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