I have a nice counter example why "config files as source code" is a bad idea.

The emscripten SDK (compile C/C++ to WASM) writes a config file as python source file when it is installed. At first glance it looks like a fairly simple key/value config file, but it cannot be parsed by a 3rd-party-tool (for instance to extract the paths to the installed emscripten SDK) unless the file is evaluated with a full-blown python interpreter.

I don't understand how this can be considered a "good idea" under any circumstances ;)