Fix Expression constant folding inside of MemberInitExpression

Microsoft.Azure.Cosmos/src/Linq/SubtreeEvaluator.cs

@@ -5,6 +5,7 @@ namespace Microsoft.Azure.Cosmos.Linq
 {
     using System;
     using System.Collections.Generic;
+    using System.Linq;
     using System.Linq.Expressions;
     using System.Reflection;
 
@@ -40,7 +41,9 @@ public override Expression Visit(Expression expression)
 
         protected override Expression VisitMemberInit(MemberInitExpression node)
         {
-            return node;
+            return Expression.MemberInit(
+                node.NewExpression,
+                node.Bindings.Select(binding => this.VisitMemberBinding(binding)));
         }
 
         private Expression EvaluateMemberAccess(Expression expression)

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/Linq/ConstantEvaluatorTests.cs

@@ -0,0 +1,46 @@
+//------------------------------------------------------------
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+//------------------------------------------------------------
+
+namespace Microsoft.Azure.Cosmos.Linq
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Globalization;
+    using System.IO;
+    using System.Linq;
+    using System.Linq.Expressions;
+    using System.Reflection;
+    using System.Text.Json.Serialization;
+    using global::Azure.Core.Serialization;
+    using Microsoft.Azure.Cosmos.Serializer;
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+    using Newtonsoft.Json;
+    using Newtonsoft.Json.Converters;
+
+    [TestClass]
+    public class ConstantEvaluatorTests
+    {
+        [TestMethod]
+        public void ClosuresAreEvaluated()
+        {
+            int a = 1;
+            // In class member init
+            Expression<Func<int, object>> closureInClassExpression = x => new TestClass { Property = x + a };
+            Expression<Func<int, object>> closureInClassExpressionExpected = x => new TestClass { Property = x + 1 };
+            Expression closureInClassExpressionActual = ConstantEvaluator.PartialEval(closureInClassExpression.Body);
+            Assert.AreEqual(closureInClassExpressionExpected.Body.ToString(), closureInClassExpressionActual.ToString());
+
+            // In anonymous object
+            Expression<Func<int, object>> closureInAnonymousObjectExpression = x => new { Property = x + a };
+            Expression<Func<int, object>> closureInAnonymousObjectExpressionExpected = x => new { Property = x + 1 };
+            Expression closureInAnonymousObjectExpressionActual = ConstantEvaluator.PartialEval(closureInAnonymousObjectExpression.Body);
+            Assert.AreEqual(closureInAnonymousObjectExpressionExpected.Body.ToString(), closureInAnonymousObjectExpressionActual.ToString());
+        }
+
+        private class TestClass
+        {
+            public int Property { get; set; }
+        }
+    }
+}