ltluatex.dtx

% \iffalse meta-comment
%
% Copyright (C) 2015-2024
% The LaTeX 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
%    https://www.latex-project.org/lppl.txt
% and version 1.3c or later is part of all distributions of LaTeX
% version 2008 or later.
%
% This file has the LPPL maintenance status "maintained".
%
%<2ekernel>%%% From File: ltluatex.dtx
%<plain>\ifx\newluafunction\undefined\else\expandafter\endinput\fi
%<tex>\ifx
%<tex>  \ProvidesFile\undefined\begingroup\def\ProvidesFile
%<tex>  #1#2[#3]{\endgroup\immediate\write-1{File: #1 #3}}
%<tex>\fi
%<*dtx>
\ProvidesFile{ltluatex.dtx}
%</dtx>
%<plain>\ProvidesFile{ltluatex.tex}
%<*plain>
% \fi
% \ProvidesFile{ltluatex.dtx}
[2024/02/11 v1.2c
% LaTeX Kernel (LuaTeX support)^^A
%\iffalse
%<plain>   LuaTeX support for plain TeX (core)%
%\fi
]
% \iffalse
%</plain>  
%<*tex>
\edef\etatcatcode{\the\catcode`\@}
\catcode`\@=11
%</tex>
%<*driver>
\documentclass{ltxdoc}

\providecommand\InternalDetectionOff{}
\providecommand\InternalDetectionOn{}

\GetFileInfo{ltluatex.dtx}
\begin{document}
\title{\filename\\(Lua\TeX{}-specific support)}
\author{David Carlisle and Joseph Wright\footnote{Significant portions
  of the code here are adapted/simplified from the packages \textsf{luatex} and
  \textsf{luatexbase} written by Heiko Oberdiek, \'{E}lie Roux,
  Manuel P\'{e}gouri\'{e}-Gonnar and Philipp Gesang.}}
\date{\filedate}
\maketitle
\setcounter{tocdepth}{2}
\tableofcontents
\DocInput{\filename}
\end{document}
%</driver>
% \fi
%
%
% \section{Overview}
%
% Lua\TeX{} adds a number of engine-specific functions to \TeX{}. Several of
% these require set up that is best done in the kernel or need related support
% functions. This file provides \emph{basic} support for Lua\TeX{} at the
% \LaTeXe{} kernel level plus as a loadable file which can be used with
% plain \TeX{} and \LaTeX{}.
%
% This file contains code for both \TeX{} (to be stored as part of the format)
% and Lua (to be loaded at the start of each job). In the Lua code, the kernel
% uses the namespace |luatexbase|.
%
% The following |\count| registers are used here for register allocation:
% \begin{itemize}
%  \item[\texttt{\string\e@alloc@attribute@count}] Attributes (default~258)
%  \item[\texttt{\string\e@alloc@ccodetable@count}] Category code tables
%    (default~259)
%  \item[\texttt{\string\e@alloc@luafunction@count}] Lua functions
%    (default~260)
%  \item[\texttt{\string\e@alloc@whatsit@count}] User whatsits (default~261)
%  \item[\texttt{\string\e@alloc@bytecode@count}] Lua bytecodes (default~262)
%  \item[\texttt{\string\e@alloc@luachunk@count}] Lua chunks (default~263)
% \end{itemize}
% (|\count 256| is used for |\newmarks| allocation and |\count 257|
% is used for\linebreak
% |\newXeTeXintercharclass| with Xe\TeX{}, with code defined in
% \texttt{ltfinal.dtx}).
% With any \LaTeXe{} kernel from 2015 onward these registers are part of
% the block in the extended area reserved by the kernel (prior to 2015 the
% \LaTeXe{} kernel did not provide any functionality for the extended
% allocation area).
%
% \section{Core \TeX{} functionality}
%
% The commands defined here are defined for
% possible inclusion in a future \LaTeX{} format, however also extracted
% to the file |ltluatex.tex| which may be used with older \LaTeX\
% formats, and with plain \TeX.
%
% \noindent
% \DescribeMacro{\newattribute}
% |\newattribute{|\meta{attribute}|}|\\
% Defines a named \cs{attribute}, indexed from~$1$
% (\emph{i.e.}~|\attribute0| is never defined). Attributes initially
% have the marker value |-"7FFFFFFF| (`unset') set by the engine.
%
% \noindent
% \DescribeMacro{\newcatcodetable}
% |\newcatcodetable{|\meta{catcodetable}|}|\\
% Defines a named \cs{catcodetable}, indexed from~$1$
% (|\catcodetable0| is never assigned). A new catcode table will be
% populated with exactly those values assigned by Ini\TeX{} (as described
% in the Lua\TeX{} manual).
%
% \noindent
% \DescribeMacro{\newluafunction}
% |\newluafunction{|\meta{function}|}|\\
% Defines a named \cs{luafunction}, indexed from~$1$. (Lua indexes
% tables from $1$ so |\luafunction0| is not available).
%
% \noindent
% \DescribeMacro{\newluacmd}
% |\newluadef{|\meta{function}|}|\\
% Like \cs{newluafunction}, but defines the command using \cs{luadef}
% instead of just assigning an integer.
%
% \noindent
% \DescribeMacro{\newprotectedluacmd}
% |\newluadef{|\meta{function}|}|\\
% Like \cs{newluacmd}, but the defined command is not expandable.
%
% \noindent
% \DescribeMacro{\newwhatsit}
% |\newwhatsit{|\meta{whatsit}|}|\\
% Defines a custom \cs{whatsit}, indexed from~$1$.
%
% \noindent
% \DescribeMacro{\newluabytecode}
% |\newluabytecode{|\meta{bytecode}|}|\\
% Allocates a number for Lua bytecode register, indexed from~$1$.
%
% \noindent
% \DescribeMacro{\newluachunkname}
% |newluachunkname{|\meta{chunkname}|}|\\
% Allocates a number for Lua chunk register, indexed from~$1$.
% Also enters the name of the register (without backslash) into the
% \verb|lua.name| table to be used in stack traces.
%
% \noindent
% \DescribeMacro{\catcodetable@initex}
% \DescribeMacro{\catcodetable@string}
% \DescribeMacro{\catcodetable@latex}
% \DescribeMacro{\catcodetable@atletter}
% Predefined category code tables with the obvious assignments. Note
% that the |latex| and |atletter| tables set the full Unicode range
% to the codes predefined by the kernel.
%
% \noindent
% \DescribeMacro{\setattribute}
% \DescribeMacro{\unsetattribute}
% |\setattribute{|\meta{attribute}|}{|\meta{value}|}|\\
% |\unsetattribute{|\meta{attribute}|}|\\
% Set and unset attributes in a manner analogous to |\setlength|. Note that
% attributes take a marker value when unset so this operation is distinct
% from setting the value to zero.
%
% \section{Plain \TeX\ interface}
%
% The \textsf{ltluatex} interface may be used with plain \TeX\ using
% |\input{ltluatex}|. This inputs |ltluatex.tex| which inputs
% |etex.src| (or |etex.sty| if used with \LaTeX)
% if it is not already input, and then defines some internal commands to
% allow the \textsf{ltluatex} interface to be defined.
%
% The \textsf{luatexbase} package interface may also be used in plain \TeX,
% as before, by inputting the package |\input luatexbase.sty|. The new
% version of \textsf{luatexbase} is based on this \textsf{ltluatex}
% code but implements a compatibility layer providing the interface
% of the original package.
%
% \section{Lua functionality}
%
% \begingroup
%
% \begingroup\lccode`~=`_
% \lowercase{\endgroup\let~}_
% \catcode`_=12
%
% \subsection{Allocators in Lua}
%
% \DescribeMacro{new_attribute}
% |luatexbase.new_attribute(|\meta{attribute}|)|\\
% Returns an allocation number for the \meta{attribute}, indexed from~$1$.
% The attribute will be initialised with the marker value |-"7FFFFFFF|
% (`unset'). The attribute allocation sequence is shared with the \TeX{}
% code but this function does \emph{not} define a token using
% |\attributedef|.
% The attribute name is recorded in the |attributes| table. A
% metatable is provided so that the table syntax can be used
% consistently for attributes declared in \TeX\ or Lua.
%
% \noindent
% \DescribeMacro{new_whatsit}
% |luatexbase.new_whatsit(|\meta{whatsit}|)|\\
% Returns an allocation number for the custom \meta{whatsit}, indexed from~$1$.
%
% \noindent
% \DescribeMacro{new_bytecode}
% |luatexbase.new_bytecode(|\meta{bytecode}|)|\\
% Returns an allocation number for a bytecode register, indexed from~$1$.
% The optional \meta{name} argument is just used for logging.
%
% \noindent
% \DescribeMacro{new_chunkname}
% |luatexbase.new_chunkname(|\meta{chunkname}|)|\\
% Returns an allocation number for a Lua chunk name for use with
% |\directlua| and |\latelua|, indexed from~$1$.
% The number is returned and also \meta{name} argument is added to the
% |lua.name| array at that index.
%
% \begin{sloppypar}
% \noindent
% \DescribeMacro{new_luafunction}
% |luatexbase.new_luafunction(|\meta{functionname}|)|\\
% Returns an allocation number for a lua function for use
% with |\luafunction|, |\lateluafunction|, and |\luadef|,
% indexed from~$1$. The optional \meta{functionname} argument
% is just used for logging.
% \end{sloppypar}
%
% These functions all require access to a named \TeX{} count register
% to manage their allocations. The standard names are those defined
% above for access from \TeX{}, \emph{e.g.}~\string\e@alloc@attribute@count,
% but these can be adjusted by defining the variable
% \texttt{\meta{type}\_count\_name} before loading |ltluatex.lua|, for example
% \begin{verbatim}
% local attribute_count_name = "attributetracker"
% require("ltluatex")
% \end{verbatim}
% would use a \TeX{} |\count| (|\countdef|'d token) called |attributetracker|
% in place of \string\e@alloc@attribute@count.
%
% \subsection{Lua access to \TeX{} register numbers}
%
% \DescribeMacro{registernumber}
% |luatexbase.registernumer(|\meta{name}|)|\\
% Sometimes (notably in the case of Lua attributes) it is necessary to
% access a register \emph{by number} that has been allocated by \TeX{}.
% This package provides a function to look up the relevant number
% using Lua\TeX{}'s internal tables. After for example
% |\newattribute\myattrib|, |\myattrib| would be defined by (say)
% |\myattrib=\attribute15|.  |luatexbase.registernumer("myattrib")|
% would then return the register number, $15$ in this case. If the string passed
% as argument does not correspond to a token defined by |\attributedef|,
% |\countdef| or similar commands, the Lua value |false| is returned.
%
% As an example, consider the input:
%\begin{verbatim}
% \newcommand\test[1]{%
% \typeout{#1: \expandafter\meaning\csname#1\endcsname^^J
% \space\space\space\space
% \directlua{tex.write(luatexbase.registernumber("#1") or "bad input")}%
% }}
%
% \test{undefinedrubbish}
%
% \test{space}
%
% \test{hbox}
%
% \test{@MM}
%
% \test{@tempdima}
% \test{@tempdimb}
%
% \test{strutbox}
%
% \test{sixt@@n}
%
% \attrbutedef\myattr=12
% \myattr=200
% \test{myattr}
%
%\end{verbatim}
%
% If the demonstration code is processed with Lua\LaTeX{} then the following
% would be produced in the log and terminal output.
%\begin{verbatim}
% undefinedrubbish: \relax
%      bad input
% space: macro:->
%      bad input
% hbox: \hbox
%      bad input
% @MM: \mathchar"4E20
%      20000
% @tempdima: \dimen14
%      14
% @tempdimb: \dimen15
%      15
% strutbox: \char"B
%      11
% sixt@@n: \char"10
%      16
% myattr: \attribute12
%      12
%\end{verbatim}
%
% Notice how undefined commands, or commands unrelated to registers
% do not produce an error, just return |false| and so print
% |bad input| here. Note also that commands defined by |\newbox| work and
% return the number of the box register even though the actual command
% holding this number is a |\chardef| defined token (there is no
% |\boxdef|).
%
% \subsection{Module utilities}
%
% \DescribeMacro{provides_module}
% |luatexbase.provides_module(|\meta{info}|)|\\
% This function is used by modules to identify themselves; the |info| should be
% a table containing information about the module. The required field
% |name| must contain the name of the module. It is recommended to provide a
% field |date| in the usual \LaTeX{} format |yyyy/mm/dd|. Optional fields
% |version| (a string) and |description| may be used if present. This
% information will be recorded in the log. Other fields are ignored.
%
% \noindent
% \DescribeMacro{module_info}
% \DescribeMacro{module_warning}
% \DescribeMacro{module_error}
% |luatexbase.module_info(|\meta{module}, \meta{text}|)|\\
% |luatexbase.module_warning(|\meta{module}, \meta{text}|)|\\
% |luatexbase.module_error(|\meta{module}, \meta{text}|)|\\
% These functions are similar to \LaTeX{}'s |\PackageError|, |\PackageWarning|
% and |\PackageInfo| in the way they format the output.  No automatic line
% breaking is done, you may still use |\n| as usual for that, and the name of
% the package will be prepended to each output line.
%
% Note that |luatexbase.module_error| raises an actual Lua error with |error()|,
% which currently means a call stack will be dumped. While this may not
% look pretty, at least it provides useful information for tracking the
% error down.
%
% \subsection{Callback management}
%
% \noindent
% \DescribeMacro{add_to_callback}
% |luatexbase.add_to_callback(|^^A
% \meta{callback}, \meta{function}, \meta{description}|)|
% Registers the \meta{function} into the \meta{callback} with a textual
% \meta{description} of the function. Functions are inserted into the callback
% in the order loaded.
%
% \noindent
% \DescribeMacro{remove_from_callback}
% |luatexbase.remove_from_callback(|\meta{callback}, \meta{description}|)|
% Removes the callback function with \meta{description} from the \meta{callback}.
% The removed function and its description
% are returned as the results of this function.
%
% \noindent
% \DescribeMacro{in_callback}
% |luatexbase.in_callback(|\meta{callback}, \meta{description}|)|
% Checks if the \meta{description} matches one of the functions added
% to the list for the \meta{callback}, returning a boolean value.
%
% \noindent
% \DescribeMacro{disable_callback}
% |luatexbase.disable_callback(|\meta{callback}|)|
% Sets the \meta{callback} to \texttt{false} as described in the Lua\TeX{}
% manual for the underlying \texttt{callback.register} built-in. Callbacks
% will only be set to false (and thus be skipped entirely) if there are
% no functions registered using the callback.
%
% \noindent
% \DescribeMacro{callback_descriptions}
% A list of the descriptions of functions registered to the specified
% callback is returned. |{}| is returned if there are no functions registered.
%
% \noindent
% \DescribeMacro{create_callback}
% |luatexbase.create_callback(|\meta{name},\meta{type},\meta{default}|)|
% Defines a user defined callback. The last argument is a default
% function or |false|.
%
% \noindent
% \DescribeMacro{call_callback}
% |luatexbase.call_callback(|\meta{name},\ldots|)|
% Calls a user defined callback with the supplied arguments.
%
% \noindent
% \DescribeMacro{declare_callback_rule}
% |luatexbase.declare_callback_rule(|\meta{name}, \meta{first}, \meta{relation}, \meta{second}|)|
% Adds an ordering constraint between two callback functions for callback \meta{name}.
%
% The kind of constraint added depends on \meta{relation}:
% \begin{description}
%   \item[before] The callback function with description \meta{first} will be
%     executed before the function with description \meta{second}.
%   \item[after] The callback function with description \meta{first} will be
%     executed after the function with description \meta{second}.
%   \item[incompatible-warning] When both a callback function with description \meta{first}
%     and with description \meta{second} is registered, then a warning is printed when
%     the callback is executed.
%   \item[incompatible-error] When both a callback function with description \meta{first}
%     and with description \meta{second} is registered, then an error is printed when
%     the callback is executed.
%   \item[unrelated] Any previously declared callback rule between \meta{first}
%     and \meta{second} gets disabled.
% \end{description}
% Every call to \texttt{declare_callback_rule} with a specific callback \meta{name}
% and descriptions \meta{first} and \meta{second} overwrites all previous calls with
% same callback and descriptions.
%
% The callback functions do not have to be registered yet when the functions is called.
% Ony the constraints for which both callback descriptions refer to callbacks
% registered at the time the callback is called will have an effect.
%
% \endgroup
%
% \MaybeStop{}
%
% \section{Implementation}
%
%    \begin{macrocode}
%<*2ekernel|tex|latexrelease>
%<2ekernel|latexrelease>\ifx\directlua\@undefined\else
%    \end{macrocode}
%
%
% \changes{v1.0j}{2015/12/02}{Remove nonlocal iteration variables (PHG)}
% \changes{v1.0j}{2015/12/02}{Assorted typos fixed (PHG)}
% \changes{v1.0j}{2015/12/02}{Remove unreachable code after calls to error() (PHG)}
% \subsection{Minimum Lua\TeX{} version}
%
% Lua\TeX{} has changed a lot over time. In the kernel support for ancient
% versions is not provided: trying to build a format with a very old binary
% therefore gives some information in the log and loading stops. The cut-off
% selected here relates to the tree-searching behaviour of |require()|:
% from version~0.60, Lua\TeX{} will correctly find Lua files in the |texmf|
% tree without `help'.
%    \begin{macrocode}
%<latexrelease>\IncludeInRelease{2015/10/01}
%<latexrelease>                 {\newluafunction}{LuaTeX}%
\ifnum\luatexversion<60 %
  \wlog{***************************************************}
  \wlog{* LuaTeX version too old for ltluatex support *}
  \wlog{***************************************************}
  \expandafter\endinput
\fi
%    \end{macrocode}
%
% \changes{v1.1n}{2020/06/10}{Define \cs{@gobble}/\cs{@firstofone} even for \LaTeX\ to allow early loading.}
% Two simple \LaTeX\ macros from |ltdefns.dtx| have to be defined here
% because ltdefns.dtx is not loaded yet when ltluatex.dtx is executed.
%    \begin{macrocode}
\long\def\@gobble#1{}
\long\def\@firstofone#1{#1}
%    \end{macrocode}
%
% \subsection{Older \LaTeX{}/Plain \TeX\ setup}
%
%    \begin{macrocode}
%<*tex>
%    \end{macrocode}
%
% Older \LaTeX{} formats don't have the primitives with `native' names:
% sort that out. If they already exist this will still be safe.
%    \begin{macrocode}
\directlua{tex.enableprimitives("",tex.extraprimitives("luatex"))}
%    \end{macrocode}
%
%    \begin{macrocode}
\ifx\e@alloc\@undefined
%    \end{macrocode}
%
% In pre-2014 \LaTeX{}, or plain \TeX{}, load |etex.{sty,src}|.
%    \begin{macrocode}
  \ifx\documentclass\@undefined
    \ifx\loccount\@undefined
      \input{etex.src}%
    \fi
    \catcode`\@=11 %
    \outer\expandafter\def\csname newfam\endcsname
                          {\alloc@8\fam\chardef\et@xmaxfam}
  \else
    \RequirePackage{etex}
    \expandafter\def\csname newfam\endcsname
                    {\alloc@8\fam\chardef\et@xmaxfam}
    \expandafter\let\expandafter\new@mathgroup\csname newfam\endcsname
  \fi
%    \end{macrocode}
%
% \subsubsection{Fixes to \texttt{etex.src}/\texttt{etex.sty}}
%
% These could and probably should be made directly in an
% update to |etex.src| which already has some Lua\TeX-specific
% code, but does not define the correct range for Lua\TeX.
%
% 2015-07-13 higher range in luatex.
%    \begin{macrocode}
\edef \et@xmaxregs {\ifx\directlua\@undefined 32768\else 65536\fi}
%    \end{macrocode}
% luatex/xetex also allow more math fam.
%    \begin{macrocode}
\edef \et@xmaxfam {\ifx\Umathcode\@undefined\sixt@@n\else\@cclvi\fi}
%    \end{macrocode}
%
%    \begin{macrocode}
\count 270=\et@xmaxregs % locally allocates \count registers
\count 271=\et@xmaxregs % ditto for \dimen registers
\count 272=\et@xmaxregs % ditto for \skip registers
\count 273=\et@xmaxregs % ditto for \muskip registers
\count 274=\et@xmaxregs % ditto for \box registers
\count 275=\et@xmaxregs % ditto for \toks registers
\count 276=\et@xmaxregs % ditto for \marks classes
%    \end{macrocode}
%
% and 256 or 16 fam. (Done above due to plain/\LaTeX\ differences in
% \textsf{ltluatex}.)
%    \begin{macrocode}
% \outer\def\newfam{\alloc@8\fam\chardef\et@xmaxfam}
%    \end{macrocode}
%
% End of proposed changes to \texttt{etex.src}
%
% \subsubsection{luatex specific settings}
%
% Switch to global cf |luatex.sty| to leave room for inserts
% not really needed for luatex but possibly most compatible
% with existing use.
%    \begin{macrocode}
\expandafter\let\csname newcount\expandafter\expandafter\endcsname
                \csname globcount\endcsname
\expandafter\let\csname newdimen\expandafter\expandafter\endcsname
                \csname globdimen\endcsname
\expandafter\let\csname newskip\expandafter\expandafter\endcsname
                \csname globskip\endcsname
\expandafter\let\csname newbox\expandafter\expandafter\endcsname
                \csname globbox\endcsname
%    \end{macrocode}
%
% Define|\e@alloc| as in \LaTeX{} (the existing macros in |etex.src| are
% hard to extend to further register types as they assume specific
% 26x and 27x count range). For compatibility the existing register
% allocation is not changed.
%
%    \begin{macrocode}
\chardef\e@alloc@top=65535
\let\e@alloc@chardef\chardef
%    \end{macrocode}
%
%    \begin{macrocode}
\def\e@alloc#1#2#3#4#5#6{%
  \global\advance#3\@ne
  \e@ch@ck{#3}{#4}{#5}#1%
  \allocationnumber#3\relax
  \global#2#6\allocationnumber
  \wlog{\string#6=\string#1\the\allocationnumber}}%
%    \end{macrocode}
%
%    \begin{macrocode}
\gdef\e@ch@ck#1#2#3#4{%
  \ifnum#1<#2\else
    \ifnum#1=#2\relax
      #1\@cclvi
      \ifx\count#4\advance#1 10 \fi
    \fi
    \ifnum#1<#3\relax
    \else
      \errmessage{No room for a new \string#4}%
    \fi
  \fi}%
%    \end{macrocode}
%
% Fix up allocations not to clash with |etex.src|.
%
%    \begin{macrocode}
\expandafter\csname newcount\endcsname\e@alloc@attribute@count
\expandafter\csname newcount\endcsname\e@alloc@ccodetable@count
\expandafter\csname newcount\endcsname\e@alloc@luafunction@count
\expandafter\csname newcount\endcsname\e@alloc@whatsit@count
\expandafter\csname newcount\endcsname\e@alloc@bytecode@count
\expandafter\csname newcount\endcsname\e@alloc@luachunk@count
%    \end{macrocode}
%
% End of conditional setup for plain \TeX\ / old \LaTeX.
%    \begin{macrocode}
\fi
%</tex>
%    \end{macrocode}
%
% \subsection{Attributes}
%
% \begin{macro}{\newattribute}
% \changes{v1.0a}{2015/09/24}{Macro added}
% \changes{v1.1q}{2020/08/02}{Move reset to $0$ inside conditional}
%   As is generally the case for the Lua\TeX{} registers we start here
%   from~$1$. Notably, some code assumes that |\attribute0| is never used so
%   this is important in this case.
%    \begin{macrocode}
\ifx\e@alloc@attribute@count\@undefined
  \countdef\e@alloc@attribute@count=258
  \e@alloc@attribute@count=\z@
\fi
\def\newattribute#1{%
  \e@alloc\attribute\attributedef
    \e@alloc@attribute@count\m@ne\e@alloc@top#1%
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\setattribute}
% \begin{macro}{\unsetattribute}
%   Handy utilities.
%    \begin{macrocode}
\def\setattribute#1#2{#1=\numexpr#2\relax}
\def\unsetattribute#1{#1=-"7FFFFFFF\relax}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \subsection{Category code tables}
%
% \begin{macro}{\newcatcodetable}
% \changes{v1.0a}{2015/09/24}{Macro added}
%   Category code tables are allocated with a limit half of that used by Lua\TeX{}
%   for everything else. At the end of allocation there needs to be an
%   initialization step. Table~$0$ is already taken (it's the global one for
%   current use) so the allocation starts at~$1$.
%    \begin{macrocode}
\ifx\e@alloc@ccodetable@count\@undefined
  \countdef\e@alloc@ccodetable@count=259
  \e@alloc@ccodetable@count=\z@
\fi
\def\newcatcodetable#1{%
  \e@alloc\catcodetable\chardef
    \e@alloc@ccodetable@count\m@ne{"8000}#1%
  \initcatcodetable\allocationnumber
}
%    \end{macrocode}
% \end{macro}
%
% \changes{v1.0l}{2015/12/18}{Load Unicode data from source}
% \begin{macro}{\catcodetable@initex}
% \changes{v1.0a}{2015/09/24}{Macro added}
% \begin{macro}{\catcodetable@string}
% \changes{v1.0a}{2015/09/24}{Macro added}
% \begin{macro}{\catcodetable@latex}
% \changes{v1.0a}{2015/09/24}{Macro added}
% \begin{macro}{\catcodetable@atletter}
% \changes{v1.0a}{2015/09/24}{Macro added}
%   Save a small set of standard tables. The Unicode data is read
%   here in using a parser simplified from that in |load-unicode-data|:
%   only the nature of letters needs to be detected.
%    \begin{macrocode}
\newcatcodetable\catcodetable@initex
\newcatcodetable\catcodetable@string
\begingroup
  \def\setrangecatcode#1#2#3{%
    \ifnum#1>#2 %
      \expandafter\@gobble
    \else
      \expandafter\@firstofone
    \fi
      {%
        \catcode#1=#3 %
        \expandafter\setrangecatcode\expandafter
          {\number\numexpr#1 + 1\relax}{#2}{#3}
      }%
  }
  \@firstofone{%
    \catcodetable\catcodetable@initex
      \catcode0=12 %
      \catcode13=12 %
      \catcode37=12 %
      \setrangecatcode{65}{90}{12}%
      \setrangecatcode{97}{122}{12}%
      \catcode92=12 %
      \catcode127=12 %
      \savecatcodetable\catcodetable@string
    \endgroup
  }%
\newcatcodetable\catcodetable@latex
\newcatcodetable\catcodetable@atletter
\begingroup
  \def\parseunicodedataI#1;#2;#3;#4\relax{%
    \parseunicodedataII#1;#3;#2 First>\relax
  }%
  \def\parseunicodedataII#1;#2;#3 First>#4\relax{%
    \ifx\relax#4\relax
      \expandafter\parseunicodedataIII
    \else
      \expandafter\parseunicodedataIV
    \fi
      {#1}#2\relax%
  }%
  \def\parseunicodedataIII#1#2#3\relax{%
    \ifnum 0%
      \if L#21\fi
      \if M#21\fi
      >0 %
      \catcode"#1=11 %
    \fi
  }%
  \def\parseunicodedataIV#1#2#3\relax{%
    \read\unicoderead to \unicodedataline
    \if L#2%
      \count0="#1 %
      \expandafter\parseunicodedataV\unicodedataline\relax
    \fi
  }%
  \def\parseunicodedataV#1;#2\relax{%
    \loop
      \unless\ifnum\count0>"#1 %
        \catcode\count0=11 %
        \advance\count0 by 1 %
    \repeat
  }%
  \def\storedpar{\par}%
  \chardef\unicoderead=\numexpr\count16 + 1\relax
  \openin\unicoderead=UnicodeData.txt %
  \loop\unless\ifeof\unicoderead %
    \read\unicoderead to \unicodedataline
    \unless\ifx\unicodedataline\storedpar
      \expandafter\parseunicodedataI\unicodedataline\relax
    \fi
  \repeat
  \closein\unicoderead
  \@firstofone{%
    \catcode64=12 %
    \savecatcodetable\catcodetable@latex
    \catcode64=11 %
    \savecatcodetable\catcodetable@atletter
   }
\endgroup
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \subsection{Named Lua functions}
%
% \begin{macro}{\newluafunction}
% \changes{v1.0a}{2015/09/24}{Macro added}
% \changes{v1.1q}{2020/08/02}{Move reset to $0$ inside conditional}
%   Much the same story for allocating Lua\TeX{} functions except here they are
%   just numbers so they are allocated in the same way as boxes.
%   Lua indexes from~$1$ so once again slot~$0$ is skipped.
%    \begin{macrocode}
\ifx\e@alloc@luafunction@count\@undefined
  \countdef\e@alloc@luafunction@count=260
  \e@alloc@luafunction@count=\z@
\fi
\def\newluafunction{%
  \e@alloc\luafunction\e@alloc@chardef
    \e@alloc@luafunction@count\m@ne\e@alloc@top
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\newluacmd, \newprotectedluacmd}
% \changes{v1.1x}{2021/12/27}{Macros added}
%   Additionally two variants are provided to make the passed control
%   sequence call the function directly.
%    \begin{macrocode}
\def\newluacmd{%
  \e@alloc\luafunction\luadef
    \e@alloc@luafunction@count\m@ne\e@alloc@top
}
\def\newprotectedluacmd{%
  \e@alloc\luafunction{\protected\luadef}
    \e@alloc@luafunction@count\m@ne\e@alloc@top
}
%    \end{macrocode}
% \end{macro}
%
% \subsection{Custom whatsits}
%
% \begin{macro}{\newwhatsit}
% \changes{v1.0a}{2015/09/24}{Macro added}
% \changes{v1.1q}{2020/08/02}{Move reset to $0$ inside conditional}
%   These are only settable from Lua but for consistency are definable
%   here.
%    \begin{macrocode}
\ifx\e@alloc@whatsit@count\@undefined
  \countdef\e@alloc@whatsit@count=261
  \e@alloc@whatsit@count=\z@
\fi
\def\newwhatsit#1{%
  \e@alloc\whatsit\e@alloc@chardef
    \e@alloc@whatsit@count\m@ne\e@alloc@top#1%
}
%    \end{macrocode}
% \end{macro}
%
% \subsection{Lua bytecode registers}
%
% \begin{macro}{\newluabytecode}
% \changes{v1.0a}{2015/09/24}{Macro added}
% \changes{v1.1q}{2020/08/02}{Move reset to $0$ inside conditional}
%   These are only settable from Lua but for consistency are definable
%   here.
%    \begin{macrocode}
\ifx\e@alloc@bytecode@count\@undefined
  \countdef\e@alloc@bytecode@count=262
  \e@alloc@bytecode@count=\z@
\fi
\def\newluabytecode#1{%
  \e@alloc\luabytecode\e@alloc@chardef
    \e@alloc@bytecode@count\m@ne\e@alloc@top#1%
}
%    \end{macrocode}
% \end{macro}
%
% \subsection{Lua chunk registers}

% \begin{macro}{\newluachunkname}
% \changes{v1.0a}{2015/09/24}{Macro added}
% \changes{v1.1q}{2020/08/02}{Move reset to $0$ inside conditional}
% As for bytecode registers, but in addition we need to add a string
% to the \verb|lua.name| table to use in stack tracing. We use the
% name of the command passed to the allocator, with no backslash.
%    \begin{macrocode}
\ifx\e@alloc@luachunk@count\@undefined
  \countdef\e@alloc@luachunk@count=263
  \e@alloc@luachunk@count=\z@
\fi
\def\newluachunkname#1{%
  \e@alloc\luachunk\e@alloc@chardef
    \e@alloc@luachunk@count\m@ne\e@alloc@top#1%
    {\escapechar\m@ne
    \directlua{lua.name[\the\allocationnumber]="\string#1"}}%
}
%    \end{macrocode}
% \end{macro}
%
% \subsection{Lua loader}
% \changes{v1.1r}{2020/08/10}{Load ltluatex Lua module during format building}
%
% Lua code loaded in the format often has to be loaded again at the
% beginning of every job, so we define a helper which allows us to avoid
% duplicated code:
%
%    \begin{macrocode}
\def\now@and@everyjob#1{%
  \everyjob\expandafter{\the\everyjob
    #1%
  }%
  #1%
}
%    \end{macrocode}
%
% Load the Lua code at the start of every job.
% For the conversion of \TeX{} into numbers at the Lua side we need some
% known registers: for convenience we use a set of systematic names, which
% means using a group around the Lua loader.
%    \begin{macrocode}
%<2ekernel>\now@and@everyjob{%
  \begingroup
    \attributedef\attributezero=0 %
    \chardef     \charzero     =0 %
%    \end{macrocode}
% Note name change required on older luatex, for hash table access.
%    \begin{macrocode}
    \countdef    \CountZero    =0 %
    \dimendef    \dimenzero    =0 %
    \mathchardef \mathcharzero =0 %
    \muskipdef   \muskipzero   =0 %
    \skipdef     \skipzero     =0 %
    \toksdef     \tokszero     =0 %
    \directlua{require("ltluatex")}
  \endgroup
%<2ekernel>}
%<latexrelease>\EndIncludeInRelease
%    \end{macrocode}
%
% \changes{v1.0b}{2015/10/02}{Fix backing out of \TeX{} code}
% \changes{v1.0c}{2015/10/02}{Allow backing out of Lua code}
%    \begin{macrocode}
%<latexrelease>\IncludeInRelease{0000/00/00}
%<latexrelease>                 {\newluafunction}{LuaTeX}%
%<latexrelease>\let\e@alloc@attribute@count\@undefined
%<latexrelease>\let\newattribute\@undefined
%<latexrelease>\let\setattribute\@undefined
%<latexrelease>\let\unsetattribute\@undefined
%<latexrelease>\let\e@alloc@ccodetable@count\@undefined
%<latexrelease>\let\newcatcodetable\@undefined
%<latexrelease>\let\catcodetable@initex\@undefined
%<latexrelease>\let\catcodetable@string\@undefined
%<latexrelease>\let\catcodetable@latex\@undefined
%<latexrelease>\let\catcodetable@atletter\@undefined
%<latexrelease>\let\e@alloc@luafunction@count\@undefined
%<latexrelease>\let\newluafunction\@undefined
%<latexrelease>\let\e@alloc@luafunction@count\@undefined
%<latexrelease>\let\newwhatsit\@undefined
%<latexrelease>\let\e@alloc@whatsit@count\@undefined
%<latexrelease>\let\newluabytecode\@undefined
%<latexrelease>\let\e@alloc@bytecode@count\@undefined
%<latexrelease>\let\newluachunkname\@undefined
%<latexrelease>\let\e@alloc@luachunk@count\@undefined
%<latexrelease>\directlua{luatexbase.uninstall()}
%<latexrelease>\EndIncludeInRelease
%    \end{macrocode}
%
% In \verb|\everyjob|, if luaotfload is available, load it and switch to TU.
%    \begin{macrocode}
%<latexrelease>\IncludeInRelease{2017/01/01}%
%<latexrelease>                 {\fontencoding}{TU in everyjob}%
%<latexrelease>\fontencoding{TU}\let\encodingdefault\f@encoding
%<latexrelease>\ifx\directlua\@undefined\else
%<2ekernel>\everyjob\expandafter{%
%<2ekernel>  \the\everyjob
%<*2ekernel,latexrelease>
  \directlua{%
  if xpcall(function ()%
             require('luaotfload-main')%
            end,texio.write_nl) then %
  local _void = luaotfload.main ()%
  else %
  texio.write_nl('Error in luaotfload: reverting to OT1')%
  tex.print('\string\\def\string\\encodingdefault{OT1}')%
  end %
  }%
  \let\f@encoding\encodingdefault
  \expandafter\let\csname ver@luaotfload.sty\endcsname\fmtversion
%</2ekernel,latexrelease>
%<latexrelease>\fi
%<2ekernel>  }
%<latexrelease>\EndIncludeInRelease
%<latexrelease>\IncludeInRelease{0000/00/00}%
%<latexrelease>                 {\fontencoding}{TU in everyjob}%
%<latexrelease>\fontencoding{OT1}\let\encodingdefault\f@encoding
%<latexrelease>\EndIncludeInRelease
%    \end{macrocode}
%
%    \begin{macrocode}
%<2ekernel|latexrelease>\fi
%</2ekernel|tex|latexrelease>
%    \end{macrocode}
%
% \subsection{Lua module preliminaries}
%
% \begingroup
%
%  \begingroup\lccode`~=`_
%  \lowercase{\endgroup\let~}_
%  \catcode`_=12
%
%    \begin{macrocode}
%<*lua>
%    \end{macrocode}
%
% Some set up for the Lua module which is needed for all of the Lua
% functionality added here.
%
% \begin{macro}{luatexbase}
% \changes{v1.0a}{2015/09/24}{Table added}
%   Set up the table for the returned functions. This is used to expose
%   all of the public functions.
%    \begin{macrocode}
luatexbase       = luatexbase or { }
local luatexbase = luatexbase
%    \end{macrocode}
% \end{macro}
%
% Some Lua best practice: use local versions of functions where possible.
% \changes{v1.1u}{2021/08/11}{Define missing local function}
% \changes{v1.2b}{2023/01/19}{Remove unused local variable tex_setattribute}
%    \begin{macrocode}
local string_gsub      = string.gsub
local tex_count        = tex.count
local tex_setcount     = tex.setcount
local texio_write_nl   = texio.write_nl
local flush_list       = node.flush_list
%    \end{macrocode}
% \changes{v1.0i}{2015/11/29}{Declare this as local before used in the module error definitions (PHG)}
%    \begin{macrocode}
local luatexbase_warning
local luatexbase_error
%    \end{macrocode}
%
% \subsection{Lua module utilities}
%
% \subsubsection{Module tracking}
%
% \begin{macro}{modules}
% \changes{v1.0a}{2015/09/24}{Function modified}
%   To allow tracking of module usage, a structure is provided to store
%   information and to return it.
%    \begin{macrocode}
local modules = modules or { }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{provides_module}
% \changes{v1.0a}{2015/09/24}{Function added}
% \changes{v1.0f}{2015/10/03}{use luatexbase\_log}
% Local function to write to the log.
%    \begin{macrocode}
local function luatexbase_log(text)
  texio_write_nl("log", text)
end
%    \end{macrocode}
%
%   Modelled on |\ProvidesPackage|, we store much the same information but
%   with a little more structure.
%    \begin{macrocode}
local function provides_module(info)
  if not (info and info.name) then
    luatexbase_error("Missing module name for provides_module")
  end
  local function spaced(text)
    return text and (" " .. text) or ""
  end
  luatexbase_log(
    "Lua module: " .. info.name
      .. spaced(info.date)
      .. spaced(info.version)
      .. spaced(info.description)
  )
  modules[info.name] = info
end
luatexbase.provides_module = provides_module
%    \end{macrocode}
% \end{macro}
%
% \subsubsection{Module messages}
%
% There are various warnings and errors that need to be given. For warnings
% we can get exactly the same formatting as from \TeX{}. For errors we have to
% make some changes. Here we give the text of the error in the \LaTeX{} format
% then force an error from Lua to halt the run. Splitting the message text is
% done using |\n| which takes the place of |\MessageBreak|.
%
% First an auxiliary for the formatting: this measures up the message
% leader so we always get the correct indent.
% \changes{v1.0j}{2015/12/02}{Declaration/use of first\_head fixed (PHG)}
%    \begin{macrocode}
local function msg_format(mod, msg_type, text)
  local leader = ""
  local cont
  local first_head
  if mod == "LaTeX" then
    cont = string_gsub(leader, ".", " ")
    first_head = leader .. "LaTeX: "
  else
    first_head = leader .. "Module "  .. msg_type
    cont = "(" .. mod .. ")"
      .. string_gsub(first_head, ".", " ")
    first_head =  leader .. "Module "  .. mod .. " " .. msg_type  .. ":"
  end
  if msg_type == "Error" then
    first_head = "\n" .. first_head
  end
  if string.sub(text,-1) ~= "\n" then
    text = text .. " "
  end
  return first_head .. " "
    .. string_gsub(
         text
	 .. "on input line "
         .. tex.inputlineno, "\n", "\n" .. cont .. " "
      )
   .. "\n"
end
%    \end{macrocode}
%
% \begin{macro}{module_info}
% \changes{v1.0a}{2015/09/24}{Function added}
% \begin{macro}{module_warning}
% \changes{v1.0a}{2015/09/24}{Function added}
% \begin{macro}{module_error}
% \changes{v1.0a}{2015/09/24}{Function added}
%   Write messages.
%    \begin{macrocode}
local function module_info(mod, text)
  texio_write_nl("log", msg_format(mod, "Info", text))
end
luatexbase.module_info = module_info
local function module_warning(mod, text)
  texio_write_nl("term and log",msg_format(mod, "Warning", text))
end
luatexbase.module_warning = module_warning
local function module_error(mod, text)
  error(msg_format(mod, "Error", text))
end
luatexbase.module_error = module_error
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% Dedicated versions for the rest of the code here.
%    \begin{macrocode}
function luatexbase_warning(text)
  module_warning("luatexbase", text)
end
function luatexbase_error(text)
  module_error("luatexbase", text)
end
%    \end{macrocode}
%
%
% \subsection{Accessing register numbers from Lua}
%
% \changes{v1.0g}{2015/11/14}{Track Lua\TeX{} changes for
%   \texttt{(new)token.create}}
% Collect up the data from the \TeX{} level into a Lua table: from
% version~0.80, Lua\TeX{} makes that easy.
% \changes{v1.0j}{2015/12/02}{Adjust hashtokens to store the result of tex.hashtokens()), not the function (PHG)}
%    \begin{macrocode}
local luaregisterbasetable = { }
local registermap = {
  attributezero = "assign_attr"    ,
  charzero      = "char_given"     ,
  CountZero     = "assign_int"     ,
  dimenzero     = "assign_dimen"   ,
  mathcharzero  = "math_given"     ,
  muskipzero    = "assign_mu_skip" ,
  skipzero      = "assign_skip"    ,
  tokszero      = "assign_toks"    ,
}
local createtoken
if tex.luatexversion > 81 then
  createtoken = token.create
elseif tex.luatexversion > 79 then
  createtoken = newtoken.create
end
local hashtokens    = tex.hashtokens()
local luatexversion = tex.luatexversion
for i,j in pairs (registermap) do
  if luatexversion < 80 then
    luaregisterbasetable[hashtokens[i][1]] =
      hashtokens[i][2]
  else
    luaregisterbasetable[j] = createtoken(i).mode
  end
end
%    \end{macrocode}
%
% \begin{macro}{registernumber}
%   Working out the correct return value can be done in two ways. For older
%   Lua\TeX{} releases it has to be extracted from the |hashtokens|. On the
%   other hand, newer Lua\TeX{}'s have |newtoken|, and whilst |.mode| isn't
%   currently documented, Hans Hagen pointed to this approach so we should be
%   OK.
%    \begin{macrocode}
local registernumber
if luatexversion < 80 then
  function registernumber(name)
    local nt = hashtokens[name]
    if(nt and luaregisterbasetable[nt[1]]) then
      return nt[2] - luaregisterbasetable[nt[1]]
    else
      return false
    end
  end
else
  function registernumber(name)
    local nt = createtoken(name)
    if(luaregisterbasetable[nt.cmdname]) then
      return nt.mode - luaregisterbasetable[nt.cmdname]
    else
      return false
    end
  end
end
luatexbase.registernumber = registernumber
%    \end{macrocode}
% \end{macro}
%
% \subsection{Attribute allocation}
%
% \begin{macro}{new_attribute}
% \changes{v1.0a}{2015/09/24}{Function added}
% \changes{v1.1c}{2017/02/18}{Parameterize count used in tracking}
%   As attributes are used for Lua manipulations its useful to be able
%   to assign from this end.
% \InternalDetectionOff
%    \begin{macrocode}
local attributes=setmetatable(
{},
{
__index = function(t,key)
return registernumber(key) or nil
end}
)
luatexbase.attributes = attributes
%    \end{macrocode}
%
%    \begin{macrocode}
local attribute_count_name =
                     attribute_count_name or "e@alloc@attribute@count"
local function new_attribute(name)
  tex_setcount("global", attribute_count_name,
                          tex_count[attribute_count_name] + 1)
  if tex_count[attribute_count_name] > 65534 then
    luatexbase_error("No room for a new \\attribute")
  end
  attributes[name]= tex_count[attribute_count_name]
  luatexbase_log("Lua-only attribute " .. name .. " = " ..
                 tex_count[attribute_count_name])
  return tex_count[attribute_count_name]
end
luatexbase.new_attribute = new_attribute
%    \end{macrocode}
% \InternalDetectionOn
% \end{macro}
%
% \subsection{Custom whatsit allocation}
%
% \begin{macro}{new_whatsit}
% \changes{v1.1c}{2017/02/18}{Parameterize count used in tracking}
% Much the same as for attribute allocation in Lua.
%    \begin{macrocode}
local whatsit_count_name = whatsit_count_name or "e@alloc@whatsit@count"
local function new_whatsit(name)
  tex_setcount("global", whatsit_count_name,
                         tex_count[whatsit_count_name] + 1)
  if tex_count[whatsit_count_name] > 65534 then
    luatexbase_error("No room for a new custom whatsit")
  end
  luatexbase_log("Custom whatsit " .. (name or "") .. " = " ..
                 tex_count[whatsit_count_name])
  return tex_count[whatsit_count_name]
end
luatexbase.new_whatsit = new_whatsit
%    \end{macrocode}
% \end{macro}
%
% \subsection{Bytecode register allocation}
%
% \begin{macro}{new_bytecode}
% \changes{v1.1c}{2017/02/18}{Parameterize count used in tracking}
% Much the same as for attribute allocation in Lua.
% The optional \meta{name} argument is used in the log if given.
%    \begin{macrocode}
local bytecode_count_name =
                         bytecode_count_name or "e@alloc@bytecode@count"
local function new_bytecode(name)
  tex_setcount("global", bytecode_count_name,
                         tex_count[bytecode_count_name] + 1)
  if tex_count[bytecode_count_name] > 65534 then
    luatexbase_error("No room for a new bytecode register")
  end
  luatexbase_log("Lua bytecode " .. (name or "") .. " = " ..
                 tex_count[bytecode_count_name])
  return tex_count[bytecode_count_name]
end
luatexbase.new_bytecode = new_bytecode
%    \end{macrocode}
% \end{macro}
%
% \subsection{Lua chunk name allocation}
%
% \begin{macro}{new_chunkname}
% \changes{v1.1c}{2017/02/18}{Parameterize count used in tracking}
% As for bytecode registers but also store the name in the
% |lua.name| table.
%    \begin{macrocode}
local chunkname_count_name =
                        chunkname_count_name or "e@alloc@luachunk@count"
local function new_chunkname(name)
  tex_setcount("global", chunkname_count_name,
                         tex_count[chunkname_count_name] + 1)
  local chunkname_count = tex_count[chunkname_count_name]
  chunkname_count = chunkname_count + 1
  if chunkname_count > 65534 then
    luatexbase_error("No room for a new chunkname")
  end
  lua.name[chunkname_count]=name
  luatexbase_log("Lua chunkname " .. (name or "") .. " = " ..
                 chunkname_count .. "\n")
  return chunkname_count
end
luatexbase.new_chunkname = new_chunkname
%    \end{macrocode}
% \end{macro}
%
% \subsection{Lua function allocation}
%
% \begin{macro}{new_luafunction}
% \changes{v1.1i}{2018/10/21}{Function added}
% \changes{v1.2c}{2023/07/02}{Ensure existing table entries not overwritten gh/1100}
% Much the same as for attribute allocation in Lua.
% The optional \meta{name} argument is used in the log if given.
%    \begin{macrocode}
local luafunction_count_name =
                         luafunction_count_name or "e@alloc@luafunction@count"
local function new_luafunction(name)
  tex_setcount("global", luafunction_count_name,
                         math.max(
                           #(lua.get_functions_table()),
                           tex_count[luafunction_count_name])
                          + 1)
  lua.get_functions_table()[tex_count[luafunction_count_name]] = false
  if tex_count[luafunction_count_name] > 65534 then
    luatexbase_error("No room for a new luafunction register")
  end
  luatexbase_log("Lua function " .. (name or "") .. " = " ..
                 tex_count[luafunction_count_name])
  return tex_count[luafunction_count_name]
end
luatexbase.new_luafunction = new_luafunction
%    \end{macrocode}
% \end{macro}
%
% \subsection{Lua callback management}
%
% The native mechanism for callbacks in Lua\TeX\ allows only one per function.
% That is extremely restrictive and so a mechanism is needed to add and
% remove callbacks from the appropriate hooks.
%
% \subsubsection{Housekeeping}
%
% The main table: keys are callback names, and values are the associated lists
% of functions. More precisely, the entries in the list are tables holding the
% actual function as |func| and the identifying description as |description|.
% Only callbacks with a non-empty list of functions have an entry in this
% list.
%
% Actually there are two tables: |realcallbacklist| directly contains the entries
% as described above while |callbacklist| only directly contains the already sorted
% entries. Other entries can be queried through |callbacklist| too which triggers a
% resort.
%
% Additionally |callbackrules| describes the ordering constraints: It contains two
% element tables with the descriptions of the constrained callback implementations.
% It can additionally contain a |type| entry indicating the kind of rule. A missing
% value indicates a normal ordering contraint.
%
% \changes{v1.2a}{2022/10/03}{Add rules for callback ordering}
%    \begin{macrocode}
local realcallbacklist = {}
local callbackrules = {}
local callbacklist = setmetatable({}, {
  __index = function(t, name)
    local list = realcallbacklist[name]
    local rules = callbackrules[name]
    if list and rules then
      local meta = {}
      for i, entry in ipairs(list) do
        local t = {value = entry, count = 0, pos = i}
        meta[entry.description], list[i] = t, t
      end
      local count = #list
      local pos = count
      for i, rule in ipairs(rules) do
        local rule = rules[i]
        local pre, post = meta[rule[1]], meta[rule[2]]
        if pre and post then
          if rule.type then
            if not rule.hidden then
              assert(rule.type == 'incompatible-warning' and luatexbase_warning
                or rule.type == 'incompatible-error' and luatexbase_error)(
                  "Incompatible functions \"" .. rule[1] .. "\" and \"" .. rule[2]
                  .. "\" specified for callback \"" .. name .. "\".")
              rule.hidden = true
            end
          else
            local post_count = post.count
            post.count = post_count+1
            if post_count == 0 then
              local post_pos = post.pos
              if post_pos ~= pos then
                local new_post_pos = list[pos]
                new_post_pos.pos = post_pos
                list[post_pos] = new_post_pos
              end
              list[pos] = nil
              pos = pos - 1
            end
            pre[#pre+1] = post
          end
        end
      end
      for i=1, count do -- The actual sort begins
        local current = list[i]
        if current then
          meta[current.value.description] = nil
          for j, cur in ipairs(current) do
            local count = cur.count
            if count == 1 then
              pos = pos + 1
              list[pos] = cur
            else
              cur.count = count - 1
            end
          end
          list[i] = current.value
        else
          -- Cycle occured. TODO: Show cycle for debugging
          -- list[i] = ...
          local remaining = {}
          for name, entry in next, meta do
            local value = entry.value
            list[#list + 1] = entry.value
            remaining[#remaining + 1] = name
          end
          table.sort(remaining)
          local first_name = remaining[1]
          for j, name in ipairs(remaining) do
            local entry = meta[name]
            list[i + j - 1] = entry.value
            for _, post_entry in ipairs(entry) do
              local post_name = post_entry.value.description
              if not remaining[post_name] then
                remaining[post_name] = name
              end
            end
          end
          local cycle = {first_name}
          local index = 1
          local last_name = first_name
          repeat
            cycle[last_name] = index
            last_name = remaining[last_name]
            index = index + 1
            cycle[index] = last_name
          until cycle[last_name]
          local length = index - cycle[last_name] + 1
          table.move(cycle, cycle[last_name], index, 1)
          for i=2, length//2 do
            cycle[i], cycle[length + 1 - i] = cycle[length + 1 - i], cycle[i]
          end
          error('Cycle occured at ' .. table.concat(cycle, ' -> ', 1, length))
        end
      end
    end
    realcallbacklist[name] = list
    t[name] = list
    return list
  end
})
%    \end{macrocode}
%
% Numerical codes for callback types, and name-to-value association (the
% table keys are strings, the values are numbers).
%    \begin{macrocode}
local list, data, exclusive, simple, reverselist = 1, 2, 3, 4, 5
local types   = {
  list        = list,
  data        = data,
  exclusive   = exclusive,
  simple      = simple,
  reverselist = reverselist,
}
%    \end{macrocode}
%
% Now, list all predefined callbacks with their current type, based on the
% Lua\TeX{} manual version~1.01. A full list of the currently-available
% callbacks can be obtained using
%  \begin{verbatim}
%    \directlua{
%      for i,_ in pairs(callback.list()) do
%        texio.write_nl("- " .. i)
%      end
%    }
%    \bye
%  \end{verbatim}
% in plain Lua\TeX{}. (Some undocumented callbacks are omitted as they are
% to be removed.)
%    \begin{macrocode}
local callbacktypes = callbacktypes or {
%    \end{macrocode}
%   Section 8.2: file discovery callbacks.
% \changes{v1.1g}{2018/05/02}{find\_sfd\_file removed}
%    \begin{macrocode}
  find_read_file     = exclusive,
  find_write_file    = exclusive,
  find_font_file     = data,
  find_output_file   = data,
  find_format_file   = data,
  find_vf_file       = data,
  find_map_file      = data,
  find_enc_file      = data,
  find_pk_file       = data,
  find_data_file     = data,
  find_opentype_file = data,
  find_truetype_file = data,
  find_type1_file    = data,
  find_image_file    = data,
%    \end{macrocode}
% \changes{v1.1g}{2018/05/02}{read\_sfd\_file removed}
%    \begin{macrocode}
  open_read_file     = exclusive,
  read_font_file     = exclusive,
  read_vf_file       = exclusive,
  read_map_file      = exclusive,
  read_enc_file      = exclusive,
  read_pk_file       = exclusive,
  read_data_file     = exclusive,
  read_truetype_file = exclusive,
  read_type1_file    = exclusive,
  read_opentype_file = exclusive,
%    \end{macrocode}
% \changes{v1.0m}{2016/02/11}{read\_cidmap\_file added}
% Not currently used by luatex but included for completeness.
% may be used by a font handler.
%    \begin{macrocode}
  find_cidmap_file   = data,
  read_cidmap_file   = exclusive,
%    \end{macrocode}
% Section 8.3: data processing callbacks.
% \changes{v1.0m}{2016/02/11}{token\_filter removed}
%    \begin{macrocode}
  process_input_buffer  = data,
  process_output_buffer = data,
  process_jobname       = data,
%    \end{macrocode}
% Section 8.4: node list processing callbacks.
% \changes{v1.0m}{2016/02/11}
% {process\_rule, [hv]pack\_quality  append\_to\_vlist\_filter added}
% \changes{v1.0n}{2016/03/13}{insert\_local\_par added}
% \changes{v1.0n}{2016/03/13}{contribute\_filter added}
% \changes{v1.1h}{2018/08/18}{append\_to\_vlist\_filter is \texttt{exclusive}}
% \changes{v1.1j}{2019/06/18}{new\_graf added}
% \changes{v1.1k}{2019/10/02}{linebreak\_filter is \texttt{exclusive}}
% \changes{v1.1k}{2019/10/02}{process\_rule is \texttt{exclusive}}
% \changes{v1.1k}{2019/10/02}{mlist\_to\_hlist is \texttt{exclusive}}
% \changes{v1.1l}{2020/02/02}{post\_linebreak\_filter is \texttt{reverselist}}
% \changes{v1.1p}{2020/08/01}{new\_graf is \texttt{exclusive}}
% \changes{v1.1w}{2021/11/17}{hpack\_quality is \texttt{exclusive}}
% \changes{v1.1w}{2021/11/17}{vpack\_quality is \texttt{exclusive}}
%    \begin{macrocode}
  contribute_filter      = simple,
  buildpage_filter       = simple,
  build_page_insert      = exclusive,
  pre_linebreak_filter   = list,
  linebreak_filter       = exclusive,
  append_to_vlist_filter = exclusive,
  post_linebreak_filter  = reverselist,
  hpack_filter           = list,
  vpack_filter           = list,
  hpack_quality          = exclusive,
  vpack_quality          = exclusive,
  pre_output_filter      = list,
  process_rule           = exclusive,
  hyphenate              = simple,
  ligaturing             = simple,
  kerning                = simple,
  insert_local_par       = simple,
% mlist_to_hlist         = exclusive,
  new_graf               = exclusive,
%    \end{macrocode}
% Section 8.5: information reporting callbacks.
% \changes{v1.0m}{2016/02/11}{show\_warning\_message added}
% \changes{v1.0p}{2016/11/17}{call\_edit added}
% \changes{v1.1g}{2018/05/02}{finish\_synctex\_callback added}
% \changes{v1.1j}{2019/06/18}{finish\_synctex\_callback renamed finish\_synctex}
% \changes{v1.1j}{2019/06/18}{wrapup\_run added}
%    \begin{macrocode}
  pre_dump             = simple,
  start_run            = simple,
  stop_run             = simple,
  start_page_number    = simple,
  stop_page_number     = simple,
  show_error_hook      = simple,
  show_warning_message = simple,
  show_error_message   = simple,
  show_lua_error_hook  = simple,
  start_file           = simple,
  stop_file            = simple,
  call_edit            = simple,
  finish_synctex       = simple,
  wrapup_run           = simple,
%    \end{macrocode}
% Section 8.6: PDF-related callbacks.
% \changes{v1.1j}{2019/06/18}{page\_objnum\_provider added}
% \changes{v1.1j}{2019/06/18}{process\_pdf\_image\_content added}
% \changes{v1.1j}{2019/10/22}{page\_objnum\_provider and process\_pdf\_image\_content classified data}
% \changes{v1.1l}{2020/02/02}{page\_order\_index added}
%    \begin{macrocode}
  finish_pdffile            = data,
  finish_pdfpage            = data,
  page_objnum_provider      = data,
  page_order_index          = data,
  process_pdf_image_content = data,
%    \end{macrocode}
% Section 8.7: font-related callbacks.
% \changes{v1.1e}{2017/03/28}{glyph\_stream\_provider added}
% \changes{v1.1g}{2018/05/02}{glyph\_not\_found added}
% \changes{v1.1j}{2019/06/18}{make\_extensible added}
% \changes{v1.1j}{2019/06/18}{font\_descriptor\_objnum\_provider added}
% \changes{v1.1l}{2020/02/02}{glyph\_info added}
% \changes{v1.1t}{2021/04/18}{input\_level\_string added}
% \changes{v1.1v}{2021/10/15}{provide\_charproc\_data added}
%    \begin{macrocode}
  define_font                     = exclusive,
  glyph_info                      = exclusive,
  glyph_not_found                 = exclusive,
  glyph_stream_provider           = exclusive,
  make_extensible                 = exclusive,
  font_descriptor_objnum_provider = exclusive,
  input_level_string              = exclusive,
  provide_charproc_data           = exclusive,
%    \end{macrocode}
% \changes{v1.0m}{2016/02/11}{pdf\_stream\_filter\_callback removed}
%    \begin{macrocode}
}
luatexbase.callbacktypes=callbacktypes
%    \end{macrocode}
%
% \changes{v1.1y}{2022/08/13}{shared\_callbacks added}
% Sometimes multiple callbacks correspond to a single underlying engine level callback.
% Then the engine level callback should be registered as long as at least one of these
% callbacks is in use. This is implemented though a shared table which counts how many
% of the involved callbacks are currently in use. The enging level callback is registered
% iff this count is not 0.
%
% We add |mlist_to_hlist| directly to the list to demonstrate this, but the handler gets
% added later when it is actually defined.
%
% All callbacks in this list are treated as user defined callbacks.
%
%    \begin{macrocode}
local shared_callbacks = {
  mlist_to_hlist = {
    callback = "mlist_to_hlist",
    count = 0,
    handler = nil,
  },
}
shared_callbacks.pre_mlist_to_hlist_filter = shared_callbacks.mlist_to_hlist
shared_callbacks.post_mlist_to_hlist_filter = shared_callbacks.mlist_to_hlist
%    \end{macrocode}
%
% \begin{macro}{callback.register}
% \changes{v1.0a}{2015/09/24}{Function modified}
%   Save the original function for registering callbacks and prevent the
%   original being used. The original is saved in a place that remains
%   available so other more sophisticated code can override the approach
%   taken by the kernel if desired.
%    \begin{macrocode}
local callback_register = callback_register or callback.register
function callback.register()
  luatexbase_error("Attempt to use callback.register() directly\n")
end
%    \end{macrocode}
% \end{macro}
%
% \subsubsection{Handlers}
%
% The handler function is registered into the callback when the
% first function is added to this callback's list. Then, when the callback
% is called, the handler takes care of running all functions in the list.
% When the last function is removed from the callback's list, the handler
% is unregistered.
%
% More precisely, the functions below are used to generate a specialized
% function (closure) for a given callback, which is the actual handler.
%
%
% The way the functions are combined together depends on
% the type of the callback. There are currently 4 types of callback, depending
% on the calling convention of the functions the callback can hold:
% \begin{description}
%   \item[simple] is for functions that don't return anything: they are called
%     in order, all with the same argument;
%   \item[data] is for functions receiving a piece of data of any type
%     except node list head (and possibly other arguments) and returning it
%     (possibly modified): the functions are called in order, and each is
%     passed the return value of the previous (and the other arguments
%     untouched, if any). The return value is that of the last function;
%   \item[list] is a specialized variant of \emph{data} for functions
%     filtering node lists. Such functions may return either the head of a
%     modified node list, or the boolean values |true| or |false|. The
%     functions are chained the same way as for \emph{data} except that for
%     the following. If
%     one function returns |false|, then |false| is immediately returned and
%     the following functions are \emph{not} called. If one function returns
%     |true|, then the same head is passed to the next function. If all
%     functions return |true|, then |true| is returned, otherwise the return
%     value of the last function not returning |true| is used.
%   \item[reverselist] is a specialized variant of \emph{list} which executes
%     functions in inverse order.
%   \item[exclusive] is for functions with more complex signatures; functions in
%     this type of callback are \emph{not} combined: An error is raised if
%     a second callback is registered.
% \end{description}
%
% Handler for |data| callbacks.
%    \begin{macrocode}
local function data_handler(name)
  return function(data, ...)
    for _,i in ipairs(callbacklist[name]) do
      data = i.func(data,...)
    end
    return data
  end
end
%    \end{macrocode}
% Default for user-defined |data| callbacks without explicit default.
%    \begin{macrocode}
local function data_handler_default(value)
  return value
end
%    \end{macrocode}
% Handler for |exclusive| callbacks. We can assume |callbacklist[name]| is not
% empty: otherwise, the function wouldn't be registered in the callback any
% more.
%    \begin{macrocode}
local function exclusive_handler(name)
  return function(...)
    return callbacklist[name][1].func(...)
  end
end
%    \end{macrocode}
% Handler for |list| callbacks.
% \changes{v1.0k}{2015/12/02}{resolve name and i.description (PHG)}
% \changes{v1.1s}{2020/12/02}{Fix return value of list callbacks}
% \changes{v1.1w}{2021/11/17}{Never pass on \texttt{true} return values for list callbacks}
%    \begin{macrocode}
local function list_handler(name)
  return function(head, ...)
    local ret
    for _,i in ipairs(callbacklist[name]) do
      ret = i.func(head, ...)
      if ret == false then
        luatexbase_warning(
          "Function `" .. i.description .. "' returned false\n"
            .. "in callback `" .. name .."'"
         )
        return false
      end
      if ret ~= true then
        head = ret
      end
    end
    return head
  end
end
%    \end{macrocode}
% Default for user-defined |list| and |reverselist| callbacks without explicit default.
%    \begin{macrocode}
local function list_handler_default(head)
return head
end
%    \end{macrocode}
% Handler for |reverselist| callbacks.
% \changes{v1.1l}{2020/02/02}{Add reverselist callback type}
%    \begin{macrocode}
local function reverselist_handler(name)
  return function(head, ...)
    local ret
    local callbacks = callbacklist[name]
    for i = #callbacks, 1, -1 do
      local cb = callbacks[i]
      ret = cb.func(head, ...)
      if ret == false then
        luatexbase_warning(
          "Function `" .. cb.description .. "' returned false\n"
            .. "in callback `" .. name .."'"
         )
        return false
      end
      if ret ~= true then
        head = ret
      end
    end
    return head
  end
end
%    \end{macrocode}
% Handler for |simple| callbacks.
%    \begin{macrocode}
local function simple_handler(name)
  return function(...)
    for _,i in ipairs(callbacklist[name]) do
      i.func(...)
    end
  end
end
%    \end{macrocode}
% Default for user-defined |simple| callbacks without explicit default.
%    \begin{macrocode}
local function simple_handler_default()
end
%    \end{macrocode}
%
% Keep a handlers table for indexed access and a table with the corresponding default functions.
%    \begin{macrocode}
local handlers  = {
  [data]        = data_handler,
  [exclusive]   = exclusive_handler,
  [list]        = list_handler,
  [reverselist] = reverselist_handler,
  [simple]      = simple_handler,
}
local defaults = {
  [data]        = data_handler_default,
  [exclusive]   = nil,
  [list]        = list_handler_default,
  [reverselist] = list_handler_default,
  [simple]      = simple_handler_default,
}
%    \end{macrocode}
%
% \subsubsection{Public functions for callback management}
%
% Defining user callbacks perhaps should be in package code,
% but impacts on |add_to_callback|.
% If a default function is not required, it may be declared as |false|.
% First we need a list of user callbacks.
%    \begin{macrocode}
local user_callbacks_defaults = {}
%    \end{macrocode}
%
% \begin{macro}{create_callback}
% \changes{v1.0a}{2015/09/24}{Function added}
% \changes{v1.0i}{2015/11/29}{Check name is not nil in error message (PHG)}
% \changes{v1.0k}{2015/12/02}{Give more specific error messages (PHG)}
% \changes{v1.1l}{2020/02/02}{Provide proper fallbacks for user-defined callbacks without user-provided default handler}
%   The allocator itself.
%    \begin{macrocode}
local function create_callback(name, ctype, default)
  local ctype_id = types[ctype]
  if not name  or name  == ""
  or not ctype_id
  then
    luatexbase_error("Unable to create callback:\n" ..
                     "valid callback name and type required")
  end
  if callbacktypes[name] then
    luatexbase_error("Unable to create callback `" .. name ..
                     "':\ncallback is already defined")
  end
  default = default or defaults[ctype_id]
  if not default then
    luatexbase_error("Unable to create callback `" .. name ..
                     "':\ndefault is required for `" .. ctype ..
                     "' callbacks")
  elseif type (default) ~= "function" then
    luatexbase_error("Unable to create callback `" .. name ..
                     "':\ndefault is not a function")
  end
  user_callbacks_defaults[name] = default
  callbacktypes[name] = ctype_id
end
luatexbase.create_callback = create_callback
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{call_callback}
% \changes{v1.0a}{2015/09/24}{Function added}
% \changes{v1.0i}{2015/11/29}{Check name is not nil in error message (PHG)}
% \changes{v1.0k}{2015/12/02}{Give more specific error messages (PHG)}
%  Call a user defined callback. First check arguments.
%    \begin{macrocode}
local function call_callback(name,...)
  if not name or name == "" then
    luatexbase_error("Unable to create callback:\n" ..
                     "valid callback name required")
  end
  if user_callbacks_defaults[name] == nil then
    luatexbase_error("Unable to call callback `" .. name
                     .. "':\nunknown or empty")
   end
  local l = callbacklist[name]
  local f
  if not l then
    f = user_callbacks_defaults[name]
  else
    f = handlers[callbacktypes[name]](name)
  end
  return f(...)
end
luatexbase.call_callback=call_callback
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{add_to_callback}
% \changes{v1.0a}{2015/09/24}{Function added}
%   Add a function to a callback. First check arguments.
% \changes{v1.0k}{2015/12/02}{Give more specific error messages (PHG)}
% \changes{v1.2a}{2022/10/03}{Add rules for callback ordering}
%    \begin{macrocode}
local function add_to_callback(name, func, description)
  if not name or name == "" then
    luatexbase_error("Unable to register callback:\n" ..
                     "valid callback name required")
  end
  if not callbacktypes[name] or
    type(func) ~= "function" or
    not description or
    description == "" then
    luatexbase_error(
      "Unable to register callback.\n\n"
        .. "Correct usage:\n"
        .. "add_to_callback(<callback>, <function>, <description>)"
    )
  end
%    \end{macrocode}
%   Then test if this callback is already in use. If not, initialise its list
%   and register the proper handler.
%    \begin{macrocode}
  local l = realcallbacklist[name]
  if l == nil then
    l = { }
    realcallbacklist[name] = l
%    \end{macrocode}
% \changes{v1.1y}{2022/08/13}{Adapted code for shared\_callbacks}
% Handle count for shared engine callbacks.
%    \begin{macrocode}
    local shared = shared_callbacks[name]
    if shared then
      shared.count = shared.count + 1
      if shared.count == 1 then
        callback_register(shared.callback, shared.handler)
      end
%    \end{macrocode}
% If it is not a user defined callback use the primitive callback register.
%    \begin{macrocode}
    elseif user_callbacks_defaults[name] == nil then
      callback_register(name, handlers[callbacktypes[name]](name))
    end
  end
%    \end{macrocode}
% \changes{v1.2a}{2022/10/03}{Add rules for callback ordering}
%  Actually register the function and give an error if more than one
%  |exclusive| one is registered.
%    \begin{macrocode}
  local f = {
    func        = func,
    description = description,
  }
  if callbacktypes[name] == exclusive then
    if #l == 1 then
      luatexbase_error(
        "Cannot add second callback to exclusive function\n`" ..
        name .. "'")
    end
  end
  table.insert(l, f)
  callbacklist[name] = nil
%    \end{macrocode}
%  Keep user informed.
%    \begin{macrocode}
  luatexbase_log(
    "Inserting `" .. description .. "' in `" .. name .. "'."
  )
end
luatexbase.add_to_callback = add_to_callback
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{declare_callback_rule}
%   \changes{v1.2a}{2022/10/03}{Add function}
%   Add an ordering constraint between two callback implementations
%    \begin{macrocode}
local function declare_callback_rule(name, desc1, relation, desc2)
  if not callbacktypes[name] or
    not desc1 or not desc2 or
    desc1 == "" or desc2 == "" then
    luatexbase_error(
      "Unable to create ordering constraint. "
        .. "Correct usage:\n"
        .. "declare_callback_rule(<callback>, <description_a>, <description_b>)"
    )
  end
  if relation == 'before' then
    relation = nil
  elseif relation == 'after' then
    desc2, desc1 = desc1, desc2
    relation = nil
  elseif relation == 'incompatible-warning' or relation == 'incompatible-error' then
  elseif relation == 'unrelated' then
  else
    luatexbase_error(
      "Unknown relation type in declare_callback_rule"
    )
  end
  callbacklist[name] = nil
  local rules = callbackrules[name]
  if rules then
    for i, rule in ipairs(rules) do
      if rule[1] == desc1 and rule[2] == desc2 or rule[1] == desc2 and rule[2] == desc1 then
        if relation == 'unrelated' then
          table.remove(rules, i)
        else
          rule[1], rule[2], rule.type = desc1, desc2, relation
        end
        return
      end
    end
    if relation ~= 'unrelated' then
      rules[#rules + 1] = {desc1, desc2, type = relation}
    end
  elseif relation ~= 'unrelated' then
    callbackrules[name] = {{desc1, desc2, type = relation}}
  end
end
luatexbase.declare_callback_rule = declare_callback_rule
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{remove_from_callback}
% \changes{v1.0a}{2015/09/24}{Function added}
% \changes{v1.0k}{2015/12/02}{adjust initialization of cb local (PHG)}
% \changes{v1.0k}{2015/12/02}{Give more specific error messages (PHG)}
% \changes{v1.1m}{2020/03/07}{Do not call callback.register for user-defined callbacks}
% \changes{v1.1y}{2022/08/13}{Adapted code for shared\_callbacks}
% \changes{v1.2a}{2022/10/03}{Add rules for callback ordering}
%   Remove a function from a callback. First check arguments.
%    \begin{macrocode}
local function remove_from_callback(name, description)
  if not name or name == "" then
    luatexbase_error("Unable to remove function from callback:\n" ..
                     "valid callback name required")
  end
  if not callbacktypes[name] or
    not description or
    description == "" then
    luatexbase_error(
      "Unable to remove function from callback.\n\n"
        .. "Correct usage:\n"
        .. "remove_from_callback(<callback>, <description>)"
    )
  end
  local l = realcallbacklist[name]
  if not l then
    luatexbase_error(
      "No callback list for `" .. name .. "'\n")
  end
%    \end{macrocode}
%  Loop over the callback's function list until we find a matching entry.
%  Remove it and check if the list is empty: if so, unregister the
%   callback handler.
%    \begin{macrocode}
  local index = false
  for i,j in ipairs(l) do
    if j.description == description then
      index = i
      break
    end
  end
  if not index then
    luatexbase_error(
      "No callback `" .. description .. "' registered for `" ..
      name .. "'\n")
  end
  local cb = l[index]
  table.remove(l, index)
  luatexbase_log(
    "Removing  `" .. description .. "' from `" .. name .. "'."
  )
  if #l == 0 then
    realcallbacklist[name] = nil
    callbacklist[name] = nil
    local shared = shared_callbacks[name]
    if shared then
      shared.count = shared.count - 1
      if shared.count == 0 then
        callback_register(shared.callback, nil)
      end
    elseif user_callbacks_defaults[name] == nil then
      callback_register(name, nil)
    end
  end
  return cb.func,cb.description
end
luatexbase.remove_from_callback = remove_from_callback
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{in_callback}
% \changes{v1.0a}{2015/09/24}{Function added}
% \changes{v1.0h}{2015/11/27}{Guard against undefined list latex/4445}
%   Look for a function description in a callback.
%    \begin{macrocode}
local function in_callback(name, description)
  if not name
    or name == ""
    or not realcallbacklist[name]
    or not callbacktypes[name]
    or not description then
      return false
  end
  for _, i in pairs(realcallbacklist[name]) do
    if i.description == description then
      return true
    end
  end
  return false
end
luatexbase.in_callback = in_callback
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{disable_callback}
% \changes{v1.0a}{2015/09/24}{Function added}
%   As we subvert the engine interface we need to provide a way to access
%   this functionality.
%    \begin{macrocode}
local function disable_callback(name)
  if(realcallbacklist[name] == nil) then
    callback_register(name, false)
  else
    luatexbase_error("Callback list for " .. name .. " not empty")
  end
end
luatexbase.disable_callback = disable_callback
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{callback_descriptions}
% \changes{v1.0a}{2015/09/24}{Function added}
% \changes{v1.0h}{2015/11/27}{Match test in in-callback latex/4445}
%   List the descriptions of functions registered for the given callback.
%   This will sort the list if necessary.
%    \begin{macrocode}
local function callback_descriptions (name)
  local d = {}
  if not name
    or name == ""
    or not realcallbacklist[name]
    or not callbacktypes[name]
    then
    return d
  else
  for k, i in pairs(callbacklist[name]) do
    d[k]= i.description
    end
  end
  return d
end
luatexbase.callback_descriptions =callback_descriptions
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{uninstall}
% \changes{v1.0e}{2015/10/02}{Function added}
%   Unlike at the \TeX{} level, we have to provide a back-out mechanism here
%   at the same time as the rest of the code. This is not meant for use by
%   anything other than \textsf{latexrelease}: as such this is
%   \emph{deliberately} not documented for users!
%    \begin{macrocode}
local function uninstall()
  module_info(
    "luatexbase",
    "Uninstalling kernel luatexbase code"
  )
  callback.register = callback_register
  luatexbase = nil
end
luatexbase.uninstall = uninstall
%    \end{macrocode}
% \end{macro}
% \begin{macro}{mlist_to_hlist}
% \changes{v1.1l}{2020/02/02}{|pre/post_mlist_to_hlist| added}
% \changes{v1.1y}{2022/08/13}{Use shared\_callback system for pre/post/mlist_to_hlist}
% \changes{v1.2c}{2023/08/03}{Fix callback type of post_mlist_to_hlist_callback}
%   To emulate these callbacks, the ``real'' |mlist_to_hlist| is replaced by a
%   wrapper calling the wrappers before and after.
%    \begin{macrocode}
create_callback('pre_mlist_to_hlist_filter', 'list')
create_callback('mlist_to_hlist', 'exclusive', node.mlist_to_hlist)
create_callback('post_mlist_to_hlist_filter', 'reverselist')
function shared_callbacks.mlist_to_hlist.handler(head, display_type, need_penalties)
  local current = call_callback("pre_mlist_to_hlist_filter", head, display_type, need_penalties)
  if current == false then
    flush_list(head)
    return nil
  end
  current = call_callback("mlist_to_hlist", current, display_type, need_penalties)
  local post = call_callback("post_mlist_to_hlist_filter", current, display_type, need_penalties)
  if post == false then
    flush_list(current)
    return nil
  end
  return post
end
%    \end{macrocode}
% \end{macro}
% \endgroup
%
%    \begin{macrocode}
%</lua>
%    \end{macrocode}
%
% Reset the catcode of |@|.
%    \begin{macrocode}
%<tex>\catcode`\@=\etatcatcode\relax
%    \end{macrocode}
%
%
% \Finale