public static void ReportUndeclaredIndexer(this ICollection<Diagnostic> diagnostics, ElementAccessExpressionSyntax node, TypeSymbol declaringType, IEnumerable<TypeSymbol> argumentTypes) { var declaringTypeName = declaringType.ToDisplayName(); var argumentTypeNames = string.Join(@", ", argumentTypes.Select(t => t.ToDisplayName())); diagnostics.Report(node.GetTextSpanRoot(), DiagnosticId.UndeclaredIndexer, declaringTypeName, argumentTypeNames); }