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|
//! Parser recognizes special macro syntax, `$var` and `$(repeat)*`, in token
//! trees.
use smallvec::SmallVec;
use syntax::SmolStr;
use crate::{tt_iter::TtIter, ExpandError};
#[derive(Debug)]
pub(crate) enum Op<'a> {
Var { name: &'a SmolStr, kind: Option<&'a SmolStr> },
Repeat { subtree: &'a tt::Subtree, kind: RepeatKind, separator: Option<Separator> },
TokenTree(&'a tt::TokenTree),
}
#[derive(Clone, Debug, PartialEq, Eq)]
pub(crate) enum RepeatKind {
ZeroOrMore,
OneOrMore,
ZeroOrOne,
}
#[derive(Clone, Debug, Eq)]
pub(crate) enum Separator {
Literal(tt::Literal),
Ident(tt::Ident),
Puncts(SmallVec<[tt::Punct; 3]>),
}
// Note that when we compare a Separator, we just care about its textual value.
impl PartialEq for Separator {
fn eq(&self, other: &Separator) -> bool {
use Separator::*;
match (self, other) {
(Ident(ref a), Ident(ref b)) => a.text == b.text,
(Literal(ref a), Literal(ref b)) => a.text == b.text,
(Puncts(ref a), Puncts(ref b)) if a.len() == b.len() => {
let a_iter = a.iter().map(|a| a.char);
let b_iter = b.iter().map(|b| b.char);
a_iter.eq(b_iter)
}
_ => false,
}
}
}
pub(crate) fn parse_template(
template: &tt::Subtree,
) -> impl Iterator<Item = Result<Op<'_>, ExpandError>> {
parse_inner(template, Mode::Template)
}
pub(crate) fn parse_pattern(
pattern: &tt::Subtree,
) -> impl Iterator<Item = Result<Op<'_>, ExpandError>> {
parse_inner(pattern, Mode::Pattern)
}
#[derive(Clone, Copy)]
enum Mode {
Pattern,
Template,
}
fn parse_inner(src: &tt::Subtree, mode: Mode) -> impl Iterator<Item = Result<Op<'_>, ExpandError>> {
let mut src = TtIter::new(src);
std::iter::from_fn(move || {
let first = src.next()?;
Some(next_op(first, &mut src, mode))
})
}
macro_rules! err {
($($tt:tt)*) => {
ExpandError::UnexpectedToken
};
}
macro_rules! bail {
($($tt:tt)*) => {
return Err(err!($($tt)*))
};
}
fn next_op<'a>(
first: &'a tt::TokenTree,
src: &mut TtIter<'a>,
mode: Mode,
) -> Result<Op<'a>, ExpandError> {
let res = match first {
tt::TokenTree::Leaf(tt::Leaf::Punct(tt::Punct { char: '$', .. })) => {
// Note that the '$' itself is a valid token inside macro_rules.
let second = match src.next() {
None => return Ok(Op::TokenTree(first)),
Some(it) => it,
};
match second {
tt::TokenTree::Subtree(subtree) => {
let (separator, kind) = parse_repeat(src)?;
Op::Repeat { subtree, separator, kind }
}
tt::TokenTree::Leaf(leaf) => match leaf {
tt::Leaf::Punct(punct) => {
static UNDERSCORE: SmolStr = SmolStr::new_inline("_");
if punct.char != '_' {
return Err(ExpandError::UnexpectedToken);
}
let name = &UNDERSCORE;
let kind = eat_fragment_kind(src, mode)?;
Op::Var { name, kind }
}
tt::Leaf::Ident(ident) => {
let name = &ident.text;
let kind = eat_fragment_kind(src, mode)?;
Op::Var { name, kind }
}
tt::Leaf::Literal(lit) => {
if is_boolean_literal(lit) {
let name = &lit.text;
let kind = eat_fragment_kind(src, mode)?;
Op::Var { name, kind }
} else {
bail!("bad var 2");
}
}
},
}
}
tt => Op::TokenTree(tt),
};
Ok(res)
}
fn eat_fragment_kind<'a>(
src: &mut TtIter<'a>,
mode: Mode,
) -> Result<Option<&'a SmolStr>, ExpandError> {
if let Mode::Pattern = mode {
src.expect_char(':').map_err(|()| err!("bad fragment specifier 1"))?;
let ident = src.expect_ident().map_err(|()| err!("bad fragment specifier 1"))?;
return Ok(Some(&ident.text));
};
Ok(None)
}
fn is_boolean_literal(lit: &tt::Literal) -> bool {
matches!(lit.text.as_str(), "true" | "false")
}
fn parse_repeat(src: &mut TtIter) -> Result<(Option<Separator>, RepeatKind), ExpandError> {
let mut separator = Separator::Puncts(SmallVec::new());
for tt in src {
let tt = match tt {
tt::TokenTree::Leaf(leaf) => leaf,
tt::TokenTree::Subtree(_) => return Err(ExpandError::InvalidRepeat),
};
let has_sep = match &separator {
Separator::Puncts(puncts) => !puncts.is_empty(),
_ => true,
};
match tt {
tt::Leaf::Ident(_) | tt::Leaf::Literal(_) if has_sep => {
return Err(ExpandError::InvalidRepeat)
}
tt::Leaf::Ident(ident) => separator = Separator::Ident(ident.clone()),
tt::Leaf::Literal(lit) => separator = Separator::Literal(lit.clone()),
tt::Leaf::Punct(punct) => {
let repeat_kind = match punct.char {
'*' => RepeatKind::ZeroOrMore,
'+' => RepeatKind::OneOrMore,
'?' => RepeatKind::ZeroOrOne,
_ => {
match &mut separator {
Separator::Puncts(puncts) => {
if puncts.len() == 3 {
return Err(ExpandError::InvalidRepeat);
}
puncts.push(punct.clone())
}
_ => return Err(ExpandError::InvalidRepeat),
}
continue;
}
};
let separator = if has_sep { Some(separator) } else { None };
return Ok((separator, repeat_kind));
}
}
}
Err(ExpandError::InvalidRepeat)
}
|
