MonoMod · monomod · May 26, 2025 · May 31, 2025 · May 31, 2025 · Aug 5, 2025
diff --git a/src/MonoMod.UnitTest/Github/Issue230.cs b/src/MonoMod.UnitTest/Github/Issue230.cs
@@ -0,0 +1,119 @@
+extern alias New;
+using New::MonoMod.RuntimeDetour;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using Mono.Cecil.Cil;
+using MonoMod.Cil;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace MonoMod.UnitTest.Github
+{
+    public class Issue230 : TestBase
+    {
+        public Issue230(ITestOutputHelper helper) : base(helper)
+        {
+        }
+
+        private class SomeType
+        {
+            public int index { get; set; }
+        }
+
+        private static readonly List<SomeType>[] _list = new List<SomeType>[4];
+
+        [Fact]
+        public void ILHookOnMonoShouldSucceed()
+        {
+            for (var i = 0; i < 3; i++)
+            {
+                _list[i] = new List<SomeType>(3);
+            }
+
+            var original = typeof(Issue230).GetMethod(nameof(Original), BindingFlags.Static | BindingFlags.NonPublic);
+
+            // Verify that applying multiple ILHooks does not throw an exception
+            using (new ILHook(original, Hook1)) 
+            using (new ILHook(original, Hook2))
+            {
+                // Running the method should succeed
+                Original();
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        private static void Original()
+        {
+            var random = new Random();
+            var enumerable = Enumerable.Range(0, 50).Select(i => new SomeType { index = random.Next(50) });
+
+            foreach (var item in enumerable)
+            {
+                _ = _list[item.index];
+            }
+        }
+
+        private static void Hook1(ILContext il)
+        {
+            var cursor = new ILCursor(il);
+
+            cursor.GotoNext(
+                MoveType.After,
+                x => x.MatchLdloc(out _),
+                x => x.Match(OpCodes.Callvirt),
+                x => x.Match(OpCodes.Ldelem_Ref));
+
+            cursor.Index--;
+
+            cursor.Emit(OpCodes.Ldc_I4_0);
+            cursor.Emit(OpCodes.Ldc_I4_3);
+            cursor.EmitCall(typeof(Issue230).GetMethod(nameof(Clamp), new[] { typeof(int), typeof(int), typeof(int) }));
+        }
+
+        private static void Hook2(ILContext il)
+        {
+            var cursor = new ILCursor(il);
+
+            if (!cursor.TryGotoNext(
+                    MoveType.After,
+                    x => x.MatchLdloc(out _),
+                    x => x.Match(OpCodes.Callvirt),
+                    x => x.Match(OpCodes.Ldelem_Ref)))
+            {
+                cursor.Index = cursor.Instrs.Count;
+            }
+            else
+            {
+                cursor.Index--;
+            }
+
+            cursor.Emit(OpCodes.Ldc_I4_0);
+            cursor.Emit(OpCodes.Ldc_I4_3);
+            cursor.EmitCall(typeof(Issue230).GetMethod(nameof(Clamp), new[] { typeof(int), typeof(int), typeof(int) })!);
+
+            if (!cursor.TryGotoNext(
+                    MoveType.Before,
+                    x => x.MatchLdloc(out _),
+                    x => x.Match(OpCodes.Callvirt),
+                    x => x.MatchStloc(out _)))
+            {
+                cursor.Index = cursor.Instrs.Count;
+            }
+
+            cursor.Emit(OpCodes.Ret);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int Clamp(int value, int min, int max)
+        {
+            if (min > max)
+                throw new ArgumentException($"'{min}' cannot be greater than {max}.");
+            if (value < min)
+                return min;
+            return value > max ? max : value;
+        }
+    }
+}