Convert % to macro, retain as comment?

Question

I often transfer files between myself and someone with little knowledge of LaTeX, for editing purposes. So far, I have managed to get most TeX-specific oddities under control (thanks to utf-8 encoding). But I am stymied by the percent symbol %.

What I wish to do is detect whenever an un-escaped % is used in the document body (OK in Preamble). If it is used, then its presence is counted. At the end of the document, I can print a message in the log file, if the count exceeds zero.

This MWE code does the counting part (I omitted the message):

\documentclass{article} % Compile using lualatex.
\newcounter{pctcount}
\begin{document}
\begingroup
\lccode`\~="0025
\lowercase{\endgroup\gdef~{\stepcounter{pctcount}\%}}
\catcode`\%=13
This line % has an unescaped percent.\par
And also % here.\par
pctcount=\arabic{pctcount}\par
\end{document}

Essentially, it changes % from a comment character, to a macro. My problem: I would also like it to retain its capability as a comment character, so that it both increments the counter, and works as a comment.

I have tried various magic tricks such as using \catcode to temporarily assign comment code 14 to an otherwise-unused character (such as the generic currency symbol). No joy, except distant demonic laughter if I randomly type too much code.

Is this possible in lualatex? Lua code acceptable.

What I am now doing, is scanning the *tex files via BASH script.

Answer 1

You don't need Lua for this, it can be done in plain LaTeX, but it isn't a nice, clean, easy-to-understand method. This is based on this answer, which is about taking the remainder of the line as a parameter. I do recommend reading that answer, as it explains what is going on much better than I can.

The next trick is to re-define '%' to do something, in this case, step the counter.

Note, though, that this entire method seems to fail with a strange error if you use \par to end the paragraph. If you just use a blank line to end the paragraph, it works fine.

\documentclass{article}
\begin{document}
\newcounter{pctcount}
\newcommand{\newlinecommand}[2]{%
  \newcommand{#1}{%
    \begingroup%
    \escapechar=\\% \catcode\endlinechar=\active% \csname\string#1\endcsname% }% \begingroup% \escapechar=\%
  \lccode`~=\endlinechar%
  \lowercase{%
    \expandafter\endgroup
    \expandafter\def\csname\string#1\endcsname##1~%
  }{\endgroup#2\space}%
}
%%% USAGE:
\newlinecommand{\emphline}{\emph{#1}}
\newlinecommand{\incrementpcount}{\stepcounter{pctcount}}
First words \emphline rest of line
some more text
% this would fail if it was after 'catcode' \par
\catcode`%=13
\def%{\incrementpcount}
This line % has an unescaped percent.
And also % here.
It is the percent sign which is a problem, though\par
This is a new paragraph
I want a literal percent here: % yay, percent sign
pctcount=\arabic{pctcount}
\end{document}