Fix #3616: local variable naming conflict with primary constructor parameters.

Author: siegfriedpammer

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

@@ -264,6 +264,32 @@ public class UnusedPrimaryCtorParameter(int unused)
 		{
 		}
 #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
 	}
 }

ICSharpCode.Decompiler/IL/Transforms/AssignVariableNames.cs

@@ -28,6 +28,7 @@
 
 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 @@ public VariableScope(ILFunction function, ILTransformContext context, VariableSc
 					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);