biblatex and `\ifblank{}`

Question

I want to change the output format of \citeauthor{} so that full names ("givenname familyname") instead of just family names are displayed. Therefore, I have to define a special format and change \citeauthor so that it uses this format for its output routine.

Like shown in the example in the biblatex manual (section 4.2.3, page 146; biblatex version 3.9), I use \ifblank{\namepartgiven} to check whether the current name has a non-empty field namepartgiven. The logic seems simple enough: If the test succeeds, \namepartgiven\space will be printed just before \namepartfamily; if the field is empty, \namepartfamily should be printed immediately, without any preceding \space. However, I wonder when \ifblank is supposed to trigger.

Consider the following example:

\documentclass{article}

\usepackage[backend=biber,bibstyle=authoryear, citestyle=authoryear-icomp]{biblatex}
\addbibresource{test.bib}

\usepackage{filecontents}
\begin{filecontents*}{test.bib}
@book{test,
  author = {John Doe and Smith},
  title = {How to write an extraordinary book},
  date = {2018}
}%    
\end{filecontents*}

\DeclareNameFormat{citeauthor}{%
%  \iffieldundef{\namepartgiven}{}%
    {\ifblank{\namepartgiven}{}{\namepartgiven\space}}%
  \namepartfamily%
  \ifnumgreater{\value{liststop}}{\value{listcount}}%
    {\ifnumgreater{\value{liststop}-1}{\value{listcount}}%
      {\multinamedelim}%
      {\finalnamedelim}%
    }%
    {\ifmorenames{\usebibmacro{name:andothers}}{}}%
}

\DeclareCiteCommand{\citeauthor}
  {\boolfalse{citetracker}%
   \usebibmacro{prenote}}%
  {\usebibmacro{citeindex}%
   \printnames[citeauthor]{author}}%
  {}
  {\midsentence*}

\begin{document}
\printbibliography

\citeauthor{test}\par\cite{test}
\end{document}

This code works as expected if \namepartgiven is not empty. However, the database contains no given name for the second author (Smith). Apparently, \ifblank doesn't trigger because the field is not present; consequently, it branches off to print the non-existent given name, followed by a space:

So, how about checking first whether the field namepartgiven is used at all before checking whether it is empty? Just activate the first line after \DeclareNameFormat{citeauthor} and compile the document again! This is what you will see:

Not surprisingly, the erroneous space right before "Smith" has disappeared. But wait, what happened to John Doe? Why has "John" gone as well?

Does anybody know what is happening here? There must be something I haven't understood correctly -- or could this be a bug in biblatex?

Answer 1

The standard styles use \ifdefvoid instead of \ifblank. The \ifblank in the docs is a remnant of the old name format scheme (see Biblatex 3.3 name formatting) when the names parts were not passed down as macros, but as arguments. The documentation was fixed in version 3.12 (commit 7f470c1).

The answer to what you want to do is even easier

\DeclareNameAlias{citeauthor}{given-family}

Answer 2

\ifblank does no expansion on its argument, so \ifblank{\namepartgive} never returns true.

Expand \namepartgiven before \ifblank acts:

\DeclareNameFormat{citeauthor}{%
  \expandafter\ifblank\expandafter{\namepartgiven}{}{\namepartgiven\space}%
  \namepartfamily 
  \ifnumgreater{\value{liststop}}{\value{listcount}}%
    {\ifnumgreater{\value{liststop}-1}{\value{listcount}}%
      {\multinamedelim}%
      {\finalnamedelim}%
    }%
    {\ifmorenames{\usebibmacro{name:andothers}}{}}%
}

If you're afraid that the argument to \ifblank needs more than one expansion step to deliver the final result, you can define

\newcommand{\ifblankx}[1]{%
  \expandafter\ifblank\expandafter{\romannumeral-`Q#1}%
}

and use \ifblankx{\namepartgiven}{<true>}{<false>}. On the other hand, if you're confident that \namepartgiven just needs one expansion step, you can use

\ifdefvoid{\namepartgiven}{<true>}{<false>}