notexcode.sty

%%
%% This is file 'notexcode.sty'.
%%
%% Copyright 2019 Takuto ASAKURA (wtsnjp)
%%   GitHub:   https://github.com/wtsnjp
%%   Twitter:  @wtsnjp
%%
%% This package is distributed under the MIT License.
%%

% -------------------------------------------------- declarations

\RequirePackage{expl3}
\ProvidesExplPackage {notexcode} {2019/07/08} {0.1.0}
  {Let's stop writing TeX macro language unconsciously}

% -------------------------------------------------- messages

\msg_new:nnn { notexcode } { primitive-found }
  {
    There~is~a~TeX~primitive~\msg_line_context: :~\exp_not:N #1
  }

% -------------------------------------------------- imprementation

\cs_new:Npn \ntcd_notexcode:n #1
  {
    \tl_map_function:nN { #1 } \__ntcd_warn_if_primitive:N
    \__ntcd_exec:n { #1 }
  }

\cs_new:Npn \__ntcd_warn_if_primitive:N #1
  {
    \int_compare:nNnTF { \tl_count:n { #1 } } = { \c_one_int }
      {
        \token_if_primitive:NT #1
          { \msg_warning:nnn { notexcode } { primitive-found } { #1 } }
      }
      { \tl_map_function:nN { #1 } \__ntcd_warn_if_primitive:N }
  }

\cs_new:Npn \__ntcd_exec:n #1 { #1 }

% -------------------------------------------------- LaTeX2e interface

%% \notexcode { <code> }
\cs_new_eq:NN \notexcode \ntcd_notexcode:n

% vim: ft=expl3 nospell:
%% EOF

test.tex

\documentclass{article}

\usepackage{notexcode}
\notexcode{\newcommand{\foo}{foo}}% LaTeX code
\notexcode{\def\bar{bar}}% TeX code

\begin{document}
Hello {\foo} and {\bar}!
\end{document}

Processing test.tex with

$ latex test.tex

will show you a warning message which looks like

Package notexcode Warning: There is a TeX primitive on line 5: \def

in your terminal and the log file.