How to check if a section title (or any heading) is the first line of a new page?

Question

I would like to be able to use an \if command to check if a \section appears on the first line of a new page. If a section heading is the first line of a new page, I would like to then adjust some of the spacing between the section heading and the header by modifying \headsep.

Is there a simple way to do this?

More info (edit): The issue arises whenever you don't forcibly add new pages to separate sections. If you were to write continuously, then, whenever TeX decides to insert a page break, the spacing arguments native to \section are suppressed iff the page break occurs right before a new section.

Hence, if, for instance, you have long, ruled headers, the lack of spacing looks odd:

As far as I know, TeX doesn't have a built-in counter for line numbering that can be used to check if a heading appears on the first line of a new page. You don't know when a page break is likely to occur, either. Thus, although I have a specific purpose for finding a way to check if something is on the first (or nth line) of a page, it might still help others with different purposes.

Answer 1

This solution requires the lineno, fancyhdr, and color packages, so it is not elegant.

First, Initiate lineno to insert line numbers to your document (use \linenumbers after begin{document}); lineno adds a counter called linenumber which you can force-reset for each new page by adding \@addtoreset{linenumber}{page} to your .cls (class/style) file.

Define a new fancypagestyle{y} that adds the required additional space (x) between header and the first line using \setlength{\headsep}{x}.

Then, when you define your \def\@makesectionhead#1{} macro that creates or prints the section number and name, add \ifnum\value{linenumber}=1\thispagestyle{y}\else\fi as the last line before closing with }.

Lastly, use \renewcommand\linenumberfont{\color{white}} to hide line numbers by changing them to white.

Answer 2

This is a rather horrible hack:

\makeatletter
\let\john@@section\section
\def\section{\goodbreak\@nobreaktrue
  \vspace*{3.5ex \@plus 1ex \@minus .2ex}\john@@section}
\makeatother

The argument of \vspace has been copied from the class definition of \section.

(It's quite hard to understand the need for this.)