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zref-check.dtx
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zref-check.dtx
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% \iffalse meta-comment
%
% File: zref-check.dtx
%
% This file is part of the LaTeX package "zref-check".
%
% Copyright (C) 2021-2023 gusbrs
%
% It may be distributed and/or modified under the conditions of the
% LaTeX Project Public License (LPPL), either version 1.3c of this
% license or (at your option) any later version. The latest version
% of this license is in the file:
%
% https://www.latex-project.org/lppl.txt
%
% and version 1.3 or later is part of all distributions of LaTeX
% version 2005/12/01 or later.
%
%
% This work is "maintained" (as per LPPL maintenance status) by gusbrs.
%
% This work consists of the files zref-check.dtx,
% zref-check.ins,
% zref-check-doc.tex,
% zref-check-code.tex,
% and the files generated from them.
%
% The released version of this package is available from CTAN.
%
% -----------------------------------------------------------------------
%
% The development version of the package can be found at
%
% https://github.com/gusbrs/zref-check
%
% for those people who are interested.
%
% -----------------------------------------------------------------------
%
% \fi
%
% \iffalse
%<*driver>
\documentclass{l3doc}
% Have \GetFileInfo pick up date and version data
\usepackage{zref-check}
\NewDocumentCommand\opt{m}{\texttt{#1}}
\MakeShortVerb{\|}
\begin{document}
\DocInput{zref-check.dtx}
\end{document}
%</driver>
% \fi
%
%
%
% \section{Initial setup}
%
% Start the \pkg{DocStrip} guards.
% \begin{macrocode}
%<*package>
% \end{macrocode}
%
% Identify the internal prefix (\LaTeX3 \pkg{DocStrip} convention).
% \begin{macrocode}
%<@@=zrefcheck>
% \end{macrocode}
%
%
% For the \texttt{chapter} and \texttt{section} checks, \pkg{zref-check} uses
% the new hook system in \pkg{ltcmdhooks}, which was released with the
% 2021/06/01 \LaTeX{} kernel. And, since we followed the move to
% \texttt{e}-type expansion, to play safe we require the 2023-11-01 kernel or
% newer.
% \begin{macrocode}
\def\zrefcheck@required@kernel{2023-11-01}
\NeedsTeXFormat{LaTeX2e}[\zrefcheck@required@kernel]
\providecommand\IfFormatAtLeastTF{\@ifl@t@r\fmtversion}
\IfFormatAtLeastTF{\zrefcheck@required@kernel}
{}
{%
\PackageError{zref-check}{LaTeX kernel too old}
{%
'zref-check' requires a LaTeX kernel \zrefcheck@required@kernel\space or newer.%
}%
}%
% \end{macrocode}
%
% Identify the package.
% \begin{macrocode}
\ProvidesExplPackage {zref-check} {2023-11-14} {0.3.5}
{Flexible cross-references with contextual checks based on zref}
% \end{macrocode}
%
% \section{Dependencies}
%
% \begin{macrocode}
\RequirePackage { zref-user }
\RequirePackage { zref-abspage }
\RequirePackage { ifdraft }
% \end{macrocode}
%
%
% \section{\pkg{zref} setup}
%
% Provide absolute counters for section and chapter, and respective \pkg{zref}
% properties, so that we can make checks about relation of chapters/sections
% regardless of internal counters, since we don't get those for the unnumbered
% (starred) ones. Thanks Ulrike Fischer for suggestions at TeX.SX about the
% proper place to make the hooks for this purpose.
% \begin{macrocode}
\newcounter { zc@abschap }
\newcounter { zc@abssec } [ zc@abschap ]
% \end{macrocode}
%
%
% If the documentclass does not define \cs{chapter} the only thing that
% happens is that the chapter counter is never incremented, and the section
% one never reset.
% \begin{macrocode}
\AddToHook { cmd / chapter / before }
{ \stepcounter { zc@abschap } }
\zref@newprop { zc@abschap } [0] { \int_use:N \c@zc@abschap }
\zref@addprop \ZREF@mainlist { zc@abschap }
% \end{macrocode}
%
% \begin{macrocode}
\AddToHook { cmd / section / before }
{ \stepcounter { zc@abssec } }
\zref@newprop { zc@abssec } [0] { \int_use:N \c@zc@abssec }
\zref@addprop \ZREF@mainlist { zc@abssec }
% \end{macrocode}
%
%
% These are the lists of properties to be used by \pkg{zref-check}, that is,
% the list of properties the references and targets store. This is the
% minimum set required, more properties may be added according to options.
% For user facing labels, we must use the \texttt{main} property list, so that
% \pkg{zref-clever} can also retrieve the properties it needs to refer to
% them.
% \begin{macrocode}
\zref@newlist { zrefcheck-check }
\zref@addprops { zrefcheck-check }
{
page , % for messages
abspage ,
zc@abschap ,
zc@abssec
}
\zref@newlist { zrefcheck-end }
\zref@addprops { zrefcheck-end }
{
abspage ,
zc@abschap ,
zc@abssec
}
% \end{macrocode}
% For \pkg{zref-vario} we only need page information, since we only perform
% \opt{above} and \opt{below} checks there.
% \begin{macrocode}
\zref@newlist { zrefcheck-zrefvario }
\zref@addprops { zrefcheck-zrefvario }
{
page , % for messages
abspage ,
}
% \end{macrocode}
%
%
% \section{Plumbing}
%
% \subsection{Auxiliary}
%
% \begin{macro}
% {
% \l_@@_tmpa_tl ,
% \l_@@_tmpb_tl ,
% \g_@@_tmpa_tl ,
% \l_@@_tmpa_int ,
% \l_@@_tmpa_bool ,
% \g_@@_tmpa_ior ,
% }
% Temporary scratch variables.
% \begin{macrocode}
\tl_new:N \l_@@_tmpa_tl
\tl_new:N \l_@@_tmpb_tl
\tl_new:N \g_@@_tmpa_tl
\int_new:N \l_@@_tmpa_int
\bool_new:N \l_@@_tmpa_bool
\ior_new:N \g_@@_tmpa_ior
% \end{macrocode}
% \end{macro}
%
% \subsection{Messages}
%
% \begin{macro}{\@@_message:nnnn, \@@_message:nnne}
% \begin{macrocode}
\cs_new_protected:Npn \@@_message:nnnn #1#2#3#4
{
\use:c { msg_ \l_@@_msglevel_tl :nnnnn }
{ zref-check } {#1} {#2} {#3} {#4}
}
\cs_generate_variant:Nn \@@_message:nnnn { nnne }
% \end{macrocode}
% \end{macro}
%
% \begin{macrocode}
\msg_new:nnn { zref-check } { check-failed }
{
Check~failed~\msg_line_context:.~
Failed~check~'#1'~for~label~'#2'~on~page~#3.
}
\msg_new:nnn { zref-check } { double-check }
{
Same~page~check~\msg_line_context:.~
Double-check~'#1'~for~label~'#2'~on~page~#3.
}
\msg_new:nnn { zref-check } { empty-label }
{
Check~failed~\msg_line_context:.~
Failed~check~'#1'~for~empty~label.
}
\msg_new:nnn { zref-check } { no-checks }
{ No~checks~for~'\iow_char:N\\zcheck'~\msg_line_context:. }
% \end{macrocode}
%
% \begin{macrocode}
\msg_new:nnn { zref-check } { check-missing }
{ Check~'#1'~not~defined~\msg_line_context:. }
\msg_new:nnn { zref-check } { property-undefined }
{ Property~'#1'~not~defined~\msg_line_context:. }
\msg_new:nnn { zref-check } { property-not-in-label }
{ Label~'#1'~has~no~property~'#2'~\msg_line_context:. }
\msg_new:nnn { zref-check } { property-not-integer }
{ Property~'#1'~for~label~'#2'~not~an~integer~\msg_line_context:. }
% \end{macrocode}
%
% \begin{macrocode}
\msg_new:nnn { zref-check } { hyperref-preamble-only }
{
Option~'hyperref'~only~available~in~the~preamble. \iow_newline:
Use~the~starred~version~of~'\iow_char:N\\zcheck'~instead.
}
\msg_new:nnn { zref-check } { missing-hyperref }
{ Missing~'hyperref'~package. \iow_newline: Setting~'hyperref=false'. }
\msg_new:nnn { zref-check } { ignore-ok-document-only }
{
Option~'#1'~only~available~in~the~document. \iow_newline:
Use~option~'msglevel'~instead.
}
\msg_new:nnn { zref-check } { option-preamble-only }
{ Option~'#1'~is~preamble~only~\msg_line_context:. }
\msg_new:nnn { zref-check } { closerange-not-positive-integer }
{
Option~'closerange'~not~a~positive~integer~\msg_line_context:.~
Using~default~value.
}
\msg_new:nnn { zref-check } { labelcmd-undefined }
{
Control~sequence~named~'#1'~used~in~option~'labelcmd'~is~not~defined.~
Using~default~value.
}
\msg_new:nnn { zref-check } { option-deprecated-with-alternative }
{
Option~'#1'~has~been~deprecated~\msg_line_context:.\iow_newline:
Use~'#2'~instead.
}
\msg_new:nnn { zref-check } { option-deprecated }
{ Option~'#1'~has~been~deprecated~\msg_line_context:. }
\msg_new:nnn { zref-check } { load-time-options }
{
'zref-check'~does~not~accept~load-time~options.~
To~configure~package~options,~use~'\iow_char:N\\zrefchecksetup'.
}
% \end{macrocode}
%
%
% \subsection{Integer testing}
%
% \begin{macro}{\@@_is_integer:n, \@@_int_to_roman:w}
% From \url{https://tex.stackexchange.com/a/244405} (thanks Enrico Gregorio,
% aka `egreg'), also see \url{https://tex.stackexchange.com/a/19769}.
% Following the \texttt{l3styleguide}, I made a copy of
% \cs{__int_to_roman:w}, since it is an internal function from the
% \texttt{int} module, but we still get a warning from \texttt{l3build doc},
% complaining about it. And we're using \cs{tl_if_empty:oTF} instead of
% \cs{tl_if_blank:oTF} as in egreg's answer, since \cs{romannumeral} is
% defined so that ``the expansion is empty if the number is zero or
% negative'', not ``blank''. A couple of comments about this technique: the
% underlying \cs{romannumeral} ignores space tokens and explicit signs
% (\texttt{+} and \texttt{-}) in the expansion and hence it can only be used
% to test positive integers; also the technique cannot distinguish whether
% it received an empty argument or if ``the expansion was empty'' as a
% result of receiving number as argument, so this must also be controlled
% for since, in our use case, this may happen.
% \begin{macrocode}
\cs_new_eq:NN \@@_int_to_roman:w \__int_to_roman:w
\prg_new_conditional:Npnn \@@_is_integer:n #1 { p, T , F , TF }
{
\tl_if_empty:oTF {#1}
{ \prg_return_false: }
{
\tl_if_empty:oTF { \@@_int_to_roman:w -0#1 }
{ \prg_return_true: }
{ \prg_return_false: }
}
}
% \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_is_integer_rgx:n}
% A possible alternative to \cs{@@_is_integer:n} is to use a straightforward
% regexp match (see \url{https://tex.stackexchange.com/a/427559}). It does
% not suffer from the mentioned caveats from the \cs{__int_to_roman:w}
% technique, however, while \cs{@@_is_integer:n} is expandable,
% \cs{@@_is_integer_rgx:n} is not. Also, \cs{@@_is_integer_rgx:n} is
% probably slower.
% \begin{macrocode}
\prg_new_protected_conditional:Npnn \@@_is_integer_rgx:n #1 { TF }
{
\regex_match:nnTF { \A\d+\Z } {#1}
{ \prg_return_true: }
{ \prg_return_false: }
}
% \end{macrocode}
% \end{macro}
%
%
%
% \subsection{Options}
%
%
% \subsubsection*{\opt{hyperref} option}
%
% \begin{variable}{\l_@@_use_hyperref_bool, \l_@@_warn_hyperref_bool}
% \begin{macrocode}
\bool_new:N \l_@@_use_hyperref_bool
\bool_new:N \l_@@_warn_hyperref_bool
\keys_define:nn { zref-check }
{
hyperref .choice: ,
hyperref / auto .code:n =
{
\bool_set_true:N \l_@@_use_hyperref_bool
\bool_set_false:N \l_@@_warn_hyperref_bool
} ,
hyperref / true .code:n =
{
\bool_set_true:N \l_@@_use_hyperref_bool
\bool_set_true:N \l_@@_warn_hyperref_bool
} ,
hyperref / false .code:n =
{
\bool_set_false:N \l_@@_use_hyperref_bool
\bool_set_false:N \l_@@_warn_hyperref_bool
} ,
hyperref .initial:n = auto ,
hyperref .default:n = auto
}
% \end{macrocode}
% \end{variable}
%
% \begin{macrocode}
\AddToHook { begindocument }
{
\@ifpackageloaded { hyperref }
{
\bool_if:NT \l_@@_use_hyperref_bool
{ \RequirePackage { zref-hyperref } }
}
{
\bool_if:NT \l_@@_warn_hyperref_bool
{ \msg_warning:nn { zref-check } { missing-hyperref } }
\bool_set_false:N \l_@@_use_hyperref_bool
}
\keys_define:nn { zref-check }
{
hyperref .code:n =
{ \msg_warning:nn { zref-check } { hyperref-preamble-only } }
}
}
% \end{macrocode}
%
%
% \subsubsection*{\opt{msglevel} option}
%
% \begin{variable}{\l_@@_msglevel_tl}
% \begin{macrocode}
\tl_new:N \l_@@_msglevel_tl
\keys_define:nn { zref-check }
{
msglevel .choice: ,
msglevel / warn .code:n =
{ \tl_set:Nn \l_@@_msglevel_tl { warning } } ,
msglevel / info .code:n =
{ \tl_set:Nn \l_@@_msglevel_tl { info } } ,
msglevel / none .code:n =
{ \tl_set:Nn \l_@@_msglevel_tl { none } } ,
msglevel / infoifdraft .code:n =
{
\ifdraft
{ \tl_set:Nn \l_@@_msglevel_tl { info } }
{ \tl_set:Nn \l_@@_msglevel_tl { warning } }
} ,
msglevel / warniffinal .code:n =
{
\ifoptionfinal
{ \tl_set:Nn \l_@@_msglevel_tl { warning } }
{ \tl_set:Nn \l_@@_msglevel_tl { info } }
} ,
msglevel .value_required:n = true ,
msglevel .initial:n = warn ,
% \end{macrocode}
% \opt{ignore} and \opt{ok} are convenience aliases for \opt{msglevel=none},
% but only for use in the document body.
% \begin{macrocode}
ignore .code:n =
{ \msg_warning:nnn { zref-check } { ignore-ok-document-only } { ignore } } ,
ignore .value_forbidden:n = true ,
ok .code:n =
{ \msg_warning:nnn { zref-check } { ignore-ok-document-only } { ok } } ,
ok .value_forbidden:n = true ,
}
% \end{macrocode}
% \end{variable}
%
% \begin{macrocode}
\AddToHook { begindocument }
{
\keys_define:nn { zref-check }
{
ignore .meta:n = { msglevel = none } ,
ok .meta:n = { msglevel = none } ,
}
}
% \end{macrocode}
%
%
% \subsubsection*{\opt{onpage} option}
%
% \begin{variable}{\l_@@_msgonpage_bool}
% \begin{macrocode}
\bool_new:N \l_@@_msgonpage_bool
\keys_define:nn { zref-check }
{
onpage .choice: ,
onpage / labelseq .code:n =
{
\bool_set_false:N \l_@@_msgonpage_bool
} ,
onpage / msg .code:n =
{
\bool_set_true:N \l_@@_msgonpage_bool
} ,
onpage / labelseqifdraft .code:n =
{
\ifdraft
{ \bool_set_false:N \l_@@_msgonpage_bool }
{ \bool_set_true:N \l_@@_msgonpage_bool }
} ,
onpage / msgiffinal .code:n =
{
\ifoptionfinal
{ \bool_set_true:N \l_@@_msgonpage_bool }
{ \bool_set_false:N \l_@@_msgonpage_bool }
} ,
onpage .value_required:n = true ,
onpage .initial:n = labelseq
}
% \end{macrocode}
% \end{variable}
%
%
% \subsubsection*{\opt{closerange} option}
%
% \begin{variable}{\l_@@_close_range_int}
% \begin{macrocode}
\int_new:N \l_@@_close_range_int
\keys_define:nn { zref-check }
{
closerange .code:n =
{
\@@_is_integer_rgx:nTF {#1}
{ \int_set:Nn \l_@@_close_range_int { \int_eval:n {#1} } }
{
\msg_warning:nn { zref-check } { closerange-not-positive-integer }
\int_set:Nn \l_@@_close_range_int { 5 }
}
} ,
closerange .value_required:n = true ,
closerange .initial:n = 5
}
% \end{macrocode}
% \end{variable}
%
%
% \subsubsection*{Package options}
%
% \pkg{zref-check} does not accept load-time options. Despite the tradition
% of so doing, Joseph Wright has a point in recommending otherwise at
% \url{https://chat.stackexchange.com/transcript/message/60360822#60360822}:
% separating ``loading the package'' from ``configuring the package'' grants
% less trouble with ``option clashes'' and with expansion of options at
% load-time.
% \begin{macrocode}
\bool_lazy_and:nnT
{ \tl_if_exist_p:c { opt@ zref-check.sty } }
{ ! \tl_if_empty_p:c { opt@ zref-check.sty } }
{ \msg_warning:nn { zref-check } { load-time-options } }
% \end{macrocode}
%
%
% \begin{macro}[int]{\zrefchecksetup}
% Provide \cs{zrefchecksetup}.
% \begin{macrocode}
\NewDocumentCommand \zrefchecksetup { m }
{ \keys_set:nn { zref-check } {#1} }
% \end{macrocode}
% \end{macro}
%
%
%
% \subsection{Position on page}
%
% Method for determining relative position within the page: the sequence in
% which the labels get shipped out, inferred from the sequence in which the
% labels occur in the \file{.aux} file.
%
% Some relevant info about the sequence of things:
% \url{https://tex.stackexchange.com/a/120978} and \texttt{texdoc lthooks},
% section ``Hooks provided by |\begin{document}|''.
%
%
% One first attempt at this was to use \cs{zref@newlabel}, which is the macro
% in which \pkg{zref} stores the label information in the aux file. When the
% \file{.aux} file is read at the beginning of the compilation, this macro is
% expanded for each of the labels. So, by redefining this macro we can feed a
% variable (a L3 sequence), and then do what it usually does, which is to
% define each label with the internal macro \cs{@newl@bel}, when the
% \file{.aux} file is read.
%
% Patching this macro for this is not possible. First, \cs{zref@newlabel} is
% one of those ``commands that look ahead'' mentioned in \pkg{ltcmdhooks}
% documentation. Indeed, \cs{@newl@bel} receives 3 arguments, and
% \cs{zref@newlabel} just passes the first, the following two will be scanned
% ahead. Second, the \pkg{ltcmdhooks} hooks are not actually available when
% the \file{.aux} file is read, they come only after |\begin{document}|.
% Hence, redefinition would be the only alternative. My attempts at this
% ended up registered at \url{https://tex.stackexchange.com/a/604744}. But
% the best result in these lines was:
%
% \begin{verbatim}
% \ZREF@Robust\edef\zref@newlabel#1{
% \noexpand\seq_gput_right:Nn \noexpand\g__zrefcheck_auxfile_lblseq_seq {#1}
% \noexpand\@newl@bel{\ZREF@RefPrefix}{#1}
% }
% \end{verbatim}
%
%
% However, better than the above is to just read it from the \file{.aux} file
% directly, which relieves us from hacking into any internals. That's what
% David Carlisle's answer at \url{https://tex.stackexchange.com/a/147705}
% does. This answer has actually been converted into the package
% \pkg{listlbls} by Norbert Melzer, but it is made to work with regular
% labels, not with \pkg{zref}'s. And it also does not really expose the
% information in a retrievable way (as far as I can tell). So, the below is
% adapted from Carlisle's answer's technique (a poor man's version of it...).
%
% There is some subtlety here as to whether this approach makes it safe for us
% to read the labels at this point without \cs{zref@wrapper@babel}. The
% common wisdom is that babel's shorthands are only active after
% |\begin{document}| (e.g., \url{https://tex.stackexchange.com/a/98897}).
% Alas, it is more complicated than that. Babel's documentation says (in
% section 9.5 Shorthands): ``To prevent problems with the loading of other
% packages after babel we reset the catcode of the character to the original
% one at the end of the package and of each language file (except with
% KeepShorthandsActive). It is re-activate[d] again at |\begin{document}|.
% We also need to make sure that the shorthands are active during the
% processing of the \file{.aux} file. Otherwise some citations may give
% unexpected results in the printout when a shorthand was used in the optional
% argument of |\bibitem| for example.'' This is done with
% |\if@filesw \immediate\write\@mainaux{...}|. In other words, the
% catcode change is written in the \file{.aux} file itself! Indeed, if you
% inspect the file, you'll find them there. Besides, there is still the
% ominous ``except with KeepShorthandsActive''.
%
% However, the \emph{method} we're using here is not quite the same as the
% usual run of the \file{.aux} file, because we're actively discarding the
% lines for which the first token is not equal to \cs{zref@newlabel}. I have
% tested the famous sensitive case for this: \pkg{babel} \opt{french} and
% labels with colons. And things worked as expected. Well, \emph{if}
% \opt{KeepShorthandsActive} is enabled \emph{with \opt{french}} and we load
% the package \emph{after babel} things do break, but not quite because of the
% colons in the labels. Even \pkg{siunitx} breaks in the same
% conditions\dots{}
%
% For reference: About what are valid characters for use in labels:
% \url{https://tex.stackexchange.com/a/18312}. About some problems with
% active colons: \url{https://tex.stackexchange.com/a/89470}. About the
% difference between L3 strings and token lists, see
% \url{https://tex.stackexchange.com/a/446381}, in particular Joseph Wright's
% comment: ``Strings are for data that will never be typeset, for example file
% names, identifiers, etc.: if the material may be used in typesetting, it
% should be a token list.'' See also moewe's (CW) answer in the same lines.
% Which suggests using L3 strings for the reference labels might be a good
% catch all approach, and possibly more robust. David Carlisle's comment
% about \pkg{inputenc} and how the strings work is a caveat (see
% \url{https://tex.stackexchange.com/q/446123#comment1516961_446381}, thanks
% David Carlisle). Still\dots{} let's stick to tradition as long as it works,
% \pkg{zref} already does a great job in this regard anyway.
%
%
% \begin{variable}{\g_@@_auxfile_lblseq_prop}
% \begin{macrocode}
\prop_new:N \g_@@_auxfile_lblseq_prop
% \end{macrocode}
% \end{variable}
%
% \begin{macrocode}
\tl_gset:Nn \g_@@_tmpa_tl { \c_sys_jobname_str .aux }
\file_if_exist:nT { \g_@@_tmpa_tl }
{
% \end{macrocode}
% Retrieve the information from the \file{.aux} file, and store it in a
% property list, so that the sequence can be retrieved in key-value fashion.
% \begin{macrocode}
\ior_open:Nn \g_@@_tmpa_ior { \g_@@_tmpa_tl }
\group_begin:
\int_zero:N \l_@@_tmpa_int
\tl_clear:N \l_@@_tmpa_tl
\tl_clear:N \l_@@_tmpb_tl
\bool_set_false:N \l_@@_tmpa_bool
\ior_map_variable:NNn \g_@@_tmpa_ior \l_@@_tmpa_tl
{
\tl_map_variable:NNn \l_@@_tmpa_tl \l_@@_tmpb_tl
{
\tl_if_eq:NnTF \l_@@_tmpb_tl { \zref@newlabel }
{
% \end{macrocode}
% Found a \cs{zref@label}, signal it.
% \begin{macrocode}
\bool_set_true:N \l_@@_tmpa_bool
}
{
\bool_if:NTF \l_@@_tmpa_bool
{
\bool_set_false:N \l_@@_tmpa_bool
\int_incr:N \l_@@_tmpa_int
\prop_gput:Nee \g_@@_auxfile_lblseq_prop
{ \l_@@_tmpb_tl }
{ \int_use:N \l_@@_tmpa_int }
}
{
% \end{macrocode}
% If there is not a match of the first token with \cs{zref@newlabel}, break
% the loop and discard the rest of the line, to ensure no babel calls to
% \cs{catcode} in the \file{.aux} file get expanded. This also breaks the
% loop and discards the rest of the \cs{zref@newlabel} lines after we got the
% label we wanted, since we reset \cs{l_@@_tmpa_bool} in the \texttt{T}
% branch.
% \begin{macrocode}
\tl_map_break:
}
}
}
}
\group_end:
\ior_close:N \g_@@_tmpa_ior
}
% \end{macrocode}
%
%
%
% The alternate method I had considered (more than that...) for this was using
% yx coordinates supplied by \pkg{zref}'s \pkg{savepos} module. However, this
% approach brought in a number of complexities, including the need to patch
% either \cs{zref@label} or \cs{ZREF@label}. In addition, the technique was
% at the bottom fundamentally flawed. Ulrike Fischer was very much right when
% she said that ``structure and position are two different beasts''
% (\url{https://github.com/ho-tex/zref/issues/12#issuecomment-880022576}). It
% is true that the checks based on it behaved decently, in normal
% circumstances, and except for outrageous label placement by the user, it
% would return the expected results. We don't really need exact coordinates
% to decide ``above/below''. Besides, it would do an exact job for the
% dedicated target macros of this package. It is also true that the ``page''
% for \cs{pageref} is stored with the value of where the \cs{label} is placed,
% wherever that may be. However, I could not conceive a situation where the
% \texttt{yx} criterion would perform clearly better than the
% \texttt{labelseq} one. And, if that's the case, and considering the
% complications it brings, this check was a slippery slope. All in all, I've
% decided to drop it.
%
% There's an interesting answer by David Carlisle at
% \url{https://tex.stackexchange.com/a/419189} to decide whether to typeset
% ``above'' or ``below'' using a method which essentially boils down to
% ``position in the \file{.aux} file''.
%
%
%
% \subsection{Counter}
%
% We need a dedicated counter for the labels generated by the checks and
% targets. The value of the counter is not relevant, we just need it to be
% able to set proper anchors with \cs{refstepcounter}. And, since I couldn't
% find a \cs{refstepcounter} equivalent in L3, we use a standard 2e counter
% here. I'm also using the technique to ensure the counter is never reset
% that is used by \file{zref-abspage.sty} and \cs{zref@require@unique}.
% Indeed, the requirements are the same, we need numbers ensured to be
% \emph{unique} in the counter.
%
% \begin{macrocode}
\begingroup
\let \@addtoreset \ltx@gobbletwo
\newcounter { zrefcheck }
\endgroup
\setcounter { zrefcheck } { 0 }
% \end{macrocode}
%
%
%
% \subsection{Label formats}
%
% \begin{macro}{\@@_check_lblfmt:n}
% \begin{syntax}
% \cs{@@_check_lblfmt:n} \Arg{check id int}
% \end{syntax}
% \begin{macrocode}
\cs_new:Npn \@@_check_lblfmt:n #1 { zrefcheck@ \int_use:N #1 }
% \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_end_lblfmt:n}
% \begin{syntax}
% \cs{@@_end_lblfmt:n} \Arg{label}
% \end{syntax}
% \begin{macrocode}
\cs_new:Npn \@@_end_lblfmt:n #1 { #1 @zrefcheck }
% \end{macrocode}
% \end{macro}
%
%
%
% \subsection{Property values}
%
%
% \begin{macro}[int]{\zrefcheck_get_astl:nnn}
% A convenience function to retrieve property values from labels. Uses
% \cs{g_@@_auxfile_lblseq_prop} for \texttt{lblseq}, and calls
% \cs{zref@extractdefault} for everything else.
%
% We cannot use the ``return value'' of \cs{@@_get_astl:nnn} or
% \cs{@@_get_asint:nnn} directly, because we need to use the retrieved
% property values as arguments in the checks, however we use here a number
% of non-expandable operations. Hence, we receive a local \texttt{tl/int}
% variable as third argument and set that, so that it is available (and
% expandable) at the place of use, and also make these functions `protected'
% (see egreg's \url{https://tex.stackexchange.com/a/572903}: ``a function
% that performs assignments should be \texttt{protected}''). For this
% reason, we do not group here, because we are passing a local variable
% around, but it is expected this function will be called within a group.
%
% We're returning \cs{c_empty_tl} in case of failure to find the intended
% property value (explicitly in \cs{zref@extractdefault}, but that is also
% what \cs{tl_clear:N} does).
%
% \begin{syntax}
% \cs{zrefcheck_get_astl:nnn} \Arg{label} \Arg{prop} \Arg{tl var}
% \end{syntax}
% \begin{macrocode}
\cs_new_protected:Npn \zrefcheck_get_astl:nnn #1#2#3
{
\tl_clear:N #3
\tl_if_eq:nnTF {#2} { lblseq }
{
\prop_get:NnNF \g_@@_auxfile_lblseq_prop {#1} #3
{
\msg_warning:nnnn { zref-check }
{ property-not-in-label } {#1} {#2}
}
}
{
% \end{macrocode}
% There are three things we need to check to ensure the information we are
% trying to retrieve here exists: the existence of \Arg{label}, the existence
% of \Arg{prop}, and whether the particular label being queried actually
% contains the property. If that's all in place, the value is passed to the
% checks, and it's their responsibility to verify the consistency of this
% value.
%
% The existence of the label is an user facing issue, and a warning for this
% is placed in \cs{@@_zcheck:nnnnn} (and done with \cs{zref@refused}). We do
% check here though for definition with \cs{zref@ifrefundefined} and silently
% do nothing if it is undefined, to reduce irrelevant warnings in a fresh
% compilation round. The other two are more ``internal'' problems, either
% some problem with the checks, or with the configuration of \pkg{zref} for
% their consumption.
% \begin{macrocode}
\zref@ifrefundefined {#1}
{}
{
\zref@ifpropundefined {#2}
{ \msg_warning:nnnn { zref-check } { property-undefined } {#2} }
{
\zref@ifrefcontainsprop {#1} {#2}
{
\tl_set:Ne #3
{ \zref@extractdefault {#1} {#2} { \c_empty_tl } }
}
{
\msg_warning:nnnn
{ zref-check } { property-not-in-label } {#1} {#2}
}
}
}
}
}
% \end{macrocode}
% \end{macro}
%
%
% \begin{variable}{\l_@@_integer_bool}
% \cs{zrefcheck_get_asint:nnn} is a very convenient wrapper around the more
% general \cs{zrefcheck_get_astl:nnn}, since almost always we'll be wanting
% to compare numbers in the checks. However, it is quite hard for it to
% ensure an integer is \emph{always} returned in the case of errors. And
% those do occur, even in a well structured document (e.g., in a first round
% of compilation). To complicate things, the L3 integer predicates are
% \emph{very} sensitive to receiving any other kind of data, and they
% \emph{scream}. To handle this \cs{zrefcheck_get_asint:nnn} uses
% \cs{l_@@_integer_bool} to signal if an integer could not be returned. To
% use this function always set \cs{l_@@_integer_bool} to true first, then
% call it as much as you need. If any of these calls got is returning
% anything which is not an integer, \cs{l_@@_integer_bool} will have been
% set to false, and you should check that this hasn't happened before
% actually comparing the integers (\cs{bool_lazy_and:nnTF} is your friend).
% \begin{macrocode}
\bool_new:N \l_@@_integer_bool
% \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_propval_tl}
% \begin{macrocode}
\tl_new:N \l_@@_propval_tl
% \end{macrocode}
% \end{variable}
%
% \begin{macro}[int]{\zrefcheck_get_asint:nnn}
% \begin{syntax}
% \cs{zrefcheck_get_asint:nnn} \Arg{label} \Arg{prop} \Arg{int var}
% \end{syntax}
% \begin{macrocode}
\cs_new_protected:Npn \zrefcheck_get_asint:nnn #1#2#3
{
\zrefcheck_get_astl:nnn {#1} {#2} { \l_@@_propval_tl }
\@@_is_integer:nTF { \l_@@_propval_tl }
{
% \end{macrocode}
% Make it an integer data type.
% \begin{macrocode}
\int_set:Nn #3 { \int_eval:n { \l_@@_propval_tl } }
}
{
\bool_set_false:N \l_@@_integer_bool
\zref@ifrefundefined {#1}
% \end{macrocode}
% Keep silent if ref is undefined to reduce irrelevant warnings in a fresh
% compilation round. Again, this is also not the point to check for undefined
% references, that's a task for \cs{@@_zcheck:nnnnn}.
% \begin{macrocode}
{ }
{
\msg_warning:nnnn { zref-check }
{ property-not-integer } {#2} {#1}
}
}
}
% \end{macrocode}
% \end{macro}
%
%
%
%
% \section{User interface}
%
%
% \subsection{\cs{zcheck}}
%
% \begin{macro}[int]{\zcheck}
% The \marg{text} argument of \cs{zcheck} should not be long, since
% \cs{hyperlink} cannot receive a long argument. Besides, there is no
% reason for it to be. Note, also, that hyperlinks crossing page boundaries
% have some known issues: \url{https://tex.stackexchange.com/a/182769},
% \url{https://tex.stackexchange.com/a/54607},
% \url{https://tex.stackexchange.com/a/179907}.
%
% \begin{syntax}
% \cs{zcheck}\meta{*}\oarg{checks/options}\marg{labels}\marg{text}
% \end{syntax}
%
% \begin{macrocode}
\NewDocumentCommand \zcheck { s O { } m m }
{ \zref@wrapper@babel \@@_zcheck:nnnn {#3} {#1} {#2} {#4} }
% \end{macrocode}
% \end{macro}
%
%
% \begin{variable}
% {
% \l_@@_zcheck_labels_seq ,
% \g_@@_id_int ,
% \l_@@_checkbeg_tl ,
% \l_@@_link_label_tl ,
% \l_@@_link_anchor_tl ,
% \l_@@_link_star_bool
% }
% \begin{macrocode}
\seq_new:N \l_@@_zcheck_labels_seq
\int_new:N \g_@@_id_int
\tl_new:N \l_@@_checkbeg_tl
\tl_new:N \l_@@_link_label_tl
\tl_new:N \l_@@_link_anchor_tl
\bool_new:N \l_@@_link_star_bool
% \end{macrocode}
% \end{variable}
%
% \begin{macro}{\@@_zcheck:nnnn}
% An intermediate internal function, which does the actual heavy lifting,
% and places \Arg{labels} as first argument, so that it can be protected by
% \cs{zref@wrapper@babel} in \cs{zcheck}. This is the same procedure as the
% one used in the definition of \cs{zref} in \file{zref-user.sty} for
% protection of \pkg{babel} active characters.
%
% \begin{syntax}
% \cs{@@_zcheck:nnnn} \Arg{labels} \Arg{*} \Arg{checks/options} \Arg{text}
% \end{syntax}
%
% \begin{macrocode}
\cs_new_protected:Npn \@@_zcheck:nnnn #1#2#3#4
{
\group_begin:
% \end{macrocode}
% Process local options and checks. We use \cs{seq_set_split:Nnn} to set
% \cs{l_@@_zcheck_labels_seq} -- instead of \cs{seq_set_from_clist:Nn} -- to
% support empty labels.
% \begin{macrocode}
\keys_set:nn { zref-check / zcheck } {#3}
\seq_set_split:Nnn \l_@@_zcheck_labels_seq { , } {#1}
% \end{macrocode}
% Names of the labels for this zcheck call.
% \begin{macrocode}
\int_gincr:N \g_@@_id_int
\tl_set:Ne \l_@@_checkbeg_tl
{ \@@_check_lblfmt:n { \g_@@_id_int } }
% \end{macrocode}
% Set checkbeg label.
% \begin{macrocode}
\zref@labelbylist { \l_@@_checkbeg_tl } { zrefcheck-check }
% \end{macrocode}
% Typeset \marg{text}, with hyperlink when appropriate. Even though the first
% argument can receive a list of labels, there is no meaningful way to set
% links to multiple targets. Hence, only the first one is considered for
% hyperlinking.
% \begin{macrocode}
\seq_get:NN \l_@@_zcheck_labels_seq \l_@@_link_label_tl
\bool_set:Nn \l_@@_link_star_bool {#2}
\zref@ifrefundefined { \l_@@_link_label_tl }
% \end{macrocode}
% If the reference is undefined, just typeset.
% \begin{macrocode}
{#4}
{
\bool_if:nTF
{
\l_@@_use_hyperref_bool &&
! \l_@@_link_star_bool
}
{
\exp_args:Ne \zrefcheck_get_astl:nnn
{ \l_@@_link_label_tl }
{ anchor } { \l_@@_link_anchor_tl }
\hyperlink { \l_@@_link_anchor_tl } {#4}
}
{#4}
}
% \end{macrocode}
% Set checkend label.
% \begin{macrocode}
\bool_if:NT \l_@@_zcheck_end_label_bool
{
\zref@labelbylist
{ \@@_end_lblfmt:n { \l_@@_checkbeg_tl } }
{ zrefcheck-end }
}
% \end{macrocode}
% Check if \meta{labels} are defined.
% \begin{macrocode}
\seq_map_inline:Nn \l_@@_zcheck_labels_seq
{ \tl_if_empty:nF {##1} { \zref@refused {##1} } }
% \end{macrocode}
% Run the checks.