Own commands not accessible in fancypagestyle environment for plain pages with fancyhdr

Question

I'm experiencing a weird bug.

If I understand correctly, LaTeX plain pages principle consists in pages following a document mark triggered by maintitle or a chapter/section mention. Each time a main title or a chapter/section LaTeX command is issued, the chapter/section mark is called. By default, that mark is displayed in the header according to the format defined by the plainpage style.

Redefining that plain page style with \fancypagestyle{plain} allows us to override this default behavior.

If I want to apply the same header/footer algorithm for ALL pages, I just need to redefine the plain page style and apply that style to the document.

However, it seems the new command I defined is not accessible in that environment for plain pages.

\documentclass{report}
\makeatletter
\usepackage{pgfopts}

% This is what we do here. We define commands like \@wgetdoc@title@maintitle
% that we need to call manually to execute their content.
\newif\if@wgetdoc@title@ownpage
\pgfkeys{
    /wgetdoc/title/.cd,
    % maintitle/.code={\ifx#1\@empty\else\edef\@wgetdoc@title@maintitle{#1}\fi},
    maintitle/.store in=\@wgetdoc@title@maintitle,
    maintitle/.value required,
    subtitle/.store in=\@wgetdoc@title@subtitle,
    author/.store in=\@wgetdoc@title@author,
    filename/.store in=\@wgetdoc@title@filename,
    ownpage/.is if=@wgetdoc@title@ownpage
}

\renewcommand{\title}[1][]{%

    % The following command is a shortcut and marginally quicker than
    % \pgfkeys{/wgetdoc/title/.cd, #1}
    % The command cannot end with the trailing / though.
    \pgfqkeys{/wgetdoc/title}{#1}

    \@ifundefined{@wgetdoc@title@filename}{

        % Do not use the following check. This macro is only available in
        % xkeyval and allows just checking if a key is defined in a family from
        % a list of families.
        \@ifundefined{@wgetdoc@title@maintitle}{
            \ClassError{wgetdoc}{You did not specify a main title}{}
        }{}

        % Check if maintitle is empty as it: maintitle=,subtitle=lorem
        % or maintitle={},subtitle=lorem
        % No need to check further as pgfkeys trims white spaces and
        % checks performed either by \ifblank (etoolbox) or
        % \@ifmtarg (ifmtarg) are lost
        \ifx\@wgetdoc@title@maintitle\@empty
            \ClassError{wgetdoc}{The main title you specified is empty}{}
        \fi

        % Custom horizontale rule only local to this environment
        \newcommand{\@wgetdoc@title@hrule}{\rule{\linewidth}{1mm}}

        % If this boolean key is absent of the title command, this will return
        % false. If it is only present, it will return true. Any
        % value other than 'true' or 'false' is non accepted and will make the
        % compilation crash.
        \if@wgetdoc@title@ownpage
            \begin{titlepage}
                \begin{center}

                    \@wgetdoc@title@hrule%
                    \vspace{0.4cm}

                    % We always need to define \par in scope for a font size
                    % change, otherwise, if the title is ever longer than a
                    % line, it will wrap to the next line with huge characters
                    % on a normal baseline.
                    {\Huge\textbf{\@wgetdoc@title@maintitle}\par}%

                    \vspace{0.4cm}%
                    \@wgetdoc@title@hrule

                    \@ifundefined{@wgetdoc@title@subtitle}{}{
                        \vspace{1.5cm}
                        {\Large{\@wgetdoc@title@subtitle}\par}%
                    }

                    \@ifundefined{@wgetdoc@title@author}{}{
                        % Adds vertical space which will not be suppressed at the
                        % beginning or end of a page. Text following that statement
                        % will be at the bottom of the page.
                        \vspace*{\fill}
                        {\emph{Author: \@wgetdoc@title@author}\par}%
                    }

                \end{center}
            \end{titlepage}%
        \else
            \begin{center}
                {\huge\textbf{\@wgetdoc@title@maintitle}\par}
                \@ifundefined{@wgetdoc@title@subtitle}{}{
                    {\large{\@wgetdoc@title@subtitle}\par}%
                }
            \end{center}
            \@ifundefined{@wgetdoc@title@author}{}{
                {\emph{Author: \@wgetdoc@title@author}\par}%
            }
            \@wgetdoc@title@hrule%
        \fi

    }{
    }
}


\usepackage{fancyhdr}
\newcommand{\@wgetdoc@header@centervalue}{}
\fancypagestyle{plain}{

    \fancyhf{}
    \@ifundefined{@wgetdoc@title@subtitle}{}{
        \renewcommand{\@wgetdoc@header@centervalue}{\@wgetdoc@title@subtitle}
    }
    \fancyhead[C]{\@wgetdoc@header@centervalue}
}
\pagestyle{plain}


\usepackage{lipsum}
\makeatother
\begin{document}

    \title[maintitle=Some title,
          subtitle=\textsc{some sub},
          author=This is me,ownpage=true]

    \chapter{My chapter name}

    \section{My section name}

    \lipsum[4-57]



\end{document}

If I remove the condition line 105 :

\@ifundefined{@wgetdoc@title@subtitle}{}{
    \renewcommand{\@wgetdoc@header@centervalue}{\@wgetdoc@title@subtitle}
}

but I let the renewcommand enabled, this is working like expected and my header is defined properly for all pages.

Any solution to this problem?

A link to the code on Github Gist, if you prefer that platform as it has line numbering: https://gist.github.com/wget/e8da2f2fb35aa741b8ddf497c827941d

Answer 1

Your problem is that the plain pagestyle is called in two places. You can easily test this by adding a \show\x:

\fancypagestyle{plain}{
    \show\x
    \fancyhf{}
    \@ifundefined{@wgetdoc@title@subtitle}{}{
        \renewcommand{\@wgetdoc@header@centervalue}{\@wgetdoc@title@subtitle}
    }
    \fancyhead[C]{\@wgetdoc@header@centervalue}
}

The first time it is called at the \pagestyle{plain}. At this time the subtitle command is not defined, and so you get almost everywhere empty headers. The second time is in the \thispagestyle{plain} in the chapter command. Now subtitle is defined as you don't call \pgfqkeys{/wgetdoc/title}{#1} in a group. So this page shows the subtitle.

On the whole I do find a bit dangerous that you base your code so much on the order of the commands. Imho it would be better to put the \pagestyle at the end of the title command if it should rely on its options.