Prevent InvalidOperationException when custom equality operator return type is not Boolean (#489)

Co-authored-by: Alexander Syrtsev <syrtsev.alexander@devexpress.com>

Author: JaleChaki

net/DevExtreme.AspNet.Data.Tests/CustomEqualTests.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using Xunit;
 
 namespace DevExtreme.AspNet.Data.Tests {
@@ -30,6 +31,18 @@ public void WithOperator() {
             );
         }
 
+        [Fact]
+        public void WrongOperator() {
+            TestFilter(
+                new[] {
+                    new DataItemWrongOperator { Value = 1 },
+                    new DataItemWrongOperator { Value = 2 }
+                },
+                "=", new DataItemWrongOperator { Value = 1 },
+                ".Where(obj => Equals(obj, {1}))"
+            );
+        }
+
         [Fact]
         public void Struct() {
             TestFilter(
@@ -82,6 +95,22 @@ public override string ToString()
                 => "{" + Value + "}";
         }
 
+        class DataItemWrongOperator {
+            public int Value;
+            [SuppressMessage("Style", "IDE0060")]
+            public static DataItemWrongOperator operator ==(DataItemWrongOperator l, DataItemWrongOperator r)
+                => null;
+            [SuppressMessage("Style", "IDE0060")]
+            public static DataItemWrongOperator operator !=(DataItemWrongOperator l, DataItemWrongOperator r)
+                => null;
+            public override bool Equals(object obj)
+                => Value == (obj as DataItemWrongOperator).Value;
+            public override int GetHashCode()
+                => Value.GetHashCode();
+            public override string ToString()
+                => "{" + Value + "}";
+        }
+
         struct DataItemStruct {
             public int Value;
             public override bool Equals(object obj)

net/DevExtreme.AspNet.Data/FilterExpressionCompiler.cs

@@ -168,7 +168,8 @@ bool HasEqualityOperator(Type type) {
             if(type == typeof(Guid) || type == typeof(DateTimeOffset) || type == typeof(TimeSpan))
                 return true;
 
-            return type.GetMethod("op_Equality", new[] { type, type }) != null;
+            var operatorMethod = type.GetMethod("op_Equality", new[] { type, type });
+            return operatorMethod != null && operatorMethod.ReturnType == typeof(bool);
         }
 
         bool HasComparisonOperator(Type type) {