It’s just compile time code execution.

The difference between those macros („procedural macros“) and regular macros is that while regular macros are pretty much only templated code that is unfolded, proc macros contain code that is run at compile time, so they are more powerful but also more dangerous from a security perspective as you would expect just compiling a program to be safe.

Also: is copy pasting ChatGPT answers a thing now even when you, as you said, don’t even know what it means??