Fix #3361: switch-value conversion was losing its target type.

Author: siegfriedpammer

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Switch.cs

@@ -67,6 +67,36 @@ public static explicit operator string(ExplicitString v)
 			}
 		}
 
+		public class ImplicitInt
+		{
+			private readonly int s;
+
+			public ImplicitInt(int s)
+			{
+				this.s = s;
+			}
+
+			public static implicit operator int(ImplicitInt v)
+			{
+				return v.s;
+			}
+		}
+
+		public class ExplicitInt
+		{
+			private readonly int s;
+
+			public ExplicitInt(int s)
+			{
+				this.s = s;
+			}
+
+			public static explicit operator int(ExplicitInt v)
+			{
+				return v.s;
+			}
+		}
+
 		public enum State
 		{
 			False,
@@ -310,6 +340,62 @@ public static void SwitchOverInt(int i)
 			}
 		}
 
+		public static void SwitchOverExplicitInt(ExplicitInt i)
+		{
+			switch ((int)i)
+			{
+				case 0:
+					Console.WriteLine("zero");
+					break;
+				case 5:
+					Console.WriteLine("five");
+					break;
+				case 10:
+					Console.WriteLine("ten");
+					break;
+				case 15:
+					Console.WriteLine("fifteen");
+					break;
+				case 20:
+					Console.WriteLine("twenty");
+					break;
+				case 25:
+					Console.WriteLine("twenty-five");
+					break;
+				case 30:
+					Console.WriteLine("thirty");
+					break;
+			}
+		}
+
+		public static void SwitchOverImplicitInt(ImplicitInt i)
+		{
+			switch (i)
+			{
+				case 0:
+					Console.WriteLine("zero");
+					break;
+				case 5:
+					Console.WriteLine("five");
+					break;
+				case 10:
+					Console.WriteLine("ten");
+					break;
+				case 15:
+					Console.WriteLine("fifteen");
+					break;
+				case 20:
+					Console.WriteLine("twenty");
+					break;
+				case 25:
+					Console.WriteLine("twenty-five");
+					break;
+				case 30:
+					Console.WriteLine("thirty");
+					break;
+			}
+		}
+
 		// SwitchDetection.UseCSharpSwitch requires more complex heuristic to identify this when compiled with Roslyn
 		public static void CompactSwitchOverInt(int i)
 		{

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -3900,30 +3900,41 @@ protected internal override TranslatedExpression VisitIfInstruction(IfInstructio
 			}
 		}
 
-		protected internal override TranslatedExpression VisitSwitchInstruction(SwitchInstruction inst, TranslationContext context)
+		internal (TranslatedExpression, IType) TranslateSwitchValue(SwitchInstruction inst, bool allowImplicitConversion)
 		{
 			TranslatedExpression value;
 			IType type;
 			if (inst.Value is StringToInt strToInt)
 			{
+				// switch-expression does not support implicit conversions at all,
+				// switch-statement does support implicit conversions in general, however, the rules are
+				// not very intuitive and in order to prevent bugs, we emit an explicit cast.
 				value = Translate(strToInt.Argument)
 					.ConvertTo(
 						strToInt.ExpectedType,
 						this,
-						allowImplicitConversion: false // switch-expression does not support implicit conversions
+						allowImplicitConversion: false
 					);
 				type = compilation.FindType(KnownTypeCode.String);
 			}
 			else
 			{
 				strToInt = null;
 				value = Translate(inst.Value);
+				type = value.Type;
 				if (inst.Type != null)
 				{
-					value = value.ConvertTo(inst.Type, this, allowImplicitConversion: true);
+					value = value.ConvertTo(inst.Type, this, allowImplicitConversion: allowImplicitConversion);
+					type = inst.Type;
 				}
-				type = value.Type;
 			}
+			return (value, type);
+		}
+
+		protected internal override TranslatedExpression VisitSwitchInstruction(SwitchInstruction inst, TranslationContext context)
+		{
+			// switch-expression does not support implicit conversions
+			var (value, type) = TranslateSwitchValue(inst, allowImplicitConversion: false);
 
 			IL.SwitchSection defaultSection = inst.GetDefaultSection();
 			SwitchExpression switchExpr = new SwitchExpression();

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -210,30 +210,7 @@ SwitchStatement TranslateSwitch(BlockContainer switchContainer, SwitchInstructio
 			var oldCaseLabelMapping = caseLabelMapping;
 			caseLabelMapping = new Dictionary<Block, ConstantResolveResult>();
 
-			TranslatedExpression value;
-			IType type;
-			if (inst.Value is StringToInt strToInt)
-			{
-				value = exprBuilder.Translate(strToInt.Argument)
-					.ConvertTo(
-						strToInt.ExpectedType,
-						exprBuilder,
-						// switch statement does support implicit conversions in general, however, the rules are
-						// not very intuitive and in order to prevent bugs, we emit an explicit cast.
-						allowImplicitConversion: false
-					);
-				type = exprBuilder.compilation.FindType(KnownTypeCode.String);
-			}
-			else
-			{
-				strToInt = null;
-				value = exprBuilder.Translate(inst.Value);
-				if (inst.Type != null)
-				{
-					value = value.ConvertTo(inst.Type, exprBuilder, allowImplicitConversion: true);
-				}
-				type = value.Type;
-			}
+			var (value, type) = exprBuilder.TranslateSwitchValue(inst, allowImplicitConversion: true);
 
 			IL.SwitchSection defaultSection = inst.GetDefaultSection();