% \iffalse meta-comment
%
% Copyright 1993-2016
% The LaTeX3 Project and any individual authors listed elsewhere
% in this file.
%
% This file is part of the LaTeX base system.
% -------------------------------------------
%
% It may be distributed and/or modified under the
% conditions of the LaTeX Project Public License, either version 1.3c
% of this license or (at your option) any later version.
% The latest version of this license is in
%    http://www.latex-project.org/lppl.txt
% and version 1.3c or later is part of all distributions of LaTeX
% version 2005/12/01 or later.
%
% This file has the LPPL maintenance status "maintained".
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% The list of all files belonging to the LaTeX base distribution is
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% information.
%
% The list of derived (unpacked) files belonging to the distribution
% and covered by LPPL is defined by the unpacking scripts (with
% extension .ins) which are part of the distribution.
%
% \fi
%
% \iffalse
%
%<*dtx>
          \ProvidesFile{latexrelease.dtx}
%</dtx>
%<driver>\ProvidesFile{latexrelease.drv}
%<fixltx2e>\ProvidesPackage{fixltx2e}
%<fixltx2e>   [2015/06/22 v2.0b fixes to LaTeX (obsolete)]
%<latexrelease>\ProvidesPackage{latexrelease}
%<*!fixltx2e>
% \fi
%         \ProvidesFile{latexrelease.dtx}
          [2016/07/04 v1.0g LaTeX release emulation and tests]
% \iffalse
%</!fixltx2e>
%<*driver>
 \documentclass{ltxdoc}
 \newcommand\Lopt[1]{\textsf{#1}}
 \let\Lpack\Lopt
 \providecommand{\file}[1]{\texttt{#1}}
 \providecommand{\MF}{\textsf{Metafont}}
 \providecommand{\danger}{\marginpar[\hfill\protect\Huge!!]{\protect\Huge!!\hfill}}
 \begin{document}
 \DocInput{latexrelease.dtx}
 \end{document}
%</driver>
% \fi
%
%
%
% \let\package\textsf
%
%
% \GetFileInfo{latexrelease.dtx}
%
% \title{The \Lpack{latexrelease} package\thanks{This file
%         has version number \fileversion, last
%         revised \filedate.}}
% \author{The \LaTeX3 Project}
% \date{\filedate}
% \MaintainedByLaTeXTeam{latex}
%  \maketitle
%
% \section{Introduction}
% Prior to the 2015 release of \LaTeX{}, essentially no changes had been
% made to the \LaTeX\ format code for some years, with all
% improvements being instead added to the package \Lpack{fixltx2e}.
%
% While this worked at a technical level it meant that you had to
% explicitly opt-in to bug fixes and improvements, and the vast
% majority of documents did not benefit.
%
% As described in \LaTeX\ News 22, a new policy is being implemented 
% in which improvements will now be added to the format by default,
% and this \Lpack{latexrelease} package may be used to ensure
% stability where needed, either by making a new format use an older
% definition of some commands, or conversely may be used to supply the
% new definitions for use with an old format.
%
% The basic use is:
%\begin{verbatim}
% \RequirePackage[2015/01/01]{latexrelease}
% \documentclass{article}
% ....
%\end{verbatim}
%
% After such a declaration the document will use definitions current
% in the January 2015 \LaTeX{}, whether the actual format being used is
% older, or newer than that date. In the former case a copy of
% |latexrelease.sty| would need to be made available for use with the
% older format.  This may be used, for example, to share a document
% between co-workers using different \LaTeX\ releases, or to protect a
% document from being affected by system updates. As well as the
% definitions within the format itself, individual packages may use
% the commands defined here to  adjust their definitions to the
% specified date as described below.
%
%
% The bulk of this package, after some initial setup and option
% handling consists of a series of |\IncludeInRelease| commands
% which have been extracted from the main source files of the \LaTeX\
% format. These contain the old and new versions of any commands with
% modified definitions.
%
% \section{Package Options}
% \begin{itemize}
% \item \emph{yyyy/mm/dd}
% The package accepts any \LaTeX\ format date as argument,% 
% although dates in the future for which the current release of this
% package has no information will generate a warning.
%
% \item%
% |current| This is the default behaviour, it does not change the
% effective date of the format but does ensure that the
% |\IncludeInRelease| command is defined.
%
% \item
% |latest| sets the effective date of the format to the release date
% of this file, so in an older format applies all patches currently
% available.
% \end{itemize}
%
%
% \section{Release Specific Code}
%
% The |\IncludeInRelease| mechanism allows the kernel developer to
% associate code with a specific date to choose different versions of
% definitions depending on the date specified as an option to the
% \Lpack{latexrelease} package. Is also available for use by package
% authors (or even in a document if necessary).
%
% \medskip
%
% \noindent\DescribeMacro{\IncludeInRelease}
% \marg{code-date}^^A
% \oarg{format-date}%^^A
% \marg{label}^^A
% \marg{message}^^A
% \meta{code}^^A
% |\EndIncludeInRelease|
%
% \begin{description}
%
% \item[\marg{code-date}] This date is associated with the \marg{code}
% argument and will be compared to the requested date in the option to
% the \Lpack{latexrelease}.
% 
% \item[\oarg{format-date}] This optional argument can be used to
% specify a format date with the code in addition to the mandatory
% \marg{code-date} argument. This can be useful for package developers
% as described below.
%
% \item[\marg{label}] The \marg{label} argument is an identifier
% (string) that within a given package must be a unique label for each
% related set of optional definitions. Per package at most one code
% block from all the |\IncludeInRelease| declarations with the same
% label will be executed.
%
% \item[\marg{message}]
% The \marg{message} is an informative string that is used in
% messages. It has no other function.
%
% \item[\meta{code}]
% Any \TeX\ code after the |\IncludeInRelease| arguments
% up until the and the following |\EndIncludeInRelease|
% is to be
% conditionally included depending on the date of the format as
% described below.
%
% \end{description}
%
% The |\IncludeInRelease| declarations with a given label should be in
% reverse chronological order in the file. The one chosen will depend
% on this order, the effective format version and the date options, as
% described below.
%
% If your package \Lpack{mypackage} defines a |\widget| command but
% has one definition using the features available in the 2015 \LaTeX\
% release, and a different definition is required for older formats
% then you can use:
%\begin{verbatim}
% \IncludeInRelease{2015/01/01}{\widget}{Widget Definition}
%  \def\widget{new version}%
% \EndIncludeInRelease
%
% \IncludeInRelease{0000/00/00}{\widget}{Widget Definition}
%  \def\widget{old version}%
% \EndIncludeInRelease
%\end{verbatim}
%
% If a document using this package is used with a format with
% effective release date of 2015/01/01 or later the new code will be
% used, otherwise the old code will be used. Note the \emph{effective
% release date} might be the original \LaTeX\ release date as shown at
% the start of every \LaTeX\ job, or it may be set by the
% \Lpack{latexrelease} package, so for example a document author who
% wants to ensure the new version is used could use
%\begin{verbatim}
% \RequirePackage[2015/01/01]{latexrelease}
% \documentclass{article}
% \usepackage{mypackage}
%\end{verbatim}
%
% If the document  is used with a \LaTeX\ format from 2014 or before,
% then \Lpack{latexrelease} will not have been part of the original
% distribution, but it may be obtained from a later \LaTeX\ release or
% from CTAN and distributed with the document, it will make an older
% \LaTeX\ release act essentially like the 2015 release.
%
% \subsection{Intermediate Package Releases}
%
% The above example works well for testing against the latex format
% but is not always ideal for controlling code by the release date of
% the \emph{package}. Suppose \LaTeX\ is not updated but in March you
% update the \Lpack{mypackage} package and modify the definition of
% |\widget|. You could code the package as:
%\begin{verbatim}
% \IncludeInRelease{2015/03/01}{\widget}{Widget Definition}
%  \def\widget{even newer improved March version}%
% \EndIncludeInRelease
%
% \IncludeInRelease{2015/01/01}{\widget}{Widget Definition}
%  \def\widget{new version}%
% \EndIncludeInRelease
%
% \IncludeInRelease{0000/00/00}{\widget}{Widget Definition}
%  \def\widget{old version}%
% \EndIncludeInRelease
%\end{verbatim}
%
% This would work and allow a document author to choose a date such as
%\begin{verbatim}
% \RequirePackage[2015/03/01]{latexrelease}
% \documentclass{article}
% \usepackage{mypackage}
%\end{verbatim}
%
% To use the latest version, however it would have disadvantage that
% until the next release of \LaTeX, by default, if the document does 
% not use \Lpack{latexrelease} to specify a date, the new improved
% code will not be selected as the effective date will be 2015/01/01
% and so the first code block will be skipped.
% 
% For this reason |\IncludeInRelease| has an optional argument that
% specifies an alternative date to use if a date option has not been
% specified to \Lpack{latexrelease}.
%\begin{verbatim}
% \IncludeInRelease{2015/03/01}[2015/01/01]{\widget}{Widget Definition}
%  \def\widget{even newer improved March version}%
% \EndIncludeInRelease
%
% \IncludeInRelease{2015/01/01}{\widget}{Widget Definition}
%  \def\widget{new version}%
% \EndIncludeInRelease
%
% \IncludeInRelease{0000/00/00}{\widget}{Widget Definition}
%  \def\widget{old version}%
% \EndIncludeInRelease
%\end{verbatim}
%
% Now, by default on a 2015/01/01 \LaTeX\ format, the first code block
% will compare the format date to the optional argument 2015/01/01
% and so will execute the \emph{even newer improved} version. The
% remaining blocks using the |\widget| label argument will all then be
% skipped.
%
% If on the other hand the document requests an explicit release date
% using \Lpack{latexrelease} then this date will be used to decide what 
% code block to include.
%
% \subsection{Using \cs{IncludeInRelease} in Packages}
%
% If |\IncludeInRelease| is used within a package then all such
% conditional code needs to be within such declarations, e.g., it is
% not possible in the above example to have the ``current'' definition
% of |\widget| somewhere in the main code and only the two older
% definitions inside |\IncludeInRelease| declarations. If you would do
% this then one of those |\IncludeInRelease| declarations would be
% included overwriting the even newer code in the main part of the
% package. As a result your package may get fragmented over time with
% various |\IncludeInRelease| declarations sprinkled throughout your
% code or you have to interrupt the reading flow by putting those
% declarations together but not necessarily in the place where they
% belong.
%
% To avoid this issue you can use the following coding
% strategy: place the current |\widget| definition in the main code
% where it correctly belongs. 
% \begin{verbatim}
%   ...
%  \def\widget {even newer improved March version}
%  \def\@widget{newly added helper command no defined in older releases}
%   ...
%\end{verbatim}
% Then, near the end of your package place
% the following:
%  \begin{verbatim}
% \IncludeInRelease{2015/03/01}[2015/01/01]{\widget}{Widget Definition}
% \EndIncludeInRelease
%
% \IncludeInRelease{2015/01/01}{\widget}{Widget Definition}
%  \def\widget{new version}%
%  \let\@widget\@undefined % this doesn't exist in earlier releases
% \EndIncludeInRelease
%
% \IncludeInRelease{0000/00/00}{\widget}{Widget Definition}
%  \def\widget{old version}%
% \EndIncludeInRelease
%\end{verbatim}
% This way the empty code block hides the other |\IncludeInRelease|
% declarations unless there is an explicit request with a date
% 2015/01/01 or earlier.
%
% Now if you make a further change to |\widget| in the future you
% simply copy the current definition into the empty block and add a new
% empty declaration with todays date and the current format date. This
% way your main code stays readable and the old versions accumulate at
% the end of the package.\footnote{Of course there may be some cases
% in which the old code has to be in a specific place within the
% package as other code depends on it (e.g., if you
% \texttt{\string\let} something to it). In that case you have to
% place the code variations in the right place in your package rather
% than accumulating them at the very end.}
%
% The only other ``extra effort'' necessary when using this approach
% is that it may be advisable to undo new definitions in the code
% block for the previous release, e.g., in the above example we
% undefined |\@widget| as that isn't available in the 2015/01/01
% release but was defined in the main code. If all your conditional
% code is within |\IncludeInRelease| declarations that wouldn't been
% necessary as the new code only gets defined if that release is
% chosen.
%
% \section{fixltx2e}
%
% As noted above, prior to the 2015 \LaTeX\ release updates to the
% \LaTeX\ kernel were not made in the format source files but were 
% made available in the \Lpack{fixltx2e} package. That package is no
% longer needed but we generate a small package from this source
% that just makes a warning message but otherwise does nothing.
%
%
%
%
%
% \StopEventually{}
%
% \section{Implementation}
%
% We require at least a somewhat sane version of \LaTeXe{}. Earlier
% ones where really quite different from one another.
%    \begin{macrocode}
%<*latexrelease>
\NeedsTeXFormat{LaTeX2e}[1996/06/01]
%    \end{macrocode}
%
% \section{Setup}
%
% \begin{macro}{\IncludeInRelease}
% \begin{macro}{\EndIncludeInRelease}
%    \begin{macrocode}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \changes{v1.0c}{2015/02/19}{Swap argument order}
%    \begin{macrocode}
\DeclareOption*{%
  \def\@IncludeInRelease#1[#2]{\@IncludeInRele@se{#1}}%
  \let\requestedpatchdate\CurrentOption}
\DeclareOption{latest}{%
  \let\requestedpatchdate\latexreleaseversion}
\DeclareOption{current}{%
  \let\requestedpatchdate\fmtversion}
%    \end{macrocode}
%
%    \begin{macrocode}
\ExecuteOptions{current}
\ProcessOptions\relax
%    \end{macrocode}
%
% Sanity check options, it allows some non-legal dates but always
% ensures |requestedLaTeXdate| gets set to a number.  Generate an
% error if there are any non digit tokens remaining after removing the
% |//|.
%    \begin{macrocode}
\def\reserved@a{%
\edef\requestedLaTeXdate{\the\count@}%
\reserved@b}
\def\reserved@b#1\\{%
\def\reserved@b{#1}%
\ifx\reserved@b\@empty\else
\PackageError{latexrelease}%
             {Unexpected option \requestedpatchdate}%
             {The option must be of the form yyyy/mm/dd}%
\fi}
\afterassignment\reserved@a
\count@\expandafter
  \@parse@version\expandafter0\requestedpatchdate//00\@nil\\
%    \end{macrocode}
%
% less precautions needed for |\fmtversion|
%    \begin{macrocode}
\edef\currentLaTeXdate{%
   \expandafter\@parse@version\fmtversion//00\@nil}
%    \end{macrocode}
%
%    \begin{macrocode}
\ifnum\requestedLaTeXdate=\currentLaTeXdate
\PackageWarningNoLine{latexrelease}{%
  Current format date selected, no patches applied.}
\expandafter\endinput
\fi
%    \end{macrocode}
%
% A newer version of latexrelease should have been distributed with
% the later format.
%    \begin{macrocode}
\ifnum\currentLaTeXdate
  >\expandafter\@parse@version\latexreleaseversion//00\@nil
\PackageWarningNoLine{latexrelease}{%
The current package is for an older LaTeX format:\MessageBreak
LaTeX \latexreleaseversion\space\MessageBreak
Obtain a newer version of this package!}
\expandafter\endinput
\fi
%    \end{macrocode}
% can't patch into the future, could make this an error
% but it has some uses to control package updates
% so allow for now.
%    \begin{macrocode}
\ifnum\requestedLaTeXdate
  >\expandafter\@parse@version\latexreleaseversion//00\@nil
\PackageWarningNoLine{latexrelease}{%
The current package is for LaTeX \latexreleaseversion:\MessageBreak
It has no patches beyond that date\MessageBreak
There may be an updated version\MessageBreak
of this package available from CTAN}
\expandafter\endinput
\fi
%    \end{macrocode}
%
% Update the format version to the requested date.
%    \begin{macrocode}
\let\fmtversion\requestedpatchdate
\let\currentLaTeXdate\requestedLaTeXdate
%    \end{macrocode}
%
%
% \section{Individual  Changes}
%
% The code for each change will be inserted at this point, extracted
% from the kernel source files.
%    
%    \begin{macrocode}
%</latexrelease>
%    \end{macrocode}
%
% \section{fixltx2e}
%
% Generate a stub \Lpack{fixltx2e} package:
%    \begin{macrocode}
%<*fixltx2e>
\NeedsTeXFormat{LaTeX2e}
\PackageWarningNoLine{fixltx2e}{%
fixltx2e is not required with releases after 2015\MessageBreak
All fixes are now in the LaTeX kernel.\MessageBreak
See the latexrelease package for details}
%</fixltx2e>
%    \end{macrocode}
%
% \Finale
%
\endinput
