Added custom exception for indexers being treated as properties during serialization (#884)

Author: michelebastione

src/MiniExcel.Core/Exceptions/MiniExcelNotSerializableException.cs

@@ -0,0 +1,7 @@
+namespace MiniExcelLib.Core.Exceptions;
+
+public class MiniExcelNotSerializableException(string message, MemberInfo member) 
+    : InvalidOperationException(message)
+{
+    public MemberInfo Member { get; } = member;
+}

src/MiniExcel.Core/Reflection/MiniExcelProperty.cs

@@ -1,3 +1,5 @@
+using MiniExcelLib.Core.Exceptions;
+
 namespace MiniExcelLib.Core.Reflection;
 
 public abstract class Member;
@@ -12,6 +14,12 @@ public MiniExcelProperty(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/MiniExcel.Core.Tests/MiniExcelIssueTests.cs

@@ -3710,4 +3710,22 @@ public void TestIssue876()
             _excelExporter.Export(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();
+            _excelExporter.Export(ms, toExport);
+        });
+    }
 }