From c0a9afc4ad6525e1ab672c691c53a037d54bec73 Mon Sep 17 00:00:00 2001
From: Siegfried Pammer <siegfriedpammer@gmail.com>
Date: Fri, 12 Dec 2025 14:00:19 +0100
Subject: [PATCH] Fix #3616: local variable naming conflict with primary
 constructor parameters.

---
 .../Pretty/ConstructorInitializers.cs         | 26 +++++++++++++++++++
 .../IL/Transforms/AssignVariableNames.cs      | 10 +++++++
 2 files changed, 36 insertions(+)

diff --git a/ICSharpCode.Decompiler.Tests/TestCases/Pretty/ConstructorInitializers.cs b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/ConstructorInitializers.cs
index c4d46b49f..2b93b1838 100644
--- a/ICSharpCode.Decompiler.Tests/TestCases/Pretty/ConstructorInitializers.cs
+++ b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/ConstructorInitializers.cs
@@ -264,6 +264,32 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 		{
 		}
 #endif
+#if OPT && EXPECTED_OUTPUT
+		public class C8(object obj)
+		{
+			public int Test()
+			{
+				object obj2 = obj;
+				if (obj2 is int)
+				{
+					return (int)obj2;
+				}
+				return 0;
+			}
+		}
+#else
+		public class C8(object obj)
+		{
+			public int Test()
+			{
+				if (obj is int result)
+				{
+					return result;
+				}
+				return 0;
+			}
+		}
+#endif
 #endif
 	}
 }
diff --git a/ICSharpCode.Decompiler/IL/Transforms/AssignVariableNames.cs b/ICSharpCode.Decompiler/IL/Transforms/AssignVariableNames.cs
index 326ffa96e..9a3cce0c8 100644
--- a/ICSharpCode.Decompiler/IL/Transforms/AssignVariableNames.cs
+++ b/ICSharpCode.Decompiler/IL/Transforms/AssignVariableNames.cs
@@ -28,6 +28,7 @@ using Humanizer.Inflections;
 
 using ICSharpCode.Decompiler.CSharp;
 using ICSharpCode.Decompiler.CSharp.OutputVisitor;
+using ICSharpCode.Decompiler.CSharp.Transforms;
 using ICSharpCode.Decompiler.CSharp.TypeSystem;
 using ICSharpCode.Decompiler.TypeSystem;
 using ICSharpCode.Decompiler.TypeSystem.Implementation;
@@ -106,6 +107,15 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					var currentLowerCaseTypeOrMemberNames = new HashSet<string>(StringComparer.Ordinal);
 					foreach (var name in CollectAllLowerCaseMemberNames(function.Method.DeclaringTypeDefinition))
 						currentLowerCaseTypeOrMemberNames.Add(name);
+					foreach (IField item in function.Method.DeclaringTypeDefinition.Fields)
+					{
+						if (TransformFieldAndConstructorInitializers.IsGeneratedPrimaryConstructorBackingField(item))
+						{
+							string name = item.Name.Substring(1, item.Name.Length - 3);
+							currentLowerCaseTypeOrMemberNames.Add(name);
+							AddExistingName(reservedVariableNames, name);
+						}
+					}
 					foreach (var name in CollectAllLowerCaseTypeNames(function.Method.DeclaringTypeDefinition))
 					{
 						currentLowerCaseTypeOrMemberNames.Add(name);