how to get the real width in X column

[libinxu01]

When I use diagbox in a X column table, the line can't fix the cell. How to get the real width of the final cell?

\documentclass{article}

\usepackage{tabularray}
\usepackage{xcolor}
\UseTblrLibrary{diagbox}

\begin{document}
	\begin{longtblr}[label=none]{
	    width=\textwidth,
		colspec={X[2]X[3]X[5]},
		vlines,hlines
	}
	\diagbox[innerwidth=0.2\textwidth]{}{} 
	& 
	\diagbox[innerwidth=0.3\textwidth]{}{} 
	& 
	\diagbox[innerwidth=0.5\textwidth]{}{}  \\
    \end{longtblr}
    
    
    
	\begin{longtblr}[label=none]{
	    width=\textwidth,
		colspec={X[2]X[3]X[5]},
		vlines,hlines
	}
	\diagbox[width=0.2\textwidth]{}{} 
	& 
	\diagbox[width=0.3\textwidth]{}{} 
	& 
	\diagbox[width=0.5\textwidth]{}{}  \\
    \end{longtblr}
    

	\begin{longtblr}[label=none]{
	    width=\textwidth,
		colspec={X[2]X[3]X[5]},
		vlines,hlines
	}
	\diagbox{}{} 
	& 
	\diagbox{}{} 
	& 
	\diagbox{}{}  \\
    \end{longtblr}

\end{document}

[muzimuzhi]

Looks like there's no public interface yet.

\documentclass{article}
\usepackage{tabularray}
\UseTblrLibrary{diagbox}

\ExplSyntaxOn
\cs_new:Npn \getCurrColWidth
  {
    \prop_item:Ne \l__column_computed_width_prop { \arabic{colnum} }
  }
\ExplSyntaxOff

\begin{document}
\begin{longtblr}[label=none]{
  width=\textwidth,
  colspec={X[2]X[3]X[5]},
  vlines,hlines
}
	\diagbox[innerwidth=\getCurrColWidth]{}{} & 
	\diagbox[innerwidth=\getCurrColWidth]{}{} & 
	\diagbox[innerwidth=\getCurrColWidth]{}{} \\
  \getCurrColWidth & \getCurrColWidth & \getCurrColWidth
\end{longtblr}
\end{document}

[muzimuzhi]

Slightly extended version, now

• \TblrGetColWidth{<n>} retrieve width of column <n>, starting at 1,
• \TblrGetColWidth{} retrieve width of current column.

Example

\documentclass{article}
\usepackage{tabularray}
\UseTblrLibrary{diagbox}

\ExplSyntaxOn
% \TblrGetColWidth{<n>} retrieve width of column <n>
% \TblrGetColWidth{}    retrieve width of current column
\NewExpandableDocumentCommand \TblrGetColWidth { m }
  {
    % \prop_show:N \l__column_computed_width_prop
    \prop_item:Ne \l__column_computed_width_prop
      { \tl_if_blank:nTF {#1} { \arabic{colnum} } {#1} }
  }
\ExplSyntaxOff

\begin{document}
\begin{longtblr}[label=none]{
  width=\textwidth,
  colspec={X[2]X[3]X[5]},
  vlines,hlines
}
	\diagbox[innerwidth=\TblrGetColWidth{}]{}{} &
	\diagbox[innerwidth=\TblrGetColWidth{}]{}{} &
	\diagbox[innerwidth=\TblrGetColWidth{}]{}{} \\
  A \TblrGetColWidth{}  & B \TblrGetColWidth{}  & C \TblrGetColWidth{ } \\
  B \TblrGetColWidth{2} & C \TblrGetColWidth{3} & A \TblrGetColWidth{1} \\
\end{longtblr}
\end{document}

[libinxu01]

I get it. Thank you so much! Love you!

[muzimuzhi]

Getting width and (total) height of table cells (in building phase) has been requested several times, see #329, #342, #406, and #461.

Below is another attempt that exposes expandable \TblrGetCellWidth and \TblrGetCellHeight which work for cells in normal and X columns, and possibly spanning several rows and columns.

\documentclass{article}
\usepackage{tabularray}

\UseTblrLibrary{diagbox}

\ExplSyntaxOn
% To be used in dim expressions, these two getters must be expandable, hence
% cannot be defined by \proNewFunction, like \cellGetText provided with library
% "functional"
\cs_new:Npn \TblrGetCellWidth  { \dim_use:N \l__tblr_cell_wd_dim }
\cs_new:Npn \TblrGetCellHeight { \dim_use:N \l__tblr_cell_ht_dim }

% helper
\cs_new:Npn \TblrIfMeasuringTF { \bool_if:NTF \lTblrMeasuringBool }

% temp workaround for lvjr/tabularray#470
\cs_new:Npn \TblrFixBelowsepAndRightsep
  {
    % In case cell sizes are affected by \belowsep and \rightsep, this fix must
    % be applied in both measuring and building phases.
    \tl_if_empty:NT \l__tblr_cell_rowspan_tl
      {
        \tl_set:Ne \l__tblr_cell_rowspan_tl
          {
            \__tblr_data_item:neen { cell }
              { \l__tblr_i_tl } { \l__tblr_j_tl } { rowspan }
          }
      }
    % FIXME: updating \belowsep unconditionally only introduces more problems
    \int_compare:nNnT { \l__tblr_cell_rowspan_tl } > { 1 }
      {
        \dim_set:Nn \belowsep
          {
            \__tblr_data_item:nen { row }
              { \int_eval:n { \l__tblr_i_tl + \l__tblr_cell_rowspan_tl - 1 } }
              { belowsep }
          }
      }
    \tl_if_empty:NT \l__tblr_cell_colspan_tl
      {
        \tl_set:Ne \l__tblr_cell_colspan_tl
          {
            \__tblr_data_item:neen { cell }
              { \l__tblr_i_tl } { \l__tblr_j_tl } { colspan }
          }
      }
    \int_compare:nNnT { \l__tblr_cell_colspan_tl } > { 1 }
      {
        \dim_set:Nn \rightsep
          {
            \__tblr_data_item:nen { column }
              { \int_eval:n { \l__tblr_j_tl + \l__tblr_cell_colspan_tl - 1 } }
              { rightsep }
          }
      }
  }
\ExplSyntaxOff

\newcommand{\onlySlash}[1][]{%
  \TblrIfMeasuringTF{%
    \diagbox{}{}%
  }{%
    \diagbox[
      innerwidth=\TblrGetCellWidth,
      height=\abovesep+\TblrGetCellHeight+\belowsep,
      #1
    ]{}{}%
  }%
}

\SetTblrInner{hlines, vlines}

\begin{document}

\begin{tblr}{
    hlines,
    vlines,
    width      = .7\linewidth,
    colspec    = { l c r X X[2] },
    rowspec    = { Q[t] Q[m] Q[b] Q[h] Q[f] },
    cells      =
      {
        appto = {%
          \smash{\rlap{\tiny\sffamily(\therownum, \thecolnum)}}%
          \onlySlash
        }
      },
  }
   & & & & \\
   \\ \\ \\ \\
\end{tblr}

\begin{tblr}{
    hlines,
    vlines,
    row{2}     = { belowsep = 0pt },
    % FIXME: larger belowsep (e.g., 10pt) resulted in vertically shifted diagbox
    row{4}     = { belowsep = 6pt },
    column{3}  = { rightsep = 12pt },
    cell{1}{1} = { r = 2, c = 1 }{ font = \bfseries, c },
    cell{2}{3} = { r = 2, c = 2 }{ font = \bfseries, c },
    cell{4}{1} = { r = 1, c = 2 }{ font = \bfseries, c },
    cell{5}{2} = { r = 1, c = 3 }{ font = \bfseries, c },
    cells      =
      {
        preto = {\TblrFixBelowsepAndRightsep},
        appto = {%
          \smash{\rlap{\tiny\sffamily(\therownum, \thecolnum)}}%
          \onlySlash[dir=NE]
        }
      },
    % vary cell sizes a bit
    column{1} = { wd = 1cm },
    row{3}    = { ht = 1cm },
  }
   & & & \\
   \\ \\ \\ \\
\end{tblr}

\end{document}