//! An NFA-based parser, which is porting from rustc mbe parsing code
//!
//! See https://github.com/rust-lang/rust/blob/70b18bc2cbac4712020019f5bf57c00905373205/compiler/rustc_expand/src/mbe/macro_parser.rs
//! Here is a quick intro to how the parser works, copied from rustc:
//!
//! A 'position' is a dot in the middle of a matcher, usually represented as a
//! dot. For example `· a $( a )* a b` is a position, as is `a $( · a )* a b`.
//!
//! The parser walks through the input a character at a time, maintaining a list
//! of threads consistent with the current position in the input string: `cur_items`.
//!
//! As it processes them, it fills up `eof_items` with threads that would be valid if
//! the macro invocation is now over, `bb_items` with threads that are waiting on
//! a Rust non-terminal like `$e:expr`, and `next_items` with threads that are waiting
//! on a particular token. Most of the logic concerns moving the · through the
//! repetitions indicated by Kleene stars. The rules for moving the · without
//! consuming any input are called epsilon transitions. It only advances or calls
//! out to the real Rust parser when no `cur_items` threads remain.
//!
//! Example:
//!
//! ```text, ignore
//! Start parsing a a a a b against [· a $( a )* a b].
//!
//! Remaining input: a a a a b
//! next: [· a $( a )* a b]
//!
//! - - - Advance over an a. - - -
//!
//! Remaining input: a a a b
//! cur: [a · $( a )* a b]
//! Descend/Skip (first item).
//! next: [a $( · a )* a b] [a $( a )* · a b].
//!
//! - - - Advance over an a. - - -
//!
//! Remaining input: a a b
//! cur: [a $( a · )* a b] [a $( a )* a · b]
//! Follow epsilon transition: Finish/Repeat (first item)
//! next: [a $( a )* · a b] [a $( · a )* a b] [a $( a )* a · b]
//!
//! - - - Advance over an a. - - - (this looks exactly like the last step)
//!
//! Remaining input: a b
//! cur: [a $( a · )* a b] [a $( a )* a · b]
//! Follow epsilon transition: Finish/Repeat (first item)
//! next: [a $( a )* · a b] [a $( · a )* a b] [a $( a )* a · b]
//!
//! - - - Advance over an a. - - - (this looks exactly like the last step)
//!
//! Remaining input: b
//! cur: [a $( a · )* a b] [a $( a )* a · b]
//! Follow epsilon transition: Finish/Repeat (first item)
//! next: [a $( a )* · a b] [a $( · a )* a b] [a $( a )* a · b]
//!
//! - - - Advance over a b. - - -
//!
//! Remaining input: ''
//! eof: [a $( a )* a b ·]
//! ```
use std::rc::Rc;
use crate::{
expander::{Binding, Bindings, Fragment},
parser::{Op, OpDelimited, OpDelimitedIter, RepeatKind, Separator},
tt_iter::TtIter,
ExpandError, MetaTemplate,
};
use super::ExpandResult;
use parser::FragmentKind::*;
use smallvec::{smallvec, SmallVec};
use syntax::SmolStr;
impl Bindings {
fn push_optional(&mut self, name: &SmolStr) {
// FIXME: Do we have a better way to represent an empty token ?
// Insert an empty subtree for empty token
let tt = tt::Subtree::default().into();
self.inner.insert(name.clone(), Binding::Fragment(Fragment::Tokens(tt)));
}
fn push_empty(&mut self, name: &SmolStr) {
self.inner.insert(name.clone(), Binding::Empty);
}
fn bindings(&self) -> impl Iterator<Item = &Binding> {
self.inner.values()
}
}
macro_rules! err {
() => {
ExpandError::BindingError(format!(""))
};
($($tt:tt)*) => {
ExpandError::BindingError(format!($($tt)*))
};
}
#[derive(Clone, Debug, Default, PartialEq, Eq)]
pub(super) struct Match {
pub(super) bindings: Bindings,
/// We currently just keep the first error and count the rest to compare matches.
pub(super) err: Option<ExpandError>,
pub(super) err_count: usize,
/// How many top-level token trees were left to match.
pub(super) unmatched_tts: usize,
/// The number of bound variables
pub(super) bound_count: usize,
}
impl Match {
fn add_err(&mut self, err: ExpandError) {
let prev_err = self.err.take();
self.err = prev_err.or(Some(err));
self.err_count += 1;
}
}
/// Matching errors are added to the `Match`.
pub(super) fn match_(pattern: &MetaTemplate, input: &tt::Subtree) -> Match {
let mut res = match_loop(pattern, &input);
res.bound_count = count(res.bindings.bindings());
return res;
fn count<'a>(bindings: impl Iterator<Item = &'a Binding>) -> usize {
bindings
.map(|it| match it {
Binding::Fragment(_) => 1,
Binding::Empty => 1,
Binding::Nested(it) => count(it.iter()),
})
.sum()
}
}
#[derive(Debug, Clone)]
enum BindingKind {
Empty(SmolStr),
Optional(SmolStr),
Fragment(SmolStr, Fragment),
Nested(usize, usize),
}
#[derive(Debug, Clone)]
struct BindingsIdx(usize, usize);
#[derive(Debug, Clone)]
enum LinkNode<T> {
Node(T),
Parent { idx: usize, len: usize },
}
#[derive(Default)]
struct BindingsBuilder {
nodes: Vec<Vec<LinkNode<Rc<BindingKind>>>>,
nested: Vec<Vec<LinkNode<usize>>>,
}
impl BindingsBuilder {
fn alloc(&mut self) -> BindingsIdx {
let idx = self.nodes.len();
self.nodes.push(Vec::new());
let nidx = self.nested.len();
self.nested.push(Vec::new());
BindingsIdx(idx, nidx)
}
fn copy(&mut self, bindings: &BindingsIdx) -> BindingsIdx {
let idx = copy_parent(bindings.0, &mut self.nodes);
let nidx = copy_parent(bindings.1, &mut self.nested);
return BindingsIdx(idx, nidx);
fn copy_parent<T>(idx: usize, target: &mut Vec<Vec<LinkNode<T>>>) -> usize
where
T: Clone,
{
let new_idx = target.len();
let len = target[idx].len();
if len < 4 {
target.push(target[idx].clone())
} else {
target.push(vec![LinkNode::Parent { idx, len }]);
}
new_idx
}
}
fn push_empty(&mut self, idx: &mut BindingsIdx, var: &SmolStr) {
self.nodes[idx.0].push(LinkNode::Node(Rc::new(BindingKind::Empty(var.clone()))));
}
fn push_optional(&mut self, idx: &mut BindingsIdx, var: &SmolStr) {
self.nodes[idx.0].push(LinkNode::Node(Rc::new(BindingKind::Optional(var.clone()))));
}
fn push_fragment(&mut self, idx: &mut BindingsIdx, var: &SmolStr, fragment: Fragment) {
self.nodes[idx.0]
.push(LinkNode::Node(Rc::new(BindingKind::Fragment(var.clone(), fragment))));
}
fn push_nested(&mut self, parent: &mut BindingsIdx, child: &BindingsIdx) {
let BindingsIdx(idx, nidx) = self.copy(&child);
self.nodes[parent.0].push(LinkNode::Node(Rc::new(BindingKind::Nested(idx, nidx))));
}
fn push_default(&mut self, idx: &mut BindingsIdx) {
self.nested[idx.1].push(LinkNode::Node(idx.0));
let new_idx = self.nodes.len();
self.nodes.push(Vec::new());
idx.0 = new_idx;
}
fn build(self, idx: &BindingsIdx) -> Bindings {
let mut bindings = Bindings::default();
self.build_inner(&mut bindings, &self.nodes[idx.0]);
bindings
}
fn build_inner(&self, bindings: &mut Bindings, link_nodes: &Vec<LinkNode<Rc<BindingKind>>>) {
let mut nodes = Vec::new();
self.collect_nodes(&link_nodes, &mut nodes);
for cmd in nodes {
match &**cmd {
BindingKind::Empty(name) => {
bindings.push_empty(name);
}
BindingKind::Optional(name) => {
bindings.push_optional(name);
}
BindingKind::Fragment(name, fragment) => {
bindings.inner.insert(name.clone(), Binding::Fragment(fragment.clone()));
}
BindingKind::Nested(idx, nested_idx) => {
let mut nested_nodes = Vec::new();
self.collect_nested(*idx, *nested_idx, &mut nested_nodes);
for (idx, iter) in nested_nodes.into_iter().enumerate() {
for (key, value) in &iter.inner {
let bindings = bindings
.inner
.entry(key.clone())
.or_insert_with(|| Binding::Nested(Vec::new()));
if let Binding::Nested(it) = bindings {
// insert empty nested bindings before this one
while it.len() < idx {
it.push(Binding::Nested(Vec::new()));
}
it.push(value.clone());
}
}
}
}
}
}
}
fn collect_nested_ref<'a>(
&'a self,
id: usize,
len: usize,
nested_refs: &mut Vec<&'a Vec<LinkNode<Rc<BindingKind>>>>,
) {
self.nested[id].iter().take(len).for_each(|it| match it {
LinkNode::Node(id) => nested_refs.push(&self.nodes[*id]),
LinkNode::Parent { idx, len } => self.collect_nested_ref(*idx, *len, nested_refs),
});
}
fn collect_nested(&self, idx: usize, nested_idx: usize, nested: &mut Vec<Bindings>) {
let last = &self.nodes[idx];
let mut nested_refs = Vec::new();
self.nested[nested_idx].iter().for_each(|it| match *it {
LinkNode::Node(idx) => nested_refs.push(&self.nodes[idx]),
LinkNode::Parent { idx, len } => self.collect_nested_ref(idx, len, &mut nested_refs),
});
nested_refs.push(last);
nested_refs.into_iter().for_each(|iter| {
let mut child_bindings = Bindings::default();
self.build_inner(&mut child_bindings, &iter);
nested.push(child_bindings)
})
}
fn collect_nodes_ref<'a>(
&'a self,
id: usize,
len: usize,
nodes: &mut Vec<&'a Rc<BindingKind>>,
) {
self.nodes[id].iter().take(len).for_each(|it| match it {
LinkNode::Node(it) => nodes.push(it),
LinkNode::Parent { idx, len } => self.collect_nodes_ref(*idx, *len, nodes),
});
}
fn collect_nodes<'a>(
&'a self,
link_nodes: &'a Vec<LinkNode<Rc<BindingKind>>>,
nodes: &mut Vec<&'a Rc<BindingKind>>,
) {
link_nodes.iter().for_each(|it| match it {
LinkNode::Node(it) => nodes.push(it),
LinkNode::Parent { idx, len } => self.collect_nodes_ref(*idx, *len, nodes),
});
}
}
#[derive(Debug, Clone)]
struct MatchState<'t> {
/// The position of the "dot" in this matcher
dot: OpDelimitedIter<'t>,
/// Token subtree stack
/// When matching against matchers with nested delimited submatchers (e.g., `pat ( pat ( .. )
/// pat ) pat`), we need to keep track of the matchers we are descending into. This stack does
/// that where the bottom of the stack is the outermost matcher.
stack: SmallVec<[OpDelimitedIter<'t>; 4]>,
/// The "parent" matcher position if we are in a repetition. That is, the matcher position just
/// before we enter the repetition.
up: Option<Box<MatchState<'t>>>,
/// The separator if we are in a repetition.
sep: Option<Separator>,
/// The KleeneOp of this sequence if we are in a repetition.
sep_kind: Option<RepeatKind>,
/// Number of tokens of seperator parsed
sep_parsed: Option<usize>,
/// Matched meta variables bindings
bindings: BindingsIdx,
/// Cached result of meta variable parsing
meta_result: Option<(TtIter<'t>, ExpandResult<Option<Fragment>>)>,
/// Is error occuried in this state, will `poised` to "parent"
is_error: bool,
}
/// Process the matcher positions of `cur_items` until it is empty. In the process, this will
/// produce more items in `next_items`, `eof_items`, and `bb_items`.
///
/// For more info about the how this happens, see the module-level doc comments and the inline
/// comments of this function.
///
/// # Parameters
///
/// - `src`: the current token of the parser.
/// - `stack`: the "parent" frames of the token tree
/// - `res`: the match result to store errors
/// - `cur_items`: the set of current items to be processed. This should be empty by the end of a
/// successful execution of this function.
/// - `next_items`: the set of newly generated items. These are used to replenish `cur_items` in
/// the function `parse`.
/// - `eof_items`: the set of items that would be valid if this was the EOF.
/// - `bb_items`: the set of items that are waiting for the black-box parser.
/// - `error_items`: the set of items in errors, used for error-resilient parsing
fn match_loop_inner<'t>(
src: TtIter<'t>,
stack: &[TtIter<'t>],
res: &mut Match,
bindings_builder: &mut BindingsBuilder,
cur_items: &mut SmallVec<[MatchState<'t>; 1]>,
bb_items: &mut SmallVec<[MatchState<'t>; 1]>,
next_items: &mut Vec<MatchState<'t>>,
eof_items: &mut SmallVec<[MatchState<'t>; 1]>,
error_items: &mut SmallVec<[MatchState<'t>; 1]>,
) {
macro_rules! try_push {
($items: expr, $it:expr) => {
if $it.is_error {
error_items.push($it);
} else {
$items.push($it);
}
};
}
while let Some(mut item) = cur_items.pop() {
while item.dot.is_eof() {
match item.stack.pop() {
Some(frame) => {
item.dot = frame;
item.dot.next();
}
None => break,
}
}
let op = match item.dot.peek() {
None => {
// We are at or past the end of the matcher of `item`.
if item.up.is_some() {
if item.sep_parsed.is_none() {
// Get the `up` matcher
let mut new_pos = *item.up.clone().unwrap();
new_pos.bindings = bindings_builder.copy(&new_pos.bindings);
// Add matches from this repetition to the `matches` of `up`
bindings_builder.push_nested(&mut new_pos.bindings, &item.bindings);
// Move the "dot" past the repetition in `up`
new_pos.dot.next();
new_pos.is_error = new_pos.is_error || item.is_error;
cur_items.push(new_pos);
}
// Check if we need a separator.
// We check the separator one by one
let sep_idx = *item.sep_parsed.as_ref().unwrap_or(&0);
let sep_len = item.sep.as_ref().map_or(0, Separator::tt_count);
if item.sep.is_some() && sep_idx != sep_len {
let sep = item.sep.as_ref().unwrap();
if src.clone().expect_separator(&sep, sep_idx) {
item.dot.next();
item.sep_parsed = Some(sep_idx + 1);
try_push!(next_items, item);
}
}
// We don't need a separator. Move the "dot" back to the beginning of the matcher
// and try to match again UNLESS we are only allowed to have _one_ repetition.
else if item.sep_kind != Some(RepeatKind::ZeroOrOne) {
item.dot = item.dot.reset();
item.sep_parsed = None;
bindings_builder.push_default(&mut item.bindings);
cur_items.push(item);
}
} else {
// If we are not in a repetition, then being at the end of a matcher means that we have
// reached the potential end of the input.
try_push!(eof_items, item);
}
continue;
}
Some(it) => it,
};
// We are in the middle of a matcher.
match op {
OpDelimited::Op(Op::Repeat { tokens, kind, separator }) => {
if matches!(kind, RepeatKind::ZeroOrMore | RepeatKind::ZeroOrOne) {
let mut new_item = item.clone();
new_item.bindings = bindings_builder.copy(&new_item.bindings);
new_item.dot.next();
let mut vars = Vec::new();
collect_vars(&mut vars, tokens);
for var in vars {
bindings_builder.push_empty(&mut new_item.bindings, &var);
}
cur_items.push(new_item);
}
cur_items.push(MatchState {
dot: tokens.iter_delimited(None),
stack: Default::default(),
up: Some(Box::new(item)),
sep: separator.clone(),
sep_kind: Some(*kind),
sep_parsed: None,
bindings: bindings_builder.alloc(),
meta_result: None,
is_error: false,
})
}
OpDelimited::Op(Op::Subtree { tokens, delimiter }) => {
if let Ok(subtree) = src.clone().expect_subtree() {
if subtree.delimiter_kind() == delimiter.map(|it| it.kind) {
item.stack.push(item.dot);
item.dot = tokens.iter_delimited(delimiter.as_ref());
cur_items.push(item);
}
}
}
OpDelimited::Op(Op::Var { kind, name, .. }) => {
if let Some(kind) = kind {
let mut fork = src.clone();
let match_res = match_meta_var(kind.as_str(), &mut fork);
match match_res.err {
None => {
// Some meta variables are optional (e.g. vis)
if match_res.value.is_some() {
item.meta_result = Some((fork, match_res));
try_push!(bb_items, item);
} else {
bindings_builder.push_optional(&mut item.bindings, &name);
item.dot.next();
cur_items.push(item);
}
}
Some(err) => {
res.add_err(err);
match match_res.value {
Some(fragment) => {
bindings_builder.push_fragment(
&mut item.bindings,
&name,
fragment,
);
}
_ => {}
}
item.is_error = true;
error_items.push(item);
}
}
}
}
OpDelimited::Op(Op::Leaf(leaf)) => {
if let Err(err) = match_leaf(&leaf, &mut src.clone()) {
res.add_err(err);
item.is_error = true;
} else {
item.dot.next();
}
try_push!(next_items, item);
}
OpDelimited::Open => {
if matches!(src.clone().next(), Some(tt::TokenTree::Subtree(..))) {
item.dot.next();
try_push!(next_items, item);
}
}
OpDelimited::Close => {
let is_delim_closed = src.peek_n(0).is_none() && !stack.is_empty();
if is_delim_closed {
item.dot.next();
try_push!(next_items, item);
}
}
}
}
}
fn match_loop(pattern: &MetaTemplate, src: &tt::Subtree) -> Match {
let mut src = TtIter::new(src);
let mut stack: SmallVec<[TtIter; 1]> = SmallVec::new();
let mut res = Match::default();
let mut error_recover_item = None;
let mut bindings_builder = BindingsBuilder::default();
let mut cur_items = smallvec![MatchState {
dot: pattern.iter_delimited(None),
stack: Default::default(),
up: None,
sep: None,
sep_kind: None,
sep_parsed: None,
bindings: bindings_builder.alloc(),
is_error: false,
meta_result: None,
}];
let mut next_items = vec![];
loop {
let mut bb_items = SmallVec::new();
let mut eof_items = SmallVec::new();
let mut error_items = SmallVec::new();
stdx::always!(next_items.is_empty());
match_loop_inner(
src.clone(),
&stack,
&mut res,
&mut bindings_builder,
&mut cur_items,
&mut bb_items,
&mut next_items,
&mut eof_items,
&mut error_items,
);
stdx::always!(cur_items.is_empty());
if error_items.len() > 0 {
error_recover_item = error_items.pop().map(|it| it.bindings);
} else if eof_items.len() > 0 {
error_recover_item = Some(eof_items[0].bindings.clone());
}
// We need to do some post processing after the `match_loop_inner`.
// If we reached the EOF, check that there is EXACTLY ONE possible matcher. Otherwise,
// either the parse is ambiguous (which should never happen) or there is a syntax error.
if src.peek_n(0).is_none() && stack.is_empty() {
if eof_items.len() == 1 {
// remove all errors, because it is the correct answer !
res = Match::default();
res.bindings = bindings_builder.build(&eof_items[0].bindings);
} else {
// Error recovery
if let Some(item) = error_recover_item {
res.bindings = bindings_builder.build(&item);
}
res.add_err(ExpandError::UnexpectedToken);
}
return res;
}
// If there are no possible next positions AND we aren't waiting for the black-box parser,
// then there is a syntax error.
//
// Another possibility is that we need to call out to parse some rust nonterminal
// (black-box) parser. However, if there is not EXACTLY ONE of these, something is wrong.
if (bb_items.is_empty() && next_items.is_empty())
|| (!bb_items.is_empty() && !next_items.is_empty())
|| bb_items.len() > 1
{
res.unmatched_tts += src.len();
while let Some(it) = stack.pop() {
src = it;
res.unmatched_tts += src.len();
}
res.add_err(err!("leftover tokens"));
if let Some(error_reover_item) = error_recover_item {
res.bindings = bindings_builder.build(&error_reover_item);
}
return res;
}
// Dump all possible `next_items` into `cur_items` for the next iteration.
else if !next_items.is_empty() {
// Now process the next token
cur_items.extend(next_items.drain(..));
match src.next() {
Some(tt::TokenTree::Subtree(subtree)) => {
stack.push(src.clone());
src = TtIter::new(subtree);
}
None if !stack.is_empty() => src = stack.pop().unwrap(),
_ => (),
}
}
// Finally, we have the case where we need to call the black-box parser to get some
// nonterminal.
else {
stdx::always!(bb_items.len() == 1);
let mut item = bb_items.pop().unwrap();
if let Some(OpDelimited::Op(Op::Var { name, .. })) = item.dot.peek() {
let (iter, match_res) = item.meta_result.take().unwrap();
match match_res.value {
Some(fragment) => {
bindings_builder.push_fragment(&mut item.bindings, &name, fragment);
}
None if match_res.err.is_none() => {
bindings_builder.push_optional(&mut item.bindings, &name);
}
_ => {}
}
if let Some(err) = match_res.err {
res.add_err(err);
}
src = iter.clone();
item.dot.next();
} else {
unreachable!()
}
cur_items.push(item);
}
stdx::always!(!cur_items.is_empty());
}
}
fn match_leaf(lhs: &tt::Leaf, src: &mut TtIter) -> Result<(), ExpandError> {
let rhs = match src.expect_leaf() {
Ok(l) => l,
Err(()) => {
return Err(err!("expected leaf: `{}`", lhs));
}
};
match (lhs, rhs) {
(
tt::Leaf::Punct(tt::Punct { char: lhs, .. }),
tt::Leaf::Punct(tt::Punct { char: rhs, .. }),
) if lhs == rhs => (),
(
tt::Leaf::Ident(tt::Ident { text: lhs, .. }),
tt::Leaf::Ident(tt::Ident { text: rhs, .. }),
) if lhs == rhs => (),
(
tt::Leaf::Literal(tt::Literal { text: lhs, .. }),
tt::Leaf::Literal(tt::Literal { text: rhs, .. }),
) if lhs == rhs => (),
_ => {
return Err(ExpandError::UnexpectedToken);
}
}
Ok(())
}
fn match_meta_var(kind: &str, input: &mut TtIter) -> ExpandResult<Option<Fragment>> {
let fragment = match kind {
"path" => Path,
"expr" => Expr,
"ty" => Type,
"pat" => Pattern,
"stmt" => Statement,
"block" => Block,
"meta" => MetaItem,
"item" => Item,
_ => {
let tt_result = match kind {
"ident" => input
.expect_ident()
.map(|ident| Some(tt::Leaf::from(ident.clone()).into()))
.map_err(|()| err!("expected ident")),
"tt" => input.expect_tt().map(Some).map_err(|()| err!()),
"lifetime" => {
input.expect_lifetime().map(Some).map_err(|()| err!("expected lifetime"))
}
"literal" => {
let neg = input.eat_char('-');
input
.expect_literal()
.map(|literal| {
let lit = literal.clone();
match neg {
None => Some(lit.into()),
Some(neg) => Some(tt::TokenTree::Subtree(tt::Subtree {
delimiter: None,
token_trees: vec![neg, lit.into()],
})),
}
})
.map_err(|()| err!())
}
// `vis` is optional
"vis" => match input.eat_vis() {
Some(vis) => Ok(Some(vis)),
None => Ok(None),
},
_ => Err(ExpandError::UnexpectedToken),
};
return tt_result.map(|it| it.map(Fragment::Tokens)).into();
}
};
let result = input.expect_fragment(fragment);
result.map(|tt| if kind == "expr" { tt.map(Fragment::Ast) } else { tt.map(Fragment::Tokens) })
}
fn collect_vars(buf: &mut Vec<SmolStr>, pattern: &MetaTemplate) {
for op in pattern.iter() {
match op {
Op::Var { name, .. } => buf.push(name.clone()),
Op::Leaf(_) => (),
Op::Subtree { tokens, .. } => collect_vars(buf, tokens),
Op::Repeat { tokens, .. } => collect_vars(buf, tokens),
}
}
}
impl<'a> TtIter<'a> {
fn expect_separator(&mut self, separator: &Separator, idx: usize) -> bool {
let mut fork = self.clone();
let ok = match separator {
Separator::Ident(lhs) if idx == 0 => match fork.expect_ident_or_underscore() {
Ok(rhs) => rhs.text == lhs.text,
_ => false,
},
Separator::Literal(lhs) if idx == 0 => match fork.expect_literal() {
Ok(rhs) => match rhs {
tt::Leaf::Literal(rhs) => rhs.text == lhs.text,
tt::Leaf::Ident(rhs) => rhs.text == lhs.text,
tt::Leaf::Punct(_) => false,
},
_ => false,
},
Separator::Puncts(lhss) if idx < lhss.len() => match fork.expect_punct() {
Ok(rhs) => rhs.char == lhss[idx].char,
_ => false,
},
_ => false,
};
if ok {
*self = fork;
}
ok
}
fn expect_tt(&mut self) -> Result<tt::TokenTree, ()> {
match self.peek_n(0) {
Some(tt::TokenTree::Leaf(tt::Leaf::Punct(punct))) if punct.char == '\'' => {
return self.expect_lifetime();
}
_ => (),
}
let tt = self.next().ok_or_else(|| ())?.clone();
let punct = match tt {
tt::TokenTree::Leaf(tt::Leaf::Punct(punct)) if punct.spacing == tt::Spacing::Joint => {
punct
}
_ => return Ok(tt),
};
let (second, third) = match (self.peek_n(0), self.peek_n(1)) {
(
Some(tt::TokenTree::Leaf(tt::Leaf::Punct(p2))),
Some(tt::TokenTree::Leaf(tt::Leaf::Punct(p3))),
) if p2.spacing == tt::Spacing::Joint => (p2.char, Some(p3.char)),
(Some(tt::TokenTree::Leaf(tt::Leaf::Punct(p2))), _) => (p2.char, None),
_ => return Ok(tt),
};
match (punct.char, second, third) {
('.', '.', Some('.'))
| ('.', '.', Some('='))
| ('<', '<', Some('='))
| ('>', '>', Some('=')) => {
let tt2 = self.next().unwrap().clone();
let tt3 = self.next().unwrap().clone();
Ok(tt::Subtree { delimiter: None, token_trees: vec![tt, tt2, tt3] }.into())
}
('-', '=', _)
| ('-', '>', _)
| (':', ':', _)
| ('!', '=', _)
| ('.', '.', _)
| ('*', '=', _)
| ('/', '=', _)
| ('&', '&', _)
| ('&', '=', _)
| ('%', '=', _)
| ('^', '=', _)
| ('+', '=', _)
| ('<', '<', _)
| ('<', '=', _)
| ('=', '=', _)
| ('=', '>', _)
| ('>', '=', _)
| ('>', '>', _)
| ('|', '=', _)
| ('|', '|', _) => {
let tt2 = self.next().unwrap().clone();
Ok(tt::Subtree { delimiter: None, token_trees: vec![tt, tt2] }.into())
}
_ => Ok(tt),
}
}
fn expect_lifetime(&mut self) -> Result<tt::TokenTree, ()> {
let punct = self.expect_punct()?;
if punct.char != '\'' {
return Err(());
}
let ident = self.expect_ident_or_underscore()?;
Ok(tt::Subtree {
delimiter: None,
token_trees: vec![
tt::Leaf::Punct(*punct).into(),
tt::Leaf::Ident(ident.clone()).into(),
],
}
.into())
}
fn eat_vis(&mut self) -> Option<tt::TokenTree> {
let mut fork = self.clone();
match fork.expect_fragment(Visibility) {
ExpandResult { value: tt, err: None } => {
*self = fork;
tt
}
ExpandResult { value: _, err: Some(_) } => None,
}
}
fn eat_char(&mut self, c: char) -> Option<tt::TokenTree> {
let mut fork = self.clone();
match fork.expect_char(c) {
Ok(_) => {
let tt = self.next().cloned();
*self = fork;
tt
}
Err(_) => None,
}
}
}