Etoolbox's \patchcmd can't find search pattern due to hyperref package

Question

I use the report class and I have learned from other questions on this site (like Remove spacing between per-chapter figures in LoF) how I can adjust the spacing between per-chapter figures in the LoF. I would like to change the traditional

\addtocontents{lof}{\protect\addvspace{10\p@}}

in the report.cls file to

\addtocontents{lof}{\protect\addvspace{15\p@}} by using this patch :

\makeatletter
\patchcmd{\@chapter}%
  {\addtocontents{lof}{\protect\addvspace{10\p@}}}% <search>
  {\addtocontents{lof}{\protect\addvspace{15\p@}}}% <replace>
  {}{}% <success><failure>
\makeatother

However, by issuing \tracingpatches I can see the following :

[debug] analyzing '\@chapter'
[debug] ++ control sequence is defined
[debug] ++ control sequence is a macro
[debug] ++ macro can be retokenized cleanly
[debug] -- search pattern not found in replacement text

Am I doing something wrong ? I don't understand why \patchcmd can't find the specified code. For the record, there are 3 other patches in my document (not modifying \@chapter) and they all work well.

Edit: While preparing a MWE, I realized that the package hyperref is the culprit, since removing it solves the problem.

\documentclass[12pt,twoside,openright]{report}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[french]{babel}
\usepackage{lmodern}
\usepackage{microtype}
\usepackage{etoolbox}
\usepackage[pdftex,colorlinks,linkcolor=blue,citecolor=red]{hyperref}
%----------------------- Patch -----------------------
\tracingpatches
\makeatletter
\patchcmd{@chapter}%

  {\addtocontents{lof}{\protect\addvspace{10\p@}}}% <search>
  {\addtocontents{lof}{\protect\addvspace{15\p@}}}% <replace>
  {}{}% <success><failure>
\makeatother
%-----------------------------------------------------
\begin{document}
\listoffigures
\chapter{A chapter}
\begin{figure}\caption{A figure}\end{figure}
\begin{figure}\caption{A figure}\end{figure}
\chapter{A chapter}
\begin{figure}\caption{A figure}\end{figure}
\begin{figure}\caption{A figure}\end{figure}
\appendix
\chapter{A chapter}
\addtocontents{lof}{\protect\addvspace{10pt}}%
\begin{figure}\caption{A figure}\end{figure}
\begin{figure}\caption{A figure}\end{figure}
\end{document}

Is there a way to fix this ? I need to keep loading the hyperref package.

Answer 1

hyperref has to define a great many internal commands to do its thing.

In this case the original definition of \@chapter is saved to \Hy@org@chapter by hyperref, \@chapter is then redefined to do some linking and then calls \Hy@org@chapter.

So the solution here is to patch \Hy@org@chapter instead of \@chapter when hyperref is loaded.

\documentclass[12pt,twoside,openright]{report}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[french]{babel}
\usepackage{lmodern}
\usepackage{microtype}
\usepackage{etoolbox}
\usepackage[pdftex,colorlinks,linkcolor=blue,citecolor=red]{hyperref}
%----------------------- Patch -----------------------
\tracingpatches
\makeatletter
\patchcmd{\Hy@org@chapter}%

  {\addtocontents{lof}{\protect\addvspace{10\p@}}}% <search>
  {\addtocontents{lof}{\protect\addvspace{15\p@}}}% <replace>
  {}{}% <success><failure>
\makeatother
%-----------------------------------------------------
\begin{document}
\listoffigures
\chapter{A chapter}
\begin{figure}\caption{A figure}\end{figure}
\begin{figure}\caption{A figure}\end{figure}
\chapter{A chapter}
\begin{figure}\caption{A figure}\end{figure}
\begin{figure}\caption{A figure}\end{figure}
\appendix
\chapter{A chapter}
\addtocontents{lof}{\protect\addvspace{10pt}}%
\begin{figure}\caption{A figure}\end{figure}
\begin{figure}\caption{A figure}\end{figure}
\end{document}

gives

and

[debug] tracing \patchcmd on input line 16
[debug] analyzing '\Hy@org@chapter'
[debug] ++ control sequence is defined
[debug] ++ control sequence is a macro
[debug] ++ macro can be retokenized cleanly
[debug] ++ search pattern found in replacement text
[debug] ++ patching possible
[debug] == retokenizing macro now

---

Alternatively, you can try to get your patch in before hyperref applies its redefinitions.

\documentclass[12pt,twoside,openright]{report}
\usepackage{etoolbox}
%----------------------- Patch -----------------------
\tracingpatches
\makeatletter
\patchcmd{@chapter}%

  {\addtocontents{lof}{\protect\addvspace{10\p@}}}% <search>
  {\addtocontents{lof}{\protect\addvspace{15\p@}}}% <replace>
  {}{}% <success><failure>
\makeatother
%-----------------------------------------------------
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[french]{babel}
\usepackage{lmodern}
\usepackage{microtype}
\usepackage[pdftex,colorlinks,linkcolor=blue,citecolor=red]{hyperref}
\begin{document}
\listoffigures
\chapter{A chapter}
\begin{figure}\caption{A figure}\end{figure}
\begin{figure}\caption{A figure}\end{figure}
\chapter{A chapter}
\begin{figure}\caption{A figure}\end{figure}
\begin{figure}\caption{A figure}\end{figure}
\appendix
\chapter{A chapter}
\addtocontents{lof}{\protect\addvspace{10pt}}%
\begin{figure}\caption{A figure}\end{figure}
\begin{figure}\caption{A figure}\end{figure}
\end{document}

Thanks to David Carlisle for suggesting that in the comments.