{}\edef \Hy@tempb {cite.\XR@prefix error when citing same bibtex entry in \externaldocument

Question

I have the following .tex file in a folder

main.tex
---
\documentclass[11pt]{article}
\usepackage{hyperref}

\title{}
\author{}

\begin{document}

\maketitle

\cite{entry}

\bibliography{bib}{}
\bibliographystyle{plain}


\end{document}

In the same folder, I have another file that uses the main one as an \externaldocument, also citing the same entry entry from the same bib file:

secondary.tex
---
\documentclass[11pt]{article}

\usepackage{hyperref}

\usepackage{xr}
\externaldocument{main}

\title{}
\author{}

\begin{document}

\maketitle

\cite{entry}

\bibliography{bib}{}
\bibliographystyle{plain}


\end{document}

The problem is that when I compile secondary.tex I get the following error, pointing to the citation:

--- TeX said ---
<argument> ... {}\edef \Hy@tempb {cite.\XR@prefix
                                                  entry\@extra@b@citeb }\ifx...l.15 \cite{entry}

Other symptoms:

• no error if I remove hyperref
• no error if I turn off \externaldocument
• no error if entry is only cited in one of the documents
• even with the error, if I persist and run bibtex and then pdflatex a couple more times the document actually compiles fine, bibliography and everything. So the error just gets ploughed over.

Answer 1

I get the error only when the aux-file doesn't contain the bibentry command (so the compilation order is crucial).

You can avoid the error by using the xr-hyper package:

\usepackage{xr-hyper}

\usepackage{hyperref}

But this doesn't prevent that you get multiply defined labels, so using a prefix for the external document should be done too.