A rewriter to support methodof and fieldof operations

of-rewrite.cs

using System;
using System.Collections.Generic;
using System.Linq;

using Mono.Cecil;
using Mono.Cecil.Cil;

class MethodProcessor {

	readonly MethodBody body;
	readonly MethodDefinition method;
	readonly ModuleDefinition module;

	ILProcessor il;

	VariableDefinition reflection_parameters;

	public MethodProcessor (MethodDefinition method)
	{
		this.method = method;
		this.body = method.Body;
		this.module = method.Module;
	}

	ILProcessor GetILProcessor ()
	{
		if (il != null)
			return il;

		return il = body.GetILProcessor ();
	}

	VariableDefinition GetReflectionParameters ()
	{
		if (reflection_parameters != null)
			return reflection_parameters;

		reflection_parameters = new VariableDefinition (module.Import (typeof (System.Reflection.ParameterInfo [])));
		body.Variables.Add (reflection_parameters);
		body.InitLocals = true;

		var il = GetILProcessor ();

		var instructions = new [] {
			il.Create (OpCodes.Ldtoken, method),
			il.Create (OpCodes.Call, ImportGetMethodFromHandle ()),
			il.Create (OpCodes.Callvirt, module.Import (typeof (System.Reflection.MethodBase).GetMethod ("GetParameters"))),
			il.Create (OpCodes.Stloc, reflection_parameters),
		};

		il.InsertBefore (body.Instructions [0], instructions);

		return reflection_parameters;
	}

	MethodReference ImportGetMethodFromHandle ()
	{
		return module.Import (typeof (System.Reflection.MethodBase).GetMethod ("GetMethodFromHandle", new [] { typeof (RuntimeMethodHandle) }));
	}

	MethodReference ImportGetFieldFromHandle ()
	{
		return module.Import (typeof (System.Reflection.FieldInfo).GetMethod ("GetFieldFromHandle", new [] { typeof (RuntimeFieldHandle) }));
	}

	TypeReference ImportMethodInfo ()
	{
		return method.Module.Import (typeof (System.Reflection.MethodInfo));
	}

	public void Run ()
	{
		foreach (var instruction in body.Instructions.ToArray ()) {

			MethodReference reference;
			if (!IsMethodCall (instruction, out reference))
				continue;

			if (!IsOfMethod (reference))
				continue;

			switch (reference.DeclaringType.Name) {
			case "Parameter":
				ProcessParameter (instruction);
				break;
			case "Property":
				ProcessProperty (instruction);
				break;
			case "Method":
				ProcessMethod (instruction);
				break;
			case "Field":
				ProcessField (instruction);
				break;
			case "Event":
				ProcessEvent (instruction);
				break;
			}
		}
 	}

	static bool IsOfMethod (MethodReference reference)
	{
		return reference.Name == "Of";
	}

	static bool IsMethodCall (Instruction instruction, out MethodReference reference)
	{
		reference = null;
		if (instruction.OpCode.FlowControl != FlowControl.Call)
			return false;

		reference = instruction.Operand as MethodReference;
		return reference != null;
	}

	void ProcessParameter (Instruction instruction)
	{
		var load_arg = instruction.Previous;

		var il = GetILProcessor ();

		var instructions = new [] {
			il.Create (OpCodes.Ldloc, GetReflectionParameters ()),
			il.Create (OpCodes.Ldc_I4, GetParameter (load_arg, method).Index),
			il.Create (OpCodes.Ldelem_Ref),
		};

		il.InsertBefore (load_arg, instructions);

		il.Remove (load_arg);
		il.Remove (instruction);		
	}

	static ParameterDefinition GetParameter (Instruction instruction, MethodDefinition method)
	{
		int index;
		switch (instruction.OpCode.Code) {
		case Code.Ldarg:
			return (ParameterDefinition) instruction.Operand;
		case Code.Ldarg_0:
		case Code.Ldarg_S:
			index = 0;
			break;
		case Code.Ldarg_1:
			index = 1;
			break;
		case Code.Ldarg_2:
			index = 2;
			break;
		default:
			throw new NotSupportedException ();
		}

		if (method.HasThis)
			index--;

		return method.Parameters [index];
	}

	void ProcessProperty (Instruction instruction)
	{
		var call_get = instruction.Previous;
		var load_subject = call_get.Previous;
		var getter = (MethodReference) call_get.Operand;
		var call_property = (MethodReference) instruction.Operand;

		var il = GetILProcessor ();

		var instructions = new [] {
			il.Create (OpCodes.Ldtoken, getter),
			il.Create (OpCodes.Call, ImportGetMethodFromHandle ()),
			il.Create (OpCodes.Castclass, ImportMethodInfo ()),
			il.Create (OpCodes.Call, call_property.DeclaringType.Resolve ().Methods.First (m => m.Name == "Of" && m.Parameters.Count > 0 && m.Parameters [0].ParameterType.Name == "MethodInfo")),
		};

		il.InsertBefore (load_subject, instructions);

		il.Remove (load_subject);
		il.Remove (call_get);
		il.Remove (instruction);
	}

	void ProcessMethod (Instruction instruction)
	{
		var new_delegate = instruction.Previous;
		var ld_ftn = new_delegate.Previous;
		var ld_this = ld_ftn.Previous;

		var il = GetILProcessor ();

		var instructions = new [] {
			il.Create (OpCodes.Ldtoken, ld_ftn.Operand as MethodReference),
			il.Create (OpCodes.Call, ImportGetMethodFromHandle ()),
			il.Create (OpCodes.Castclass, ImportMethodInfo ()),
		};

		il.InsertBefore (ld_this, instructions);

		il.Remove (ld_this);
		il.Remove (ld_ftn);
		il.Remove (new_delegate);
		il.Remove (instruction);
	}

	void ProcessField (Instruction instruction)
	{
		var load_field = instruction.Previous;
		var load_this = IsStatic (load_field.OpCode) ? load_field.Previous : null;

		var il = GetILProcessor ();

		var instructions = new [] {
			il.Create (OpCodes.Ldtoken, load_field.Operand as FieldReference),
			il.Create (OpCodes.Call, ImportGetFieldFromHandle ()),
		};

		il.InsertBefore (load_this ?? load_field, instructions);

		if (load_this != null)
			il.Remove (load_this);
		il.Remove (load_field);
		il.Remove (instruction);
	}

	static bool IsStatic (OpCode code)
	{
		return code == OpCodes.Ldsfld;
	}

	void ProcessEvent (Instruction instruction)
	{
		var call_event = (MethodReference) instruction.Operand;
		var load_field = instruction.Previous;
		var load_this = IsStatic (load_field.OpCode) ? load_field.Previous : null;

		var il = GetILProcessor ();

		var instructions = new [] {
			il.Create (OpCodes.Ldtoken, load_field.Operand as FieldReference),
			il.Create (OpCodes.Call, ImportGetFieldFromHandle ()),
			il.Create (OpCodes.Call, call_event.DeclaringType.Resolve ().Methods.First (m => m.Name == "Of" && m.Parameters.Count > 0 && m.Parameters [0].ParameterType.Name == "FieldInfo")),
		};

		il.InsertBefore (load_this ?? load_field, instructions);

		if (load_this != null)
			il.Remove (load_this);
		il.Remove (load_field);
		il.Remove (instruction);
	}
}

static class ILProcessorRocks {

	public static void InsertBefore (this ILProcessor il, Instruction target, IEnumerable<Instruction> instructions)
	{
		foreach (var instruction in instructions)
			il.InsertBefore (target, instruction);
	}
}

class Program {

	static void Main (string [] args)
	{
		var module = ModuleDefinition.ReadModule (args [0]);

		foreach (var type in module.Types) {
			foreach (var method in type.Methods) {
				if (!method.HasBody)
					continue;

				var processor = new MethodProcessor (method);
				processor.Run ();
			}
		}

		module.Write (args [0]);
	}
}