dotnet/wpf · error · TypeNameParserException

SR.InvalidCharInTypeName

Error message

SR.InvalidCharInTypeName

What it means

GenericTypeNameParser.ThrowOnBadInput throws TypeNameParserException (SR.InvalidCharInTypeName) when the scanner encounters a character that cannot appear in a generic type name, reporting the offending character and the full input text. It is the error exit of the parser loop reached from ParseName, ParseList, P_XamlTypeName, P_SimpleTypeName, and P_TypeParameters.

Solutions

  1. Fix the type name string so it is syntactically valid (balanced brackets, valid identifier characters)
  2. Validate/normalize the type string before passing it to XAML type resolution
  3. Use Type.GetType or the fully qualified type reference instead of hand-built names

Example fix

// before
var type = new XamlTypeName("ns", "List[Int32"); // unclosed subscript
// after
var type = new XamlTypeName("ns", "List[Int32]");
Defensive patterns

Strategy: try-catch

Validate before calling

// validate the type name string before parsing
if (string.IsNullOrWhiteSpace(typeName) || typeName.Count(c => c == '[') != typeName.Count(c => c == ']'))
    throw new FormatException($"Malformed type name: {typeName}");

Type guard

static bool LooksLikeTypeName(string s) => !string.IsNullOrWhiteSpace(s) && s.Count(c => c=='[') == s.Count(c => c==']');

Try / catch

try { var name = ParseGenericTypeName(input); }
catch (TypeNameParserException ex) { /* invalid char in type name: ex.Message includes char and input */ }

Prevention

When it happens

Trigger: Parsing a type name string (e.g. from x:Type markup extension or XamlType resolution) containing an invalid character — stray punctuation, unclosed brackets, spaces in wrong positions, or truncated generic syntax.

Common situations: Hand-written type name strings in XAML x:Type references; dynamically built type names with malformed generic arity syntax (e.g. "List(Of T" ); typos in assembly-qualified type references.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/158151104887f1c3. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/Parser/GenericTypeNameParser.cs:252

        // Subscript        ::= ‘[’ ‘,’* ‘]’
        //
        private void P_RepeatingSubscript()
        {
            // caller checks this.
            Debug.Assert(_scanner.Token == GenericTypeNameScannerToken.SUBSCRIPT);

            do
            {
                Callout_Subscript(_scanner.MultiCharTokenText);
                _scanner.Read();
            }
            while (_scanner.Token == GenericTypeNameScannerToken.SUBSCRIPT);
        }

        private void ThrowOnBadInput()
        {
            throw new TypeNameParserException(SR.Format(SR.InvalidCharInTypeName, _scanner.ErrorCurrentChar, _inputText));
        }

        private void StartStack()
        {
            _stack = new Stack<TypeNameFrame>();
            TypeNameFrame frame;
            frame = new TypeNameFrame();
            _stack.Push(frame);
        }

        private void Callout_FoundName(string prefix, string name)
        {
            TypeNameFrame frame = new TypeNameFrame
            {
                Name = name
            };
            string ns = _prefixResolver(prefix);
            frame.Namespace = ns ?? throw new TypeNameParserException(SR.Format(SR.PrefixNotFound, prefix));

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