Nested use of \ifcsname needs protection

Question

I have a macro \command to ensure that the names of macros in my documentation are consistently formatted. Been work great, until I had an urge to procrastinate and had this brilliant idea that I can easily catch most spelling errors of the macro names, by checking that the macro exists.

Seems simple enough. So I added:

\ifcsname#1\endcsname%
\else%
    \par\textbf{\textcolor{red}{\textbackslash#1} is not defined.}
\fi%

to the macro that does the formating, where #1 is the name of the macro. This seems to work fine in the basic case as illustrated by the MWE below that produces:

and correctly tells me that bfseriess and \foo are not defined.

However, if I attempt to use this in a nested fashion

\command{foo=\command{MyDef}}

I get the error message

Missing \endcsname inserted.

<to be read again> 
              \protect 
l.25 \command{foo=\command{MyDef}}

Question:

I have a feeling that the solution is in the question listed in the references but I don't know exactly how to \protect things. So, what changes can I make to the \command macro so that I can uncomment the last line in the MWE and the proper error messages.

Reference:

• What is the difference between Fragile and Robust commands?

Code:

\documentclass{article}
\usepackage{xcolor}

%% The last line should not produce any error 
%% messages (red text) if these two are defined.
%
%\newcommand*{\foo}{}%
%\newcommand*{\MyDef}{}%

\newcommand{\command}[1]{%
    \textbf{\textbackslash#1}%
    %% Since this is used to typeset macro names, we
    %% can check for typos by ensuring the macro exists
    \ifcsname#1\endcsname%
    \else%
        \par\fcolorbox{red}{red!20}{\textcolor{blue}{\textbackslash#1} is not defined.}
    \fi%
}%


\begin{document}
To bold text use \command{textbf} or \command{bfseriess}.

A useful token is \command{foo}.

This token needs to be set with: 
%\command{foo=\command{MyDef}}
\end{document}

Answer 1

I'm not at all sure what the intended behaviour is when the argument to \command isn't a command name, but this does something:

\documentclass{article}
\usepackage{xcolor}

%% The last line should not produce any error 
%% messages (red text) if these two are defined.
%
%\newcommand*{\foo}{}%
%\newcommand*{\MyDef}{}%

\protected\def\command#1{%
    \textbf{\textbackslash#1}%
    %% Since this is used to typeset macro names, we
    %% can check for typos by ensuring the macro exists
    \ifcsname\detokenize{#1}\endcsname%
    \else%
        \par\fcolorbox{red}{red!20}{\textcolor{blue}{\textbackslash#1} is not defined.}
    \fi%
}%


\begin{document}
To bold text use \command{textbf} or \command{bfseriess}.

A useful token is \command{foo}.

This token needs to be set with: 
\command{foo=\command{MyDef}}
\end{document}

---

Or updated as requested in comments to strip the argument before =

\documentclass{article}
\usepackage{xcolor}

%% The last line should not produce any error 
%% messages (red text) if these two are defined.
%
%\newcommand*{\foo}{}%
%\newcommand*{\MyDef}{}%

\protected\def\command#1{%
    \textbf{\textbackslash#1}%
    %% Since this is used to typeset macro names, we
    %% can check for typos by ensuring the macro exists
    \ifcsname\expandafter\beforeeq\detokenize{#1}=\beforeeq\endcsname%
    \else%
        \par\fcolorbox{red}{red!20}{\textcolor{blue}{\textbackslash\expandafter\beforeeq\detokenize{#1}=\beforeeq} is not defined.}
    \fi%
}%

\def\beforeeq#1=#2\beforeeq{#1}

\begin{document}
To bold text use \command{textbf} or \command{bfseriess}.

A useful token is \command{foo}.

This token needs to be set with: 
\command{foo=\command{MyDef}}
\end{document}

Answer 2

By simply imitating the definition of \doifundefined from ConTeXt (defined in file syst-gen.mkii), adding \detokenize to the definition works.

\newcommand\command[1]
    {\textbf{\textbackslash#1}%
    %% Since this is used to typeset macro names, we
    %% can check for typos by ensuring the macro exists
     \ifcsname\detokenize{#1}\endcsname%
    \else%
        \par\fcolorbox{red}{red!20}{\textcolor{blue}{\textbackslash#1} is not defined.}
    \fi%
}% 

Answer 3

I would go for something like:

\documentclass{article}
\begin{document}
\makeatletter
\def\mytypeset#1{%
\def\command##1{%
     \ifcsname##1\endcsname%
        \expandafter\@firstoftwo
    \else%
        \expandafter\@secondoftwo
    \fi%
}%
 \def\z{\detokenize{#1}}
 \command{\z}{\fbox{TRUE}}{\fbox{FALSE}}
}


\mytypeset{deff{f}f}

\mytypeset{def}

\mytypeset{foo=\command{MyDef}}
\end{document}

Note that when you are checking for a "nested" command, as a matter of fact the code checks to see if:

  foo=\command{MyDef}

is a defined macro! With csname...endcsname, arbitrary commands of any characters ca be used. You can have a command !$%.#!.o>,p\def} for example. You can add the follow snippet to the example that demonstrates the concept.

\expandafter\def\csname My$Def\endcsname{MyDef...}

\mytypeset{My$Def}

% prints MyDef...
\csname My$Def\endcsname

\My$Def now is a command and prints MyDef.., when executed.