Fix #2283: string.to.int instruction entails a conversion to string of the input value

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

@@ -37,6 +37,36 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 		}
 
+		public class ImplicitString
+		{
+			private readonly string s;
+
+			public ImplicitString(string s)
+			{
+				this.s = s;
+			}
+
+			public static implicit operator string(ImplicitString v)
+			{
+				return v.s;
+			}
+		}
+
+		public class ExplicitString
+		{
+			private readonly string s;
+
+			public ExplicitString(string s)
+			{
+				this.s = s;
+			}
+
+			public static explicit operator string(ExplicitString v)
+			{
+				return v.s;
+			}
+		}
+
 		public enum State
 		{
 			False,
@@ -379,6 +409,68 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 		}
 
+		public static string SwitchOverImplicitString(ImplicitString s)
+		{
+			switch (s)
+			{
+				case "First case":
+					return "Text1";
+				case "Second case":
+					return "Text2";
+				case "Third case":
+					return "Text3";
+				case "Fourth case":
+					return "Text4";
+				case "Fifth case":
+					return "Text5";
+				case "Sixth case":
+					return "Text6";
+				case "Seventh case":
+					return "Text7";
+				case "Eighth case":
+					return "Text8";
+				case "Ninth case":
+					return "Text9";
+				case "Tenth case":
+					return "Text10";
+				case "Eleventh case":
+					return "Text11";
+				default:
+					return "Default";
+			}
+		}
+
+		public static string SwitchOverExplicitString(ExplicitString s)
+		{
+			switch ((string)s)
+			{
+				case "First case":
+					return "Text1";
+				case "Second case":
+					return "Text2";
+				case "Third case":
+					return "Text3";
+				case "Fourth case":
+					return "Text4";
+				case "Fifth case":
+					return "Text5";
+				case "Sixth case":
+					return "Text6";
+				case "Seventh case":
+					return "Text7";
+				case "Eighth case":
+					return "Text8";
+				case "Ninth case":
+					return "Text9";
+				case "Tenth case":
+					return "Text10";
+				case "Eleventh case":
+					return "Text11";
+				default:
+					return "Default";
+			}
+		}
+
 #if !ROSLYN
 		public static string SwitchOverBool(bool b)
 		{

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -3642,6 +3642,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		protected internal override TranslatedExpression VisitSwitchInstruction(SwitchInstruction inst, TranslationContext context)
 		{
 			TranslatedExpression value;
+			IType type;
 			if (inst.Value is StringToInt strToInt)
 			{
 				value = Translate(strToInt.Argument)
@@ -3650,11 +3651,13 @@ namespace ICSharpCode.Decompiler.CSharp
 						this,
 						allowImplicitConversion: false // switch-expression does not support implicit conversions
 					);
+				type = compilation.FindType(KnownTypeCode.String);
 			}
 			else
 			{
 				strToInt = null;
 				value = Translate(inst.Value);
+				type = value.Type;
 			}
 
 			IL.SwitchSection defaultSection = inst.GetDefaultSection();
@@ -3683,7 +3686,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				else
 				{
 					long val = section.Labels.Values.Single();
-					var rr = statementBuilder.CreateTypedCaseLabel(val, value.Type, strToInt?.Map).Single();
+					var rr = statementBuilder.CreateTypedCaseLabel(val, type, strToInt?.Map).Single();
 					ses.Pattern = astBuilder.ConvertConstantValue(rr);
 				}
 				ses.Body = TranslateSectionBody(section);

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -144,12 +144,14 @@ namespace ICSharpCode.Decompiler.CSharp
 			// unpack nullable type, if necessary:
 			// we need to do this in all cases, because there are nullable bools and enum types as well.
 			type = NullableType.GetUnderlyingType(type);
+
 			if (type.IsKnownType(KnownTypeCode.Boolean))
 			{
 				value = i != 0;
 			}
-			else if (type.IsKnownType(KnownTypeCode.String) && map != null)
+			else if (map != null)
 			{
+				Debug.Assert(type.IsKnownType(KnownTypeCode.String));
 				var keys = map.Where(entry => entry.Value == i).Select(entry => entry.Key);
 				foreach (var key in keys)
 					yield return new ConstantResolveResult(type, key);
@@ -196,6 +198,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			caseLabelMapping = new Dictionary<Block, ConstantResolveResult>();
 
 			TranslatedExpression value;
+			IType type;
 			if (inst.Value is StringToInt strToInt)
 			{
 				value = exprBuilder.Translate(strToInt.Argument)
@@ -204,11 +207,13 @@ namespace ICSharpCode.Decompiler.CSharp
 						exprBuilder,
 						allowImplicitConversion: true
 					);
+				type = exprBuilder.compilation.FindType(KnownTypeCode.String);
 			}
 			else
 			{
 				strToInt = null;
 				value = exprBuilder.Translate(inst.Value);
+				type = value.Type;
 			}
 
 			IL.SwitchSection defaultSection = inst.GetDefaultSection();
@@ -229,7 +234,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				}
 				else
 				{
-					var values = section.Labels.Values.SelectMany(i => CreateTypedCaseLabel(i, value.Type, strToInt?.Map)).ToArray();
+					var values = section.Labels.Values.SelectMany(i => CreateTypedCaseLabel(i, type, strToInt?.Map)).ToArray();
 					if (section.HasNullLabel)
 					{
 						astSection.CaseLabels.Add(new CaseLabel(new NullReferenceExpression()));