Unused global option(s) with kvoptions string option

Question

\begin{filecontents}{foo.cls}
\NeedsTeXFormat{LaTeX2e}
\ProvidesClass{foo}

\RequirePackage{kvoptions}
\SetupKeyvalOptions{family=myoptions,prefix=myoptions@}

\DeclareStringOption[scriptsize]{bibsize}

\ProcessKeyvalOptions{myoptions}\relax
\DeclareOption*{\PassOptionsToClass{\CurrentOption}{article}}
\ProcessOptions\relax

\LoadClass[a4paper, twoside]{article}

\def\bibfont{\csname \myoptions@bibsize\endcsname}
\end{filecontents}

\documentclass[bibsize=footnotesize]{foo}

\begin{document}
Foo bar
\end{document}

Works fine, but raises the warning:

LaTeX Warning: Unused global option(s):
    [bibsize].

Answer 1

The unused option list warning really wasn't designed for keyval options, just 10pt etc as used by the standard classes. It's probably possible to improve kvoptions handling here but the warning doesn't always make sense. if you have foo=false is the option foo used or not?

It's better not to warn than make spurious warning so I would simply silence it and arrange the class using kv parsing simply empties the unused list:

\NeedsTeXFormat{LaTeX2e}
\ProvidesClass{foo}

\RequirePackage{kvoptions}
\SetupKeyvalOptions{family=myoptions,prefix=myoptions@}

\DeclareStringOption[scriptsize]{bibsize}

\ProcessKeyvalOptions{myoptions}\relax
\DeclareOption*{\PassOptionsToClass{\CurrentOption}{article}}
\ProcessOptions\relax

\LoadClass[a4paper, twoside]{article}

\let\@unusedoptionlist\@empty%<<<<<<<<<<<<<<<<<<<<<<<<

\def\bibfont{\csname \myoptions@bibsize\endcsname}

For any new code use the built in key/value option handling in LaTeX, not the older package based versions. (A similar issue with the unused option list was just raised there)

Answer 2

The following would port your option to LaTeX's built in key=val option handler.

\begin{filecontents}{foo.cls}
\NeedsTeXFormat{LaTeX2e}
\ProvidesClass{foo}

\DeclareKeys[myoptions]
  {
    bibsize .store = \myoptions@bibsize,
    unknown .code  = \PassOptionsToClass{\CurrentOption}{article}
  }
\SetKeys[myoptions]{bibsize=scriptsize}

\ProcessKeyOptions[myoptions]

\LoadClass[a4paper, twoside]{article}

\def\bibfont{\csname \myoptions@bibsize\endcsname}
\end{filecontents}

\documentclass[bibsize=footnotesize]{foo}

\begin{document}
Foo bar {\bibfont bibfont}
\end{document}

---

Alternative solution, just to show stuff using expkv-opt (disclaimer: I'm the author of expkv-opt).

\begin{filecontents}{foo.cls}
\NeedsTeXFormat{LaTeX2e}
\ProvidesClass{foo}

\RequirePackage{expkv-opt, expkv-def}
\ekvdefinekeys{myoptions}
  {
    store   bibsize = \myoptions@bibsize,
    initial bibsize = scriptsize,
    unknown code    = \PassOptionsToClass{\CurrentOption}{article},
    unknown noval   = \PassOptionsToClass{\CurrentOption}{article}
  }
\ekvoUseUnknownHandlers* % for the next ekvoProcess use set's unknown handlers
\ekvoProcessLocalOptions{myoptions} % these are forwarded to article
\ekvoProcessFutureOptions{myoptions} % these aren't, article doesn't support it

\LoadClass[a4paper, twoside]{article}

\def\bibfont{\csname \myoptions@bibsize\endcsname}
\end{filecontents}

\documentclass[bibsize=footnotesize]{foo}

\begin{document}
Foo bar {\bibfont bibfont}.
\end{document}