Error with tagging-project, 'ocgx2' package and TOC

Question

This mwe:

\DocumentMetadata{testphase=new-or-1}

\documentclass{book}
\usepackage{hyperref}
\usepackage[ocgcolorlinks]{ocgx2}

\begin{document}
\tableofcontents
\chapter{first chapter}
\end{document}

produces, in the console, the following error:

(./ocgx2.toc
! Undefined control sequence.
\pdf_object_new:nn ...\__pdf_backend_object_new:n 
                                                 {#1}
l.1 ...\numberline {1}first chapter}{3}{chapter.1}
                                                 % 

The error occurs only with the ocgcolorlinks option.

Finally, all my documents with this 'configuration' (i.e. the simultaneous presence of the testphase=new-or-1 key, the ocgcolorlinks option and the \tableofcontents command) always compiled correctly.

Answer 1

There are a couple of oversights in the compatibility code: the approach being used to make PDF objects is one we've adjusted, and the older one is being used here. For the present, use:

\DocumentMetadata{testphase=new-or-1}
\ExplSyntaxOn
\cs_gset_eq:NN \__pdf_backend_object_new:n \pdf_object_new:n
\cs_gset_protected:Npn \pdf_object_write:nn #1#2
  {
    \exp_args:Nee \__pdf_backend_object_write:nnn
      { \__pdf_object_retrieve:n {#1} }
      { \prop_item:Nn \g__pdf_object_prop {#1} } {#2}
    \bool_gset_true:N \g__pdf_init_bool
  }
\ExplSyntaxOff
\documentclass{book}
\usepackage{hyperref}
\usepackage[ocgcolorlinks]{ocgx2}
\begin{document}
\tableofcontents
\chapter{first chapter}
\end{document}