Macro parsel::define_keywords
source · macro_rules! define_keywords { ($vis:vis mod $modname:ident { $($kw:ident => $name:ident;)* $(_ => $underscore_name:ident;)? }) => { ... }; (@private $string:expr => $name:ident;) => { ... }; }
Expand description
Declares a module containing custom keywords as defined by custom_keyword!
, and a
Keywords
marker type for CustomIdent
implementing
KeywordList
.
§Caveats
Due to a limitation in Rust’s macro system, if you want to match a bare underscore,
_
in itself, then you need to list it as the last item in the list of keywords.
define_keywords!{
mod kw {
foo => Foo;
bar => Bar;
quux => Quux;
_ => Underscore; // if present, the underscore has to be last
}
}
// Idiom for using `CustomIdent`
type MyIdent = CustomIdent<kw::Keywords>;
// Valid keywords in this language
let id_self: MyIdent = "self".parse()?;
assert_eq!(id_self, "self");
let id_async: MyIdent = "async".parse()?;
assert_eq!(id_async, "async");
let id_baz: MyIdent = "baz".parse()?;
assert_eq!(id_baz, "baz");
let id_multi_part: MyIdent = "multi_part".parse()?;
assert_eq!(id_multi_part, "multi_part");
let _: kw::Bar = "bar".parse()?;
let _: kw::Underscore = "_".parse()?;
// Invalid keywords
let invalid: Result<MyIdent> = "quux".parse();
assert_eq!(
invalid.unwrap_err().to_string(),
"expected identifier, found keyword",
);
let invalid_underscore: Result<MyIdent> = "_".parse();
assert_eq!(
invalid_underscore.unwrap_err().to_string(),
"expected identifier, found keyword",
);
let invalid_quux: Result<kw::Quux> = "somethingelse".parse();
assert_eq!(
invalid_quux.unwrap_err().to_string(),
"expected keyword `quux`",
);
let kw_bar = kw::Bar::default();
let kw_quux = kw::Quux::default();
let some_stream = quote![#kw_quux #kw_bar #kw_quux];
let actual_tokens: Vec<_> = some_stream.clone().into_iter().collect();
let expected_tokens = ["quux", "bar", "quux"].map(|x| TokenTree::from(ident(x)));
assert_eq!(some_stream.to_string(), "quux bar quux");
assert!(matches!(actual_tokens, expected_tokens));
// Ensure that the generated `Keywords` struct implements `KeywordList`
// and is default-constructible, trivially-copiable
fn assert_keyword_list<K>(_: K)
where
K: Copy + Default + KeywordList
{}
assert_keyword_list(kw::Keywords);