From 38c53b82c8c34d5582cc6405bb48b55e97d8dd8b Mon Sep 17 00:00:00 2001
From: Hafez <a.hafez852@gmail.com>
Date: Mon, 11 Jul 2022 14:38:22 +0200
Subject: [PATCH 1/2] test(types): test $let as a possible expression to
 $addFields

---
 test/types/PipelineStage.test.ts | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/test/types/PipelineStage.test.ts b/test/types/PipelineStage.test.ts
index 5c97a53fd41..37968a3b366 100644
--- a/test/types/PipelineStage.test.ts
+++ b/test/types/PipelineStage.test.ts
@@ -392,3 +392,26 @@ const stages3: PipelineStage[] = [
     }
   }
 ];
+
+const stages4: PipelineStage[] = [
+  {
+    $addFields: {
+      usersCount: {
+        $let: {
+          vars: {
+            users: { $push: '$user' }
+          },
+          in: {
+            $reduce: {
+              input: '$users',
+              initialValue: 0,
+              in: {
+                $cond: { if: { $isArray: '$$this' }, then: { $size: '$$this' }, else: '$$this' }
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+];

From 0897fea89af993c7adef63e1bea589db6c7256ed Mon Sep 17 00:00:00 2001
From: Hafez <a.hafez852@gmail.com>
Date: Mon, 11 Jul 2022 14:46:54 +0200
Subject: [PATCH 2/2] fix(types): add $let as a possible expression to
 $addFields

---
 types/expressions.d.ts | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/types/expressions.d.ts b/types/expressions.d.ts
index 10ee0bf1559..988b0357568 100644
--- a/types/expressions.d.ts
+++ b/types/expressions.d.ts
@@ -2448,7 +2448,8 @@ declare module 'mongoose' {
     BinaryExpression |
     FunctionExpression |
     ObjectIdExpression |
-    ConditionalExpressionOperator;
+    ConditionalExpressionOperator |
+    Expression.Let;
 
   export type ObjectIdExpression =
     TypeExpressionOperatorReturningObjectId;