Unstrip Exception Handlers (#157)

* Unstrip Exception Handlers

* Handle ExceptionType more strictly

Author: ds5678

Il2CppInterop.Generator/Utils/UnstripTranslator.cs

@@ -4,6 +4,7 @@
 using AsmResolver.DotNet.Collections;
 using AsmResolver.DotNet.Signatures;
 using AsmResolver.PE.DotNet.Cil;
+using AsmResolver.PE.DotNet.Metadata.Tables;
 using Il2CppInterop.Generator.Contexts;
 using Il2CppInterop.Generator.Extensions;
 using Il2CppInterop.Generator.Passes;
@@ -341,13 +342,91 @@ public static bool TranslateMethod(MethodDefinition original, MethodDefinition t
             newLabel.Instruction = instructionMap[oldLabel.Instruction!];
         }
 
+        // Copy exception handlers
+        foreach (var exceptionHandler in original.CilMethodBody.ExceptionHandlers)
+        {
+            var newExceptionHandler = new CilExceptionHandler
+            {
+                HandlerType = exceptionHandler.HandlerType
+            };
+
+            switch (exceptionHandler.TryStart)
+            {
+                case null:
+                    break;
+                case CilInstructionLabel { Instruction: not null } tryStart:
+                    newExceptionHandler.TryStart = new CilInstructionLabel(instructionMap[tryStart.Instruction]);
+                    break;
+                default:
+                    return false;
+            }
+
+            switch (exceptionHandler.TryEnd)
+            {
+                case null:
+                    break;
+                case CilInstructionLabel { Instruction: not null } tryEnd:
+                    newExceptionHandler.TryEnd = new CilInstructionLabel(instructionMap[tryEnd.Instruction]);
+                    break;
+                default:
+                    return false;
+            }
+
+            switch (exceptionHandler.HandlerStart)
+            {
+                case null:
+                    break;
+                case CilInstructionLabel { Instruction: not null } handlerStart:
+                    newExceptionHandler.HandlerStart = new CilInstructionLabel(instructionMap[handlerStart.Instruction]);
+                    break;
+                default:
+                    return false;
+            }
+
+            switch (exceptionHandler.HandlerEnd)
+            {
+                case null:
+                    break;
+                case CilInstructionLabel { Instruction: not null } handlerEnd:
+                    newExceptionHandler.HandlerEnd = new CilInstructionLabel(instructionMap[handlerEnd.Instruction]);
+                    break;
+                default:
+                    return false;
+            }
+
+            switch (exceptionHandler.FilterStart)
+            {
+                case null:
+                    break;
+                case CilInstructionLabel { Instruction: not null } filterStart:
+                    newExceptionHandler.FilterStart = new CilInstructionLabel(instructionMap[filterStart.Instruction]);
+                    break;
+                default:
+                    return false;
+            }
+
+            switch (exceptionHandler.ExceptionType?.ToTypeSignature())
+            {
+                case null:
+                    break;
+                case CorLibTypeSignature { ElementType: ElementType.Object }:
+                    newExceptionHandler.ExceptionType = imports.Module.CorLibTypeFactory.Object.ToTypeDefOrRef();
+                    break;
+                default:
+                    // In the future, we will throw exact exceptions, but we don't right now,
+                    // so attempting to catch a specific exception type will always fail.
+                    return false;
+            }
+
+            target.CilMethodBody.ExceptionHandlers.Add(newExceptionHandler);
+        }
+
         return true;
     }
 
     public static void ReplaceBodyWithException(MethodDefinition newMethod, RuntimeAssemblyReferences imports)
     {
-        newMethod.CilMethodBody!.LocalVariables.Clear();
-        newMethod.CilMethodBody.Instructions.Clear();
+        newMethod.CilMethodBody = new(newMethod);
         var processor = newMethod.CilMethodBody.Instructions;
 
         processor.Add(OpCodes.Ldstr, "Method unstripping failed");