Redefine \newcommand to insert code at start and end of custom macros

Question

I would like to be able to insert code into the definitions of my custom macros, without having to modify each macro definition. This seemed like a simple case of redefining \newcommand, but this turns out not to be so easy (well for me anyway). I end up with:

Illegal parameter number in definition of \MacroB.
to be read again
1 l.45 \newcommand*{\MacroB}[1]{b#1b}

My guess is that somewhere I need to double up the # but I don't understand why, and guessing which ones need to be doubled up did not work. So perhaps that is not the problem.

Notes:

• The MWE below compiles fine -- one needs to uncomment the \def\EnableTrace{} to see the problem.
• The goal of this is to build up a stack trace of macros as they are being called.

Code:

%\def\EnableTrace{}
\documentclass{article}
%% All packages included here...
\usepackage{xparse}
\usepackage{letltxmacro}
%% Start of custom macros...
\ifdefined\EnableTrace
    \newcounter{NestingDepth}
    \newcommand{\StartMacro}[1]{%
        \typeout{*** DEBUG: (Depth=\arabic{NestingDepth}) Started macro "\string#1".}%
        \stepcounter{NestingDepth}%
    }%
    \newcommand{\EndMacro}[1]{%
        \addtocounter{NestingDepth}{-1}%
        \typeout{*** DEBUG: (Depth=\arabic{NestingDepth}) Completed macro "\string#1".}%
    }%
    % --------------
    \LetLtxMacro{\OldNewcommand}{\newcommand}%
    \RenewDocumentCommand{\newcommand}{%
        s%    #1 = * (ignored for now to keep the code below simple)
        m%    #2 = macro name
        O{1}% #3 = number of paramaters
        o%    #4 = default value for first optional parameter (if there is one)
        m%    #5 = code to execute
    }{%
        %
        \ifnum#3=1\relax
            \OldNewcommand{#2}{\StartMacro{#2}#5\EndMacro{#2}}%
        \else
            \IfBooleanTF{#4}{%
                % first parameter of macro being defined is optional, as default value is provided
                \OldNewcommand{#2}[#3][#4]{\StartMacro{#2}#5\EndMacro{#2}}%
            }{%
                % first parameter of macro being defined is mandatory
                \OldNewcommand{#2}[#3]{\StartMacro{#2}#5\EndMacro{#2}}%
            }%
        \fi
    }%
\fi
\newcommand{\MacroB}[1]{b#1b}%
\newcommand{\MacroA}[1]{a\MacroB{#1}a}%
\begin{document}
\MacroA{XXX}
\MacroB{YYY}
\end{document}

Answer 1

There are strange conditionals in your code. Moreover, \IfBooleanTF is for arguments of type s or t, not for o.

\documentclass{article}
\usepackage{xparse}

\newif\ifEnableTrace
\newcounter{NestingDepth}
\let\latexnewcommand\newcommand

\newcommand{\StartMacro}[1]{%
  \ifEnableTrace
    \typeout{**** DEBUG: (Depth=\arabic{NestingDepth}) Started macro `\string#1'.}%
    \stepcounter{NestingDepth}%
  \fi
}
\newcommand{\EndMacro}[1]{%
  \ifEnableTrace
    \addtocounter{NestingDepth}{-1}%
    \typeout{**** DEBUG: (Depth=\arabic{NestingDepth}) Completed macro `\string#1'.}%
  \fi
}

\NewDocumentCommand{\NewCommand}{smO{0}om}{%
  \IfBooleanTF{#1}
    {\IfNoValueTF{#4}{\latexnewcommand*{#2}[#3]}{\latexnewcommand*{#2}[#3][#4]}}%
    {\IfNoValueTF{#4}{\latexnewcommand{#2}[#3]}{\latexnewcommand{#2}[#3][#4]}}%
  {\StartMacro{#2}#5\EndMacro{#2}}%
}

% if you want to enable tracing
\let\newcommand\NewCommand

\newcommand*{\MacroB}[1]{b#1b}
\newcommand*{\MacroA}[1]{a\MacroB{#1}a}

\begin{document}

\MacroA{XXX}

\MacroB{YYY}

\EnableTracetrue

\MacroA{XXX}

\MacroB{YYY}

\end{document}

Here's the terminal output

**** DEBUG: (Depth=0) Started macro `\MacroA'.
**** DEBUG: (Depth=1) Started macro `\MacroB'.
**** DEBUG: (Depth=1) Completed macro `\MacroB'.
**** DEBUG: (Depth=0) Completed macro `\MacroA'.
**** DEBUG: (Depth=0) Started macro `\MacroB'.
**** DEBUG: (Depth=0) Completed macro `\MacroB'.

Answer 2

You use

\ifnum#3=1\relax
  \OldNewcommand{#2}{\StartMacro{#2}#5\EndMacro{#2}}%
\else

which… after checking you pass \newcommand\…[1] gives you something like \newcommand\…[0].

\ifnum#3=1\relax
  \OldNewcommand{#2}[1]{\StartMacro{#2}#5\EndMacro{#2}}%
\else

works.

By the way… why is it necessary the \ifnum at all? Just leaving the “else” branch of that \ifnum is enough:

%\def\EnableTrace{}
\documentclass{article}

%% All packages included here...
\usepackage{xparse}
\usepackage{letltxmacro}


%% Start of custom macros...
\ifdefined\EnableTrace
    \newcounter{NestingDepth}
    \newcommand*{\StartMacro}[1]{%
        \typeout{**** DEBUG: (Depth=\arabic{NestingDepth}) Started macro "\string#1".}%
        \stepcounter{NestingDepth}%
    }%
    \newcommand*{\EndMacro}[1]{%
        \addtocounter{NestingDepth}{-1}%
        \typeout{**** DEBUG: (Depth=\arabic{NestingDepth}) Completed macro "\string#1".}%
    }%
    % --------------
    \LetLtxMacro{\OldNewcommand}{\newcommand}%
    \RenewDocumentCommand{\newcommand}{%
        s%    #1 = * (ignored for now to keep the code below simple)
        m%    #2 = macro name
        O{1}% #3 = number of paramaters
        o%    #4 = default value for first optional parameter (if there is one)
        m%    #5 = code to execute
    }{%
        %
%       \ifnum#3=1\relax
%           \OldNewcommand{#2}{\StartMacro{#2}#5\EndMacro{#2}}%
%       \else
            \IfBooleanTF{#4}{%
                % first parameter of macro being defined is optional, as default value is provided
                \OldNewcommand{#2}[#3][#4]{\StartMacro{#2}#5\EndMacro{#2}}%
            }{%
                % first parameter of macro being defined is mandatory
                \OldNewcommand{#2}[#3]{\StartMacro{#2}#5\EndMacro{#2}}%
            }%
%       \fi
    }%
\fi

\newcommand*{\MacroB}[1]{b#1b}%
\newcommand*{\MacroA}[1]{a\MacroB{#1}a}%

\begin{document}
\MacroA{XXX}

\MacroB{YYY}
\end{document}

---

By the way, why not default the number of arguments to [0] so it works exactly as the original \newcommand?