Added custom exception for indexers being treated as properties during serialization (#885)

Mirrors #884 on the maintenance branch

Author: michelebastione

src/MiniExcel/Exceptions/MiniExcelNotSerializableException.cs

@@ -0,0 +1,15 @@
+using System;
+using System.Reflection;
+
+namespace MiniExcelLibs.Exceptions
+{
+    public class MiniExcelNotSerializableException : InvalidOperationException
+    {
+        public MemberInfo Member { get; }
+        
+        public MiniExcelNotSerializableException(string message, MemberInfo member) :  base(message)
+        {
+            Member = member;
+        }
+    }
+}

src/MiniExcel/Reflection/Property.cs

@@ -2,6 +2,7 @@
 using System.Collections.Concurrent;
 using System.Linq;
 using System.Reflection;
+using MiniExcelLibs.Exceptions;
 
 namespace MiniExcelLibs
 {
@@ -18,7 +19,13 @@ public Property(PropertyInfo property)
         {
             Name = property.Name;
             Info = property;
-
+            
+            if (property.GetIndexParameters().Length != 0)
+            {
+                const string msg = "Types containing indexers cannot be serialized. Please remove them or decorate them with MiniExcelIgnoreAttribute.";
+                throw new MiniExcelNotSerializableException(msg, property);
+            }
+            
             if (property.CanRead)
             {
                 CanRead = true;

tests/MiniExcelTests/MiniExcelIssueTests.cs

@@ -4719,4 +4719,22 @@ public void TestIssue876()
             MiniExcel.SaveAs(outputPath.ToString(), sheets);
         });
     }
+    
+    private class Issue880
+    {
+        public string Test { get; set; }
+        public string this[int i] => "";
+    }
+    
+    [Fact]
+    public void TestIssue880_ShouldThrowNotSerializableException()
+    {
+        Issue880[] toExport = [new() { Test = "test" }];
+        
+        Assert.Throws<MiniExcelNotSerializableException>(() =>
+        {
+            using var ms = new MemoryStream();
+            ms.SaveAs(toExport);
+        });
+    }
 }