diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs
index a4f600560ae..dcf5fd86929 100644
--- a/compiler/rustc_trait_selection/src/traits/coherence.rs
+++ b/compiler/rustc_trait_selection/src/traits/coherence.rs
@@ -9,7 +9,6 @@ use crate::infer::InferOk;
use crate::solve::inspect;
use crate::solve::inspect::{InspectGoal, ProofTreeInferCtxtExt, ProofTreeVisitor};
use crate::traits::engine::TraitEngineExt;
-use crate::traits::outlives_bounds::InferCtxtExt as _;
use crate::traits::query::evaluate_obligation::InferCtxtExt;
use crate::traits::select::{IntercrateAmbiguityCause, TreatInductiveCycleAs};
use crate::traits::structural_normalize::StructurallyNormalizeExt;
@@ -21,7 +20,7 @@ use crate::traits::{
};
use rustc_data_structures::fx::FxIndexSet;
use rustc_errors::Diagnostic;
-use rustc_hir::def_id::{DefId, CRATE_DEF_ID, LOCAL_CRATE};
+use rustc_hir::def_id::{DefId, LOCAL_CRATE};
use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, TyCtxtInferExt};
use rustc_infer::traits::{util, TraitEngine};
use rustc_middle::traits::query::NoSolution;
@@ -36,7 +35,6 @@ use rustc_session::lint::builtin::COINDUCTIVE_OVERLAP_IN_COHERENCE;
use rustc_span::symbol::sym;
use rustc_span::DUMMY_SP;
use std::fmt::Debug;
-use std::iter;
use std::ops::ControlFlow;
/// Whether we do the orphan check relative to this crate or
@@ -417,41 +415,8 @@ fn impl_intersection_has_negative_obligation(
plug_infer_with_placeholders(infcx, universe, (impl1_header.impl_args, impl2_header.impl_args));
- for (predicate, _) in util::elaborate(
- tcx,
- tcx.predicates_of(impl2_def_id).instantiate(tcx, impl2_header.impl_args),
- ) {
- let Some(negative_predicate) = predicate.as_predicate().flip_polarity(tcx) else {
- continue;
- };
-
- let ref infcx = infcx.fork();
- let ocx = ObligationCtxt::new(infcx);
-
- ocx.register_obligation(Obligation::new(
- tcx,
- ObligationCause::dummy(),
- param_env,
- negative_predicate,
- ));
- if !ocx.select_all_or_error().is_empty() {
- continue;
- }
-
- // FIXME: We could use the assumed_wf_types from both impls, I think,
- // if that wasn't implemented just for LocalDefId, and we'd need to do
- //the normalization ourselves since this is totally fallible...
- let outlives_env = OutlivesEnvironment::new(param_env);
-
- let errors = infcx.resolve_regions(&outlives_env);
- if !errors.is_empty() {
- continue;
- }
-
- return true;
- }
-
- false
+ util::elaborate(tcx, tcx.predicates_of(impl2_def_id).instantiate(tcx, impl2_header.impl_args))
+ .any(|(clause, _)| try_prove_negated_where_clause(infcx, clause, param_env))
}
fn plug_infer_with_placeholders<'tcx>(
@@ -566,60 +531,47 @@ fn plug_infer_with_placeholders<'tcx>(
});
}
-/// Try to prove that a negative impl exist for the obligation or its supertraits.
-///
-/// If such a negative impl exists, then the obligation definitely must not hold
-/// due to coherence, even if it's not necessarily "knowable" in this crate. Any
-/// valid impl downstream would not be able to exist due to the overlapping
-/// negative impl.
-#[instrument(level = "debug", skip(infcx))]
-fn negative_impl_exists<'tcx>(
- infcx: &InferCtxt<'tcx>,
- o: &PredicateObligation<'tcx>,
- body_def_id: DefId,
+fn try_prove_negated_where_clause<'tcx>(
+ root_infcx: &InferCtxt<'tcx>,
+ clause: ty::Clause<'tcx>,
+ param_env: ty::ParamEnv<'tcx>,
) -> bool {
- // Try to prove a negative obligation exists for super predicates
- for pred in util::elaborate(infcx.tcx, iter::once(o.predicate)) {
- if prove_negated_obligation(infcx.fork(), &o.with(infcx.tcx, pred), body_def_id) {
- return true;
- }
- }
-
- false
-}
-
-#[instrument(level = "debug", skip(infcx))]
-fn prove_negated_obligation<'tcx>(
- infcx: InferCtxt<'tcx>,
- o: &PredicateObligation<'tcx>,
- body_def_id: DefId,
-) -> bool {
- let tcx = infcx.tcx;
-
- let Some(o) = o.flip_polarity(tcx) else {
+ let Some(negative_predicate) = clause.as_predicate().flip_polarity(root_infcx.tcx) else {
return false;
};
- let param_env = o.param_env;
- let ocx = ObligationCtxt::new(&infcx);
- ocx.register_obligation(o);
- let errors = ocx.select_all_or_error();
+ // FIXME(with_negative_coherence): the infcx has region contraints from equating
+ // the impl headers as requirements. Given that the only region constraints we
+ // get are involving inference regions in the root, it shouldn't matter, but
+ // still sus.
+ //
+ // We probably should just throw away the region obligations registered up until
+ // now, or ideally use them as assumptions when proving the region obligations
+ // that we get from proving the negative predicate below.
+ let ref infcx = root_infcx.fork();
+ let ocx = ObligationCtxt::new(infcx);
+
+ ocx.register_obligation(Obligation::new(
+ infcx.tcx,
+ ObligationCause::dummy(),
+ param_env,
+ negative_predicate,
+ ));
+ if !ocx.select_all_or_error().is_empty() {
+ return false;
+ }
+
+ // FIXME: We could use the assumed_wf_types from both impls, I think,
+ // if that wasn't implemented just for LocalDefId, and we'd need to do
+ // the normalization ourselves since this is totally fallible...
+ let outlives_env = OutlivesEnvironment::new(param_env);
+
+ let errors = infcx.resolve_regions(&outlives_env);
if !errors.is_empty() {
return false;
}
- let body_def_id = body_def_id.as_local().unwrap_or(CRATE_DEF_ID);
-
- let ocx = ObligationCtxt::new(&infcx);
- let Ok(wf_tys) = ocx.assumed_wf_types(param_env, body_def_id) else {
- return false;
- };
-
- let outlives_env = OutlivesEnvironment::with_bounds(
- param_env,
- infcx.implied_bounds_tys(param_env, body_def_id, wf_tys),
- );
- infcx.resolve_regions(&outlives_env).is_empty()
+ true
}
/// Returns whether all impls which would apply to the `trait_ref`
diff --git a/compiler/rustc_trait_selection/src/traits/engine.rs b/compiler/rustc_trait_selection/src/traits/engine.rs
index 4fc63580c3b..d9a1a98191d 100644
--- a/compiler/rustc_trait_selection/src/traits/engine.rs
+++ b/compiler/rustc_trait_selection/src/traits/engine.rs
@@ -40,7 +40,7 @@ impl<'tcx> TraitEngineExt<'tcx> for dyn TraitEngine<'tcx> {
(TraitSolver::Classic | TraitSolver::Next | TraitSolver::NextCoherence, true) => {
Box::new(NextFulfillmentCtxt::new(infcx))
}
- _ => bug!(
+ (TraitSolver::Next, false) => bug!(
"incompatible combination of -Ztrait-solver flag ({:?}) and InferCtxt::next_trait_solver ({:?})",
infcx.tcx.sess.opts.unstable_opts.trait_solver,
infcx.next_trait_solver()
diff --git a/tests/ui/coherence/coherence-overlap-with-regions.rs b/tests/ui/coherence/coherence-overlap-with-regions.rs
index 9f237986acf..9945c8e6cfd 100644
--- a/tests/ui/coherence/coherence-overlap-with-regions.rs
+++ b/tests/ui/coherence/coherence-overlap-with-regions.rs
@@ -1,5 +1,11 @@
// known-bug: unknown
+// This fails because we currently perform negative coherence in coherence mode.
+// This means that when looking for a negative predicate, we also assemble a
+// coherence-unknowable predicate. Since confirming the negative impl has region
+// obligations, we don't prefer the impl over the unknowable predicate
+// unconditionally and instead flounder.
+
#![feature(negative_impls)]
#![feature(rustc_attrs)]
#![feature(with_negative_coherence)]
diff --git a/tests/ui/coherence/negative-coherence-considering-regions.rs b/tests/ui/coherence/negative-coherence-considering-regions.rs
index 167c7fa211f..597a5972628 100644
--- a/tests/ui/coherence/negative-coherence-considering-regions.rs
+++ b/tests/ui/coherence/negative-coherence-considering-regions.rs
@@ -1,6 +1,12 @@
// revisions: any_lt static_lt
//[static_lt] known-bug: unknown
+// This fails because we currently perform negative coherence in coherence mode.
+// This means that when looking for a negative predicate, we also assemble a
+// coherence-unknowable predicate. Since confirming the negative impl has region
+// obligations, we don't prefer the impl over the unknowable predicate
+// unconditionally and instead flounder.
+
#![feature(negative_impls)]
#![feature(with_negative_coherence)]