work on #989 (WIP)

base/ltpara.dtx

@@ -1,6 +1,6 @@
 % \iffalse meta-comment
 %
-%% File: ltpara.dtx (C) Copyright 2020-2021
+%% File: ltpara.dtx (C) Copyright 2020-2023
 %       Frank Mittelbach, LaTeX Team
 %
 % It may be distributed and/or modified under the conditions of the
@@ -15,7 +15,7 @@
 %
 %    \begin{macrocode}
 \def\ltparaversion{v1.0k}
-\def\ltparadate{2022/05/13}
+\def\ltparadate{2023/01/30}
 %    \end{macrocode}
 %<*driver>
 \documentclass{l3doc}
@@ -729,6 +729,8 @@
 %    for error recovery and so altering \cs{tex_everypar:D}  all the
 %    time should be a tiny bit faster.
 %    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{2023/06/01}
+%<latexrelease>       {\g_@@_standard_everypar_tl}{minipage~ fix}
 \tl_new:N \g_@@_standard_everypar_tl
 %    \end{macrocode}
 %    Here is now its definition:
@@ -769,7 +771,27 @@
 %    \begin{macrocode}
   \group_begin:
     \tex_everypar:D {}
-    \skip_zero:N \tex_parskip:D
+%    \end{macrocode}
+%    There has been a long-standing problem with \LaTeX's minipages in
+%    that invisible material at the beginning of a minipage (such as a
+%    \cs{color} setting) would result in \cs{parskip} being added in
+%    front of the first paragraph---something that is not done by
+%    \TeX{} if a vertical list is completely empty. As this is
+%    happening on a very low-level in the engine it wasn't really
+%    possible to find out of this \cs{parskip} was added or if a space
+%    we see in front of the current point is legitimate. However, with
+%    the new paragraph handling we are in a better position: while we
+%    still don't know if there is such a space or not, we know know
+%    that we have just created an empty paragraph. Thus, if we now set
+%    \cs{parskip} to \texttt{-\parskip} the two will cancel each other
+%    if present and if the first was ignored because the vertical list
+%    was empty, then the second will be ignored too because it is
+%    still empty. Of course, we don't want to cancel always but only
+%    at the start of a minipage and that is signaled with the
+%    \texttt{@minipage} switch.
+%    \begin{macrocode}
+    \skip_set:Nn \tex_parskip:D
+         {\if@minipage -\tex_parskip:D \else \c_zero_skip \fi:}
     \tex_noindent:D
   \group_end:
 %    \end{macrocode}
@@ -800,6 +822,31 @@
   \@@_handle_indent:
 % \the \everypar           % <--- done differently below
 }
+%<latexrelease>\EndIncludeInRelease
+%<latexrelease>\IncludeInRelease{2021/06/01}
+%<latexrelease>       {\g_@@_standard_everypar_tl}{minipage~ fix}
+%<latexrelease>
+%<latexrelease>\tl_gset:Nn \g__para_standard_everypar_tl {
+%<latexrelease>  \box_gset_to_last:N \g_para_indent_box
+%<latexrelease>  \group_begin:
+%<latexrelease>    \tex_par:D
+%<latexrelease>  \group_end:
+%<latexrelease>  \tex_everypar:D { \msg_error:nnnn { hooks }{ para-mode }{before}{vertical} }
+%<latexrelease>  \@kernel@before@para@before
+%<latexrelease>  \hook_use:n {para/before}
+%<latexrelease>  \group_begin:
+%<latexrelease>    \tex_everypar:D {}
+%<latexrelease>    \skip_zero:N \tex_parskip:D
+%<latexrelease>    \tex_noindent:D
+%<latexrelease>  \group_end:
+%<latexrelease>  \tex_everypar:D{\g__para_standard_everypar_tl}
+%<latexrelease>  \@kernel@before@para@begin
+%<latexrelease>  \hook_use:n {para/begin}
+%<latexrelease>  \if_mode_horizontal: \else:
+%<latexrelease>    \msg_error:nnnn { hooks }{ para-mode }{begin}{vertical} \fi:
+%<latexrelease>  \__para_handle_indent:
+%<latexrelease>}
+%<latexrelease>\EndIncludeInRelease
 %    \end{macrocode}
 %  \end{macro}
 %

base/testfiles-search/tlb-minipage-01.lvt

@@ -0,0 +1,49 @@
+\documentclass{article}
+
+\input{test2e}
+
+
+\usepackage{hyperref,color}
+
+\showoutput
+
+\begin{document}
+
+\START
+
+\fbox{%
+  \begin{minipage}{10cm}%       % no issue
+  \begin{itemize}
+    \item abc \par xyz
+  \end{itemize}
+  \end{minipage}%
+}
+
+\fbox{%
+  \begin{minipage}{10cm}% 
+  \LinkTargetOff               % no issue if anchor/dest is suppressed
+  \begin{enumerate}
+    \item abc \par xyz
+  \end{enumerate}
+  \end{minipage}%
+}
+
+\fbox{%
+  \begin{minipage}{10cm}%
+  \begin{enumerate}
+    \item abc\label{b} \par xyz % hyperref backref is the issue
+  \end{enumerate}
+  \end{minipage}%
+}
+
+\fbox{%
+  \begin{minipage}{10cm}%
+  \color{red}                  % color is the issue
+  \begin{enumerate}
+    \item abc \par xyz
+  \end{enumerate}
+  \end{minipage}%
+}
+
+\end{document}
+