Clojurians Log v2

Normally it's done by throwing an exception. But I understand you want more of a "warn". I'd say that's normally done by printing. Since you'd be connected to a REPL, you would see something being printed. This is what the compiler does to notify you of warnings.

throw exception?

is unreachable code intentionally added by the macro?

I don’t want to throw an exception. the code will still work.

I just want to notify the ide to annotate something.

I don't know if cider annotate anything. Maybe look at clojure-lsp and how it can unravel macroses

imagine for a very very simple case that I have a my-if macro, and during the macro expansion, it realizes that the else part is unreachable. the code still works, but it would be nice to notify the user of this fact.

in common lisp and slime, the macro expander is allowed to raise a warning condition.

conditions being a generalization of exceptions used in CL

I'm not aware if similar technic exist in clojure

I think the most used mechanism for this would be clj-kondo hooks. https://github.com/clj-kondo/clj-kondo/blob/master/doc/hooks.md