CTAN sync 202010030301

1 files changed, 454 insertions, 77 deletions

diff --git a/macros/latex/base/ltfiles.dtx b/macros/latex/base/ltfiles.dtx
index 33594a7b91..835f600e32 100644
--- a/macros/latex/base/ltfiles.dtx
+++ b/macros/latex/base/ltfiles.dtx
@@ -32,7 +32,7 @@
 %<*driver>
 % \fi
 \ProvidesFile{ltfiles.dtx}
-             [2019/11/11 v1.2f LaTeX Kernel (File Handling)]
+             [2020/08/21 v1.2i LaTeX Kernel (File Handling)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltfiles.dtx}
@@ -47,6 +47,8 @@
   Chris Rowley\and
   Rainer Sch\"opf}
 
+\providecommand\pkg[1]{\texttt{#1}}
+
 \begin{document}
  \MaintainedByLaTeXTeam{latex}
  \maketitle
@@ -55,6 +57,8 @@
 %</driver>
 % \fi
 %
+% \providecommand\hook[1]{\texttt{#1}}
+%
 %
 % \changes{v1.0h}{1994/05/21}{Use new error commands}
 % \changes{v1.0n}{1994/11/17}
@@ -62,6 +66,7 @@
 % \changes{v1.0u}{1995/07/13}{Updates to docu}
 % \changes{v1.1m}{2015/02/21}
 %         {Removed autoload support}
+% \changes{v1.2i}{2020/08/21}{Integration of new hook management interface}
 %
 % \section{File Handling}
 %
@@ -234,18 +239,28 @@
 % \changes{v0.9e}{1993/12/09}{Hook added}
 %    \begin{macrocode}
 %</2ekernel>
-%<latexrelease>\IncludeInRelease{2017/04/15}%
-%<latexrelease>  {\document}{Save language for hyphenation}%
+%<latexrelease>\IncludeInRelease{2020/10/01}%
+%<latexrelease>  {\document}{Added hook to load l3backend code}%
 %<*2ekernel|latexrelease>
+\def\document{%
 %    \end{macrocode}
-%    Cancel the |\begingroup| from |\begin|.
+%    We do cancel the grouping as part of the \cs{begin} handling
+%    (this is now done inside \cs{begin} instead) so that the
+%    \hook{env/\meta{env}/begin} hook is not hidden inside \cs{begingroup}
+%    \texttt{...} \cs{endgroup}.
 %    \begin{macrocode}
-\def\document{\endgroup
+%  \endgroup
 %    \end{macrocode}
-%    If some options on |\documentclass| haven't been used by any
-%    package we will now give a warning since this is most certainly a
-%    misspelling.
+%    
 %    \begin{macrocode}
+  \UseOneTimeHook{begindocument/before}%
+  \@kernel@after@begindocument@before
+%    \end{macrocode}
+%
+% Added hook to load \textsf{l3backend} code:
+% \changes{v1.2h}{2020/06/05}{Added hook to load \textsf{l3backend} code}
+%    \begin{macrocode}
+  \@expl@sys@load@backend@@
   \ifx\@unusedoptionlist\@empty\else
     \@latex@warning@no@line{Unused global option(s):^^J%
             \@spaces[\@unusedoptionlist]}%
@@ -348,9 +363,11 @@
 % \changes{v1.1e}{1996/04/24}
 %            {(DPC) Reset \cs{AtBeginDocument} eg for latex/1297}
 %    \begin{macrocode}
-  \let\AtBeginDocument\@firstofone
-  \@begindocumenthook
+  \@kernel@before@begindocument
+  \UseOneTimeHook{begindocument}%
+  \@kernel@after@begindocument
 %    \end{macrocode}
+%    
 %    Most of the following assignments will be done globally in case
 %    the user adds something like |\begin{multicols}| to the document
 %    hook, i.e. starts are group in |\begin{document}|.
@@ -399,13 +416,128 @@
 %    \begin{macrocode}
   \global\let\do\noexpand
 %    \end{macrocode}
+%
+%    \begin{macrocode}
+  \UseOneTimeHook{begindocument/end}%
+%    \end{macrocode}
 % \changes{v1.1c}{1995/12/05}{\cs{ignorespaces} added for latex/1933}
-%    Use of |\AtBeginDocument| hook might mean that we are already in
+%    Use of the hook might mean that we are already in
 %    horizontal mode, so ignore the space after |\begin{document}|.
 %    \begin{macrocode}
   \ignorespaces}
+%    \end{macrocode}
+%
+%    The \hook{begindocument} hook already existed in the kernel since
+%    1994 under the name \cs{atbegindocumenthook} the 
+%    additional ones are originally from the \pkg{etoolbox}
+%    package under the names \cs{@endpreamblehook} \cs{afterpreamble}.
+%    \begin{macrocode}
+\NewHook{begindocument}
+\NewHook{begindocument/before}
+\NewHook{begindocument/end}
+%    \end{macrocode}
+
+
+
+%  \begin{macro}{\@kernel@after@begindocument@before,
+%                \@kernel@before@begindocument,
+%                \@kernel@after@begindocument}
+%
+%    Above we used two kernel only hooks to be run after the public
+%    \hook{begindocument/before} and after \hook{begindocument}
+%    hooks.
+%
+%    In \cs{@kernel@after@begindocument@before} we already place one
+%    action: drop the fast execution code for the
+%    \hook{env/document/begin} hook. That hook marks the end of the
+%    preamble and should therefore only be run once. In a normal 
+%    document that is anyway the case (so the code would just sit
+%    there taking up space afterwards, which these days is rather
+%    harmless), however, in more complicated scenarios where several
+%    full documents are combined to a single document it might get
+%    applied several times with harmful effects. We therefore
+%    explicitly drop it at this point. the coing is somewhat obscure
+%    due to the name of the macro which requires constructing.
+%    \begin{macrocode}
+\edef \@kernel@after@begindocument@before {%
+  \let\expandafter\noexpand\csname
+       __hook env/document/begin\endcsname
+  \noexpand\@empty}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\let \@kernel@before@begindocument \@empty
+\let \@kernel@after@begindocument \@empty
+%    \end{macrocode}
+%    
+%  \end{macro}
+%
+
+%
+%    \begin{macrocode}
 %</2ekernel|latexrelease>
 %<latexrelease>\EndIncludeInRelease
+%    \end{macrocode}
+%    
+%    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{2017/04/15}%
+%<latexrelease>  {\document}{Save language for hyphenation}%
+%<latexrelease>
+%<latexrelease>\def\document{\endgroup
+%<latexrelease>  \ifx\@unusedoptionlist\@empty\else
+%<latexrelease>    \@latex@warning@no@line{Unused global option(s):^^J%
+%<latexrelease>            \@spaces[\@unusedoptionlist]}%
+%<latexrelease>  \fi
+%<latexrelease>  \@colht\textheight
+%<latexrelease>  \@colroom\textheight \vsize\textheight
+%<latexrelease>  \columnwidth\textwidth
+%<latexrelease>  \@clubpenalty\clubpenalty
+%<latexrelease>  \if@twocolumn
+%<latexrelease>    \advance\columnwidth -\columnsep
+%<latexrelease>    \divide\columnwidth\tw@ \hsize\columnwidth \@firstcolumntrue
+%<latexrelease>  \fi
+%<latexrelease>  \hsize\columnwidth \linewidth\hsize
+%<latexrelease>  \begingroup\@floatplacement\@dblfloatplacement
+%<latexrelease>    \makeatletter\let\@writefile\@gobbletwo
+%<latexrelease>    \global \let \@multiplelabels \relax
+%<latexrelease>    \@input{\jobname.aux}%
+%<latexrelease>  \endgroup
+%<latexrelease>  \if@filesw
+%<latexrelease>    \immediate\openout\@mainaux\jobname.aux
+%<latexrelease>    \immediate\write\@mainaux{\relax}%
+%<latexrelease>  \fi
+%<latexrelease>  \process@table
+%<latexrelease>  \let\glb@currsize\@empty  % Force math initialization.
+%<latexrelease>  \normalsize
+%<latexrelease>  \everypar{}%
+%<latexrelease>  \ifx\normalsfcodes\@empty
+%<latexrelease>    \ifnum\sfcode`\.=\@m
+%<latexrelease>      \let\normalsfcodes\frenchspacing
+%<latexrelease>    \else
+%<latexrelease>      \let\normalsfcodes\nonfrenchspacing
+%<latexrelease>    \fi
+%<latexrelease>  \fi
+%<latexrelease>  \ifx\document@default@language\m@ne
+%<latexrelease>    \chardef\document@default@language\language
+%<latexrelease>  \fi
+%<latexrelease>  \@noskipsecfalse
+%<latexrelease>  \let \@refundefined \relax
+%<latexrelease>  \let\AtBeginDocument\@firstofone
+%<latexrelease>  \@begindocumenthook
+%<latexrelease>  \ifdim\topskip<1sp\global\topskip 1sp\relax\fi
+%<latexrelease>  \global\@maxdepth\maxdepth
+%<latexrelease>  \global\let\@begindocumenthook\@undefined
+%<latexrelease>  \ifx\@listfiles\@undefined
+%<latexrelease>    \global\let\@filelist\relax
+%<latexrelease>    \global\let\@addtofilelist\@gobble
+%<latexrelease>  \fi
+%<latexrelease>  \gdef\do##1{\global\let ##1\@notprerr}%
+%<latexrelease>  \@preamblecmds
+%<latexrelease>  \global\let \@nodocument \relax
+%<latexrelease>  \global\let\do\noexpand
+%<latexrelease>  \ignorespaces}
+%<latexrelease>\EndIncludeInRelease
+%<latexrelease>
 %<latexrelease>\IncludeInRelease{0000/00/00}%
 %<latexrelease>  {\document}{Save language for hyphenation}
 %<latexrelease>\def\document{\endgroup
@@ -539,26 +671,14 @@
 %    \end{macrocode}
 %
 %
-% \begin{macro}{\includeonly}
+%  \begin{macro}{\include,\includeonly}
+% \changes{v0.9p}{1994/01/18}
+%         {Use \cs{@input@} so include files are listed.}
 % \changes{v1.0p}{1995/04/22}{Allow blanks in argument}
 % \changes{v1.2a}{2019/07/01}{Support UTF-8}
-%    \begin{macrocode}
-%</2ekernel>
-%<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2019/10/01}%
-%<latexrelease>                 {\includeonly}{Spaces in file names}%
-\def\includeonly#1{%
-  \@partswtrue
-  \set@curr@file{\zap@space#1 \@empty}%
-  \let\@partlist\@curr@file
-  }
-\@onlypreamble\includeonly
-%    \end{macrocode}
-% \end{macro}
+% \changes{v1.2g}{2020/05/02}{Improved support for spaces in filenames
+%    (gh/217)}
 %
-% \begin{macro}{\include}
-% \changes{v0.9p}{1994/01/18}
-%         {Use \cs{@input@} so include files are listed.}
 % In the definition of |\include|, |\def\reserved@b| changed to
 % |\edef\reserved@b| to be consistent with the |\edef| in
 % |\includeonly|.
@@ -572,21 +692,113 @@
 %
 % Made |\include| check for being used inside an |\include|'d file, as
 % this will not work and cause surprising results.
+% \changes{v1.2g}{2020/05/02}{Get rid of leading and trailing spaces
+%    from the filename (gh/217)}
+% \changes{v1.2g}{2020-05-02}{Pass the filename to \cs{@include} by
+%    value instead of by reference (gh/217)} 
+%
+%    \begin{macrocode}
+%</2ekernel>
+%<*2ekernel|latexrelease>
+%<latexrelease>\IncludeInRelease{2020/10/01}%
+%<latexrelease>                 {\includeonly}{Spaces in file names}%
+%    \end{macrocode}
+%    
 %    \begin{macrocode}
 \def\include#1{\relax
   \ifnum\@auxout=\@partaux
     \@latex@error{\string\include\space cannot be nested}\@eha
   \else
-  \set@curr@file{#1 }%
-  \expandafter\@include\@curr@file
+%    \end{macrocode}
+%    Here the normalisation will add |.tex| for all files, (it uses the
+%    the same normalisation as the hooks), so we need to remove that
+%    manually.  \cs{@strip@tex@ext} does that.
+%    \begin{macrocode}
+    \set@curr@file{#1}%
+    \edef\@curr@file{\@strip@tex@ext\@curr@file}%
+%    \end{macrocode}
+%    For historical reasons \cs{@include} expects an argument
+%    delimited by a space. This is kept (though uncessary now) to avoid
+%    errors in other packages that use \cs{@include} directly.
+%    \begin{macrocode}
+    \expandafter\@include\expandafter{\@curr@file} % deliberate space
   \fi}
 %    \end{macrocode}
-% \end{macro}
 %
+%    Here in \cs{includeonly} we also need to strip |.tex| after
+%    normalisation:
+%    \begin{macrocode}
+\def\includeonly#1{%
+  \@partswtrue
+%    \end{macrocode}
+%    Because the argument to |\includeonly| is a comma-separated list
+%    of filenames where there may be comma's precedeing some of the
+%    filenames or trailing them. Therefore we need to take the list
+%    apart, remove the unwanted spaces while leaving the spaces
+%    \emph{in} the filenames intact.
+%    \begin{macrocode}
+  \let\@partlist\@empty
+  \@for\reserved@a:=#1 \do
+    {%
+      \expandafter\set@curr@file\expandafter{\reserved@a}%
+      \ifx\@partlist\@empty
+        \edef\@partlist{\@strip@tex@ext\@curr@file}%
+      \else
+        \edef\@partlist{\@partlist,\@strip@tex@ext\@curr@file}%
+      \fi
+    }%
+  }
+\@onlypreamble\includeonly
+%    \end{macrocode}
+% \end{macro}
 %
+%  \begin{macro}{\@strip@tex@ext,\@strip@tex@ext@aux}
+%    These macros take a (\cs{detokenize}d file name and remove any
+%    |.tex| extension).  Extra care is taken to not remove the string
+%    |.tex| from the middle of a file name:  it is only removed if it's
+%    the very last thing in the file name.
 %    \begin{macrocode}
+\def\reserved@a#1{%
+\def\@strip@tex@ext##1{%
+  \expandafter\@strip@tex@ext@aux
+    ##1\@nil\@nil
+     #1\@nil\relax\@nnil}
+\def\@strip@tex@ext@aux##1#1\@nil##2\@nnil{%
+  \ifx\relax##2\@empty
+    \expandafter\@cdr\expandafter\@empty\@cdr{}##1%
+  \else##1\fi}}%
+\expandafter\reserved@a
+\expandafter{\detokenize{.tex}}
 %</2ekernel|latexrelease>
+%    \end{macrocode}
+%  \end{macro}
+%
+%    \begin{macrocode}
+%<latexrelease>\EndIncludeInRelease
+%<latexrelease>\IncludeInRelease{2019/10/01}%
+%<latexrelease>                 {\includeonly}{Spaces in file names}%
+%<latexrelease>
+%<latexrelease>\def\includeonly#1{%
+%<latexrelease>  \@partswtrue
+%<latexrelease>  \set@curr@file{\zap@space#1 \@empty}%
+%<latexrelease>  \let\@partlist\@curr@file
+%<latexrelease>  }
+%<latexrelease>
+%<latexrelease>\def\include#1{\relax
+%<latexrelease>  \ifnum\@auxout=\@partaux
+%<latexrelease>    \@latex@error{\string\include\space cannot be nested}\@eha
+%<latexrelease>  \else
+%<latexrelease>    \set@curr@file{#1 }%
+%<latexrelease>    \expandafter\@include\@curr@file
+%<latexrelease>  \fi}
+%<latexrelease>
+%<latexrelease>\let\@strip@tex@ext\@undefined
+%<latexrelease>\let\@strip@tex@ext@aux\@undefined
+%<latexrelease>
 %<latexrelease>\EndIncludeInRelease
+%    \end{macrocode}
+%    
+%    \begin{macrocode}
 %<latexrelease>\IncludeInRelease{0000/00/00}%
 %<latexrelease>                 {\includeonly}{Spaces in file names}%
 %<latexrelease>\def\includeonly#1{%
@@ -601,14 +813,22 @@
 %<latexrelease>\EndIncludeInRelease
 %<*2ekernel>
 %    \end{macrocode}
-
 %
 % \begin{macro}{\@include}
+% \changes{v1.2g}{2020/05/02}{Support spaces in filenames by enclosing
+%    the names of \texttt{.aux}-files in quotes (gh/217)}
+%    \begin{macrocode}
+%</2ekernel>
+%<*2ekernel|latexrelease>
+%<latexrelease>\IncludeInRelease{2020/10/01}%
+%<latexrelease>                 {\@include}{Spaces in file names and hooks}%
+%    \end{macrocode}
+%    
 %    \begin{macrocode}
 \def\@include#1 {%
   \clearpage
   \if@filesw
-    \immediate\write\@mainaux{\string\@input{#1.aux}}%
+    \immediate\write\@mainaux{\string\@input{"#1.aux"}}%
   \fi
   \@tempswatrue
   \if@partsw
@@ -620,11 +840,41 @@
   \if@tempswa
     \let\@auxout\@partaux
     \if@filesw
-      \immediate\openout\@partaux #1.aux
+      \immediate\openout\@partaux "#1.aux"
       \immediate\write\@partaux{\relax}%
     \fi
+%    \end{macrocode}
+%    Now before going to the hooks we need to set \cs{CurrentFile}:
+%    \begin{macrocode}
+%-----------------------------------------
+    \@filehook@set@CurrentFile
+%    \end{macrocode}
+%    Execute the \texttt{before} hooks just after we switched the
+%    \texttt{.aux} file \ldots
+%    \begin{macrocode}
+    \UseHook{include/before}%
+    \UseHook{include/before/#1}%
+%-----------------------------------------
     \@input@{#1.tex}%
+%-----------------------------------------
+%    \end{macrocode}
+%    \ldots{} then \texttt{end} hooks \ldots
+%    \begin{macrocode}
+    \UseHook{include/end/#1}%
+    \UseHook{include/end}%
+%-----------------------------------------
     \clearpage
+%-----------------------------------------
+%    \end{macrocode}
+%    \ldots{} and after the \cs{clearpage} the \texttt{after} hooks
+%    followed by another \cs{clearpage} just in case new material got
+%    added (after all we need to be in  well defined state after the
+%    \cs{include}).
+%    \begin{macrocode}
+    \UseHook{include/after/#1}%
+    \UseHook{include/after}%
+    \clearpage
+%-----------------------------------------
     \@writeckpt{#1}%
     \if@filesw
       \immediate\closeout\@partaux
@@ -640,6 +890,45 @@
     \@nameuse{cp@#1}%
   \fi
   \let\@auxout\@mainaux}
+%<latexrelease>\EndIncludeInRelease
+%</2ekernel|latexrelease>
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{0000/00/00}%
+%<latexrelease>                 {\@include}{Spaces in file names}%
+%<latexrelease>\def\@include#1 {%
+%<latexrelease>  \clearpage
+%<latexrelease>  \if@filesw
+%<latexrelease>    \immediate\write\@mainaux{\string\@input{#1.aux}}%
+%<latexrelease>  \fi
+%<latexrelease>  \@tempswatrue
+%<latexrelease>  \if@partsw
+%<latexrelease>    \@tempswafalse
+%<latexrelease>    \edef\reserved@b{#1}%
+%<latexrelease>    \@for\reserved@a:=\@partlist\do
+%<latexrelease>      {\ifx\reserved@a\reserved@b\@tempswatrue\fi}%
+%<latexrelease>  \fi
+%<latexrelease>  \if@tempswa
+%<latexrelease>    \let\@auxout\@partaux
+%<latexrelease>    \if@filesw
+%<latexrelease>      \immediate\openout\@partaux #1.aux
+%<latexrelease>      \immediate\write\@partaux{\relax}%
+%<latexrelease>    \fi
+%<latexrelease>    \@input@{#1.tex}%
+%<latexrelease>    \clearpage
+%<latexrelease>    \@writeckpt{#1}%
+%<latexrelease>    \if@filesw
+%<latexrelease>      \immediate\closeout\@partaux
+%<latexrelease>    \fi
+%<latexrelease>  \else
+%<latexrelease>    \deadcycles\z@
+%<latexrelease>    \@nameuse{cp@#1}%
+%<latexrelease>  \fi
+%<latexrelease>  \let\@auxout\@mainaux}
+%<latexrelease>
+%<latexrelease>\EndIncludeInRelease
+%<*2ekernel>
 %    \end{macrocode}
 % \end{macro}
 %
@@ -688,7 +977,6 @@
 %
 %
 %
-
 %  \begin{macro}{\@curr@file}
 %  \begin{macro}{\set@curr@file}
 %
@@ -698,8 +986,8 @@
 %   the code in \texttt{utf8.def}). By setting \cs{escapchar} to
 %   \texttt{-1} we ensure that we don't get a backslash in front. As a
 %   result we end up with all characters as catcode 12 (plus
-%   spaces). We then sometimes add quotes around the contruct
-%   (removing any existing inner quotes. Somes we only remove the
+%   spaces). We then sometimes add quotes around the construct
+%   (removing any existing inner quotes. Sometimes we only remove the
 %   quotes if they have been supplied by the user. There is clearly
 %   some room for improvement.
 %
@@ -716,11 +1004,11 @@
 %  \changes{v1.2c}{2019/10/11}{Remove one brace group}
 %  \changes{v1.2d}{2019/10/26}{remove quotes}
 %  \changes{v1.2e}{2019/11/09}{expand and \cs{string} before removing quotes}
+%
+%    The definition below is from 2019 and only used during kernel
+%    bootstrapping, later on in \texttt{ltfilehook.dtx} it will get
+%    overwritten.
 %    \begin{macrocode}
-%</2ekernel>
-%<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2019/10/01}%
-%<latexrelease>                 {\set@curr@file}{Quote file names}%
 \def\set@curr@file#1{%
   \begingroup
     \escapechar\m@ne
@@ -747,6 +1035,10 @@
 %           -> ""
 %\end{verbatim}
 %    \begin{macrocode}
+%</2ekernel>
+%<*2ekernel|latexrelease>
+%<latexrelease>\IncludeInRelease{2019/10/01}%
+%<latexrelease>                 {\quote@name}{Quote file names}%
 \def\quote@name#1{"\quote@@name#1\@gobble""}
 \def\quote@@name#1"{#1\quote@@name}
 %    \end{macrocode}
@@ -828,12 +1120,11 @@
 %</2ekernel|latexrelease>
 %<latexrelease>\EndIncludeInRelease
 %<latexrelease>\IncludeInRelease{0000/00/00}%
-%<latexrelease>                 {\set@curr@file}{Quote file names}%
+%<latexrelease>                 {\quote@name}{Quote file names}%
 %<latexrelease>
 %<latexrelease>\let\quote@name\@undefined
 %<latexrelease>\let\quote@@name\@undefined
 %<latexrelease>\let\unquote@name\@undefined
-%<latexrelease>\let\set@curr@file\@undefined
 %<latexrelease>
 %<latexrelease>\let\IfFileExists@\@undefined
 %<latexrelease>
@@ -873,25 +1164,14 @@
 %
 %
 % \begin{macro}{\InputIfFileExists}
-% \changes{v0.9b}
-%         {1993/12/04}{Macro added}
-% \changes{v0.9p}
-%         {1994/01/18}{New Definition}
-% \changes{v0.3b}{1994/03/13}
-%         {Use new cmd \cs{@addtofilelist}}
-% Now define |\InputIfFileExists| to input |#1| if it seems to exist.
-% Immediately prior to the input, |#2| is executed.
-% If the file |#1| does not exist, execute `|#3|'.
-% \changes{v1.0t}{1995/05/25}
-%         {(CAR) added \cs{long}}
-% \changes{v1.1o}{2019/02/07}{Expand \cs{@filef@und} before executing
-%   second argument (github/109)}
-% \changes{v1.2b}{2019/08/27}{Make command robust}
-%    \begin{macrocode}
-%</2ekernel>
-%<latexrelease>\IncludeInRelease{2019/10/01}%
-%<latexrelease>  {\InputIfFileExists}{Don't lose the file name}%
-%<*2ekernel|latexrelease>
+%
+%    Now define |\InputIfFileExists| to input |#1| if it seems to exist.
+%    Immediately prior to the input, |#2| is executed.
+%    If the file |#1| does not exist, execute `|#3|'.
+%
+%    This here is a temporary definition for the kernel. The real one
+%    comes somewhat later in the file \texttt{ltfilehook.dtx}.
+%
 %    \begin{macrocode}
 \DeclareRobustCommand \InputIfFileExists[2]{%
   \IfFileExists{#1}%
@@ -908,25 +1188,23 @@
 %    Swap two arguments and return them unbraced (like
 %   \cs{@firstoftwo} etc).
 %    \begin{macrocode}
+%</2ekernel>
+%<*2ekernel|latexrelease>
+%<latexrelease>\IncludeInRelease{2019/10/01}%
+%<latexrelease>  {\@swaptwoargs}{Don't lose the file name}%
 \long\def\@swaptwoargs#1#2{#2#1}
 %    \end{macrocode}
-%  \end{macro}
-%
 %
 %    \begin{macrocode}
 %</2ekernel|latexrelease>
 %<latexrelease>\EndIncludeInRelease
 %<latexrelease>\IncludeInRelease{0000/00/00}%
-%<latexrelease>  {\InputIfFileExists}{Don't lose the file name}%
-%<latexrelease>\long\def \InputIfFileExists#1#2{%
-%<latexrelease>  \IfFileExists{#1}%
-%<latexrelease>    {#2\@addtofilelist{#1}\@@input \@filef@und}}
-%<latexrelease>
+%<latexrelease>  {\@swaptwoargs}{Don't lose the file name}%
 %<latexrelease>\let\@swaptwoargs\@undefined
 %<latexrelease>\EndIncludeInRelease
 %<*2ekernel>
 %    \end{macrocode}
-%
+%  \end{macro}
 %
 %
 %  \begin{macro}{\input}
@@ -943,20 +1221,51 @@
 %    Define |\@iinput| (i.e., |\input|) in terms of
 %    |\InputIfIfileExists|.
 % \changes{v0.9b}{1993/12/04}{Macro reimplemented}
+%
+%   Changes to \cs{@iinput}: adapt to the changes to
+%   \cs{@missingfileerror}.
 %    \begin{macrocode}
 %</2ekernel>
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2019/10/01}%
-%<latexrelease>                 {\@iinput}{Quote file names}%
+%<latexrelease>\IncludeInRelease{2020/10/01}%
+%<latexrelease>                 {\@iinput}{Change in file error handling}%
 \def\@iinput#1{%
   \InputIfFileExists{#1}{}%
   {\filename@parse\@curr@file
    \edef\reserved@a{\noexpand\@missingfileerror
      {\filename@area\filename@base}%
      {\ifx\filename@ext\relax tex\else\filename@ext\fi}}%
+%    \end{macrocode}
+%   This line now just sets \cs[no-index]{@missingfile@\meta{part}}:
+%    \begin{macrocode}
+   \reserved@a
+%    \end{macrocode}
+%   Now here we have to use it.  The file here is guaranteed to exist,
+%   because \cs{@missingfileerror} ensures so, but we have to use
+%   \cs{InputIfFileExists} because it executes the file hooks.
+%    \begin{macrocode}
+   \edef\reserved@a{\noexpand\@iinput{%
+     \@missingfile@area\@missingfile@base.\@missingfile@ext}}%
    \reserved@a}}
 %</2ekernel|latexrelease>
 %<latexrelease>\EndIncludeInRelease
+%    \end{macrocode}
+%    
+%    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{2019/10/01}%
+%<latexrelease>                 {\@iinput}{Quote file names}%
+%<latexrelease>
+%<latexrelease>\def\@iinput#1{%
+%<latexrelease>  \InputIfFileExists{#1}{}%
+%<latexrelease>  {\filename@parse\@curr@file
+%<latexrelease>   \edef\reserved@a{\noexpand\@missingfileerror
+%<latexrelease>     {\filename@area\filename@base}%
+%<latexrelease>     {\ifx\filename@ext\relax tex\else\filename@ext\fi}}%
+%<latexrelease>   \reserved@a}}
+%<latexrelease>\EndIncludeInRelease
+%    \end{macrocode}
+%
+%    \begin{macrocode}
 %<latexrelease>\IncludeInRelease{0000/00/00}%
 %<latexrelease>                 {\@iinput}{Quote file names}%
 %<latexrelease>\def\@iinput#1{%
@@ -1001,6 +1310,11 @@
 %    \end{macrocode}
 %  \end{macro}
 %
+%
+%
+%
+%
+%
 % \begin{macro}{\@missingfileerror}
 % This `error' command avoids \TeX's primitive missing file loop.
 %
@@ -1018,7 +1332,16 @@
 %         {Move here from ltclass}
 % \changes{v1.0w}{1995/10/06}
 %         {Autoload error}
+%
+%   Changes to \cs{@missingfileerror}:  rather than trying to input the
+%   file by force, now \cs{@missingfileerror} just returns three
+%   \cs[no-index]{@missingfile@\meta{part}} and the caller macro is
+%   responsible for doing the right thing with it.
 %    \begin{macrocode}
+%</2ekernel>
+%<*2ekernel|latexrelease>
+%<latexrelease>\IncludeInRelease{2020/10/01}%
+%<latexrelease>        {\@missingfileerror}{Do not load missing file immediately}%
 \gdef\@missingfileerror#1#2{%
      \typeout{^^J! LaTeX Error: File `#1.#2' not found.^^J^^J%
       Type X to quit or <RETURN> to proceed,^^J%
@@ -1027,20 +1350,74 @@
       {\endlinechar\m@ne
        \global\read\m@ne to\@gtempa}%
     \ifx\@gtempa\@empty
+%    \end{macrocode}
+%   If the user answers with \meta{return}, fallback to the |.tex| file
+%   (previously it did nothing).
+%    \begin{macrocode}
+      \let\@missingfile@area\@empty
+      \let\@missingfile@base\@empty
+      \def\@missingfile@ext{tex}%
     \else
-      \def\reserved@a{x}\ifx\reserved@a\@gtempa\batchmode\@@end\fi
-      \def\reserved@a{X}\ifx\reserved@a\@gtempa\batchmode\@@end\fi
+%    \end{macrocode}
+%   Use \cs{batchmode}\cs{read}|-1 to |\meta{tl} to end the \TeX{} run,
+%   same as \pkg{expl3} does (it was \cs{batchmode}\cs{@@end} before).
+%    \begin{macrocode}
+      \def\reserved@b{\batchmode\read-1 to \reserved@a}%
+      \def\reserved@a{x}\ifx\reserved@a\@gtempa\reserved@b\fi
+      \def\reserved@a{X}\ifx\reserved@a\@gtempa\reserved@b\fi
       \filename@parse\@gtempa
       \edef\filename@ext{%
         \ifx\filename@ext\relax#2\else\filename@ext\fi}%
      \edef\reserved@a{%
-       \noexpand\InputIfFileExists
+%    \end{macrocode}
+%   Only check \cs{IfFileExists} (it was \cs{InputIfFileExists}).
+%    \begin{macrocode}
+       \noexpand\IfFileExists
          {\filename@area\filename@base.\filename@ext}%
-         {}%
+%    \end{macrocode}
+%   If the file exists, define \cs[no-index]{@missingfile@\meta{part}}.
+%    \begin{macrocode}
+         {\def\noexpand\@missingfile@area{\filename@area}%
+          \def\noexpand\@missingfile@base{\filename@base}%
+          \def\noexpand\@missingfile@ext {\filename@ext}}%
          {\noexpand\@missingfileerror
             {\filename@area\filename@base}{\filename@ext}}}%
       \reserved@a
-    \fi}
+    \fi
+}
+%</2ekernel|latexrelease>
+%<latexrelease>\EndIncludeInRelease
+%    \end{macrocode}
+%    
+%    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{0000/00/00}%
+%<latexrelease>        {\@missingfileerror}{Do not load missing file immediately}%
+%<latexrelease>
+%<latexrelease>\gdef\@missingfileerror#1#2{%
+%<latexrelease>     \typeout{^^J! LaTeX Error: File `#1.#2' not found.^^J^^J%
+%<latexrelease>      Type X to quit or <RETURN> to proceed,^^J%
+%<latexrelease>      or enter new name. (Default extension: #2)^^J}%
+%<latexrelease>     \message{Enter file name: }%
+%<latexrelease>      {\endlinechar\m@ne
+%<latexrelease>       \global\read\m@ne to\@gtempa}%
+%<latexrelease>    \ifx\@gtempa\@empty
+%<latexrelease>    \else
+%<latexrelease>      \def\reserved@a{x}\ifx\reserved@a\@gtempa\batchmode\@@end\fi
+%<latexrelease>      \def\reserved@a{X}\ifx\reserved@a\@gtempa\batchmode\@@end\fi
+%<latexrelease>      \filename@parse\@gtempa
+%<latexrelease>      \edef\filename@ext{%
+%<latexrelease>        \ifx\filename@ext\relax#2\else\filename@ext\fi}%
+%<latexrelease>     \edef\reserved@a{%
+%<latexrelease>       \noexpand\InputIfFileExists
+%<latexrelease>         {\filename@area\filename@base.\filename@ext}%
+%<latexrelease>         {}%
+%<latexrelease>         {\noexpand\@missingfileerror
+%<latexrelease>            {\filename@area\filename@base}{\filename@ext}}}%
+%<latexrelease>      \reserved@a
+%<latexrelease>    \fi}
+%<latexrelease>
+%<latexrelease>\EndIncludeInRelease
+%<*2ekernel>
 %    \end{macrocode}
 % \end{macro}
 %