fix: use of dropped constant in setting vline

Leftover of 85d3712 (refactor: use quarks to distinguish dash from text,
2024-04-06).

tabularray/tabularray.sty

@@ -1392,7 +1392,7 @@
     \group_begin:
     \keys_set_groups:nnn { tblr/__vline } { text } {#3}
     \tl_if_eq:NnF \l__tblr_vline_dash_tl
-      { \exp_not:n { \c__tblr_text_tl } }
+      { \exp_not:n { \q__tblr_text } }
       {
         \__tblr_set_vline_num:n {#1}
         \tl_clear:N \l__tblr_vline_dash_tl

tabularray/testfiles/tblr-hvline.lvt

@@ -0,0 +1,41 @@
+\input{regression-test}
+\documentclass{article}
+
+\usepackage{tabularray}
+
+\ExplSyntaxOn
+\debug_on:n { check-declarations , check-expressions , deprecation }
+% skip table typesetting
+\cs_gset_eq:NN \__tblr_build_whole: \prg_do_nothing:
+\ExplSyntaxOff
+
+\begin{document}
+
+\START
+
+\SetTblrTracing{+hline,+vline}
+
+\BEGINTEST{Empty hline/vline text}
+\begin{tblr}{
+  hlines, vlines,
+  hline{1}={text=},
+  vline{1}={text=},
+}
+  a
+\end{tblr}
+\ENDTEST
+
+% lvjr/tabularray#303
+\BEGINTEST{Fragile hline/vline text}
+\begin{tblr}{
+  hlines, vlines,
+  hline{1}={text={\def\x{}\small\rlap{--h--}}},
+  vline{1}={text={\clap{\textbf{v}}}},
+}
+  a
+\end{tblr}
+\ENDTEST
+
+\END
+
+\end{document}

tabularray/testfiles/tblr-hvline.tlg

@@ -0,0 +1,56 @@
+This is a generated file for the l3build validation system.
+Don't change this file in any respect.
+============================================================
+TEST 1: Empty hline/vline text
+============================================================
+> The spec list hline_1 contains the pairs:.
+>  {[1]/@hline-count}  =>  {1}.
+>  {[2]/@hline-count}  =>  {1}.
+>  {[1]/@hline-count}  =>  {1}.
+>  {[1][1](1)/@dash}  =>  {\q__tblr_dash solid}.
+>  {[2]/@hline-count}  =>  {1}.
+>  {[2][1](1)/@dash}  =>  {\q__tblr_dash solid}.
+>  {[1](1)/@hline-height}  =>  {0.4pt}.
+>  {[1]/@hline-height}  =>  {0.4pt}.
+>  {[2](1)/@hline-height}  =>  {0.4pt}.
+>  {[2]/@hline-height}  =>  {0.4pt}.
+> The spec list vline_1 contains the pairs:.
+>  {[1]/@vline-count}  =>  {1}.
+>  {[2]/@vline-count}  =>  {1}.
+>  {[1]/@vline-count}  =>  {1}.
+>  {[1][1](1)/@dash}  =>  {\q__tblr_dash solid}.
+>  {[2]/@vline-count}  =>  {1}.
+>  {[1][2](1)/@dash}  =>  {\q__tblr_dash solid}.
+>  {[1](1)/@vline-width}  =>  {0.4pt}.
+>  {[1]/@vline-width}  =>  {0.4pt}.
+>  {[2](1)/@vline-width}  =>  {0.4pt}.
+>  {[2]/@vline-width}  =>  {0.4pt}.
+============================================================
+============================================================
+TEST 2: Fragile hline/vline text
+============================================================
+> The spec list hline_1 contains the pairs:.
+>  {[1]/@hline-count}  =>  {1}.
+>  {[2]/@hline-count}  =>  {1}.
+>  {[1]/@hline-count}  =>  {1}.
+>  {[1][1](1)/@dash}  =>  {\q__tblr_text \def \x {}\small \rlap {--h--}}.
+>  {[2]/@hline-count}  =>  {1}.
+>  {[2][1](1)/@dash}  =>  {\q__tblr_dash solid}.
+>  {[1](1)/@hline-height}  =>  {6.19849pt}.
+>  {[1]/@hline-height}  =>  {6.19849pt}.
+>  {[2](1)/@hline-height}  =>  {0.4pt}.
+>  {[2]/@hline-height}  =>  {0.4pt}.
+> The spec list vline_1 contains the pairs:.
+>  {[1]/@vline-count}  =>  {1}.
+>  {[2]/@vline-count}  =>  {1}.
+>  {[1]/@vline-count}  =>  {1}.
+>  {[1][1](1)/@dash}  =>  {\q__tblr_text \clap {\textbf {v}}}.
+>  {[2]/@vline-count}  =>  {1}.
+>  {[1][2](1)/@dash}  =>  {\q__tblr_dash solid}.
+>  {[1](1)/@vline-width}  =>  {0.0pt}.
+>  {[1]/@vline-width}  =>  {0.0pt}.
+>  {[2](1)/@vline-width}  =>  {0.4pt}.
+>  {[2]/@vline-width}  =>  {0.4pt}.
+============================================================
+***************
+[test] 0 error(s) encountered.