SourceGen Blog1, value Provider example

IncrementalValuesProvider.cs

IncrementalValuesProvider<ClassDeclarationSyntax> calculatorClassesProvider = context.SyntaxProvider.CreateSyntaxProvider(
  predicate: (SyntaxNode node, CancellationToken cancelToken) =>
  {
    //the predicate should be super lightweight to filter out items that are not of interest quickly
    return node is ClassDeclarationSyntax classDeclaration && classDeclaration.Identifier.ToString() == "Calculator";
  },
  transform: (GeneratorSyntaxContext ctx, CancellationToken cancelToken) =>
  {
    //the transform is called only when the predicate returns true, so it can do a bit more heavyweight work but should mainly be about getting the data we want to work with later
    var classDeclaration = (ClassDeclarationSyntax)ctx.Node;
    return classDeclaration;
  });