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turn compute_goal_fast_path into a single match #156038

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Merged
rust-bors merged 1 commit into from
May 8, 2026
+57 −32
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turn compute_goal_fast_path into a single match #156038

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89 changes: 57 additions & 32 deletions compiler/rustc_trait_selection/src/solve/delegate.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@ use rustc_infer::traits::solve::{FetchEligibleAssocItemResponse, Goal};
use rustc_middle::traits::query::NoSolution;
use rustc_middle::traits::solve::Certainty;
use rustc_middle::ty::{
self, MayBeErased, Ty, TyCtxt, TypeFlags, TypeFoldable, TypeVisitableExt as _, TypingMode,
self, MayBeErased, Ty, TyCtxt, TypeFlags, TypeFoldable, TypeVisitableExt, TypingMode,
};
use rustc_span::{DUMMY_SP, Span};

Expand Down Expand Up @@ -73,51 +73,60 @@ impl<'tcx> rustc_next_trait_solver::delegate::SolverDelegate for SolverDelegate<
goal: Goal<'tcx, ty::Predicate<'tcx>>,
span: Span,
) -> Option<Certainty> {
if let Some(trait_pred) = goal.predicate.as_trait_clause() {
if self.shallow_resolve(trait_pred.self_ty().skip_binder()).is_ty_var()
let pred = goal.predicate.kind();
match pred.skip_binder() {
ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_pred)) => {
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let trait_pred = pred.rebind(trait_pred);

if self.shallow_resolve(trait_pred.self_ty().skip_binder()).is_ty_var()
// We don't do this fast path when opaques are defined since we may
// eventually use opaques to incompletely guide inference via ty var
// self types.
// FIXME: Properly consider opaques here.
&& self.known_no_opaque_types_in_storage()
{
return Some(Certainty::AMBIGUOUS);
}

if trait_pred.polarity() == ty::PredicatePolarity::Positive {
match self.0.tcx.as_lang_item(trait_pred.def_id()) {
Some(LangItem::Sized) | Some(LangItem::MetaSized) => {
let predicate = self.resolve_vars_if_possible(goal.predicate);
if sizedness_fast_path(self.tcx, predicate, goal.param_env) {
return Some(Certainty::Yes);
{
Some(Certainty::AMBIGUOUS)
} else if trait_pred.polarity() == ty::PredicatePolarity::Positive {
match self.0.tcx.as_lang_item(trait_pred.def_id()) {
Some(LangItem::Sized) | Some(LangItem::MetaSized) => {
let predicate = self.resolve_vars_if_possible(goal.predicate);
if sizedness_fast_path(self.tcx, predicate, goal.param_env) {
return Some(Certainty::Yes);
} else {
None
}
}
}
Some(LangItem::Copy | LangItem::Clone) => {
let self_ty =
self.resolve_vars_if_possible(trait_pred.self_ty().skip_binder());
// Unlike `Sized` traits, which always prefer the built-in impl,
// `Copy`/`Clone` may be shadowed by a param-env candidate which
// could force a lifetime error or guide inference. While that's
// not generally desirable, it is observable, so for now let's
// ignore this fast path for types that have regions or infer.
if !self_ty
.has_type_flags(TypeFlags::HAS_FREE_REGIONS | TypeFlags::HAS_INFER)
&& self_ty.is_trivially_pure_clone_copy()
{
return Some(Certainty::Yes);
Some(LangItem::Copy | LangItem::Clone) => {
let self_ty =
self.resolve_vars_if_possible(trait_pred.self_ty().skip_binder());
// Unlike `Sized` traits, which always prefer the built-in impl,
// `Copy`/`Clone` may be shadowed by a param-env candidate which
// could force a lifetime error or guide inference. While that's
// not generally desirable, it is observable, so for now let's
// ignore this fast path for types that have regions or infer.
if !self_ty
.has_type_flags(TypeFlags::HAS_FREE_REGIONS | TypeFlags::HAS_INFER)
&& self_ty.is_trivially_pure_clone_copy()
{
return Some(Certainty::Yes);
} else {
None
}
}
_ => None,
}
_ => {}
} else {
None
}
}
}

let pred = goal.predicate.kind();
match pred.no_bound_vars()? {
ty::PredicateKind::DynCompatible(def_id) if self.0.tcx.is_dyn_compatible(def_id) => {
Some(Certainty::Yes)
}
ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(outlives)) => {
if outlives.has_escaping_bound_vars() {
return None;
}

self.0.sub_regions(
SubregionOrigin::RelateRegionParamBound(span, None),
outlives.1,
Expand All @@ -127,6 +136,10 @@ impl<'tcx> rustc_next_trait_solver::delegate::SolverDelegate for SolverDelegate<
Some(Certainty::Yes)
}
ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(outlives)) => {
if outlives.has_escaping_bound_vars() {
return None;
}

self.0.register_type_outlives_constraint(
outlives.0,
outlives.1,
Expand All @@ -137,6 +150,10 @@ impl<'tcx> rustc_next_trait_solver::delegate::SolverDelegate for SolverDelegate<
}
ty::PredicateKind::Subtype(ty::SubtypePredicate { a, b, .. })
| ty::PredicateKind::Coerce(ty::CoercePredicate { a, b }) => {
if a.has_escaping_bound_vars() || b.has_escaping_bound_vars() {
return None;
}

match (self.shallow_resolve(a).kind(), self.shallow_resolve(b).kind()) {
(&ty::Infer(ty::TyVar(a_vid)), &ty::Infer(ty::TyVar(b_vid))) => {
self.sub_unify_ty_vids_raw(a_vid, b_vid);
Expand All @@ -146,13 +163,21 @@ impl<'tcx> rustc_next_trait_solver::delegate::SolverDelegate for SolverDelegate<
}
}
ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, _)) => {
if ct.has_escaping_bound_vars() {
return None;
}

if self.shallow_resolve_const(ct).is_ct_infer() {
Some(Certainty::AMBIGUOUS)
} else {
None
}
}
ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg)) => {
if arg.has_escaping_bound_vars() {
return None;
}

let arg = self.shallow_resolve_term(arg);
if arg.is_trivially_wf(self.tcx) {
Some(Certainty::Yes)
Expand Down
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