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Fix parser stack overflow #22513

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Fix parser stack overflow #22513

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8e86766
Fix stack overflow on deeply nested call expressions
Jun 2, 2026
61e626a
Add test for deeply nested recursion limit
Jun 2, 2026
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2 changes: 1 addition & 1 deletion Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ exclude = ["crates/proc-macro-srv/proc-macro-test/imp"]
resolver = "2"

[workspace.package]
rust-version = "1.95"
rust-version = "1.94"
edition = "2024"
license = "MIT OR Apache-2.0"
authors = ["rust-analyzer team"]
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19 changes: 18 additions & 1 deletion crates/parser/src/grammar/expressions.rs
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Expand Up @@ -246,6 +246,23 @@ fn expr_bp(
m: Option<Marker>,
r: Restrictions,
bp: u8,
) -> Option<(CompletedMarker, BlockLike)> {
if !p.check_recursion_limit() {

@ChayimFriedman2 ChayimFriedman2 Jun 3, 2026 •
edited by rustbot
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This is, of course, not enough. Many functions in the parser recurse.

I'm not yet sure whether we want such thing, though.

View changes since the review

@Veykril Veykril Jun 3, 2026

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if we want to fix this we should do what rustc does which is growing the stack on demand

@ChayimFriedman2 ChayimFriedman2 Jun 3, 2026

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And there are also plenty of places besides parsing that will need that (although parsing is the most important).

@Veykril Veykril Jun 3, 2026

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Yea hir-def lowering does as well at the very least

if let Some(m) = m {
m.abandon(p);
}
return None;
}
let res = expr_bp_inner(p, m, r, bp);
p.decrease_recursion_limit();
res
}

fn expr_bp_inner(
p: &mut Parser<'_>,
m: Option<Marker>,
r: Restrictions,
bp: u8,
) -> Option<(CompletedMarker, BlockLike)> {
let m = m.unwrap_or_else(|| {
let m = p.start();
Expand Down Expand Up @@ -315,7 +332,7 @@ fn expr_bp(

// test binop_resets_statementness
// fn f() { v = {1}&2; }
expr_bp(p, None, Restrictions { prefer_stmt: false, ..r }, op_bp);
expr_bp_inner(p, None, Restrictions { prefer_stmt: false, ..r }, op_bp);
lhs = m.complete(p, if is_range { RANGE_EXPR } else { BIN_EXPR });
}
Some((lhs, BlockLike::NotBlock))
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18 changes: 18 additions & 0 deletions crates/parser/src/parser.rs
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Expand Up @@ -37,9 +37,11 @@ pub(crate) struct Parser<'t> {
/// into this vec, keeping `Event` itself a flat 8-byte enum.
errors: Vec<String>,
steps: Cell<u32>,
depth: u32,
}

const PARSER_STEP_LIMIT: usize = if cfg!(debug_assertions) { 150_000 } else { 15_000_000 };
const PARSER_DEPTH_LIMIT: u32 = 256;

impl<'t> Parser<'t> {
pub(super) fn new(inp: &'t Input) -> Parser<'t> {
Expand All @@ -49,6 +51,7 @@ impl<'t> Parser<'t> {
events: Vec::with_capacity(2 * inp.len()),
errors: Vec::new(),
steps: Cell::new(0),
depth: 0,
}
}

Expand All @@ -75,6 +78,21 @@ impl<'t> Parser<'t> {
self.inp.kind(self.pos + n)
}

pub(crate) fn check_recursion_limit(&mut self) -> bool {
if self.depth > PARSER_DEPTH_LIMIT {
self.error("recursion limit exceeded");
return false;
}
self.depth += 1;
true
}

pub(crate) fn decrease_recursion_limit(&mut self) {
if self.depth > 0 {
self.depth -= 1;
}
}

/// Checks if the current token is `kind`.
pub(crate) fn at(&self, kind: SyntaxKind) -> bool {
self.nth_at(0, kind)
Expand Down
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