Vertical space is wrong when \multicolumn spans the last column about latex2e

[u-fischer]

related problems with vertical spaces (the second one can also be seen with tabularx instead of tabu):

https://tex.stackexchange.com/q/429272/87678
https://tex.stackexchange.com/questions/429307/problem-with-new-array-sty-colortbl-sty-and-tabu-sty

[FrankMittelbach]

Fix for the issues is most likely

\def\@xargarraycr#1{\unskip\gdef\do@row@strut
 {\@tempdima #1\advance\@tempdima \dp\@arstrutbox
   \vrule \@depth\@tempdima \@width\z@\global\let\do@row@strut\relax}%
   \ifnum\@multicnt >\z@ \do@row@strut \fi\cr}

though that needs a bit more testing.

The colortbl patch as suggested by David in a rush may not be quite right but once done probably also fixes the other two mentioned cases (though not 100% sure of the tabu case yet)

[FrankMittelbach]

In addition to what @davidcarlisle already suggested as a patch to colortbl it needs a few more lines:

\def\@classz{\@classx
   \@tempcnta \count@
   \prepnext@tok
\expandafter\CT@extract\the\toks\@tempcnta\columncolor!\@nil
   \@addtopreamble{%
    \setbox\z@\hbox\bgroup\bgroup
      \CT@everycr{}%
      \ifcase \@chnum
      \hskip\stretch{.5}\kern\z@
      \d@llarbegin
      \insert@column
      \d@llarend\do@row@strut\hskip\stretch{.5}\or
      \d@llarbegin \insert@column \d@llarend\do@row@strut \hfill \or
      \hfill\kern\z@ \d@llarbegin \insert@column \d@llarend\do@row@strut \or
%% FMi: replace      
\setbox\ar@mcellbox\vbox
       \@startpbox{\@nextchar}\insert@column \@endpbox
    \ar@align@mcell
    \do@row@strut \or
%    $\vcenter
%   \@startpbox{\@nextchar}\insert@column \@endpbox $\or
    \vtop \@startpbox{\@nextchar}\insert@column \@endpbox
%% FMi add     
    \do@row@strut
    \or
    \vbox \@startpbox{\@nextchar}\insert@column \@endpbox
%% FMi add      
    \do@row@strut
  \fi
 \egroup\egroup
\begingroup
  \CT@setup
  \CT@column@color
  \CT@row@color
  \CT@cell@color
  \CT@do@color
\endgroup
        \@tempdima\ht\z@
        \advance\@tempdima\minrowclearance
        \vrule\@height\@tempdima\@width\z@
        \unhbox\z@}%
  \prepnext@tok}

after that the examples on SX run for me.

[dcpurton]

I still get slightly different output for this tabu example:

\documentclass{article}
\usepackage{colortbl}
\usepackage{tabu}
\pagestyle{empty}
\begin{document}
\begin{tabu}{|l|X|}
  \hline
  Row 1 & \\
  \hline
  Row 2 & \\[5mm]
  \hline
  Row 3 & \\[5mm]
  \hline
  Row 4 & \\[5mm]
  \hline
\end{tabu}
\end{document}

With array 2016/10/06 v2.4d and colortbl 2012/02/13 v1.0a I get:

With array 2018/04/07 v2.4g including the patch in this thread and colortbl from https://tex.stackexchange.com/q/429272/87678 with the patch from this thread added I get:

[u-fischer]

This looks as if the new code corrects a bug in tabu. In your first output tabu added 10mm instead of 5mm.

[FrankMittelbach]

@dcpurton I think @u-fischer is right: looking into the generated page one sees a rule of with a depth of roughly twice of what is requested (plus roughly a baselineskip). With the new version (including the patches) that is gone. Replacing tabu with tabularx doesn't show that behavior (ie fine in both versions).

[dcpurton]

@u-fischer and @FrankMittelbach, I agree, the old behaviour of tabu does seem wrong (and I've even wondered about it before). It's a pity it will break old documents, but maybe that can't be helped. Thanks for dealing with this.

[FrankMittelbach]

I just fixed the array part of the problem and will upload that the moment the internet connection is a bit more stable over here. I also arranged for the package to rollback to the 2017 behavior if there is a rollback request so that older documents should still show the wrong (but probably used) behavior with tabu and the like.
In addition colortbl needs changing (as outlined above) so I pass that on to @davidcarlisle.

[davidcarlisle]

I have updated colortbl, hopefully in a version that works with old or new array package code

davidcarlisle/dpctex@3766c2b

[FrankMittelbach]

fixed with the recent updates