typealias Node = Syntax.Type

final class Rewriter : SyntaxRewriter {
    var tokens: [(String, ancestors: [Node])] = []
    var ancestors: [Node] = []

    override func visit(_ token: TokenSyntax) -> Syntax {
         tokens.append((token.text, ancestors: ancestors))
         return super.visit(token)
    }

    override func visit(_ node: SwiftSyntax.UnknownDeclSyntax) -> DeclSyntax {
        ancestors.append(type(of: node))
        let r = super.visit(node)
        ancestors.removeLast()
        return r
    }

    override func visit(_ node: SwiftSyntax.UnknownExprSyntax) -> ExprSyntax {
        ancestors.append(type(of: node))
        let r = super.visit(node)
        ancestors.removeLast()
        return r
    }

    … ETC FOR EVERY OTHER SYNTAX NODE…
}