Fix incorrect position of inserted instructions

Author: mistzzt

ModLocalizer/Extensions/InstructionExtensions.cs

@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Linq;
 using dnlib.DotNet.Emit;
 
@@ -16,5 +17,40 @@ public static void Insert(this IList<Instruction> inst, int index, IEnumerable<I
                 inst.Insert(index, instruction);
             }
         }
+
+        /// <summary>
+        /// Inserts a group of instructions into given instructions at the arbitrary last.
+        /// </summary>
+        public static void AppendLast(this IList<Instruction> inst, IEnumerable<Instruction> instructions)
+        {
+            // create a copy of instructions to be inserted
+            var list = instructions.ToList();
+            if (!list.Any())
+            {
+                return;
+            }
+
+            // valid target method should have `ret` as last instruction
+            var retInst = inst.Last();
+            if (retInst.OpCode != OpCodes.Ret)
+            {
+                throw new ArgumentOutOfRangeException(nameof(inst), "Invalid method instructions.");
+            }
+
+            // alter the last instruction of the target
+            var first = list.First();
+            retInst.OpCode = first.OpCode;
+            retInst.Operand = first.Operand;
+
+            // prepare instruction list
+            list.Remove(first);
+            list.Add(OpCodes.Ret.ToInstruction());
+
+            // insert into the target
+            foreach (var instruction in list)
+            {
+                inst.Add(instruction);
+            }
+        }
     }
 }

ModLocalizer/TranslationEmitter.cs

@@ -81,13 +81,9 @@ public TranslationEmitter(ModuleDef module, string gameCulture, string modName)
                 type.Methods.Add(loadMethod);
             }
 
-            var instructions = loadMethod.Body.Instructions;
-
-            // to prevert `call Localizer_setTranslation<>` being transfer target
-            instructions[instructions.Count - 1].OpCode = OpCodes.Ldarg_0; // ret -> ldarg.0
-
-            instructions.Insert(instructions.Count, new[]
+            loadMethod.Body.Instructions.AppendLast(new[]
             {
+                OpCodes.Ldarg_0.ToInstruction(),
                 OpCodes.Call.ToInstruction(_modSetTranslationMethod),
                 OpCodes.Ret.ToInstruction()
             });
@@ -111,7 +107,7 @@ public void Emit(MethodDef method, string propertyName, string content)
                 MethodSig.CreateInstance(new ClassSig(_modTranslationType)),
                 method.DeclaringType.BaseType);
 
-            instructions.Insert(instructions.Count - 1, new[]
+            instructions.AppendLast(new[]
             {
                 OpCodes.Ldarg_0.ToInstruction(),
                 OpCodes.Call.ToInstruction(translationPropertyGetter),
@@ -190,7 +186,7 @@ private string AddTranslation(string key, string @default, string content)
         {
             var instructions = _modSetTranslationMethod.Body.Instructions;
 
-            instructions.Insert(instructions.Count - 1, new[]
+            instructions.AppendLast(new[]
             {
                 OpCodes.Ldarg_0.ToInstruction(),
                 OpCodes.Ldstr.ToInstruction(key),