Footnote with automatic final period not working with "Ibid."

Question

I'm using this solution to automatically add a period at the end of every footnote; the code should insert a period only if the footnote does not already end with a period, a question mark or a bang.

However, one too much period is added when I use citestyle=authoryear-ibid in biblatex (with authoryear-ibid "immediately repeated citations are replaced by the abbreviation ‘"Ibid.’").

This is what i get:

MWE:

\documentclass{book}
\usepackage[
    style=chicago-authordate,
    citestyle=authoryear-ibid,
    ibidpage=true,
]{biblatex}
\addbibresource{bibliografia.bib}
% This macro inserts a period only if the footnote does not end with a period, a question mark or a bang
\makeatletter%
\long\def@makefntext#1{%
  \parindent 1em\noindent \hb@xt@ 1.8em{\hss@makefnmark}#1%
  \ifnum\the\spacefactor<3000.\fi}
\makeatother
\begin{document}
This works \footcite{Gomme1956} 
Here one too many period is added \footcite{Gomme1956}
\end{document}

How can I avoid that one too much period is added?

Answer 1

biblatex changes the space factors of certain punctuation commands for a finer control over punctuation and to avoid punctuation clashes. In this case the period produced by biblatex has space factor 1006 (\blx@sf@period), so we need to check against that as well

\documentclass{book}
\usepackage[
  style=chicago-authordate,
  citestyle=authoryear-ibid,
  ibidpage=true,
]{biblatex}
\addbibresource{biblatex-examples.bib}
\makeatletter%
\long\def@makefntext#1{%
  \parindent 1em\noindent \hb@xt@ 1.8em{\hss@makefnmark}#1%
  \ifnum\the\spacefactor<3000
    \ifnum\the\spacefactor=\blx@sf@period
    \else
    .%
    \fi
  \fi}
\makeatother
\begin{document}
This works \footcite{sigfridsson}
Here one too many period is added \footcite{sigfridsson}
Lorem\footnote{Blob}
\end{document}

Note that you don't need the extra code at all if the only footnotes you are ever using are produced by \footcite: biblatex automatically adds the period.