Crash caused by <PrivateImplementationDetails> in MonoMod.MonoModRules

[WEGFan]

Description

MonoMod will crash if a method in MonoMod.MonoModRules contains <PrivateImplementationDetails> called during patch. Mostly because of initializing an array of primitive types or having a switch with more than 6 case and the compiler optimizes the code to <PrivateImplementationDetails>.

MonoMod version: 21.6.21.1

Example

SharpLab link

namespace MonoMod {
    public static class MonoModRules {
        static MonoModRules() {
            bool[] boolArray = {true, true, true, true, true, true, true, true};
            byte[] byteArray = {1, 2, 3};
            sbyte[] sbyteArray = {-1, 2, -3};
            char[] charArray = {'a', 'b', 'c'};
            short[] shortArray = {-1, 2, -3};
            ushort[] ushortArray = {1, 2, 3};
            int[] intArray = {-1, 2, -3};
            nint[] nintArray = {-1, 2, -3};
            uint[] uintArray = {1, 2, 3};
            nuint[] nuintArray = {1, 2, 3};
            long[] longArray = {-1, 2, -3};
            ulong[] ulongArray = {1, 2, 3};
            float[] floatArray = {-1, 2, -3};
            double[] doubleArray = {-1, 2, -3};
            string str = "a";
            switch (str) {
                case "a":
                    break;
                case "b":
                    break;
                case "c":
                    break;
                case "d":
                    break;
                case "e":
                    break;
                case "f":
                    break;
                case "g":
                    break;
            }
        }
    }
}

Compile this code to MonoMod.PrivateImplementationDetails.mm.dll and run MonoMod.exe MonoMod.exe, then MonoMod will crash with the following log:

MonoMod 21.6.21.1
[MonoMod] Reading input file into module.
[MonoMod] [Main] Scanning for mods in directory.
[MonoMod] [ReadMod] Loading mod dir: D:\My Documents\Rider\PrivateImplementationDetailsTest\PrivateImplementationDetailsTest.Mod.mm\bin\net452
[MonoMod] [ReadMod] Loading mod: D:\My Documents\Rider\PrivateImplementationDetailsTest\PrivateImplementationDetailsTest.Mod.mm\bin\net452\MonoMod.PrivateImplementationDetailsTest.mm.dll
[MonoMod] [Main] mm.AutoPatch();
[MonoMod] [AutoPatch] Parsing rules in loaded mods
[MonoMod] [RulesModder] [Write] Writing modded module into output stream.
System.TypeInitializationException: The type initializer for 'MonoMod.MonoModRules' threw an exception. ---> System.MissingFieldException: Field not found: '<PrivateImplementationDetails>.039058C6F2C0CB492C533B0A4D14EF77CC0F78ABCCCED5287D84A1A2011CFB81'.
   at MonoMod.MonoModRules..cctor()
   --- End of inner exception stack trace ---
   at System.Runtime.CompilerServices.RuntimeHelpers._RunClassConstructor(RuntimeType type)
   at MonoMod.InlineRT.MonoModRulesManager.ExecuteRules(MonoModder self, TypeDefinition orig)
   at MonoMod.MonoModder.ParseRules(ModuleDefinition mod)
   at MonoMod.MonoModder.AutoPatch()
   at MonoMod.Program.Main(String[] args)