Wrong link anchor with floats and logical sections

[matteofg]

Below the emc:

\documentclass{book}
\usepackage{graphicx}
\usepackage{hyperref}

\makeatletter
\newcommand\@myback@floats{%
  \counterwithout{figure}{chapter}
  \setcounter{figure}{0}}
\AddToHook{cmd/backmatter/after}{\@myback@floats}
\makeatother

\begin{document}
\listoffigures

\chapter{lorem}
\begin{figure}
  \includegraphics{example-image-a}
  \caption{A}
\end{figure}
\begin{figure}
  \includegraphics{example-image-b}
  \caption{B}
\end{figure}

\backmatter
\chapter{ipsum}
\begin{figure}
  \includegraphics{example-image-c}
  \caption{C}
\end{figure}

\end{document}

In this specific case, the anchor associated with Figure 1 redirects to Figure 1.1

[muzimuzhi]

Duplicate destinations are used.

pdfTeX warning (ext4): destination with the same identifier (name{figure.1.1}) 
has been already used, duplicate ignored
<to be read again> 
                   \relax 
l.37   \caption{C}

Looks like a LaTeX2e issue. The \counterwithout only updated the \the<counter> representation, but not the \theH<counter>, which was moved from hyperref to the LaTeX kernel since LaTeX 2024-11-01.

In your case, after \counterwithout{figure}{chapter}, \show\thefigure \show\theHfigure gave

> \thefigure=macro:
->\arabic {figure}.
l.29 \show\thefigure
                    

> \theHfigure=macro:
->\theHchapter .\the \value {figure}.
l.31 \show\theHfigure

[muzimuzhi]

Reported to LaTeX2e: latex3/latex2e#1829.

[matteofg]

Duplicate destinations are used.

It was fairly obvious to me when examining the .lof file

\addvspace {10\p@ }
\contentsline {figure}{\numberline {1.1}{\ignorespaces A}}{4}{figure.1.1}%
\contentsline {figure}{\numberline {1.2}{\ignorespaces B}}{4}{figure.1.2}%
\addvspace {10\p@ }
\contentsline {figure}{\numberline {1}{\ignorespaces C}}{6}{figure.1.1}%

I trust that someone from the LaTeX Project team will either respond from this repository or transfer the issue to the appropriate one.

[FrankMittelbach]

Reported to LaTeX2e: latex3/latex2e#1829.

There is normally no need to do that as we can reassign a bug to a different repository given that both live below latex3/. But it is holiday season so it might take a few days:-)

[u-fischer]

I can't test now, but you are resetting manually the figure counter to zero, and once you do such manually settings you are responsible to set also \theHfigure.

I also have the impression that you misuse \couterwithout to change the figure representation. What figure numbering do you want if there are two chapters with figures in the backmatter?

But looking at the log I think the actual problem is with the backmatter command. I will check later.

[u-fischer]

As expected the real problem is the \backmatter command. In the standard class it sets \@mainmatterfalse and so chapters are unnumbered and do not reset counters of elements like footnotes or figures. Generally speaking the class does not expect that you use that in the backmatter.

If you want to do it, and so reset counters and change their representation, you should also set the \theHcounter representation to something sensible.

[matteofg]

also have the impression that you misuse \couterwithout to change the figure representation.

This is the same approach used by memoir to adjust figure/table numbering in the backmatter.

What figure numbering do you want if there are two chapters with figures in the backmatter?

The posted example is an mwe. My general idea is to number figures and tables continuously across the frontmatter and backmatter, in order to have unique references:

1. frontmatter: 1, 2, 3, ...
2. mainmatter: 1.1, 1.2, ... 2.1, ...
3. backmatter: 4, 5, ...

Generally speaking the class does not expect that you use that in the backmatter.

I consider this a limitation, but I understand that modifying the standard classes at this stage could break existing documents, which is understandably not desirable.

For me, the issue is resolved. If I run into difficulties, I’ll ask on SE.