How do I determine in which order packages have been loaded?

Question

The \listfiles command will give the list of all loaded files (and therefore also packages) at the end of the .log file, but how do I determine from inside LaTeX, whether package A was loaded before package B or vice versa?

Answer 1

You can access the list as a comma separated list of filenames in \@filelist

If you need this check after \begin{document} use \listfiles so LaTeX saves that information.

\listfiles does

  \@for\@currname:=\@filelist\do{%
      .....

to iterate over this list.

So for example you could define

\makeatletter

\def\test#1#2{%
\def\hmma{#1.sty}%
\let\hmmb\@empty
\@for\@currname:=\@filelist\do{%
   \ifx\@currname\hmma
     \def\hmmb{#2.sty}%
   \fi
   \ifx\@currname\hmmb
       \typeout{#1 loaded before #2}%
   \fi}}

then using this as:

\test{marginnote}{geometry}

will type out

marginnote loaded before geometry

if that is in fact the case.

As noted in the comments you might want to use different comand names in production code, also if the two .sty are removed from the test you can test other files such as class and def files that are listed by LaTeX, but would need to explicitly use the extension, so \test{marginnote.sty}{geometry.sty}

Answer 2

Here's a way: the code from \usepackage{xparse} to \ExplSyntaxOff should go before checking any package, of course. The definition of the \test command is just for showing that the code works, though, and can be removed.

\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
\seq_new:N \l_pkgfirst_list_seq
\bool_new:N \l_pkgfirst_tmpa_bool
\cs_generate_variant:Nn \seq_set_split:Nnn { Nnx }
\NewDocumentCommand{\ifpackagefirst}{mmmm}
  {
   \bool_set_false:N \l_pkgfirst_tmpa_bool
   \seq_set_split:Nnx \l_pkgfirst_list_seq {,} { \use:c { @filelist} }
   \seq_if_in:NnT \l_pkgfirst_list_seq {#1} { \bool_set_true:N \l_pkgfirst_tmpa_bool }
   \seq_if_in:NnT \l_pkgfirst_list_seq {#2} { \bool_set_true:N \l_pkgfirst_tmpa_bool }
   \bool_if:NTF \l_pkgfirst_tmpa_bool
     { \pkgfirst_compare:nnnn {#1}{#2}{#3}{#4} }
     { \msg_term:x {OOPS,~packages~not~both~loaded} }
  }
\cs_new:Npn \pkgfirst_compare:nnnn #1 #2 #3 #4
  {
   \bool_set_false:N \l_pkgfirst_tmpa_bool
   \seq_map_inline:Nn \l_pkgfirst_list_seq
     {
      \str_if_eq:nnT { #1 } { ##1 }
        { \prg_map_break:n { \bool_set_true:N \l_pkgfirst_tmpa_bool } }
      \str_if_eq:nnT { #2 } { ##1 }
        { \prg_map_break:n { \bool_set_false:N \l_pkgfirst_tmpa_bool } }
     }
   \bool_if:NTF \l_pkgfirst_tmpa_bool {#3} {#4}
  }


\NewDocumentCommand\test{m m}
  {\ifpackagefirst{#1}{#2}{\msg_term:x {#1~before~#2}}{\msg_term:x {#1~after~#2}}}

\ExplSyntaxOff

\usepackage{graphicx}
\usepackage{imakeidx}
\usepackage{kantlipsum}


\test{graphicx.sty}{imakeidx.sty}

\test{imakeidx.sty}{kantlipsum.sty}

\test{kantlipsum.sty}{graphicx.sty}

\test{pippo.sty}{pluto.sty}

\stop

This is the output:

*************************************************
* graphicx.sty before imakeidx.sty
*************************************************
*************************************************
* imakeidx.sty before kantlipsum.sty
*************************************************
*************************************************
* kantlipsum.sty after graphicx.sty
*************************************************
*************************************************
* OOPS, packages not both loaded
*************************************************

Usage:

\ifpackagefirst{package1.sty}{package2.sty}
  {code to be executed if 1 has been loaded before 2}
  {code to be executed if 2 has been loaded before 1}

If the packages are not both loaded, no code will be executed.

Answer 3

A way to check for file order is to check the order of the files loaded in the @filelist.

\documentclass{book}
\usepackage{graphicx}
\usepackage{longtable}
\usepackage{verse}
\usepackage{hyperref}
\usepackage{caption}
\newcounter{ctr}
\makeatletter
\let\afilelist\@filelist
\begin{document}
% Just to see files
\@for\next:=\afilelist\do{%
 \next, \par
}
% Command factory
\stepcounter{ctr}
\@for\next:=\afilelist\do{%
      \expandafter\edef\csname @\next\endcsname{\thectr}
     \stepcounter{ctr}
}

% Define macro to check order
\def\checkpkgorder#1#2{%
   \edef\X{\csname @#1\endcsname}
    \edef\Y{\csname @#2\endcsname}
    \expandafter\ifnum\X\expandafter<\Y
      Yes loaded earlier \X, \Y
     \else
      No loaded later \X, \Y
   \fi
}

\checkpkgorder{book.cls}{ifxetex.sty}
\end{document}