Why is there an extra link box for long URLs when using hyperref and lineno?

Question

Please consider this MWE:

\documentclass{article}
\usepackage{lineno}
\usepackage{hyperref}
% \linenumbers
\begin{document}
\url{https://www.this-is-a-very-long-url.com/this-is-a-very-long-url/this-is-a-very-long-url/this-is-a-very-long-url.html}
\end{document}

Using pdflatex, this results in:

If we uncomment the \linenumbers line, an additional (small) colored box is drawn before the URL:

Using xelatex, the box is drawn around the line number:

What's the reason for this extra box? Is there a way to avoid it?

Answer 1

the line number is in a box which is placed while the link is build, so it is linked too.

With a current texsystem (texlive 2021) you can avoid it. But this requires to patch an internal command of lineno as the deactivation code must be at the correct box level:

\documentclass{article}
\usepackage{lineno}
\usepackage{hyperref}
\usepackage{iftex,etoolbox}
\ifxetex
\newcommand\runninglinkoff{\special{pdf: nolink}}
\newcommand\runninglinkon {\special{pdf:  link}}
\fi
\ifpdftex
\newcommand\runninglinkoff{\pdfrunninglinkoff}
\newcommand\runninglinkon {\pdfrunninglinkon}
\fi
\ifluatex
\protected\def\runninglinkoff{\pdfextension linkstate 1 }
\protected\def\runninglinkon {\pdfextension linkstate 0 }
\fi
\makeatletter
\patchcmd@LN@depthbox{\box@tempboxa}{\runninglinkoff\box@tempboxa \runninglinkon}{}{\fail}
\makeatother

\begin{document}
\linenumbers 
\url{https://www.this-is-a-very-long-url.com/this-is-a-very-long-url/this-is-a-very-long-url/this-is-a-very-long-url.html}
\end{document}