I guess I see what you mean if we want to get very technical about what a syntax extension is. But I think for the purpose of this discussion, it’s reasonable to think of macro_rules! as a part of the Rust language. Practically speaking, it is syntax provided by the language team, not just users of the language who are free to extend the syntax by usingmacro_rules! to do so.
https://fprijate.github.io/tlborm/mbe-macro-rules.html#%3A~%3Atext=macro_rules!+With%2Cfollowing+form%3A
I guess I see what you mean if we want to get very technical about what a syntax extension is. But I think for the purpose of this discussion, it’s reasonable to think of
macro_rules!as a part of the Rust language. Practically speaking, it is syntax provided by the language team, not just users of the language who are free to extend the syntax by usingmacro_rules!to do so.