Where macros live

Decided

D-0077, settled by the language’s author: part of spec §18. Older text cites it as 18.77.

A macro is a declaration: private by default, pub macro to export, invoked as #dep::name from a dependency, usable before its declaration. An expansion may invoke macros, to a depth of 64, but may not declare one, so the set of macros is known before any expansion runs (§12.5)