Gh1585 allowing \fpeval in array preamble

base/doc/ltnews41.tex

@@ -385,6 +385,25 @@ \subsection{\pkg{multicol}:\ Full support for extended marks}
 
 
 
+\subsection{\pkg{array}:\ Improve preamble setup code for \texttt{p} and friends}
+
+While the preamble of a \env{tabular} or \env{array} is being built
+the arguments to \texttt{p}, \texttt{m}, or \texttt{b} columns were
+expanded several times. That is normally harmless because that
+argument contains usually just a dimension. However, in a case like
+\verb=p{\fpeval{15}pt}= this resulted in an error, because \cs{fpeval}
+was expanded a few times, but not often enough to result in a single
+number. This has now been corrected and the argument is not expanded
+at all to allow for such edge cases as well as the extension available
+with the \pkg{calc} package, such as \verb=p{\widthof{AAAAAA}}= (the
+latter was possible before but needed to be taken into account while
+the correction was implemented.
+%
+\githubissue{1585}
+
+
+
+
 %\section{Changes to files in the \pkg{cyrillic} category}
 
 \begin{thebibliography}{9}\frenchspacing

required/latex-lab/testfiles-OR/tagging-002-longtable.pvt

@@ -13,4 +13,4 @@
 \begin{longtable}{p{3cm}}
  Test\footnote{abc}\\
 \end{longtable}
-\end{document}
+\end{document}

required/latex-lab/update-OR-all.sh

@@ -59,7 +59,8 @@ l3build save -cconfig-OR \
 	memoir-001 \
 	scrartcl-001 \
 	tlb-multicol-marks-tagged \
-	tagging-001
+	tagging-001 \
+	tagging-002-longtable
 
 l3build save -cconfig-OR-luatex \
 	footmisc-003 \

required/tools/array.dtx

@@ -39,7 +39,7 @@
 %    \begin{macrocode}
 %<+package>\NeedsTeXFormat{LaTeX2e}[2024/06/01]
 %<+package>\ProvidesPackage{array}
-%<+package>         [2024/10/17 v2.6g Tabular extension package (FMi)]
+%<+package>         [2024/12/17 v2.6h Tabular extension package (FMi)]
 %
 % \fi
 %
@@ -2242,7 +2242,7 @@ Bug reports can be opened (category \texttt{#1}) at\\%
 %
 %
 %
-% \begin{macro}{\@startpbox}
+% \begin{macro}{\@startpbox,\@startpbox@action}
 %    In =\@classz=  the macro =\@startpbox= is used.
 %    The width of the \textsf{parbox} is passed as an argument.
 %    =\vcenter=, =\vtop= or =\vbox= are already in the
@@ -2286,6 +2286,19 @@ Bug reports can be opened (category \texttt{#1}) at\\%
       \everypar{}}%
    }
 %    \end{macrocode}
+%
+% \changes{v2.6h}{2024/12/17}{New \cs{@startpbox@action} to do the real work
+%    after preamble  was built (gh/1585)}
+%    Starting with 2.6h \cs{@startpbox} is only used during the
+%    built-up of the preamble changing there to \cs{@startpbox@action}
+%    To do the real work. For an explanation of this code see
+%    the documentation in \cs{@mkpream}. We keep the \cs{@startpbox}
+%    definition on top-level in case there are tabular packages that
+%    built the preamble differently and expect that it contains
+%    \cs{@startpbox} (\pkg{longtable} at the moment).
+%    \begin{macrocode}
+\let\@startpbox@action\@startpbox
+%    \end{macrocode}
 % \end{macro}
 %
 % \begin{macro}{\@endpbox}
@@ -3285,12 +3298,23 @@ Bug reports can be opened (category \texttt{#1}) at\\%
 %    simple length expression, but with the calc package involved it
 %    could break under an "\edef" operation, which is how the preamble
 %    is constructed. We now make use of "\unexpanded" here to prevent that. The
-%    "\expandafter" gymnastics is necessary to expand the "#1" at least
+%    "\expandafter" gymnastics is necessary to expand the "#1" exactly
 %    once (since it will get "\@nextchar" as its value and need its
-%    content!
+%    content). However, once added to the preamble, no further
+%    expansion should happen if the preamble is extended. Therefore we
+%    change from \cs{@startpbox} to \cs{@startpbox@action}. The latter
+%    then has a trivial definition and expands (including its
+%    argument) to itself while the preamble is being built. Outside of this
+%    preamble built-up \cs{@startpbox@action} that does the actual work.
+%    The definition for \cs{@startpbox} is only ever used  during
+% \changes{v2.6h}{2024/12/17}{Expand argument of \cs{@startpbox}
+%      exactly once while the preamble is built and use
+%      \cs{@startpbox@action} later to do the real work (gh/1585)}
 %    \begin{macrocode}
    \def\@startpbox##1{\unexpanded\expandafter{\expandafter
-                      \@startpbox\expandafter{##1}}}\let\@endpbox\relax
+                      \@startpbox@action\expandafter{##1}}}%
+   \def\@startpbox@action##1{\unexpanded{\@startpbox@action{##1}}}%
+   \let\@endpbox\relax
    \let\do@row@strut\relax
    \let\ar@align@mcell\relax
 %    \end{macrocode}

required/tools/changes.txt

@@ -5,6 +5,16 @@ completeness or accuracy and it contains some references to files that
 are not part of the distribution.
 =======================================================================
 
+2024-12-18  Frank Mittelbach  <[email protected]>
+
+	* array.dtx (section{The macros \texttt{\textbackslash @classz}):
+	Expand argument of \@startpbox exactly once while the preamble is built
+	and use \@@startpbox later to do the real work (gh/1585)
+
+	* longtable.dtx (subsection{The \env{longtable} environment}):
+	Initialize \@startpbox@action instead of \@startpbox
+	to match array change (gh/1585)
+
 2024-11-12  Frank Mittelbach  <[email protected]>
 	* multicol.dtx (subsection{Tagging support}):
 	Added another socket to support tagging.

required/tools/longtable.dtx

@@ -38,7 +38,7 @@
 %<driver> \ProvidesFile{longtable.drv}
 % \fi
 %         \ProvidesFile{longtable.dtx}
-          [2024-10-27 v4.22 Multi-page Table package (DPC)]
+          [2024-12-18 v4.23 Multi-page Table package (DPC)]
 %
 % \iffalse
 %<*driver>
@@ -1249,10 +1249,13 @@
 % \package{array} V2.0h. We do not need to set "\d@llarbegin" and
 % "\d@llarend"  as the \package{array} package gives them the correct
 % values at the top level.
+% \changes{v4.23}{2024/12/17}{Initialize \cs{@startpbox@action} instead
+%       of \cs{@startpbox} to match array change (gh/1585)}
 %    \begin{macrocode}
     \advance\@tempdima\extrarowheight
     \col@sep\tabcolsep
-    \let\@startpbox\LT@startpbox\let\LT@LL@FM@cr\@arraycr
+    \let\@startpbox@action\LT@startpbox
+    \let\LT@LL@FM@cr\@arraycr
   \fi
 %    \end{macrocode}
 % The rest of this macro is mainly based on \package{array} package, but

required/tools/testfiles/github-1585.lvt

@@ -0,0 +1,27 @@
+% This should not produce errors
+\documentclass{article}
+
+\input{test2e}
+
+\usepackage{array}
+
+\begin{document}
+
+\START
+
+\typeout{This should show no errors but did!}
+
+\newcommand\hidden{\fpeval{15}pt}
+
+\begin{tabular}{p{\fpeval{15}pt}p{\hidden}p{\fpeval{15}pt}p{\fpeval{15}pt}}
+a & b & c & d
+\end{tabular}
+
+
+\begin{tabular}{p{\fpeval{15}pt}lll}
+a & b & c & d
+\end{tabular}
+
+\newpage
+\TIMO
+\end{document}

required/tools/testfiles/github-1585.tlg

@@ -0,0 +1,10 @@
+This is a generated file for the LaTeX2e validation system.
+Don't change this file in any respect.
+This should show no errors but did!
+LaTeX Font Info:    External font `cmex10' loaded for size
+(Font)              <7> on input line ....
+LaTeX Font Info:    External font `cmex10' loaded for size
+(Font)              <5> on input line ....
+[1
+]
+(github-1585.aux)