Improve error message for record inheritance without parameter list

.github/copilot-instructions.md

@@ -70,6 +70,7 @@ var symbolInfo = semanticModel.GetSymbolInfo(expression);
 - **Cancellation**: Always thread `CancellationToken` through async operations
 - **MEF Lifecycle**: Use `[ImportingConstructor]` with obsolete attribute for MEF v2 compatibility
 - **PROTOTYPE Comments**: Only used to track follow-up work in feature branches and are disallowed in main branch
+- **Code Formatting**: Avoid trailing spaces and blank lines (lines with only whitespace). Ensure all lines either have content or are completely empty.
 
 ## Common Gotchas
 

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -6567,6 +6567,9 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="ERR_UnexpectedArgumentList" xml:space="preserve">
     <value>Unexpected argument list.</value>
   </data>
+  <data name="ERR_UnexpectedArgumentListInBaseTypeWithoutParameterList" xml:space="preserve">
+    <value>Cannot pass arguments to the base type without a parameter list on the type declaration. Consider adding an empty parameter list to '{0}'.</value>
+  </data>
   <data name="ERR_UnexpectedOrMissingConstructorInitializerInRecord" xml:space="preserve">
     <value>A constructor declared in a type with parameter list must have 'this' constructor initializer.</value>
   </data>

src/Compilers/CSharp/Portable/Errors/ErrorCode.cs

@@ -2435,6 +2435,7 @@ internal enum ErrorCode
         HDN_RedundantPatternStackGuard = 9337,
 
         ERR_BadVisBaseType = 9338,
+        ERR_UnexpectedArgumentListInBaseTypeWithoutParameterList = 9339,
 
         // Note: you will need to do the following after adding errors:
         //  1) Update ErrorFacts.IsBuildOnlyDiagnostic (src/Compilers/CSharp/Portable/Errors/ErrorFacts.cs)

src/Compilers/CSharp/Portable/Errors/ErrorFacts.cs

@@ -2543,6 +2543,7 @@ or ErrorCode.HDN_RedundantPattern
                 or ErrorCode.WRN_RedundantPattern
                 or ErrorCode.HDN_RedundantPatternStackGuard
                 or ErrorCode.ERR_BadVisBaseType
+                or ErrorCode.ERR_UnexpectedArgumentListInBaseTypeWithoutParameterList
                     => false,
             };
 #pragma warning restore CS8524 // The switch expression does not handle some values of its input type (it is not exhaustive) involving an unnamed enum value.

src/Compilers/CSharp/Portable/Symbols/Source/SourceNamedTypeSymbol_Bases.cs

@@ -27,7 +27,7 @@ internal partial class SourceNamedTypeSymbol
         private ImmutableArray<NamedTypeSymbol> _lazyInterfaces;
 
         /// <summary>
-        /// Gets the BaseType of this type. If the base type could not be determined, then 
+        /// Gets the BaseType of this type. If the base type could not be determined, then
         /// an instance of ErrorType is returned. If this kind of type does not have a base type
         /// (for example, interfaces), null is returned. Also the special class System.Object
         /// always has a BaseType of null.
@@ -638,10 +638,24 @@ private Tuple<NamedTypeSymbol, ImmutableArray<NamedTypeSymbol>> MakeOneDeclaredB
 
             void checkPrimaryConstructorBaseType(BaseTypeSyntax baseTypeSyntax, TypeSymbol baseType)
             {
-                if (baseTypeSyntax is PrimaryConstructorBaseTypeSyntax primaryConstructorBaseType &&
-                    (TypeKind != TypeKind.Class || baseType.TypeKind == TypeKind.Interface || ((TypeDeclarationSyntax)decl.SyntaxReference.GetSyntax()).ParameterList is null))
+                if (baseTypeSyntax is PrimaryConstructorBaseTypeSyntax primaryConstructorBaseType)
                 {
-                    diagnostics.Add(ErrorCode.ERR_UnexpectedArgumentList, primaryConstructorBaseType.ArgumentList.Location);
+                    var typeDecl = (TypeDeclarationSyntax)decl.SyntaxReference.GetSyntax();
+
+                    // Check if this is a class inheriting from a class but missing a parameter list
+                    if (TypeKind == TypeKind.Class &&
+                        baseType.TypeKind != TypeKind.Interface &&
+                        typeDecl.ParameterList is null)
+                    {
+                        diagnostics.Add(ErrorCode.ERR_UnexpectedArgumentListInBaseTypeWithoutParameterList,
+                            primaryConstructorBaseType.ArgumentList.Location,
+                            this.Name);
+                    }
+                    // Other cases where argument lists are not allowed
+                    else if (TypeKind != TypeKind.Class || baseType.TypeKind == TypeKind.Interface)
+                    {
+                        diagnostics.Add(ErrorCode.ERR_UnexpectedArgumentList, primaryConstructorBaseType.ArgumentList.Location);
+                    }
                 }
             }
         }