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Implement ${count()} metavariable expression

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Ryo Yoshida 2023-05-28 19:54:36 +09:00
parent 9ebaa85d37
commit 0d4d1d7e3b
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7 changed files with 389 additions and 29 deletions
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32
crates/mbe/src/parser.rs
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@ -52,7 +52,8 @@ impl MetaTemplate {
pub(crate) enum Op {
Var { name: SmolStr, kind: Option<MetaVarKind>, id: tt::TokenId },
Ignore { name: SmolStr, id: tt::TokenId },
Index { depth: u32 },
Index { depth: usize },
Count { name: SmolStr, depth: Option<usize> },
Repeat { tokens: MetaTemplate, kind: RepeatKind, separator: Option<Separator> },
Subtree { tokens: MetaTemplate, delimiter: tt::Delimiter },
Literal(tt::Literal),
@ -295,9 +296,13 @@ fn parse_metavar_expr(src: &mut TtIter<'_>) -> Result<Op, ()> {
let ident = args.expect_ident()?;
Op::Ignore { name: ident.text.clone(), id: ident.span }
}
"index" => {
let depth = if args.len() == 0 { 0 } else { args.expect_u32_literal()? };
Op::Index { depth }
"index" => Op::Index { depth: parse_depth(&mut args)? },
"count" => {
let ident = args.expect_ident()?;
// `${count(t)}` and `${count(t,)}` have different meanings. Not sure if this is a bug
// but that's how it's implemented in rustc as of this writing. See rust-lang/rust#111904.
let depth = if try_eat_comma(&mut args) { Some(parse_depth(&mut args)?) } else { None };
Op::Count { name: ident.text.clone(), depth }
}
_ => return Err(()),
};
@ -308,3 +313,22 @@ fn parse_metavar_expr(src: &mut TtIter<'_>) -> Result<Op, ()> {
Ok(op)
}
fn parse_depth(src: &mut TtIter<'_>) -> Result<usize, ()> {
if src.len() == 0 {
Ok(0)
} else if let tt::Leaf::Literal(lit) = src.expect_literal()? {
// Suffixes are not allowed.
lit.text.parse().map_err(|_| ())
} else {
Err(())
}
}
fn try_eat_comma(src: &mut TtIter<'_>) -> bool {
if let Some(tt::TokenTree::Leaf(tt::Leaf::Punct(tt::Punct { char: ',', .. }))) = src.peek_n(0) {
let _ = src.next();
return true;
}
false
}