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Report better WF obligation leaf obligations in new solver

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This commit is contained in:
Michael Goulet 2024-05-16 20:29:54 -04:00
parent 97bf25c8cf
commit 119c7bbef7
16 changed files with 117 additions and 108 deletions
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77
compiler/rustc_trait_selection/src/solve/fulfill.rs
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@ -384,39 +384,64 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
return ControlFlow::Break(self.obligation.clone());
}
// FIXME: Could we extract a trait ref from a projection here too?
let tcx = goal.infcx().tcx;
// FIXME: Also, what about considering >1 layer up the stack? May be necessary
// for normalizes-to.
let Some(parent_trait_pred) = goal.goal().predicate.to_opt_poly_trait_pred() else {
return ControlFlow::Break(self.obligation.clone());
let pred_kind = goal.goal().predicate.kind();
let child_mode = match pred_kind.skip_binder() {
ty::PredicateKind::Clause(ty::ClauseKind::Trait(parent_trait_pred)) => {
ChildMode::Trait(pred_kind.rebind(parent_trait_pred))
}
ty::PredicateKind::NormalizesTo(normalizes_to)
if matches!(
normalizes_to.alias.kind(tcx),
ty::AliasTermKind::ProjectionTy | ty::AliasTermKind::ProjectionConst
) =>
{
ChildMode::Trait(pred_kind.rebind(ty::TraitPredicate {
trait_ref: normalizes_to.alias.trait_ref(tcx),
polarity: ty::PredicatePolarity::Positive,
}))
}
ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(_)) => {
ChildMode::WellFormedObligation
}
_ => {
return ControlFlow::Break(self.obligation.clone());
}
};
let tcx = goal.infcx().tcx;
let mut impl_where_bound_count = 0;
for nested_goal in candidate.instantiate_nested_goals(self.span()) {
let make_obligation = |cause| Obligation {
cause,
param_env: nested_goal.goal().param_env,
predicate: nested_goal.goal().predicate,
recursion_depth: self.obligation.recursion_depth + 1,
};
let obligation;
match nested_goal.source() {
GoalSource::Misc => {
match (child_mode, nested_goal.source()) {
(ChildMode::Trait(_), GoalSource::Misc) => {
continue;
}
GoalSource::ImplWhereBound => {
obligation = Obligation {
cause: derive_cause(
tcx,
candidate.kind(),
self.obligation.cause.clone(),
impl_where_bound_count,
parent_trait_pred,
),
param_env: nested_goal.goal().param_env,
predicate: nested_goal.goal().predicate,
recursion_depth: self.obligation.recursion_depth + 1,
};
(ChildMode::Trait(parent_trait_pred), GoalSource::ImplWhereBound) => {
obligation = make_obligation(derive_cause(
tcx,
candidate.kind(),
self.obligation.cause.clone(),
impl_where_bound_count,
parent_trait_pred,
));
impl_where_bound_count += 1;
}
GoalSource::InstantiateHigherRanked => {
// Skip over a higher-ranked predicate.
(_, GoalSource::InstantiateHigherRanked) => {
obligation = self.obligation.clone();
}
(ChildMode::WellFormedObligation, _) => {
obligation = make_obligation(self.obligation.cause.clone());
}
}
// Skip nested goals that aren't the *reason* for our goal's failure.
@ -436,6 +461,18 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
}
}
#[derive(Copy, Clone)]
enum ChildMode<'tcx> {
// Try to derive an `ObligationCause::{ImplDerived,BuiltinDerived}`,
// and skip all `GoalSource::Misc`, which represent useless obligations
// such as alias-eq which may not hold.
Trait(ty::PolyTraitPredicate<'tcx>),
// Skip trying to derive an `ObligationCause` from this obligation, and
// report *all* sub-obligations as if they came directly from the parent
// obligation.
WellFormedObligation,
}
fn derive_cause<'tcx>(
tcx: TyCtxt<'tcx>,
candidate_kind: ProbeKind<'tcx>,