From daa0b9caff7d48b298ecbaa0f7f875fb7b1b303b Mon Sep 17 00:00:00 2001
From: Siegfried Pammer <siegfriedpammer@gmail.com>
Date: Mon, 7 Mar 2022 23:21:15 +0100
Subject: [PATCH] Fix #2640: Invalid implicit enum value for unordered items

(cherry picked from commit 1ee3384a056a7ef908bf1bc49c77e0ed6196a393)
---
 ICSharpCode.Decompiler.Tests/TestCases/Pretty/EnumTests.cs | 6 ++++++
 ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs          | 7 ++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/ICSharpCode.Decompiler.Tests/TestCases/Pretty/EnumTests.cs b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/EnumTests.cs
index 169d1c001..4d3a13fc9 100644
--- a/ICSharpCode.Decompiler.Tests/TestCases/Pretty/EnumTests.cs
+++ b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/EnumTests.cs
@@ -28,6 +28,12 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			Item2
 		}
 
+		public enum OutOfOrderMembers
+		{
+			Item1 = 1,
+			Item0 = 0
+		}
+
 		public enum LongBasedEnum : long
 		{
 			Item1,
diff --git a/ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs b/ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs
index f9e8594a8..43d54cae2 100644
--- a/ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs
+++ b/ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs
@@ -1405,7 +1405,12 @@ namespace ICSharpCode.Decompiler.CSharp
 					firstValue = currentValue;
 					first = false;
 				}
-				else if (!allConsecutive && !allPowersOfTwo)
+				else if (currentValue < previousValue)
+				{
+					// If the values are out of order, we fallback to displaying all values.
+					return EnumValueDisplayMode.All;
+				}
+				else if ((!allConsecutive && !allPowersOfTwo))
 				{
 					// We already know that the values are neither consecutive nor all powers of 2,
 					// so we can abort, and just display all values as-is.