>(populateResult.child.name);
+
+  if (!leanResult) return;
   expectType<string>(leanResult.child.name);
 }
\ No newline at end of file
diff --git a/types/index.d.ts b/types/index.d.ts
index 951a79f6759..1a5acb6588c 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -1469,7 +1469,7 @@ declare module 'mongoose' {
 
   type QueryWithHelpers<ResultType, DocType, THelpers = {}, RawDocType = DocType> = Query<ResultType, DocType, THelpers, RawDocType> & THelpers;
 
-  type UnpackedIntersection<T, U> = T extends (infer A)[]
+  type UnpackedIntersection<T, U> = T extends null ? null : T extends (infer A)[]
     ? (Omit<A, keyof U> & U)[]
     : keyof U extends never
     ? T