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fix(frontend): make path_to breadth-first #730

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merged 4 commits into from
Jul 29, 2024
Merged

fix(frontend): make path_to breadth-first #730

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e637a2c
fix(frontend): make `path_to` breadth-first
Jun 20, 2024
274bab2
Fix breadth-first trait resolution.
maximebuyse Jul 23, 2024
59f1190
Make breadth-first in path_to consider all starting points to avoid i…
maximebuyse Jul 25, 2024
3c6296a
Improve fix for looping behavior in impl_expr computation.
maximebuyse Jul 29, 2024
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108 changes: 62 additions & 46 deletions frontend/exporter/src/traits.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -76,7 +76,6 @@ pub mod rustc {
pub(crate) mod search_clause {
use crate::prelude::UnderOwnerState;
use crate::rustc_utils::*;
use crate::{IntoPredicateId, PredicateId};
use rustc_middle::ty::*;

fn predicates_to_poly_trait_predicates<'tcx>(
Expand Down Expand Up @@ -201,60 +200,77 @@ pub mod rustc {
.collect()
}

#[tracing::instrument(level = "trace", skip(s))]
#[tracing::instrument(level = "trace", skip(s, param_env))]
fn path_to(
self,
s: &S,
target: PolyTraitRef<'tcx>,
param_env: rustc_middle::ty::ParamEnv<'tcx>,
) -> Option<Path<'tcx>> {
let tcx = s.base().tcx;
if predicate_equality(self.upcast(tcx), target.upcast(tcx), param_env, s) {
return Some(vec![]);

/// A candidate projects `self` along a path reaching some
/// predicate. A candidate is selected when its predicate
/// is the one expected, aka `target`.
#[derive(Debug)]
struct Candidate<'tcx> {
path: Path<'tcx>,
pred: PolyTraitPredicate<'tcx>,
}

let recurse = |p: Self| {
if p == self {
return None;
use std::collections::VecDeque;
let mut candidates: VecDeque<Candidate<'tcx>> = vec![Candidate {
path: vec![],
pred: self,
}]
.into();

let target_pred = target.upcast(tcx);
let mut seen = std::collections::HashSet::new();

while let Some(candidate) = candidates.pop_front() {
{
// If a predicate was already seen, we know it is
// not the one we are looking for: we skip it.
if seen.contains(&candidate.pred) {
continue;
}
seen.insert(candidate.pred.clone());
}
p.path_to(s, target, param_env)
};
fn cons<T>(hd: T, tail: Vec<T>) -> Vec<T> {
vec![hd].into_iter().chain(tail.into_iter()).collect()
}
self.parents_trait_predicates(s)
.into_iter()
.filter_map(|(index, p)| {
recurse(p).map(|path| {
cons(
PathChunk::Parent {
predicate: p,
index,
},

// if the candidate equals the target, let's return its path
if predicate_equality(candidate.pred.upcast(tcx), target_pred, param_env, s) {
return Some(candidate.path);
}

// otherwise, we add to the queue all paths reachable from the candidate
for (index, parent_pred) in candidate.pred.parents_trait_predicates(s) {
let mut path = candidate.path.clone();
path.push(PathChunk::Parent {
predicate: parent_pred.clone(),
index,
});
candidates.push_back(Candidate {
pred: parent_pred.clone(),
path,
});
}
for (item, binder) in candidate.pred.associated_items_trait_predicates(s) {
for (index, parent_pred) in binder.skip_binder().into_iter() {
let mut path = candidate.path.clone();
path.push(PathChunk::AssocItem {
item,
predicate: parent_pred.clone(),
index,
});
candidates.push_back(Candidate {
pred: parent_pred.clone(),
path,
)
})
})
.max_by_key(|path| path.len())
.or_else(|| {
self.associated_items_trait_predicates(s)
.into_iter()
.filter_map(|(item, binder)| {
binder.skip_binder().into_iter().find_map(|(index, p)| {
recurse(p).map(|path| {
cons(
PathChunk::AssocItem {
item,
predicate: p,
index,
},
path,
)
})
})
})
.max_by_key(|path| path.len())
})
});
}
}
}
None
}
}
}
Expand Down Expand Up @@ -311,7 +327,7 @@ pub mod rustc {
}
}
impl<'tcx> IntoImplExpr<'tcx> for rustc_middle::ty::PolyTraitRef<'tcx> {
#[tracing::instrument(level = "trace", skip(s))]
#[tracing::instrument(level = "trace", skip(s, param_env))]
fn impl_expr<S: UnderOwnerState<'tcx>>(
&self,
s: &S,
Expand Down Expand Up @@ -414,7 +430,7 @@ pub mod rustc {
Some((new_clause_no_binder, impl_expr, span.sinto(s)))
}

#[tracing::instrument(level = "trace", skip(s))]
#[tracing::instrument(level = "trace", skip(s, param_env))]
pub fn select_trait_candidate<'tcx, S: UnderOwnerState<'tcx>>(
s: &S,
param_env: rustc_middle::ty::ParamEnv<'tcx>,
Expand Down
2 changes: 2 additions & 0 deletions frontend/exporter/src/types/new/predicate_id.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,7 @@ mod rustc {
}

impl<'tcx, S: UnderOwnerState<'tcx>> IntoPredicateId<'tcx, S> for ty::Predicate<'tcx> {
#[tracing::instrument(level = "trace", skip(s))]
fn predicate_id(&self, s: &S) -> PredicateId {
// Here, we need to be careful about not hashing a `crate::Predicate`,
// but `crate::Binder<crate::PredicateKind>` instead,
Expand All @@ -37,6 +38,7 @@ mod rustc {
}

impl<'tcx, S: UnderOwnerState<'tcx>> IntoPredicateId<'tcx, S> for ty::PolyTraitPredicate<'tcx> {
#[tracing::instrument(level = "trace", skip(s))]
fn predicate_id(&self, s: &S) -> PredicateId {
use ty::Upcast;
let predicate: ty::Predicate<'tcx> = (*self).upcast(s.base().tcx);
Expand Down
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