checklab.tex

 % Making those `Label(s) have changed\dots' messages more explicit
%
% The \LaTeX{} kernel produces the messages when something, while the
% |.aux| file is being scanned (after the \cs{AtEndDocument} tokens
% have been executed), sets the \cs{if@tempswa} switch with the
% command \cs{@tempswatrue}.
%
% (This fact can be used by packages, such as my |footmisc.sty|, to
% piggy-back on the message; but it's nice in that circumstance and
% others to be sure where the message is coming from.)
%
% This is a jiffy patch to the kernel so that it produces a
% (\cs{typeout}) message for each label \emph{it} thinks has changed.
%
% Usage: Incorporate this code into a package or class file,       or
%        \input this file from a package or class file,            or
%        \makeatletter \input{checklab} \makeatother in your document
%                                                    preamble
%
% This software jiffy is placed in the public domain.  Do with it as
% you wish, though I have to say I would prefer you not to claim it
% as your own (otoh, it's the product of a twisted mind, so probably
% not an attractive thing to claim).
%
% Robin Fairbairns (rf10@cl.cam.ac.uk)
% Produced in this form 1999/01/15
%
\def\@testdef #1#2#3{%
  \def\reserved@a{#3}%
  \expandafter \ifx \csname #1@#2\endcsname \reserved@a
  \else
    \@tempswatrue
    \typeout{label change: #1@#2 was
      \expandafter \ifx \csname #1@#2\endcsname \relax
        unset
      \else
        \csname#1@#2\endcsname\space
      \fi
      now #3}%
  \fi
}