Auto merge of #18317 - lnicola:sync-from-rust, r=Veykril

minor: sync from downstream

4 files changed, 42 insertions, 30 deletions

diff --git a/compiler/rustc_trait_selection/src/solve/delegate.rs b/compiler/rustc_trait_selection/src/solve/delegate.rs
index 5c344930314..df9ac2b80fd 100644
--- a/compiler/rustc_trait_selection/src/solve/delegate.rs
+++ b/compiler/rustc_trait_selection/src/solve/delegate.rs
@@ -223,6 +223,8 @@ impl<'tcx> rustc_next_trait_solver::delegate::SolverDelegate for SolverDelegate<
         if eligible { Ok(Some(node_item.item.def_id)) } else { Ok(None) }
     }
 
+    // FIXME: This actually should destructure the `Result` we get from transmutability and
+    // register candidates. We probably need to register >1 since we may have an OR of ANDs.
     fn is_transmutable(
         &self,
         param_env: ty::ParamEnv<'tcx>,
diff --git a/compiler/rustc_trait_selection/src/solve/fulfill.rs b/compiler/rustc_trait_selection/src/solve/fulfill.rs
index c6e3ba3c957..53e5420d27a 100644
--- a/compiler/rustc_trait_selection/src/solve/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/solve/fulfill.rs
@@ -2,18 +2,19 @@ use std::marker::PhantomData;
 use std::mem;
 use std::ops::ControlFlow;
 
+use rustc_data_structures::thinvec::ExtractIf;
 use rustc_infer::infer::InferCtxt;
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::solve::{CandidateSource, GoalSource, MaybeCause};
 use rustc_infer::traits::{
     self, FromSolverError, MismatchedProjectionTypes, Obligation, ObligationCause,
-    ObligationCauseCode, PredicateObligation, SelectionError, TraitEngine,
+    ObligationCauseCode, PredicateObligation, PredicateObligations, SelectionError, TraitEngine,
 };
 use rustc_middle::bug;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::{self, TyCtxt};
-use rustc_next_trait_solver::solve::{GenerateProofTree, SolverDelegateEvalExt as _};
-use tracing::instrument;
+use rustc_next_trait_solver::solve::{GenerateProofTree, HasChanged, SolverDelegateEvalExt as _};
+use tracing::{instrument, trace};
 
 use super::Certainty;
 use super::delegate::SolverDelegate;
@@ -49,8 +50,8 @@ struct ObligationStorage<'tcx> {
     /// We cannot eagerly return these as error so we instead store them here
     /// to avoid recomputing them each time `select_where_possible` is called.
     /// This also allows us to return the correct `FulfillmentError` for them.
-    overflowed: Vec<PredicateObligation<'tcx>>,
-    pending: Vec<PredicateObligation<'tcx>>,
+    overflowed: PredicateObligations<'tcx>,
+    pending: PredicateObligations<'tcx>,
 }
 
 impl<'tcx> ObligationStorage<'tcx> {
@@ -58,13 +59,13 @@ impl<'tcx> ObligationStorage<'tcx> {
         self.pending.push(obligation);
     }
 
-    fn clone_pending(&self) -> Vec<PredicateObligation<'tcx>> {
+    fn clone_pending(&self) -> PredicateObligations<'tcx> {
         let mut obligations = self.pending.clone();
         obligations.extend(self.overflowed.iter().cloned());
         obligations
     }
 
-    fn take_pending(&mut self) -> Vec<PredicateObligation<'tcx>> {
+    fn take_pending(&mut self) -> PredicateObligations<'tcx> {
         let mut obligations = mem::take(&mut self.pending);
         obligations.append(&mut self.overflowed);
         obligations
@@ -81,15 +82,13 @@ impl<'tcx> ObligationStorage<'tcx> {
             // we get all obligations involved in the overflow. We pretty much check: if
             // we were to do another step of `select_where_possible`, which goals would
             // change.
-            self.overflowed.extend(self.pending.extract_if(|o| {
+            // FIXME: <https://github.com/Gankra/thin-vec/pull/66> is merged, this can be removed.
+            self.overflowed.extend(ExtractIf::new(&mut self.pending, |o| {
                 let goal = o.clone().into();
                 let result = <&SolverDelegate<'tcx>>::from(infcx)
                     .evaluate_root_goal(goal, GenerateProofTree::No)
                     .0;
-                match result {
-                    Ok((has_changed, _)) => has_changed,
-                    _ => false,
-                }
+                matches!(result, Ok((HasChanged::Yes, _)))
             }));
         })
     }
@@ -113,7 +112,7 @@ impl<'tcx, E: 'tcx> FulfillmentCtxt<'tcx, E> {
         &self,
         infcx: &InferCtxt<'tcx>,
         obligation: &PredicateObligation<'tcx>,
-        result: &Result<(bool, Certainty), NoSolution>,
+        result: &Result<(HasChanged, Certainty), NoSolution>,
     ) {
         if let Some(inspector) = infcx.obligation_inspector.get() {
             let result = match result {
@@ -181,7 +180,11 @@ where
                         continue;
                     }
                 };
-                has_changed |= changed;
+
+                if changed == HasChanged::Yes {
+                    has_changed = true;
+                }
+
                 match certainty {
                     Certainty::Yes => {}
                     Certainty::Maybe(_) => self.obligations.register(obligation),
@@ -196,14 +199,11 @@ where
         errors
     }
 
-    fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>> {
+    fn pending_obligations(&self) -> PredicateObligations<'tcx> {
         self.obligations.clone_pending()
     }
 
-    fn drain_unstalled_obligations(
-        &mut self,
-        _: &InferCtxt<'tcx>,
-    ) -> Vec<PredicateObligation<'tcx>> {
+    fn drain_unstalled_obligations(&mut self, _: &InferCtxt<'tcx>) -> PredicateObligations<'tcx> {
         self.obligations.take_pending()
     }
 }
@@ -401,6 +401,7 @@ impl<'tcx> BestObligation<'tcx> {
                                         nested_goal.source(),
                                         GoalSource::ImplWhereBound
                                             | GoalSource::InstantiateHigherRanked
+                                            | GoalSource::AliasWellFormed
                                     ) && match self.consider_ambiguities {
                                         true => {
                                             matches!(
@@ -415,6 +416,13 @@ impl<'tcx> BestObligation<'tcx> {
                         })
                     });
                 }
+
+                // Prefer a non-rigid candidate if there is one.
+                if candidates.len() > 1 {
+                    candidates.retain(|candidate| {
+                        !matches!(candidate.kind(), inspect::ProbeKind::RigidAlias { .. })
+                    });
+                }
             }
         }
 
@@ -429,8 +437,11 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
         self.obligation.cause.span
     }
 
+    #[instrument(level = "trace", skip(self, goal), fields(goal = ?goal.goal()))]
     fn visit_goal(&mut self, goal: &inspect::InspectGoal<'_, 'tcx>) -> Self::Result {
         let candidates = self.non_trivial_candidates(goal);
+        trace!(candidates = ?candidates.iter().map(|c| c.kind()).collect::<Vec<_>>());
+
         let [candidate] = candidates.as_slice() else {
             return ControlFlow::Break(self.obligation.clone());
         };
@@ -464,17 +475,13 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
                     polarity: ty::PredicatePolarity::Positive,
                 }))
             }
-            ty::PredicateKind::Clause(
-                ty::ClauseKind::WellFormed(_) | ty::ClauseKind::Projection(..),
-            )
-            | ty::PredicateKind::AliasRelate(..) => ChildMode::PassThrough,
-            _ => {
-                return ControlFlow::Break(self.obligation.clone());
-            }
+            _ => ChildMode::PassThrough,
         };
 
         let mut impl_where_bound_count = 0;
         for nested_goal in candidate.instantiate_nested_goals(self.span()) {
+            trace!(nested_goal = ?(nested_goal.goal(), nested_goal.source(), nested_goal.result()));
+
             let make_obligation = |cause| Obligation {
                 cause,
                 param_env: nested_goal.goal().param_env,
@@ -501,7 +508,7 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
                 (_, GoalSource::InstantiateHigherRanked) => {
                     obligation = self.obligation.clone();
                 }
-                (ChildMode::PassThrough, _) => {
+                (ChildMode::PassThrough, _) | (_, GoalSource::AliasWellFormed) => {
                     obligation = make_obligation(self.obligation.cause.clone());
                 }
             }
diff --git a/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs b/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
index 254620e0b59..4975a9ce0c7 100644
--- a/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
+++ b/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
@@ -292,7 +292,8 @@ impl<'a, 'tcx> InspectGoal<'a, 'tcx> {
                         | inspect::ProbeKind::Root { .. }
                         | inspect::ProbeKind::TryNormalizeNonRigid { .. }
                         | inspect::ProbeKind::TraitCandidate { .. }
-                        | inspect::ProbeKind::OpaqueTypeStorageLookup { .. } => {
+                        | inspect::ProbeKind::OpaqueTypeStorageLookup { .. }
+                        | inspect::ProbeKind::RigidAlias { .. } => {
                             // Nested probes have to prove goals added in their parent
                             // but do not leak them, so we truncate the added goals
                             // afterwards.
@@ -316,7 +317,8 @@ impl<'a, 'tcx> InspectGoal<'a, 'tcx> {
             inspect::ProbeKind::Root { result }
             | inspect::ProbeKind::TryNormalizeNonRigid { result }
             | inspect::ProbeKind::TraitCandidate { source: _, result }
-            | inspect::ProbeKind::OpaqueTypeStorageLookup { result } => {
+            | inspect::ProbeKind::OpaqueTypeStorageLookup { result }
+            | inspect::ProbeKind::RigidAlias { result } => {
                 // We only add a candidate if `shallow_certainty` was set, which means
                 // that we ended up calling `evaluate_added_goals_and_make_canonical_response`.
                 if let Some(shallow_certainty) = shallow_certainty {
diff --git a/compiler/rustc_trait_selection/src/solve/select.rs b/compiler/rustc_trait_selection/src/solve/select.rs
index 257fd263b94..1661852903c 100644
--- a/compiler/rustc_trait_selection/src/solve/select.rs
+++ b/compiler/rustc_trait_selection/src/solve/select.rs
@@ -177,7 +177,8 @@ fn to_selection<'tcx>(
         | ProbeKind::UpcastProjectionCompatibility
         | ProbeKind::OpaqueTypeStorageLookup { result: _ }
         | ProbeKind::Root { result: _ }
-        | ProbeKind::ShadowedEnvProbing => {
+        | ProbeKind::ShadowedEnvProbing
+        | ProbeKind::RigidAlias { result: _ } => {
             span_bug!(span, "didn't expect to assemble trait candidate from {:#?}", cand.kind())
         }
     })