pgfgantt: Start the week on Sunday?

Question

I want my Gantt chart to display with the week starting on Sunday. You can see this in the second gantt chart in the MWE. How do I accomplish that without explicitly writing out each week?

My use case is for project management and the work week starts on Sunday.

Minimum Working Example

\documentclass[a4paper]{article}
\usepackage{pgfgantt}

\begin{document}

\begin{ganttchart}[
  hgrid,
  vgrid,
  x unit = 1cm,
  time slot format=isodate
  ]{2022-06-19}{2022-07-01}
  \gantttitlecalendar{year, month, week, day, weekday=shortname} \\
\end{ganttchart}

\begin{ganttchart}[
  hgrid,
  vgrid,
  x unit = 1cm,
  time slot format=isodate
  ]{2022-06-19}{2022-07-01}
  \gantttitlecalendar{year, month} \\
  \gantttitle{Week 1}{7}
  \gantttitle{Week 2}{6} \\
  \gantttitlecalendar{day, weekday=shortname} \\
\end{ganttchart}

\end{document}

The ideal solution would be to have an option to switch the week day start from meaning Monday to Sunday. But I think that's hard coded. I have checked the TikZ manual's relevant sections (89.1.3 Typesetting Dates) and didn't find anything that helps me.

The only other question that mentions a similar topic is Tikz calendar with week starting on Sunday but it was unhelpful because it didn't modify when the week started and does not use pgfgantt.

Answer 1

The start day is indeed hard coded but it's not too difficult to change. The original calendar/week/.code uses Sunday in the \ifdate{} part of the code. We simply need to change this to Saturday to have weeks begin on Sunday. I don't know if the package author would be open to feature requests, but this would be a very simple addition to make to allow a different start day.

\documentclass[a4paper]{article}
\usepackage{pgfgantt}
\makeatletter
\ganttset{
  calendar/week/.code={%
    \ifgtt@calendar@eol\ganttnewline\fi%
    \begingroup%
    \gtt@calendar@slots=1\relax%
    \gtt@calendar@weeknumber=#1\relax%
    \pgfcalendar{}{\gtt@calendar@startdate}{\gtt@calendar@enddate}{%
      \ifdate{Saturday}{%
        \gtt@calendar@startofweek=\pgfcalendarcurrentjulian\relax%
        \advance\gtt@calendar@startofweek by1\relax%
        \advance\gtt@calendar@startofweek by-\gtt@calendar@slots\relax%
        \pgfcalendarjuliantodate{\gtt@calendar@startofweek}%
          {\startyear}{\startmonth}{\startday}%
        \def\currentweek{\the\gtt@calendar@weeknumber}%
        \gantttitle{%
          \ganttvalueof{calendar week text}%
        }{%
          \the\gtt@calendar@slots%
        }%
        \gtt@calendar@slots=1\relax%
        \advance\gtt@calendar@weeknumber by1\relax%
      }{%
        \advance\gtt@calendar@slots by1%
      }%
      \ifdate{equals=\pgfcalendarendiso}{%
        \ifnum\gtt@calendar@slots=1\relax\else%
          \advance\gtt@calendar@slots by-1\relax%
          \gtt@calendar@startofweek=\pgfcalendarcurrentjulian\relax%
          \advance\gtt@calendar@startofweek by1\relax%
          \advance\gtt@calendar@startofweek by-\gtt@calendar@slots\relax%
          \pgfcalendarjuliantodate{\gtt@calendar@startofweek}%
            {\startyear}{\startmonth}{\startday}%
          \def\currentweek{\the\gtt@calendar@weeknumber}%
          \gantttitle{%
            \ganttvalueof{calendar week text}%
          }{%
            \the\gtt@calendar@slots%
          }%
        \fi%
      }{}%
    }%
    \endgroup%
    \gtt@calendar@eoltrue%
  }
}
\makeatother
\begin{document}

\begin{ganttchart}[
  hgrid,
  vgrid,
  x unit = 1cm,
  time slot format=isodate
  ]{2022-06-19}{2022-07-01}
  \gantttitlecalendar{year, month, week, day, weekday=shortname} \\
\end{ganttchart}

\end{document}