When using \KeyValue, lttemplates and xtemplate have different results

[Sophanatprime]

Brief outline of the bug

When using \KeyValue, lttemplates and xtemplate have different results. lttemplates may cause endless loop.

Minimal example showing the bug

\RequirePackage{latexbug}
\documentclass{article}

\ifdefined\NewTemplateType
  \NewTemplateType{foo}{0}    % current LaTeX version
\else
  \usepackage{xtemplate}      % TeXLive 2023
  \DeclareObjectType{foo}{0}
\fi

\def\foocode{}
\DeclareTemplateInterface{foo}{FOO}{0}
  {
    foo.code : tokenlist ,
    code.foo : tokenlist = \KeyValue{foo.code} ,
  }
\DeclareTemplateCode{foo}{FOO}{0}
  {
    foo.code = \foocode ,
    code.foo = \foocode ,
  }
  {\AssignTemplateKeys (\foocode)}

\DeclareInstance{foo}{i1}{FOO}{ foo.code=A }
\DeclareInstance{foo}{i2}{FOO}{ code.foo=B }

\begin{document}

\UseInstance{foo}{i1}

\UseInstance{foo}{i2}

\end{document}

Overleaf with TeXLive 2023 works well, but on my computer, there is an endless loop.

It seems there is no \__xtemplate_assign_tokenlist: in lttemplates
https://github.com/latex3/latex3/blob/1a856471a905fe70b564ff645f6f390bd2a019af/l3packages/xtemplate/xtemplate-2023-10-10.sty#L971-L995

I simply put them in the preamble replaced xtemplate with template and changed \__xtemplate_if_key_value:oTF to \__template_if_key_value:VTF, it works as in TeXLive 2023.

Log file (required) and possibly PDF file

demo.log

[josephwright]

Ah, I see what's happened - I streamlined the auxiliaries a bit, but I'd not allowed for the fact that there needs to be different handling for token lists and registers in terms for \KeyValue. A fix will be in later today in dev for the 2024-11-01 release.

[muzimuzhi]

947d414 (Re-factor internals for template var setting, 2024-04-15) merged various \__template_assign_<type>: to a centric \__template_assign_variable:. But for commalist/clist and tokenlist/tl types, a V-type expansion was lost when a template value starts with \KeyValue.

Try this

\RequirePackage{latexbug}
\documentclass{article}

\ExplSyntaxOn
\cs_undefine:N \__template_assign_variable:
\cs_new_protected:Npn \__template_assign_variable:
  {
    \exp_args:Nee \__template_assign_variable:nn
      { \__template_map_var_type: }
      { \bool_if:NT \l__template_global_bool { g } }
  }

\cs_new_protected:Npn \__template_assign_variable:nn #1#2
  {
    \str_case_e:nnTF { #1 }
      {
        { tl } {}
        { clist } {}
      }
      % tl and clist need :NV if \l__template_value_tl starts with \KeyValue
      % see https://github.com/latex3/latex2e/commit/947d41437824b2a69ef0a3644128c574ae6f72df
      { \__template_assign_variable:cc { #1 _ #2 set:NV } { #1 _ #2 set:Nn } }
      { \__template_assign_variable:cc { #1 _ #2 set:Nn } { #1 _ #2 set:Nn } }
  }

\cs_new_protected:Npn \__template_assign_variable:NN #1#2
  {
    \__template_if_key_value:VTF \l__template_value_tl
      {
        \__template_key_to_value:
        \tl_put_right:Ne \l__template_assignments_tl
          {
            #1 \exp_not:V \l__template_var_tl
             { \exp_not:V \l__template_value_tl }
          }
      }
      {
        \tl_put_right:Ne \l__template_assignments_tl
          {
            #2 \exp_not:V \l__template_var_tl
             { \exp_not:V \l__template_value_tl }
          }
      }
    \tl_show:N \l__template_assignments_tl
  }
\cs_generate_variant:Nn \__template_assign_variable:NN {cc}
\ExplSyntaxOff
\ExplSyntaxOff

\ifdefined\NewTemplateType
  \NewTemplateType{foo}{0}    % current LaTeX version
\else
  \usepackage{xtemplate}      % TeXLive 2023
  \DeclareObjectType{foo}{0}
\fi

\def\foocode{}
\DeclareTemplateInterface{foo}{FOO}{0}
  {
    foo.code : tokenlist ,
    code.foo : tokenlist = \KeyValue{foo.code} ,
  }
\DeclareTemplateCode{foo}{FOO}{0}
  {
    foo.code = \foocode ,
    code.foo = \foocode ,
  }
  {\AssignTemplateKeys (\foocode)}

\DeclareInstance{foo}{i1}{FOO}{ foo.code=A }
\DeclareInstance{foo}{i2}{FOO}{ code.foo=B }

\begin{document}

\UseInstance{foo}{i1} % typesets "(A)"

\UseInstance{foo}{i2} % typesets "(B)"

\end{document}

[josephwright]

We also need to cover fp: I think might be best to use a low-level test here (\token_if_macro:NTF), as this really is about how things are implemented.

[josephwright]

Also, there are some stray braces (likely going back a long way - perhaps we had o-type expansion at one point). @muzimuzhi do you want to make a PR or are you happy to leave to me to fix?

[muzimuzhi]

As I'm far from familiar with lttemplate, I'm happy to leave this to you :).

[muzimuzhi]

We also need to cover fp

Not necessary, as \fp_set:Nn \l_tmpa_fp {\l_tmpa_fp } is a valid assignment. But as \token_if_macro:NTF is faster than \str_case_e:nnTF, expanding fp once does no harm too.

BTW the test needed here is similar to the logic in \__exp_eval_register:N except for the \tex_the:D for registers.

[josephwright]

We also need to cover fp

Not necessary, as \fp_set:Nn \l_tmpa_fp {\l_tmpa_fp } is a valid assignment. But as \token_if_macro:NTF is faster than \str_case_e:nnTF, expanding fp once does no harm too.

True but I think we might be best off simply making a clear distinction. Anyway, do you want to do it, or should I?

[muzimuzhi]

As I'm far from familiar with lttemplate, I'm happy to leave this to you :).

[josephwright]

I have a shorter approach I'll go with: PR very shortly