marginnote always on left side of the page

Question

I would like to be able to use marginnote in a two-sided book, but have all notes appear on the left margin. There is an older solution to this problem here, and there's a parallel older answer that puts all notes on the right margin here. Neither of those solutions work any longer, however, because of updates to marginnote.

There is a working solution for putting all notes on the right margin here, but I'm unfortunately not capable of adapting it to the left margin by myself.

Small example

\documentclass[twoside]{book}
\usepackage{marginnote}
\usepackage{lipsum}

\begin{document}

\lipsum[1]\marginnote{test test test test test}
\lipsum[1-2]\marginnote{test test test test test}
\lipsum[1-2]\marginnote{test test test test test}
\lipsum[1-2]\marginnote{test test test test test}
\lipsum[1-2]\marginnote{test test test test test}
\lipsum[1-2]

\end{document}

Answer 1

Per this answer, there is an analogous cludge to the marginnote package to put everything on the left, obtained by preserving the other case from the code defining \@mn@@@marginnote. This is given below.

\documentclass[twoside]{book}
\usepackage{marginnote}
\usepackage{lipsum}
%
%
\makeatletter
\long\def\@mn@@@marginnote[#1]#2[#3]{%
  \begingroup
    \ifmmode\mn@strut\let\@tempa\mn@vadjust\else
      \if@inlabel\leavevmode\fi
      \ifhmode\mn@strut\let\@tempa\mn@vadjust\else\let\@tempa\mn@vlap\fi
    \fi
    \@tempa{%
      \vbox to\z@{%
        \vss
        \@mn@margintest
        \if@reversemargin\if@tempswa
            \@tempswafalse
          \else
            \@tempswatrue
        \fi\fi

          \llap{%
            \vbox to\z@{\kern\marginnotevadjust\kern #3
              \vbox to\z@{%
                \hsize\marginparwidth
                \linewidth\hsize
                \kern-\parskip
                %\mn@parboxrestore
                \marginfont\raggedleftmarginnote\strut\hspace{\z@}%
                \ignorespaces#1\endgraf
                \vss
              }%
              \vss
            }%
            \if@mn@verbose
              \PackageInfo{marginnote}{xpos seems to be \@mn@currxpos}%
            \fi
            \begingroup
              \ifx\@mn@currxpos\relax\else\ifx\@mn@currpos\@empty\else
                  \kern\@mn@currxpos
              \fi\fi
              \ifx\@mn@currpage\relax
                \let\@mn@currpage\@ne
              \fi
              \if@twoside\ifodd\@mn@currpage\relax
                  \kern-\oddsidemargin
                \else
                  \kern-\evensidemargin
                \fi
              \else
                \kern-\oddsidemargin
              \fi
              \kern-1in
            \endgroup
            \kern\marginparsep
          }%
      }%
    }%
  \endgroup
}
\makeatother
%
\begin{document}

\lipsum[1]\marginnote{test test test test test}
\lipsum[1-2]\marginnote{test test test test test}
\lipsum[1-2]\marginnote{test test test test test}
\lipsum[1-2]\marginnote{test test test test test}
\lipsum[1-2]\marginnote{test test test test test}
\lipsum[1-2]

\end{document}

Note that there is a line %\mn@parboxrestore which I have commented out (because it didn't work on my system with it not commented out). This is almost surely because the version of marginnote in my system is not the most recent, but this snippet of code is taken from marginnote.sty, which can be found (for example) at this URL. It would be worth trying this on your system with this line uncommented.

Answer 2

As there are tests for twoside everywhere in the code (and it affects spacing and other things), it is imho the best to locally set twoside to false:

\documentclass[twoside]{book}
\usepackage[centering,marginparwidth=2.5cm,paperheight=10cm]{geometry}
\usepackage{marginnote}
\usepackage{lipsum}
\usepackage{etoolbox}

\makeatletter
\patchcmd{\@mn@@@marginnote}{\begingroup}{\begingroup\@twosidefalse}{}{\fail}
\reversemarginpar
\makeatother

\begin{document}

\lipsum[1]\marginnote{test test test test test}
\lipsum[1-2]\marginnote{test test test test test}
\lipsum[1-2]\marginnote{test test test test test}
\lipsum[1-2]\marginnote{test test test test test}
\lipsum[1-2]\marginnote{test test test test test}
\lipsum[1-2]

\end{document}