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[ty] Use regular hash-set in cycle detector #22367

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[ty] Use regular hash-set in cycle detector #22367

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d11d5e1
[ty] Use regular hash-set in cycle dedector
MichaReiser Jan 4, 2026
97c6489
Reduce remove calls
MichaReiser Jan 4, 2026
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36 changes: 17 additions & 19 deletions crates/ty_python_semantic/src/types/cyclic.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,9 +24,8 @@ use std::cmp::Eq;
use std::hash::Hash;
use std::marker::PhantomData;

use rustc_hash::FxHashMap;
use rustc_hash::{FxHashMap, FxHashSet};

use crate::FxIndexSet;
use crate::types::Type;

/// Maximum recursion depth for cycle detection.
Expand Down Expand Up @@ -64,7 +63,7 @@ pub struct CycleDetector<Tag, T, R> {
/// If the type we're visiting is present in `seen`, it indicates that we've hit a cycle (due
/// to a recursive type); we need to immediately short circuit the whole operation and return
/// the fallback value. That's why we pop items off the end of `seen` after we've visited them.
seen: RefCell<FxIndexSet<T>>,
seen: RefCell<FxHashSet<T>>,

/// Unlike `seen`, this field is a pure performance optimisation (and an essential one). If the
/// type we're trying to normalize is present in `cache`, it doesn't necessarily mean we've hit
Expand All @@ -86,7 +85,7 @@ pub struct CycleDetector<Tag, T, R> {
impl<Tag, T: Hash + Eq + Clone, R: Clone> CycleDetector<Tag, T, R> {
pub fn new(fallback: R) -> Self {
CycleDetector {
seen: RefCell::new(FxIndexSet::default()),
seen: RefCell::new(FxHashSet::default()),
cache: RefCell::new(FxHashMap::default()),
depth: Cell::new(0),
fallback,
Expand All @@ -99,24 +98,23 @@ impl<Tag, T: Hash + Eq + Clone, R: Clone> CycleDetector<Tag, T, R> {
return val.clone();
}

// We hit a cycle
if !self.seen.borrow_mut().insert(item.clone()) {
return self.fallback.clone();
}

// Check depth limit to prevent stack overflow from recursive generic types
// with growing specializations (e.g., C[set[T]] -> C[set[set[T]]] -> ...)
let current_depth = self.depth.get();
if current_depth >= MAX_RECURSION_DEPTH {
self.seen.borrow_mut().pop();
return self.fallback.clone();
}
self.depth.set(current_depth + 1);

// We hit a cycle
if !self.seen.borrow_mut().insert(item.clone()) {
return self.fallback.clone();
}

self.depth.set(current_depth + 1);
let ret = func();

self.depth.set(current_depth);
self.seen.borrow_mut().pop();
self.seen.borrow_mut().remove(&item);
self.cache.borrow_mut().insert(item, ret.clone());

ret
Expand All @@ -127,24 +125,24 @@ impl<Tag, T: Hash + Eq + Clone, R: Clone> CycleDetector<Tag, T, R> {
return Some(val.clone());
}

// We hit a cycle
if !self.seen.borrow_mut().insert(item.clone()) {
return Some(self.fallback.clone());
}

// Check depth limit to prevent stack overflow from recursive generic protocols
// with growing specializations (e.g., C[set[T]] -> C[set[set[T]]] -> ...)
let current_depth = self.depth.get();
if current_depth >= MAX_RECURSION_DEPTH {
self.seen.borrow_mut().pop();
return Some(self.fallback.clone());
}

// We hit a cycle
if !self.seen.borrow_mut().insert(item.clone()) {
return Some(self.fallback.clone());
}

self.depth.set(current_depth + 1);

let ret = func()?;

self.depth.set(current_depth);
self.seen.borrow_mut().pop();
self.seen.borrow_mut().remove(&item);
self.cache.borrow_mut().insert(item, ret.clone());

Some(ret)
Expand Down