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use crate::{tt, mbe};
use crate::tt_cursor::TtCursor;
/// This module parses a raw `tt::TokenStream` into macro-by-example token
/// stream. This is a *mostly* identify function, expect for handling of
/// `$var:tt_kind` and `$(repeat),*` constructs.
pub fn parse(tt: &tt::Subtree) -> Option<mbe::MacroRules> {
let mut parser = TtCursor::new(tt);
let mut rules = Vec::new();
while !parser.is_eof() {
rules.push(parse_rule(&mut parser)?)
}
Some(mbe::MacroRules { rules })
}
fn parse_rule(p: &mut TtCursor) -> Option<mbe::Rule> {
let lhs = parse_subtree(p.eat_subtree()?)?;
p.expect_char('=')?;
p.expect_char('>')?;
let rhs = parse_subtree(p.eat_subtree()?)?;
Some(mbe::Rule { lhs, rhs })
}
fn parse_subtree(tt: &tt::Subtree) -> Option<mbe::Subtree> {
let mut token_trees = Vec::new();
let mut p = TtCursor::new(tt);
while let Some(tt) = p.eat() {
let child: mbe::TokenTree = match tt {
tt::TokenTree::Leaf(leaf) => match leaf {
tt::Leaf::Punct(tt::Punct { char: '$' }) => {
if p.at_ident().is_some() {
mbe::Leaf::from(parse_var(&mut p)?).into()
} else {
parse_repeat(&mut p)?.into()
}
}
tt::Leaf::Punct(tt::Punct { char }) => {
mbe::Leaf::from(mbe::Punct { char: *char }).into()
}
tt::Leaf::Ident(tt::Ident { text }) => {
mbe::Leaf::from(mbe::Ident { text: text.clone() }).into()
}
tt::Leaf::Literal(tt::Literal { text }) => {
mbe::Leaf::from(mbe::Literal { text: text.clone() }).into()
}
},
tt::TokenTree::Subtree(subtree) => parse_subtree(subtree)?.into(),
};
token_trees.push(child);
}
Some(mbe::Subtree {
token_trees,
delimiter: tt.delimiter,
})
}
fn parse_var(p: &mut TtCursor) -> Option<mbe::Var> {
let ident = p.eat_ident().unwrap();
let text = ident.text.clone();
let kind = if p.at_char(':') {
p.bump();
if let Some(ident) = p.eat_ident() {
Some(ident.text.clone())
} else {
p.rev_bump();
None
}
} else {
None
};
Some(mbe::Var { text, kind })
}
fn parse_repeat(p: &mut TtCursor) -> Option<mbe::Repeat> {
let subtree = p.eat_subtree().unwrap();
let subtree = parse_subtree(subtree)?;
let sep = p.eat_punct()?;
let (separator, rep) = match sep.char {
'*' | '+' | '?' => (None, sep.char),
char => (Some(mbe::Punct { char }), p.eat_punct()?.char),
};
let kind = match rep {
'*' => mbe::RepeatKind::ZeroOrMore,
'+' => mbe::RepeatKind::OneOrMore,
'?' => mbe::RepeatKind::ZeroOrMore,
_ => return None,
};
p.bump();
Some(mbe::Repeat {
subtree,
kind,
separator,
})
}
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