From 768cb02f0bf54104d8f435f8cd6736557e346886 Mon Sep 17 00:00:00 2001
From: Daniel Grunwald <daniel@danielgrunwald.de>
Date: Thu, 1 Jun 2023 15:02:52 +0200
Subject: [PATCH] Fix #2964: Better error message when a method only contains a
 single ret instruction.

---
 .../TestCases/ILPretty/EmptyBodies.cs            |  2 +-
 ICSharpCode.Decompiler/IL/BlockBuilder.cs        |  9 ---------
 ICSharpCode.Decompiler/IL/ILReader.cs            | 16 ++++++++++++++++
 3 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/EmptyBodies.cs b/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/EmptyBodies.cs
index 6945a1db1..73998e2bd 100644
--- a/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/EmptyBodies.cs
+++ b/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/EmptyBodies.cs
@@ -5,7 +5,7 @@ internal class EmptyBodies
 	}
 	public static int RetInt()
 	{
-		return (int)/*Error near IL_0001: Stack underflow*/;
+		/*Error: Method body consists only of 'ret', but nothing is being returned. Decompiled assembly might be a reference assembly.*/;
 	}
 	public static void Nop()
 	{
diff --git a/ICSharpCode.Decompiler/IL/BlockBuilder.cs b/ICSharpCode.Decompiler/IL/BlockBuilder.cs
index be06a5034..c21881673 100644
--- a/ICSharpCode.Decompiler/IL/BlockBuilder.cs
+++ b/ICSharpCode.Decompiler/IL/BlockBuilder.cs
@@ -129,15 +129,6 @@ namespace ICSharpCode.Decompiler.IL
 		{
 			CreateContainerStructure();
 			mainContainer.SetILRange(new Interval(0, body.GetCodeSize()));
-			if (!basicBlocks.Any())
-			{
-				mainContainer.Blocks.Add(new Block {
-					Instructions = {
-						new InvalidBranch("Empty body found. Decompiled assembly might be a reference assembly.")
-					}
-				});
-				return;
-			}
 
 			currentContainer = mainContainer;
 			foreach (var block in basicBlocks.OrderBy(b => b.StartILOffset))
diff --git a/ICSharpCode.Decompiler/IL/ILReader.cs b/ICSharpCode.Decompiler/IL/ILReader.cs
index 8b1072967..901076a22 100644
--- a/ICSharpCode.Decompiler/IL/ILReader.cs
+++ b/ICSharpCode.Decompiler/IL/ILReader.cs
@@ -457,6 +457,13 @@ namespace ICSharpCode.Decompiler.IL
 		{
 			reader.Reset();
 			StoreStackForOffset(0, ImmutableStack<ILVariable>.Empty);
+			if (reader.Length == 0)
+			{
+				blocksByOffset[0].Block.Instructions.Add(
+					new InvalidBranch("Empty body found. Decompiled assembly might be a reference assembly.")
+				);
+				return;
+			}
 			ILParser.SetBranchTargets(ref reader, isBranchTarget);
 			PrepareBranchTargetsAndStacksForExceptionHandlers();
 
@@ -1480,9 +1487,18 @@ namespace ICSharpCode.Decompiler.IL
 		private ILInstruction Return()
 		{
 			if (methodReturnStackType == StackType.Void)
+			{
 				return new IL.Leave(mainContainer);
+			}
+			else if (currentInstructionStart == 0)
+			{
+				Debug.Assert(expressionStack.Count == 0 && currentStack.IsEmpty);
+				return new InvalidBranch("Method body consists only of 'ret', but nothing is being returned. Decompiled assembly might be a reference assembly.");
+			}
 			else
+			{
 				return new IL.Leave(mainContainer, Pop(methodReturnStackType));
+			}
 		}
 
 		private ILInstruction DecodeLdstr()