From a3191f19e2d6ccf66fba596be9fb8013cef57b01 Mon Sep 17 00:00:00 2001
From: Siegfried Pammer <siegfriedpammer@gmail.com>
Date: Fri, 16 Sep 2022 23:46:49 +0200
Subject: [PATCH] Fix #2763: Improve decompilation of switch-on-enum by
 preserving enum type information when inlining local variables into
 SwitchInstruction.Value.

---
 .../TestCases/Pretty/Switch.cs                | 35 +++++++++++++++++++
 .../CSharp/ExpressionBuilder.cs               |  4 +++
 .../CSharp/StatementBuilder.cs                |  4 +++
 .../IL/Instructions/SwitchInstruction.cs      | 11 +++++-
 .../IL/Transforms/ILInlining.cs               |  6 ++++
 5 files changed, 59 insertions(+), 1 deletion(-)

diff --git a/ICSharpCode.Decompiler.Tests/TestCases/Pretty/Switch.cs b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/Switch.cs
index f49d3ea682..374752ba39 100644
--- a/ICSharpCode.Decompiler.Tests/TestCases/Pretty/Switch.cs
+++ b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/Switch.cs
@@ -74,6 +74,16 @@ public enum State
 			Null
 		}
 
+		public enum KnownColor
+		{
+			DarkBlue,
+			DarkCyan,
+			DarkGoldenrod,
+			DarkGray,
+			DarkGreen,
+			DarkKhaki
+		}
+
 		private static char ch1767;
 
 #if !ROSLYN
@@ -1474,5 +1484,30 @@ public static void Issue1767(string s)
 					break;
 			}
 		}
+
+		public static void Issue2763(int value)
+		{
+			switch ((KnownColor)value)
+			{
+				case KnownColor.DarkBlue:
+					Console.WriteLine("DarkBlue");
+					break;
+				case KnownColor.DarkCyan:
+					Console.WriteLine("DarkCyan");
+					break;
+				case KnownColor.DarkGoldenrod:
+					Console.WriteLine("DarkGoldenrod");
+					break;
+				case KnownColor.DarkGray:
+					Console.WriteLine("DarkGray");
+					break;
+				case KnownColor.DarkGreen:
+					Console.WriteLine("DarkGreen");
+					break;
+				case KnownColor.DarkKhaki:
+					Console.WriteLine("DarkKhaki");
+					break;
+			}
+		}
 	}
 }
diff --git a/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs b/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs
index 0c167800bf..e964073951 100644
--- a/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs
+++ b/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs
@@ -3819,6 +3819,10 @@ protected internal override TranslatedExpression VisitSwitchInstruction(SwitchIn
 			{
 				strToInt = null;
 				value = Translate(inst.Value);
+				if (inst.Type != null)
+				{
+					value = value.ConvertTo(inst.Type, this, allowImplicitConversion: true);
+				}
 				type = value.Type;
 			}
 
diff --git a/ICSharpCode.Decompiler/CSharp/StatementBuilder.cs b/ICSharpCode.Decompiler/CSharp/StatementBuilder.cs
index 32d46b6433..1db19abe8a 100644
--- a/ICSharpCode.Decompiler/CSharp/StatementBuilder.cs
+++ b/ICSharpCode.Decompiler/CSharp/StatementBuilder.cs
@@ -226,6 +226,10 @@ SwitchStatement TranslateSwitch(BlockContainer switchContainer, SwitchInstructio
 			{
 				strToInt = null;
 				value = exprBuilder.Translate(inst.Value);
+				if (inst.Type != null)
+				{
+					value = value.ConvertTo(inst.Type, exprBuilder, allowImplicitConversion: true);
+				}
 				type = value.Type;
 			}
 
diff --git a/ICSharpCode.Decompiler/IL/Instructions/SwitchInstruction.cs b/ICSharpCode.Decompiler/IL/Instructions/SwitchInstruction.cs
index aa3a55a564..ad0d0a9a4b 100644
--- a/ICSharpCode.Decompiler/IL/Instructions/SwitchInstruction.cs
+++ b/ICSharpCode.Decompiler/IL/Instructions/SwitchInstruction.cs
@@ -20,6 +20,7 @@
 using System.Diagnostics;
 using System.Linq;
 
+using ICSharpCode.Decompiler.TypeSystem;
 using ICSharpCode.Decompiler.Util;
 
 namespace ICSharpCode.Decompiler.IL
@@ -42,6 +43,12 @@ partial class SwitchInstruction
 		/// </summary>
 		public bool IsLifted;
 
+		/// <summary>
+		/// Additional type information used to interpret the value instruction.
+		/// Set by ILInlining to preserve stack information that would otherwise be lost.
+		/// </summary>
+		public IType? Type;
+
 		public SwitchInstruction(ILInstruction value)
 			: base(OpCode.SwitchInstruction)
 		{
@@ -82,7 +89,9 @@ public override void WriteTo(ITextOutput output, ILAstWritingOptions options)
 			output.Write("switch");
 			if (IsLifted)
 				output.Write(".lifted");
-			output.Write(" (");
+			output.Write(' ');
+			Type?.WriteTo(output);
+			output.Write('(');
 			value.WriteTo(output, options);
 			output.Write(") ");
 			output.MarkFoldStart("{...}");
diff --git a/ICSharpCode.Decompiler/IL/Transforms/ILInlining.cs b/ICSharpCode.Decompiler/IL/Transforms/ILInlining.cs
index d9326c8419..b77494f465 100644
--- a/ICSharpCode.Decompiler/IL/Transforms/ILInlining.cs
+++ b/ICSharpCode.Decompiler/IL/Transforms/ILInlining.cs
@@ -600,6 +600,12 @@ static bool NonAggressiveInlineInto(ILInstruction next, FindResult findResult, I
 				case OpCode.YieldReturn:
 					return true;
 				case OpCode.SwitchInstruction:
+					// Preserve type info on switch instruction, if we're inlining a local variable into the switch-value slot.
+					if (v.Kind != VariableKind.StackSlot && loadInst.SlotInfo == SwitchInstruction.ValueSlot)
+					{
+						((SwitchInstruction)parent).Type ??= v.Type;
+					}
+					return true;
 				//case OpCode.BinaryNumericInstruction when parent.SlotInfo == SwitchInstruction.ValueSlot:
 				case OpCode.StringToInt when parent.SlotInfo == SwitchInstruction.ValueSlot:
 					return true;