bjoernager/rust
bjoernager/rust
1
Fork 0
Code Issues Pull requests Activity

Avoid unbounded O(n^2) when parsing nested type args

Browse source 
When encountering code like `f::<f::<f::<f::<f::<f::<f::<f::<...` with
unmatched closing angle brackets, add a linear check that avoids the
exponential behavior of the parse recovery mechanism.

Fix #117080.
This commit is contained in:
Esteban Küber 2023-10-24 22:22:52 +00:00
parent 855444ec54
commit 2dec1bc685
4 changed files with 55 additions and 6 deletions
Download patch file Download diff file Expand all files Collapse all files

25
compiler/rustc_parse/src/parser/path.rs
View file

@ -487,10 +487,24 @@ impl<'a> Parser<'a> {
// Take a snapshot before attempting to parse - we can restore this later.
let snapshot = is_first_invocation.then(|| self.clone());
self.angle_bracket_nesting += 1;
debug!("parse_generic_args_with_leading_angle_bracket_recovery: (snapshotting)");
match self.parse_angle_args(ty_generics) {
Ok(args) => Ok(args),
Ok(args) => {
self.angle_bracket_nesting -= 1;
Ok(args)
}
Err(mut e) if self.angle_bracket_nesting > 10 => {
self.angle_bracket_nesting -= 1;
// When encountering severely malformed code where there are several levels of
// nested unclosed angle args (`f::<f::<f::<f::<...`), we avoid severe O(n^2)
// behavior by bailing out earlier (#117080).
e.emit();
rustc_errors::FatalError.raise();
}
Err(e) if is_first_invocation && self.unmatched_angle_bracket_count > 0 => {
self.angle_bracket_nesting -= 1;
// Swap `self` with our backup of the parser state before attempting to parse
// generic arguments.
let snapshot = mem::replace(self, snapshot.unwrap());
@ -520,8 +534,8 @@ impl<'a> Parser<'a> {
// Make a span over ${unmatched angle bracket count} characters.
// This is safe because `all_angle_brackets` ensures that there are only `<`s,
// i.e. no multibyte characters, in this range.
let span =
lo.with_hi(lo.lo() + BytePos(snapshot.unmatched_angle_bracket_count));
let span = lo
.with_hi(lo.lo() + BytePos(snapshot.unmatched_angle_bracket_count.into()));
self.sess.emit_err(errors::UnmatchedAngle {
span,
plural: snapshot.unmatched_angle_bracket_count > 1,
@ -531,7 +545,10 @@ impl<'a> Parser<'a> {
self.parse_angle_args(ty_generics)
}
}
Err(e) => Err(e),
Err(e) => {
self.angle_bracket_nesting -= 1;
Err(e)
}
}
}