[Bug] [tabularray-dev] X column do not compute the width when there is a merged cell

[mariuslp]

Tell us about the system on which the bug was produced

• Distribution and year (e.g., TeXLive 2025): TeXLive 2025
• Engine used (e.g., LuaLaTeX): pdfLatex
• Operating system (e.g., Gentoo Linux): whatever overleaf uses

Please outline the bug as you have found it

Using the tabularray-dev.sty from the dev-version branch, the width of X cells is not computed correctly if two cells are merged horizontally. Note that the code correctly works with version 2025A.

Setting the width attribute does not solve it either.

Share a minimum working example to reproduce the bug

\documentclass{article}
\usepackage{tabularray-dev} 

\begin{document}
% works
\begin{tblr}{
  colspec = {lllXX},
  hlines,
  vlines,
}
    1-1 & 1-2 & 1-3 & very very long text in the X column & sooooooooooooo very much long it will not stop and continue \\
    2-1 & 2-2 & 2-3 & 2-4 & 2-5 \\ 
\end{tblr}

% does not work
\begin{tblr}{
  colspec = {lllXX},
  hlines,
  vlines,
}
    1-1 & \SetCell[c=2]{c} merged & 1-3 & very very long text in the X column & sooooooooooooo very much long it will not stop and continue \\
    2-1 & 2-2 & 2-3 & 2-4 & 2-5 \\ 
\end{tblr}

% also does not work
\begin{tblr}{
  colspec = {lllXX},
  hlines,
  vlines,
}
    1-1 & 1-2 & \SetCell[c=2]{c} merged & very very long text in the X column & sooooooooooooo very much long it will not stop and continue \\
    2-1 & 2-2 & 2-3 & 2-4 & 2-5 \\ 
\end{tblr}
\end{document}

Output:

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• What the expected output should be
• Log files

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• System information
• Outline of the bug, including MWE for reproduction