\cs_new:Npn
  \show_until_if:w  % warning on this line
  #1 \if^^zw  % warning on this line
  { \tl_show:n {#1} }
\show_until_if:^^7  % warning on this line
  \tex_if:D  % warning on this line
  \if_charcode:^^77  % warning on this line
  \if^^3aw  % warning on this line