babel conflicts with, I think, refcount

Question

The following code is continued from this post and this one. The following code compiles ok without babel but not with it. See the console output below. Is there a way resolve this issue?

\documentclass{article}
\usepackage{afterpage}
\usepackage[french]{babel} % no error if uncommented
\usepackage{mwe}
\usepackage{refcount}
\usepackage{tocloft}
\usepackage{xparse}
\usepackage{xwatermark} % ruled out

\newlistof{encl}{encl}{List of enclosed items}

\NewDocumentCommand
{\addencl}
{ m }
{
  \refstepcounter{encl}
  \addcontentsline{encl}{encl}{\theencl. #1}
}

\NewDocumentCommand
{\getencl}
{ m }
{
  E{\small NCL} \# \getrefnumber{#1}
}

\begin{document}
\newwatermark*[page=\getpagerefnumber{encl:bar}]{Bar}
\newwatermark*[page=\getpagerefnumber{encl:foo}]{Foo}

\listofencl

%\verb|\getrefnumber{encl:foo}|:\getrefnumber{encl:foo}
%\verb|\getpagerefnumber{encl:foo}|:\getpagerefnumber{encl:foo}

\getencl{encl:bar}~is~on~page~\getpagerefnumber{encl:bar}

\getencl{encl:foo}~is~on~page~\getpagerefnumber{encl:foo}

\newpage

%\refstepcounter{encl}
\addencl{Bar}\label{encl:bar}
\includegraphics[width=\linewidth]{example-image-a}

\newpage

\addencl{Foo}\label{encl:foo}
\includegraphics[width=\linewidth]{example-image-b}

%\newwatermark*{}


\end{document}

Console output:

ERROR: Missing \endcsname inserted.

--- TeX said --- \unskip l.36 \getencl{encl:bar} ~is~on~page~\getpagerefnumber{encl:bar} --- HELP --- From the .log file...

The control sequence marked should not appear between \csname and \endcsname.

Answer 1

When babel-french is active, the colon has a special meaning: “remove a possible space, add a nonbreaking space and print the colon”.

Indeed, you get

! Missing \endcsname inserted.
<to be read again> 
                   \unskip 

LaTeX makes provision so that \ref or \pageref take care of babel shorthands such as :, ? and ! for French and " for German. This cannot be done with \getrefnumber or \getpagerefnumber, because the protection needs assignments, in this case setting a switch so that the colon shorthand, for instance, produces a standard colon.

The refcount commands want and need to be fully expandable and so no assignment can take place during their job: expandability is the feature for which refcount was born.

In general, I recommend avoiding babel shorthands in labels.

For your specific problem, where you use no macros in the argument to \get(page)refnumber, you can use \detokenize:

\documentclass{article}
\usepackage[french]{babel} % no error if uncommented
\usepackage{refcount}
\usepackage{tocloft}
\usepackage{xparse}
\usepackage{xwatermark} % ruled out

\newlistof{encl}{encl}{List of enclosed items}

\NewDocumentCommand{\addencl}{ m }
 {%
  \refstepcounter{encl}%
  \addcontentsline{encl}{encl}{\theencl. #1}%
 }

\NewDocumentCommand{\getencl}{ m }
 {%
  E{\small NCL} \# \getrefnumber{\detokenize{#1}}%
 }

\newcommand{\bgetpagerefnumber}[1]{\getpagerefnumber{\detokenize{#1}}}

\begin{document}

\newwatermark*[page=\bgetpagerefnumber{encl:bar}]{Bar}
\newwatermark*[page=\bgetpagerefnumber{encl:foo}]{Foo}

\listofencl

\getencl{encl:bar}~is~on~page~\bgetpagerefnumber{encl:bar}

\getencl{encl:foo}~is~on~page~\bgetpagerefnumber{encl:foo}

\newpage

%\refstepcounter{encl}
\addencl{Bar}\label{encl:bar}
\includegraphics[width=\linewidth]{example-image-a}

\newpage

\addencl{Foo}\label{encl:foo}
\includegraphics[width=\linewidth]{example-image-b}

%\newwatermark*{}


\end{document}

But it's much simpler using encl-foo.

Answer 2

It will work if you use \string: in place of : at a number of locations.

\documentclass{article}
\usepackage{afterpage}
\usepackage[french]{babel} % no error if uncommented
\usepackage{mwe}
\usepackage{refcount}
\usepackage{tocloft}
\usepackage{xparse}
\usepackage{xwatermark} % ruled out

\newlistof{encl}{encl}{List of enclosed items}

\NewDocumentCommand
{\addencl}
{ m }
{
  \refstepcounter{encl}
  \addcontentsline{encl}{encl}{\theencl. #1}
}

\NewDocumentCommand
{\getencl}
{ m }
{
  E{\small NCL} \# \getrefnumber{#1}
}

\begin{document}
\newwatermark*[page=\getpagerefnumber{encl\string:bar}]{Bar}
\newwatermark*[page=\getpagerefnumber{encl\string:foo}]{Foo}

\listofencl

%\verb|\getrefnumber{encl:foo}|:\getrefnumber{encl:foo}
%\verb|\getpagerefnumber{encl:foo}|:\getpagerefnumber{encl:foo}

\getencl{encl\string:bar}~is~on~page~\getpagerefnumber{encl\string:bar}

\getencl{encl\string:foo}~is~on~page~\getpagerefnumber{encl\string:foo}

\newpage

%\refstepcounter{encl}
\addencl{Bar}\label{encl:bar}
\includegraphics[width=\linewidth]{example-image-a}

\newpage

\addencl{Foo}\label{encl:foo}
\includegraphics[width=\linewidth]{example-image-b}

%\newwatermark*{}


\end{document}

Output:

Note: I initially added \detokenize to the document commands defined, but there remained a problem with \getpagerefnumber.