Issue with negative exponents when using output-exponent-marker

[adamliter]

When compiling the following document with TeX Live 2020 and version 2020/02/25 v2.8b of siunitx, I get the following result:

\documentclass{article}
\usepackage{siunitx}
\sisetup{output-exponent-marker=\ensuremath{e}}
\begin{document}
\num{2.74e-7}
\end{document}

When compiling with TeX Live 2021 and version 2022-02-15 v3.0.49 of siunitx, I get the following result:

In this second case, it seems like the negative is being treated as a minus sign for the purposes of spacing. I'm guessing this is a bug, right? Thanks!

If you happen to have a fix you could suggest for the time being while TeX Live is frozen, I'd really appreciate it! 😄

[josephwright]

In place fix

\documentclass{article}
\usepackage{siunitx}
\ExplSyntaxOn
\cs_gset:Npn \__siunitx_number_output_exponent_auxi:nnnnn #1#2#3#4#5
  {
    \bool_lazy_or:nnT
      {
        \bool_lazy_and_p:nn
          { \l__siunitx_number_unity_mantissa_bool }
          { \str_if_eq_p:nn { #3 . #4 } { 1. } }
      }
      {
        ! \bool_lazy_or_p:nn
          { \str_if_eq_p:nn { #3 . #4 } { 1. } }
          { \tl_if_blank_p:n {#3} }
      }
      {
        \bool_if:NTF \l__siunitx_number_tight_bool
          { \exp_not:N \mathord }
          { \use:n }
            { \exp_not:V \l__siunitx_number_exponent_product_tl }
      }
    \exp_not:n {#5}
    \exp_not:V \l__siunitx_number_exponent_base_tl
    ^
      { \__siunitx_number_output_exponent_auxiii:nnn { } {#1} {#2} }
  }
\cs_gset:Npn \__siunitx_number_output_exponent_auxii:nnnnn #1#2#3#4#5
  {
    \exp_not:n {#5}
    \exp_not:V \l__siunitx_number_output_exp_marker_tl
    \__siunitx_number_output_exponent_auxiii:nnn { \mathord } {#1} {#2}
  }
\cs_gset:Npn \__siunitx_number_output_exponent_auxiii:nnn #1#2#3
  {
    \tl_if_blank:nTF {#2}
      {
        \bool_lazy_and:nnT
          { \l__siunitx_number_implicit_plus_bool }
          { ! \str_if_eq_p:nn {#3} { 0 } }
          { #1 + }
      }
      { \exp_not:n {#1#2} }
    \__siunitx_number_output_digits:nn { integer } {#3}
  }
\ExplSyntaxOff
\sisetup{output-exponent-marker=\mathrm{e}}
\begin{document}
\num{2.74e-7}
\end{document}