Alignment of margin floats

Question

I am using the code from margin-floats-and-hyperlinks. It works nicely, however the figure generated is not left aligned in the margin as the caption below it is. I also tried \raggedright as suggested in align-figure-to-the-right-with-raggedleft.

MWE

\documentclass{report}
\usepackage{geometry}
\geometry{
  showframe=true,
  includeheadfoot,
  includemp,
  marginparwidth=3.5cm,
  marginparsep=1.5em,
  hmargin={3cm,1.5cm},
  vmargin={2cm,2cm},
  headsep=2ex,
  footskip=3ex
}
%
%https://tex.stackexchange.com/questions/27348/margin-floats-and-hyperlinks
\usepackage{placeins}

\makeatletter
% Margin float environment
\newsavebox{\@tufte@margin@floatbox}
\newenvironment{@tufte@margin@float}[2][-1.2ex]%
  {\FloatBarrier% process all floats before this point so the figure/table numbers stay in order.
  \begin{lrbox}{\@tufte@margin@floatbox}%
  \begin{minipage}{\marginparwidth}%
    \def\@captype{#2}%
    \hbox{}\vspace*{#1}%
    \noindent%
  }
  {\end{minipage}%
  \end{lrbox}%
  \marginpar{\usebox{\@tufte@margin@floatbox}}%
  }

% Margin figure environment
\newenvironment{marginfigure}[1][-1.2ex]%
  {\begin{@tufte@margin@float}[#1]{figure}
  }
  {\end{@tufte@margin@float}}

% Margin table environment
\newenvironment{margintable}[1][-1.2ex]%
  {\begin{@tufte@margin@float}[#1]{table}
  }
  {\end{@tufte@margin@float}}

\makeatother

\begin{document}
  \begin{marginfigure}
    %\raggedright
    \rule{3cm}{2cm}
    \caption{A long caption so that we get at least two lines}
  \end{marginfigure}
\end{document}

Answer 1

You have a spurious space in the definition of marginfigure and margintable:

% Margin figure environment
\newenvironment{marginfigure}[1][-1.2ex]%
  {\begin{@tufte@margin@float}[#1]{figure}% <--- added '%'
  }
  {\end{@tufte@margin@float}}

% Margin table environment
\newenvironment{margintable}[1][-1.2ex]%
  {\begin{@tufte@margin@float}[#1]{table}% <--- added '%'
  }
  {\end{@tufte@margin@float}}

As a reference, see What is the use of percent signs (%) at the end of lines?. Alternatively, you could insert an \ignorespaces at the start of the environments.