macro_rules-style syntax matching for procedural macros.
This crate is work-in-progress, incomplete, and probably buggy!
Example:
rust
rules!(tokens => {
($finish:ident ($($found:ident)*) # [ $($inner:tt)* ] $($rest:tt)*) => {
for f in found {
do_something(finish, f, inner, rest[0]);
}
}
(foo $($bar:expr)?) => {
match bar {
Some(e) => foo_with_expr(e),
None => foo_no_expr(),
}
}
});
Add proc-macro-rules = "0.3.0" (or proc-macro-rules = "0.2.1" for versions between 1.31 and 1.56) to your Cargo.toml.
Import the rules macro with use proc_macro_rules::rules, then use with rules!(tokens => { branches }); where tokens is an expression which evaluates to a TokenStream (such as the argument in the definition of a procedural macro).
Each branch in branches should have the form ( pattern ) => { body } where pattern is a macro-rules-style pattern (using all the same syntax for meta-variables, AST nodes, repetition, etc.) and body is rust code executed when the pattern is matched. Within body, any meta-variables in the pattern are bound to variables of an appropriate type from either the proc_macro2 or syn crates. Where a meta-variable is inside a repetition or option clause, it will be wrapped in a Vec or Option, respectively.
For example, in the first branch in the above example ident has type syn::Ident and inner has type Vec<proc_macro2::TokenTree>.
Use cargo build to build, cargo test --all to test.
Contributions are very welcome! It would be great to know things which are missing or incorrect (in general we should have the same behaviour as macro_rules, so anything different is incorrect). Issues, code, docs, tests, and corrections are all welcome.