TIL eager macro expansion can mean very different things.
Rust macros must expand to valid code, so eager macro expansion allows illegal intermediate states: https://docs.rs/eager/0.1.0/eager/macro.eager.html#macro-expansions
Elisp macros are expanded at runtime unless expansion is eager: https://dgutov.github.io/blog/2013/04/07/emacs-24-dot-3-s-killer-feature-eager-macro-expansion/