From a68cc5c4b723639e019e9a986b3abde97027e353 Mon Sep 17 00:00:00 2001
From: Valeri Karpov <val@karpov.io>
Date: Mon, 15 Apr 2024 12:59:30 -0400
Subject: [PATCH] types(query+populate): apply populate overrides to doc
 `toObject()` result

Fix #14441
---
 test/types/populate.test.ts | 46 +++++++++++++++++++++++++++++++++++++
 types/query.d.ts            | 16 +++++++++++--
 2 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/test/types/populate.test.ts b/test/types/populate.test.ts
index c846e7b346e..fe9afa4ef84 100644
--- a/test/types/populate.test.ts
+++ b/test/types/populate.test.ts
@@ -373,3 +373,49 @@ async function gh13070() {
   const doc2 = await Child.populate<{ child: IChild }>(doc, 'child');
   const name: string = doc2.child.name;
 }
+
+function gh14441() {
+  interface Parent {
+    child?: Types.ObjectId;
+    name?: string;
+  }
+  const ParentModel = model<Parent>(
+    'Parent',
+    new Schema({
+      child: { type: Schema.Types.ObjectId, ref: 'Child' },
+      name: String
+    })
+  );
+
+  interface Child {
+    name: string;
+  }
+  const childSchema: Schema = new Schema({ name: String });
+  model<Child>('Child', childSchema);
+
+  ParentModel.findOne({})
+    .populate<{ child: Child }>('child')
+    .orFail()
+    .then(doc => {
+      expectType<string>(doc.child.name);
+      const docObject = doc.toObject();
+      expectType<string>(docObject.child.name);
+    });
+
+  ParentModel.findOne({})
+    .populate<{ child: Child }>('child')
+    .lean()
+    .orFail()
+    .then(doc => {
+      expectType<string>(doc.child.name);
+    });
+
+  ParentModel.find({})
+    .populate<{ child: Child }>('child')
+    .orFail()
+    .then(docs => {
+      expectType<string>(docs[0]!.child.name);
+      const docObject = docs[0]!.toObject();
+      expectType<string>(docObject.child.name);
+    });
+}
diff --git a/types/query.d.ts b/types/query.d.ts
index 1e97ad6331d..71e3a03ec24 100644
--- a/types/query.d.ts
+++ b/types/query.d.ts
@@ -205,6 +205,18 @@ declare module 'mongoose' {
     ? (ResultType extends any[] ? Require_id<FlattenMaps<RawDocType>>[] : Require_id<FlattenMaps<RawDocType>>)
     : ResultType;
 
+  type MergePopulatePaths<RawDocType, ResultType, QueryOp, Paths, TQueryHelpers> = QueryOp extends QueryOpThatReturnsDocument
+    ? ResultType extends null
+      ? ResultType
+      : ResultType extends (infer U)[]
+        ? U extends Document
+          ? HydratedDocument<MergeType<RawDocType, Paths>, Record<string, never>, TQueryHelpers>[]
+          : (MergeType<U, Paths>)[]
+        : ResultType extends Document
+          ? HydratedDocument<MergeType<RawDocType, Paths>, Record<string, never>, TQueryHelpers>
+          : MergeType<ResultType, Paths>
+    : MergeType<ResultType, Paths>;
+
   class Query<ResultType, DocType, THelpers = {}, RawDocType = DocType, QueryOp = 'find'> implements SessionOperation {
     _mongooseOptions: MongooseQueryOptions<DocType>;
 
@@ -608,7 +620,7 @@ declare module 'mongoose' {
       model?: string | Model<any, THelpers>,
       match?: any
     ): QueryWithHelpers<
-      UnpackedIntersection<ResultType, Paths>,
+      MergePopulatePaths<RawDocType, ResultType, QueryOp, Paths, THelpers>,
       DocType,
       THelpers,
       UnpackedIntersection<RawDocType, Paths>,
@@ -617,7 +629,7 @@ declare module 'mongoose' {
     populate<Paths = {}>(
       options: PopulateOptions | (PopulateOptions | string)[]
     ): QueryWithHelpers<
-      UnpackedIntersection<ResultType, Paths>,
+      MergePopulatePaths<RawDocType, ResultType, QueryOp, Paths, THelpers>,
       DocType,
       THelpers,
       UnpackedIntersection<RawDocType, Paths>,