rust-syntax-macros-declarative

The mechanics of declarative macros (macro_rules!) in Rust: matcher and transcriber syntax, every fragment specifier, repetition operators, follow-set restrictions, mixed-site hygiene, $crate, TT-munching recursion, #[macro_export] and #[macro_use] scoping, and the edition 2024 expr widening.

Cross-references: [[rust-syntax-macros-procedural]] (when to graduate to proc-macros) [[rust-syntax-edition-2024]] (edition 2024 expr widening, pat 2021 widening) [[rust-syntax-pattern-matching]] (same matcher-style mindset).

When to use this skill

User writes a macro_rules! my_macro { ... } and the matcher does not compile or does not match the call site
User asks "which fragment specifier should I use for X" (ident vs expr vs tt vs path)
User writes a repetition $( ... )* and gets E0617 ("ambiguity") or duplicate-binding errors
User writes #[macro_export] and the macro fails to find its own helper items from a downstream crate
User implements a counter / TT-muncher and hits "recursion limit reached"
User upgrades to edition 2024 and an expr fragment now matches _ or const { ... } where it did not before
User asks "what is $crate", "what is $tt", "why does my macro see my outer x and not the caller's x"
User mixes #[macro_use] with the 2018+ path-based import and is confused which one to use