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remove has_nested from builtin candidates #143571

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Merged
merged 1 commit into from
Jul 8, 2025
+54 −66
Merged

remove has_nested from builtin candidates #143571

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9 changes: 2 additions & 7 deletions compiler/rustc_middle/src/traits/select.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -97,20 +97,15 @@ pub type EvaluationCache<'tcx, ENV> = Cache<(ENV, ty::PolyTraitPredicate<'tcx>),
pub enum SelectionCandidate<'tcx> {
/// A built-in implementation for the `Sized` trait. This is preferred
/// over all other candidates.
SizedCandidate {
has_nested: bool,
},
SizedCandidate,

/// A builtin implementation for some specific traits, used in cases
/// where we cannot rely an ordinary library implementations.
///
/// The most notable examples are `Copy` and `Clone`. This is also
/// used for the `DiscriminantKind` and `Pointee` trait, both of which have
/// an associated type.
BuiltinCandidate {
/// `false` if there are no *further* obligations.
has_nested: bool,
},
BuiltinCandidate,

/// Implementation of transmutability trait.
TransmutabilityCandidate,
Expand Down
26 changes: 11 additions & 15 deletions compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -80,11 +80,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
}
Some(LangItem::DiscriminantKind) => {
// `DiscriminantKind` is automatically implemented for every type.
candidates.vec.push(BuiltinCandidate { has_nested: false });
candidates.vec.push(BuiltinCandidate);
}
Some(LangItem::PointeeTrait) => {
// `Pointee` is automatically implemented for every type.
candidates.vec.push(BuiltinCandidate { has_nested: false });
candidates.vec.push(BuiltinCandidate);
}
Some(LangItem::Sized) => {
self.assemble_builtin_sized_candidate(
Expand Down Expand Up @@ -365,7 +365,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
{
debug!(?self_ty, ?obligation, "assemble_fused_iterator_candidates",);

candidates.vec.push(BuiltinCandidate { has_nested: false });
candidates.vec.push(BuiltinCandidate);
}
}

Expand Down Expand Up @@ -810,7 +810,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
hir::Movability::Movable => {
// Movable coroutines are always `Unpin`, so add an
// unconditional builtin candidate.
candidates.vec.push(BuiltinCandidate { has_nested: false });
candidates.vec.push(BuiltinCandidate);
}
}
}
Expand Down Expand Up @@ -1122,10 +1122,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
sizedness: SizedTraitKind,
) {
match self.sizedness_conditions(obligation, sizedness) {
BuiltinImplConditions::Where(nested) => {
candidates
.vec
.push(SizedCandidate { has_nested: !nested.skip_binder().is_empty() });
BuiltinImplConditions::Where(_nested) => {
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we could change assembly to not actually collect the nested types to avoid creating a vec only to drop it again. Doing this results in some additional code duplication so I didn't do it here 😁

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Yes, I'll do it in that other PR anyways lol

candidates.vec.push(SizedCandidate);
}
BuiltinImplConditions::None => {}
BuiltinImplConditions::Ambiguous => {
Expand All @@ -1143,10 +1141,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
candidates: &mut SelectionCandidateSet<'tcx>,
) {
match conditions {
BuiltinImplConditions::Where(nested) => {
candidates
.vec
.push(BuiltinCandidate { has_nested: !nested.skip_binder().is_empty() });
BuiltinImplConditions::Where(_) => {
candidates.vec.push(BuiltinCandidate);
}
BuiltinImplConditions::None => {}
BuiltinImplConditions::Ambiguous => {
Expand All @@ -1160,7 +1156,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
_obligation: &PolyTraitObligation<'tcx>,
candidates: &mut SelectionCandidateSet<'tcx>,
) {
candidates.vec.push(BuiltinCandidate { has_nested: false });
candidates.vec.push(BuiltinCandidate);
}

fn assemble_candidate_for_tuple(
Expand All @@ -1171,7 +1167,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
let self_ty = self.infcx.shallow_resolve(obligation.self_ty().skip_binder());
match self_ty.kind() {
ty::Tuple(_) => {
candidates.vec.push(BuiltinCandidate { has_nested: false });
candidates.vec.push(BuiltinCandidate);
}
ty::Infer(ty::TyVar(_)) => {
candidates.ambiguous = true;
Expand Down Expand Up @@ -1215,7 +1211,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
let self_ty = self.infcx.resolve_vars_if_possible(obligation.self_ty());

match self_ty.skip_binder().kind() {
ty::FnPtr(..) => candidates.vec.push(BuiltinCandidate { has_nested: false }),
ty::FnPtr(..) => candidates.vec.push(BuiltinCandidate),
ty::Bool
| ty::Char
| ty::Int(_)
Expand Down
79 changes: 38 additions & 41 deletions compiler/rustc_trait_selection/src/traits/select/confirmation.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -37,13 +37,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
candidate: SelectionCandidate<'tcx>,
) -> Result<Selection<'tcx>, SelectionError<'tcx>> {
Ok(match candidate {
SizedCandidate { has_nested } => {
let data = self.confirm_builtin_candidate(obligation, has_nested);
SizedCandidate => {
let data = self.confirm_builtin_candidate(obligation);
ImplSource::Builtin(BuiltinImplSource::Misc, data)
}

BuiltinCandidate { has_nested } => {
let data = self.confirm_builtin_candidate(obligation, has_nested);
BuiltinCandidate => {
let data = self.confirm_builtin_candidate(obligation);
ImplSource::Builtin(BuiltinImplSource::Misc, data)
}

Expand Down Expand Up @@ -249,50 +249,47 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
}
}

#[instrument(level = "debug", skip(self), ret)]
fn confirm_builtin_candidate(
&mut self,
obligation: &PolyTraitObligation<'tcx>,
has_nested: bool,
) -> PredicateObligations<'tcx> {
debug!(?obligation, ?has_nested, "confirm_builtin_candidate");

debug!(?obligation, "confirm_builtin_candidate");
let tcx = self.tcx();
let obligations = if has_nested {
let trait_def = obligation.predicate.def_id();
let conditions = match tcx.as_lang_item(trait_def) {
Some(LangItem::Sized) => {
self.sizedness_conditions(obligation, SizedTraitKind::Sized)
}
Some(LangItem::MetaSized) => {
self.sizedness_conditions(obligation, SizedTraitKind::MetaSized)
}
Some(LangItem::PointeeSized) => {
bug!("`PointeeSized` is removing during lowering");
}
Some(LangItem::Copy | LangItem::Clone) => self.copy_clone_conditions(obligation),
Some(LangItem::FusedIterator) => self.fused_iterator_conditions(obligation),
other => bug!("unexpected builtin trait {trait_def:?} ({other:?})"),
};
let BuiltinImplConditions::Where(types) = conditions else {
bug!("obligation {:?} had matched a builtin impl but now doesn't", obligation);
};
let types = self.infcx.enter_forall_and_leak_universe(types);

let cause = obligation.derived_cause(ObligationCauseCode::BuiltinDerived);
self.collect_predicates_for_types(
obligation.param_env,
cause,
obligation.recursion_depth + 1,
trait_def,
types,
)
} else {
PredicateObligations::new()
let trait_def = obligation.predicate.def_id();
let conditions = match tcx.as_lang_item(trait_def) {
Some(LangItem::Sized) => self.sizedness_conditions(obligation, SizedTraitKind::Sized),
Some(LangItem::MetaSized) => {
self.sizedness_conditions(obligation, SizedTraitKind::MetaSized)
}
Some(LangItem::PointeeSized) => {
bug!("`PointeeSized` is removing during lowering");
}
Some(LangItem::Copy | LangItem::Clone) => self.copy_clone_conditions(obligation),
Some(LangItem::FusedIterator) => self.fused_iterator_conditions(obligation),
Some(
LangItem::Destruct
| LangItem::DiscriminantKind
| LangItem::FnPtrTrait
| LangItem::PointeeTrait
| LangItem::Tuple
| LangItem::Unpin,
) => BuiltinImplConditions::Where(ty::Binder::dummy(vec![])),
other => bug!("unexpected builtin trait {trait_def:?} ({other:?})"),
};
let BuiltinImplConditions::Where(types) = conditions else {
bug!("obligation {:?} had matched a builtin impl but now doesn't", obligation);
};
let types = self.infcx.enter_forall_and_leak_universe(types);

debug!(?obligations);

obligations
let cause = obligation.derived_cause(ObligationCauseCode::BuiltinDerived);
self.collect_predicates_for_types(
obligation.param_env,
cause,
obligation.recursion_depth + 1,
trait_def,
types,
)
}

#[instrument(level = "debug", skip(self))]
Expand Down
6 changes: 3 additions & 3 deletions compiler/rustc_trait_selection/src/traits/select/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1834,7 +1834,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {

// We prefer `Sized` candidates over everything.
let mut sized_candidates =
candidates.iter().filter(|c| matches!(c.candidate, SizedCandidate { has_nested: _ }));
candidates.iter().filter(|c| matches!(c.candidate, SizedCandidate));
if let Some(sized_candidate) = sized_candidates.next() {
// There should only ever be a single sized candidate
// as they would otherwise overlap.
Expand Down Expand Up @@ -1986,8 +1986,8 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
// Don't use impl candidates which overlap with other candidates.
// This should pretty much only ever happen with malformed impls.
if candidates.iter().all(|c| match c.candidate {
SizedCandidate { has_nested: _ }
| BuiltinCandidate { has_nested: _ }
SizedCandidate
| BuiltinCandidate
| TransmutabilityCandidate
| AutoImplCandidate
| ClosureCandidate { .. }
Expand Down
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