From 0f4d1d08c4dc5a2220780d0bed2b02c5a135510c Mon Sep 17 00:00:00 2001
From: Michele Bastione <michele.bastione@gmail.com>
Date: Tue, 7 Oct 2025 23:38:44 +0200
Subject: [PATCH] Added custom exception for indexers being treated as
 properties during serialization

Mirrors #884 on the maintenance branch
---
 .../MiniExcelNotSerializableException.cs       | 15 +++++++++++++++
 src/MiniExcel/Reflection/Property.cs           |  9 ++++++++-
 tests/MiniExcelTests/MiniExcelIssueTests.cs    | 18 ++++++++++++++++++
 3 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100644 src/MiniExcel/Exceptions/MiniExcelNotSerializableException.cs

diff --git a/src/MiniExcel/Exceptions/MiniExcelNotSerializableException.cs b/src/MiniExcel/Exceptions/MiniExcelNotSerializableException.cs
new file mode 100644
index 00000000..f86f82cf
--- /dev/null
+++ b/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;
+        }
+    }
+}
diff --git a/src/MiniExcel/Reflection/Property.cs b/src/MiniExcel/Reflection/Property.cs
index 2156402e..61cfef96 100644
--- a/src/MiniExcel/Reflection/Property.cs
+++ b/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;
diff --git a/tests/MiniExcelTests/MiniExcelIssueTests.cs b/tests/MiniExcelTests/MiniExcelIssueTests.cs
index a4be971d..1cdc95c9 100644
--- a/tests/MiniExcelTests/MiniExcelIssueTests.cs
+++ b/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);
+        });
+    }
 }
\ No newline at end of file