BibLaTeX (authoryear) 當日期為空時放置空括號

Question 1

這裡的根本問題是，與其他命令不同，\print(field|list|names|date)該命令\printtext事先並不知道它是否會列印某些內容。因此，即使後來發現沒有任何內容要列印，它也將始終套用格式化參數。這意味著我們最終會得到一對空括號。

解決這個問題的一種方法是在呼叫之前檢查是否要列印某些內容\printtext。

雖然某些biblatex代碼使用\ifthenelse大多數較新的代碼使用etoolbox's \ifboolexpr。請注意，內部 forbiblatex沒有字段date，如果您想測試 a 是否存在，date最好測試 foryear

\renewbibmacro*{issue+date}{%
  \ifboolexpr{test {\iffieldundef{issue}} and test {\iffieldundef{year}}}
    {}
    {\printtext[parens]{%
       \printfield{issue}%
       \setunit*{\addspace}%
       \usebibmacro{date}}%
     \newunit}}

也可以看看https://github.com/plk/biblatex/issues/793。

有些人可能會對biblatex-apa最近實現的一個版本感興趣\printtext，該版本會自動檢查是否列印某些內容，如果不列印則抑制格式。看https://github.com/plk/biblatex-apa/pull/99。如果事實證明該命令沒有任何負面影響，我們可能會考慮將其移至核心biblatex，但它需要更多測試（並且實現感覺很像作弊）。

\documentclass[british]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{csquotes}

\usepackage[style=authoryear, backend=biber]{biblatex}

\renewbibmacro*{issue+date}{%
  \printtexte[parens]{%
    \printfield{issue}%
    \setunit*{\addspace}%
    \usebibmacro{date}}%
  \newunit}

% implement \printtexte
\makeatletter
% Optional parens/brackets
% Thanks to egreg from https://tex.stackexchange.com/questions/53068/how-to-check-if-a-macro-value-is-empty-or-will-not-create-text-with-plain-tex-co
% for this test for expanded emptiness so that we can easily opt to not print parens around nothing
% Without this, it is very messy - you have to test all potential fields for defness first and this
% is messy because the fields in the additional info vary betwee entrytypes
\def\foreverunspace{%
  \ifnum\lastnodetype=11
    \unskip\foreverunspace
  \else
    \ifnum\lastnodetype=12
      \unkern\foreverunspace
    \else
      \ifnum\lastnodetype=13
        \unpenalty\foreverunspace
      \fi
    \fi
  \fi
}

% we need a way to save the state of the punctuation buffer
% cf. \blx@initunit in biblatex.sty for what we need to copy

% this uses the internal implementation of etoolbox toggles
% fingers crossed no one messes with it
\newrobustcmd*{\apablx@savetoggle}[1]{%
  \csletcs{apablx@savedtoggle@#1}{etb@tgl@#1}}

\newrobustcmd*{\apablx@restoretoggle}[1]{%
  \csletcs{etb@tgl@#1}{apablx@savedtoggle@#1}}

\newrobustcmd*{\apablx@savepunctstate}{%
  \apablx@savetoggle{blx@block}%
  \apablx@savetoggle{blx@unit}%
  \apablx@savetoggle{blx@insert}%
  \apablx@savetoggle{blx@lastins}%
  \apablx@savetoggle{blx@keepunit}%
  \let\apablx@savd@unitpunct\blx@unitpunct
  \let\apablx@savd@puncthook\abx@puncthook}

\newrobustcmd*{\apablx@restorepunctstate}{%
  \global\apablx@restoretoggle{blx@block}%
  \global\apablx@restoretoggle{blx@unit}%
  \global\apablx@restoretoggle{blx@insert}%
  \global\apablx@restoretoggle{blx@lastins}%
  \global\apablx@restoretoggle{blx@keepunit}%
  \global\let\blx@unitpunct\apablx@savd@unitpunct
  \global\let\abx@puncthook\apablx@savd@puncthook}

% printtext that checks if it would print anything
\newrobustcmd{\printtexte}[2][]{%
  \apablx@savepunctstate
  \setbox0=\hbox{#2\foreverunspace}%
  \apablx@restorepunctstate
  \ifdim\wd0=0pt
  \else
    \ifblank{#1}
      {\printtext{#2}}
      {\printtext[#1]{#2}}%
  \fi}
\makeatother


\begin{filecontents}{\jobname.bib}
@article{test,
  author       = {Author, A.},
  journaltitle = {A Journal},
  title        = {A Title},
  pubstate     = {inpreparation},
}
\end{filecontents}
\addbibresource{\jobname.bib}


\begin{document}
\autocite{test}
\printbibliography
\end{document}

Answer