Rollup merge of #121497 - lcnr:coherence-suggest-increasing-recursion-limit, r=compiler-errors

`-Znext-solver=coherence`: suggest increasing recursion limit

r? `@compiler-errors`

compiler/rustc_infer/src/traits/mod.rs

@@ -135,16 +135,18 @@ pub struct FulfillmentError<'tcx> {
 
 #[derive(Clone)]
 pub enum FulfillmentErrorCode<'tcx> {
-    /// Inherently impossible to fulfill; this trait is implemented if and only if it is already implemented.
+    /// Inherently impossible to fulfill; this trait is implemented if and only
+    /// if it is already implemented.
     Cycle(Vec<PredicateObligation<'tcx>>),
     SelectionError(SelectionError<'tcx>),
     ProjectionError(MismatchedProjectionTypes<'tcx>),
     SubtypeError(ExpectedFound<Ty<'tcx>>, TypeError<'tcx>), // always comes from a SubtypePredicate
     ConstEquateError(ExpectedFound<Const<'tcx>>, TypeError<'tcx>),
     Ambiguity {
-        /// Overflow reported from the new solver `-Znext-solver`, which will
+        /// Overflow is only `Some(suggest_recursion_limit)` when using the next generation
-        /// be reported as an regular error as opposed to a fatal error.
+        /// trait solver `-Znext-solver`. With the old solver overflow is eagerly handled by
-        overflow: bool,
+        /// emitting a fatal error instead.
+        overflow: Option<bool>,
     },
 }
 

compiler/rustc_infer/src/traits/structural_impls.rs

@@ -47,8 +47,10 @@ impl<'tcx> fmt::Debug for traits::FulfillmentErrorCode<'tcx> {
             ConstEquateError(ref a, ref b) => {
                 write!(f, "CodeConstEquateError({a:?}, {b:?})")
             }
-            Ambiguity { overflow: false } => write!(f, "Ambiguity"),
+            Ambiguity { overflow: None } => write!(f, "Ambiguity"),
-            Ambiguity { overflow: true } => write!(f, "Overflow"),
+            Ambiguity { overflow: Some(suggest_increasing_limit) } => {
+                write!(f, "Overflow({suggest_increasing_limit})")
+            }
             Cycle(ref cycle) => write!(f, "Cycle({cycle:?})"),
         }
     }

compiler/rustc_middle/src/traits/solve.rs

@@ -60,7 +60,6 @@ pub enum Certainty {
 
 impl Certainty {
     pub const AMBIGUOUS: Certainty = Certainty::Maybe(MaybeCause::Ambiguity);
-    pub const OVERFLOW: Certainty = Certainty::Maybe(MaybeCause::Overflow);
 
     /// Use this function to merge the certainty of multiple nested subgoals.
     ///
@@ -79,15 +78,12 @@ impl Certainty {
             (Certainty::Yes, Certainty::Yes) => Certainty::Yes,
             (Certainty::Yes, Certainty::Maybe(_)) => other,
             (Certainty::Maybe(_), Certainty::Yes) => self,
-            (Certainty::Maybe(MaybeCause::Ambiguity), Certainty::Maybe(MaybeCause::Ambiguity)) => {
+            (Certainty::Maybe(a), Certainty::Maybe(b)) => Certainty::Maybe(a.unify_with(b)),
-                Certainty::Maybe(MaybeCause::Ambiguity)
-            }
-            (Certainty::Maybe(MaybeCause::Ambiguity), Certainty::Maybe(MaybeCause::Overflow))
-            | (Certainty::Maybe(MaybeCause::Overflow), Certainty::Maybe(MaybeCause::Ambiguity))
-            | (Certainty::Maybe(MaybeCause::Overflow), Certainty::Maybe(MaybeCause::Overflow)) => {
-                Certainty::Maybe(MaybeCause::Overflow)
         }
     }
+
+    pub const fn overflow(suggest_increasing_limit: bool) -> Certainty {
+        Certainty::Maybe(MaybeCause::Overflow { suggest_increasing_limit })
     }
 }
 
@@ -99,7 +95,21 @@ pub enum MaybeCause {
     /// or we hit a case where we just don't bother, e.g. `?x: Trait` goals.
     Ambiguity,
     /// We gave up due to an overflow, most often by hitting the recursion limit.
-    Overflow,
+    Overflow { suggest_increasing_limit: bool },
+}
+
+impl MaybeCause {
+    fn unify_with(self, other: MaybeCause) -> MaybeCause {
+        match (self, other) {
+            (MaybeCause::Ambiguity, MaybeCause::Ambiguity) => MaybeCause::Ambiguity,
+            (MaybeCause::Ambiguity, MaybeCause::Overflow { .. }) => other,
+            (MaybeCause::Overflow { .. }, MaybeCause::Ambiguity) => self,
+            (
+                MaybeCause::Overflow { suggest_increasing_limit: a },
+                MaybeCause::Overflow { suggest_increasing_limit: b },
+            ) => MaybeCause::Overflow { suggest_increasing_limit: a || b },
+        }
+    }
 }
 
 #[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, HashStable, TypeFoldable, TypeVisitable)]

compiler/rustc_trait_selection/src/solve/alias_relate.rs

@@ -36,11 +36,13 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         let Goal { param_env, predicate: (lhs, rhs, direction) } = goal;
 
         let Some(lhs) = self.try_normalize_term(param_env, lhs)? else {
-            return self.evaluate_added_goals_and_make_canonical_response(Certainty::OVERFLOW);
+            return self
+                .evaluate_added_goals_and_make_canonical_response(Certainty::overflow(true));
         };
 
         let Some(rhs) = self.try_normalize_term(param_env, rhs)? else {
-            return self.evaluate_added_goals_and_make_canonical_response(Certainty::OVERFLOW);
+            return self
+                .evaluate_added_goals_and_make_canonical_response(Certainty::overflow(true));
         };
 
         let variance = match direction {

compiler/rustc_trait_selection/src/solve/eval_ctxt/mod.rs

@@ -7,6 +7,7 @@ use rustc_infer::infer::{
     BoundRegionConversionTime, DefineOpaqueTypes, InferCtxt, InferOk, TyCtxtInferExt,
 };
 use rustc_infer::traits::query::NoSolution;
+use rustc_infer::traits::solve::MaybeCause;
 use rustc_infer::traits::ObligationCause;
 use rustc_middle::infer::canonical::CanonicalVarInfos;
 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
@@ -29,7 +30,7 @@ use std::ops::ControlFlow;
 use crate::traits::vtable::{count_own_vtable_entries, prepare_vtable_segments, VtblSegment};
 
 use super::inspect::ProofTreeBuilder;
-use super::{search_graph, GoalEvaluationKind};
+use super::{search_graph, GoalEvaluationKind, FIXPOINT_STEP_LIMIT};
 use super::{search_graph::SearchGraph, Goal};
 use super::{GoalSource, SolverMode};
 pub use select::InferCtxtSelectExt;
@@ -154,10 +155,6 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
         self.search_graph.solver_mode()
     }
 
-    pub(super) fn local_overflow_limit(&self) -> usize {
-        self.search_graph.local_overflow_limit()
-    }
-
     /// Creates a root evaluation context and search graph. This should only be
     /// used from outside of any evaluation, and other methods should be preferred
     /// over using this manually (such as [`InferCtxtEvalExt::evaluate_root_goal`]).
@@ -167,7 +164,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
         f: impl FnOnce(&mut EvalCtxt<'_, 'tcx>) -> R,
     ) -> (R, Option<inspect::GoalEvaluation<'tcx>>) {
         let mode = if infcx.intercrate { SolverMode::Coherence } else { SolverMode::Normal };
-        let mut search_graph = search_graph::SearchGraph::new(infcx.tcx, mode);
+        let mut search_graph = search_graph::SearchGraph::new(mode);
 
         let mut ecx = EvalCtxt {
             search_graph: &mut search_graph,
@@ -388,9 +385,12 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
                 && source != GoalSource::ImplWhereBound
         };
 
-        if response.value.certainty == Certainty::OVERFLOW && !keep_overflow_constraints() {
+        if let Certainty::Maybe(MaybeCause::Overflow { .. }) = response.value.certainty
-            (Certainty::OVERFLOW, false)
+            && !keep_overflow_constraints()
-        } else {
+        {
+            return (response.value.certainty, false);
+        }
+
         let has_changed = !response.value.var_values.is_identity_modulo_regions()
             || !response.value.external_constraints.opaque_types.is_empty();
 
@@ -398,7 +398,6 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
             self.instantiate_and_apply_query_response(param_env, original_values, response);
         (certainty, has_changed)
     }
-    }
 
     fn compute_goal(&mut self, goal: Goal<'tcx, ty::Predicate<'tcx>>) -> QueryResult<'tcx> {
         let Goal { param_env, predicate } = goal;
@@ -466,8 +465,8 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
         let inspect = self.inspect.new_evaluate_added_goals();
         let inspect = core::mem::replace(&mut self.inspect, inspect);
 
-        let mut response = Ok(Certainty::OVERFLOW);
+        let mut response = Ok(Certainty::overflow(false));
-        for _ in 0..self.local_overflow_limit() {
+        for _ in 0..FIXPOINT_STEP_LIMIT {
             // FIXME: This match is a bit ugly, it might be nice to change the inspect
             // stuff to use a closure instead. which should hopefully simplify this a bit.
             match self.evaluate_added_goals_step() {

compiler/rustc_trait_selection/src/solve/fulfill.rs

@@ -24,7 +24,7 @@ use super::{Certainty, InferCtxtEvalExt};
 /// It is also likely that we want to use slightly different datastructures
 /// here as this will have to deal with far more root goals than `evaluate_all`.
 pub struct FulfillmentCtxt<'tcx> {
-    obligations: Vec<PredicateObligation<'tcx>>,
+    obligations: ObligationStorage<'tcx>,
 
     /// The snapshot in which this context was created. Using the context
     /// outside of this snapshot leads to subtle bugs if the snapshot
@@ -33,6 +33,57 @@ pub struct FulfillmentCtxt<'tcx> {
     usable_in_snapshot: usize,
 }
 
+#[derive(Default)]
+struct ObligationStorage<'tcx> {
+    /// Obligations which resulted in an overflow in fulfillment itself.
+    ///
+    /// 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>>,
+}
+
+impl<'tcx> ObligationStorage<'tcx> {
+    fn register(&mut self, obligation: PredicateObligation<'tcx>) {
+        self.pending.push(obligation);
+    }
+
+    fn clone_pending(&self) -> Vec<PredicateObligation<'tcx>> {
+        let mut obligations = self.pending.clone();
+        obligations.extend(self.overflowed.iter().cloned());
+        obligations
+    }
+
+    fn take_pending(&mut self) -> Vec<PredicateObligation<'tcx>> {
+        let mut obligations = mem::take(&mut self.pending);
+        obligations.extend(self.overflowed.drain(..));
+        obligations
+    }
+
+    fn unstalled_for_select(&mut self) -> impl Iterator<Item = PredicateObligation<'tcx>> {
+        mem::take(&mut self.pending).into_iter()
+    }
+
+    fn on_fulfillment_overflow(&mut self, infcx: &InferCtxt<'tcx>) {
+        infcx.probe(|_| {
+            // IMPORTANT: we must not use solve any inference variables in the obligations
+            // as this is all happening inside of a probe. We use a probe to make sure
+            // 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| {
+                let goal = o.clone().into();
+                let result = infcx.evaluate_root_goal(goal, GenerateProofTree::Never).0;
+                match result {
+                    Ok((has_changed, _)) => has_changed,
+                    _ => false,
+                }
+            }));
+        })
+    }
+}
+
 impl<'tcx> FulfillmentCtxt<'tcx> {
     pub fn new(infcx: &InferCtxt<'tcx>) -> FulfillmentCtxt<'tcx> {
         assert!(
@@ -40,7 +91,10 @@ impl<'tcx> FulfillmentCtxt<'tcx> {
             "new trait solver fulfillment context created when \
             infcx is set up for old trait solver"
         );
-        FulfillmentCtxt { obligations: Vec::new(), usable_in_snapshot: infcx.num_open_snapshots() }
+        FulfillmentCtxt {
+            obligations: Default::default(),
+            usable_in_snapshot: infcx.num_open_snapshots(),
+        }
     }
 
     fn inspect_evaluated_obligation(
@@ -67,40 +121,24 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
         obligation: PredicateObligation<'tcx>,
     ) {
         assert_eq!(self.usable_in_snapshot, infcx.num_open_snapshots());
-        self.obligations.push(obligation);
+        self.obligations.register(obligation);
     }
 
     fn collect_remaining_errors(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
-        self.obligations
+        let mut errors: Vec<_> = self
+            .obligations
+            .pending
             .drain(..)
-            .map(|obligation| {
+            .map(|obligation| fulfillment_error_for_stalled(infcx, obligation))
-                let code = infcx.probe(|_| {
+            .collect();
-                    match infcx
-                        .evaluate_root_goal(obligation.clone().into(), GenerateProofTree::IfEnabled)
-                        .0
-                    {
-                        Ok((_, Certainty::Maybe(MaybeCause::Ambiguity))) => {
-                            FulfillmentErrorCode::Ambiguity { overflow: false }
-                        }
-                        Ok((_, Certainty::Maybe(MaybeCause::Overflow))) => {
-                            FulfillmentErrorCode::Ambiguity { overflow: true }
-                        }
-                        Ok((_, Certainty::Yes)) => {
-                            bug!("did not expect successful goal when collecting ambiguity errors")
-                        }
-                        Err(_) => {
-                            bug!("did not expect selection error when collecting ambiguity errors")
-                        }
-                    }
-                });
 
-                FulfillmentError {
+        errors.extend(self.obligations.overflowed.drain(..).map(|obligation| FulfillmentError {
-                    obligation: obligation.clone(),
+            root_obligation: obligation.clone(),
-                    code,
+            code: FulfillmentErrorCode::Ambiguity { overflow: Some(true) },
-                    root_obligation: obligation,
+            obligation,
-                }
+        }));
-            })
+
-            .collect()
+        errors
     }
 
     fn select_where_possible(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
@@ -108,79 +146,27 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
         let mut errors = Vec::new();
         for i in 0.. {
             if !infcx.tcx.recursion_limit().value_within_limit(i) {
-                // Only return true errors that we have accumulated while processing;
+                self.obligations.on_fulfillment_overflow(infcx);
-                // keep ambiguities around, *including overflows*, because they shouldn't
+                // Only return true errors that we have accumulated while processing.
-                // be considered true errors.
                 return errors;
             }
 
             let mut has_changed = false;
-            for obligation in mem::take(&mut self.obligations) {
+            for obligation in self.obligations.unstalled_for_select() {
                 let goal = obligation.clone().into();
                 let result = infcx.evaluate_root_goal(goal, GenerateProofTree::IfEnabled).0;
                 self.inspect_evaluated_obligation(infcx, &obligation, &result);
                 let (changed, certainty) = match result {
                     Ok(result) => result,
                     Err(NoSolution) => {
-                        errors.push(FulfillmentError {
+                        errors.push(fulfillment_error_for_no_solution(infcx, obligation));
-                            obligation: obligation.clone(),
-                            code: match goal.predicate.kind().skip_binder() {
-                                ty::PredicateKind::Clause(ty::ClauseKind::Projection(_)) => {
-                                    FulfillmentErrorCode::ProjectionError(
-                                        // FIXME: This could be a `Sorts` if the term is a type
-                                        MismatchedProjectionTypes { err: TypeError::Mismatch },
-                                    )
-                                }
-                                ty::PredicateKind::NormalizesTo(..) => {
-                                    FulfillmentErrorCode::ProjectionError(
-                                        MismatchedProjectionTypes { err: TypeError::Mismatch },
-                                    )
-                                }
-                                ty::PredicateKind::AliasRelate(_, _, _) => {
-                                    FulfillmentErrorCode::ProjectionError(
-                                        MismatchedProjectionTypes { err: TypeError::Mismatch },
-                                    )
-                                }
-                                ty::PredicateKind::Subtype(pred) => {
-                                    let (a, b) = infcx.enter_forall_and_leak_universe(
-                                        goal.predicate.kind().rebind((pred.a, pred.b)),
-                                    );
-                                    let expected_found = ExpectedFound::new(true, a, b);
-                                    FulfillmentErrorCode::SubtypeError(
-                                        expected_found,
-                                        TypeError::Sorts(expected_found),
-                                    )
-                                }
-                                ty::PredicateKind::Coerce(pred) => {
-                                    let (a, b) = infcx.enter_forall_and_leak_universe(
-                                        goal.predicate.kind().rebind((pred.a, pred.b)),
-                                    );
-                                    let expected_found = ExpectedFound::new(false, a, b);
-                                    FulfillmentErrorCode::SubtypeError(
-                                        expected_found,
-                                        TypeError::Sorts(expected_found),
-                                    )
-                                }
-                                ty::PredicateKind::Clause(_)
-                                | ty::PredicateKind::ObjectSafe(_)
-                                | ty::PredicateKind::Ambiguous => {
-                                    FulfillmentErrorCode::SelectionError(
-                                        SelectionError::Unimplemented,
-                                    )
-                                }
-                                ty::PredicateKind::ConstEquate(..) => {
-                                    bug!("unexpected goal: {goal:?}")
-                                }
-                            },
-                            root_obligation: obligation,
-                        });
                         continue;
                     }
                 };
                 has_changed |= changed;
                 match certainty {
                     Certainty::Yes => {}
-                    Certainty::Maybe(_) => self.obligations.push(obligation),
+                    Certainty::Maybe(_) => self.obligations.register(obligation),
                 }
             }
 
@@ -193,13 +179,84 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
     }
 
     fn pending_obligations(&self) -> Vec<PredicateObligation<'tcx>> {
-        self.obligations.clone()
+        self.obligations.clone_pending()
     }
 
     fn drain_unstalled_obligations(
         &mut self,
         _: &InferCtxt<'tcx>,
     ) -> Vec<PredicateObligation<'tcx>> {
-        std::mem::take(&mut self.obligations)
+        self.obligations.take_pending()
     }
 }
+
+fn fulfillment_error_for_no_solution<'tcx>(
+    infcx: &InferCtxt<'tcx>,
+    obligation: PredicateObligation<'tcx>,
+) -> FulfillmentError<'tcx> {
+    let code = match obligation.predicate.kind().skip_binder() {
+        ty::PredicateKind::Clause(ty::ClauseKind::Projection(_)) => {
+            FulfillmentErrorCode::ProjectionError(
+                // FIXME: This could be a `Sorts` if the term is a type
+                MismatchedProjectionTypes { err: TypeError::Mismatch },
+            )
+        }
+        ty::PredicateKind::NormalizesTo(..) => {
+            FulfillmentErrorCode::ProjectionError(MismatchedProjectionTypes {
+                err: TypeError::Mismatch,
+            })
+        }
+        ty::PredicateKind::AliasRelate(_, _, _) => {
+            FulfillmentErrorCode::ProjectionError(MismatchedProjectionTypes {
+                err: TypeError::Mismatch,
+            })
+        }
+        ty::PredicateKind::Subtype(pred) => {
+            let (a, b) = infcx.enter_forall_and_leak_universe(
+                obligation.predicate.kind().rebind((pred.a, pred.b)),
+            );
+            let expected_found = ExpectedFound::new(true, a, b);
+            FulfillmentErrorCode::SubtypeError(expected_found, TypeError::Sorts(expected_found))
+        }
+        ty::PredicateKind::Coerce(pred) => {
+            let (a, b) = infcx.enter_forall_and_leak_universe(
+                obligation.predicate.kind().rebind((pred.a, pred.b)),
+            );
+            let expected_found = ExpectedFound::new(false, a, b);
+            FulfillmentErrorCode::SubtypeError(expected_found, TypeError::Sorts(expected_found))
+        }
+        ty::PredicateKind::Clause(_)
+        | ty::PredicateKind::ObjectSafe(_)
+        | ty::PredicateKind::Ambiguous => {
+            FulfillmentErrorCode::SelectionError(SelectionError::Unimplemented)
+        }
+        ty::PredicateKind::ConstEquate(..) => {
+            bug!("unexpected goal: {obligation:?}")
+        }
+    };
+    FulfillmentError { root_obligation: obligation.clone(), code, obligation }
+}
+
+fn fulfillment_error_for_stalled<'tcx>(
+    infcx: &InferCtxt<'tcx>,
+    obligation: PredicateObligation<'tcx>,
+) -> FulfillmentError<'tcx> {
+    let code = infcx.probe(|_| {
+        match infcx.evaluate_root_goal(obligation.clone().into(), GenerateProofTree::Never).0 {
+            Ok((_, Certainty::Maybe(MaybeCause::Ambiguity))) => {
+                FulfillmentErrorCode::Ambiguity { overflow: None }
+            }
+            Ok((_, Certainty::Maybe(MaybeCause::Overflow { suggest_increasing_limit }))) => {
+                FulfillmentErrorCode::Ambiguity { overflow: Some(suggest_increasing_limit) }
+            }
+            Ok((_, Certainty::Yes)) => {
+                bug!("did not expect successful goal when collecting ambiguity errors")
+            }
+            Err(_) => {
+                bug!("did not expect selection error when collecting ambiguity errors")
+            }
+        }
+    });
+
+    FulfillmentError { obligation: obligation.clone(), code, root_obligation: obligation }
+}

compiler/rustc_trait_selection/src/solve/mod.rs

@@ -42,6 +42,17 @@ pub use fulfill::FulfillmentCtxt;
 pub(crate) use normalize::deeply_normalize_for_diagnostics;
 pub use normalize::{deeply_normalize, deeply_normalize_with_skipped_universes};
 
+/// How many fixpoint iterations we should attempt inside of the solver before bailing
+/// with overflow.
+///
+/// We previously used  `tcx.recursion_limit().0.checked_ilog2().unwrap_or(0)` for this.
+/// However, it feels unlikely that uncreasing the recursion limit by a power of two
+/// to get one more itereation is every useful or desirable. We now instead used a constant
+/// here. If there ever ends up some use-cases where a bigger number of fixpoint iterations
+/// is required, we can add a new attribute for that or revert this to be dependant on the
+/// recursion limit again. However, this feels very unlikely.
+const FIXPOINT_STEP_LIMIT: usize = 8;
+
 #[derive(Debug, Clone, Copy)]
 enum SolverMode {
     /// Ordinary trait solving, using everywhere except for coherence.

compiler/rustc_trait_selection/src/solve/search_graph.rs

@@ -1,3 +1,5 @@
+use crate::solve::FIXPOINT_STEP_LIMIT;
+
 use super::inspect;
 use super::inspect::ProofTreeBuilder;
 use super::SolverMode;
@@ -99,7 +101,6 @@ impl<'tcx> ProvisionalCacheEntry<'tcx> {
 
 pub(super) struct SearchGraph<'tcx> {
     mode: SolverMode,
-    local_overflow_limit: usize,
     /// The stack of goals currently being computed.
     ///
     /// An element is *deeper* in the stack if its index is *lower*.
@@ -116,10 +117,9 @@ pub(super) struct SearchGraph<'tcx> {
 }
 
 impl<'tcx> SearchGraph<'tcx> {
-    pub(super) fn new(tcx: TyCtxt<'tcx>, mode: SolverMode) -> SearchGraph<'tcx> {
+    pub(super) fn new(mode: SolverMode) -> SearchGraph<'tcx> {
         Self {
             mode,
-            local_overflow_limit: tcx.recursion_limit().0.checked_ilog2().unwrap_or(0) as usize,
             stack: Default::default(),
             provisional_cache: Default::default(),
             cycle_participants: Default::default(),
@@ -130,10 +130,6 @@ impl<'tcx> SearchGraph<'tcx> {
         self.mode
     }
 
-    pub(super) fn local_overflow_limit(&self) -> usize {
-        self.local_overflow_limit
-    }
-
     /// Update the stack and reached depths on cache hits.
     #[instrument(level = "debug", skip(self))]
     fn on_cache_hit(&mut self, additional_depth: usize, encountered_overflow: bool) {
@@ -277,7 +273,7 @@ impl<'tcx> SearchGraph<'tcx> {
             }
 
             inspect.goal_evaluation_kind(inspect::WipCanonicalGoalEvaluationKind::Overflow);
-            return Self::response_no_constraints(tcx, input, Certainty::OVERFLOW);
+            return Self::response_no_constraints(tcx, input, Certainty::overflow(true));
         };
 
         // Try to fetch the goal from the global cache.
@@ -370,7 +366,7 @@ impl<'tcx> SearchGraph<'tcx> {
             } else if is_coinductive_cycle {
                 Self::response_no_constraints(tcx, input, Certainty::Yes)
             } else {
-                Self::response_no_constraints(tcx, input, Certainty::OVERFLOW)
+                Self::response_no_constraints(tcx, input, Certainty::overflow(false))
             };
         } else {
             // No entry, we push this goal on the stack and try to prove it.
@@ -398,7 +394,7 @@ impl<'tcx> SearchGraph<'tcx> {
                 // of this we continuously recompute the cycle until the result
                 // of the previous iteration is equal to the final result, at which
                 // point we are done.
-                for _ in 0..self.local_overflow_limit() {
+                for _ in 0..FIXPOINT_STEP_LIMIT {
                     let result = prove_goal(self, inspect);
                     let stack_entry = self.pop_stack();
                     debug_assert_eq!(stack_entry.input, input);
@@ -431,7 +427,8 @@ impl<'tcx> SearchGraph<'tcx> {
                     } else if stack_entry.has_been_used == HasBeenUsed::COINDUCTIVE_CYCLE {
                         Self::response_no_constraints(tcx, input, Certainty::Yes) == result
                     } else if stack_entry.has_been_used == HasBeenUsed::INDUCTIVE_CYCLE {
-                        Self::response_no_constraints(tcx, input, Certainty::OVERFLOW) == result
+                        Self::response_no_constraints(tcx, input, Certainty::overflow(false))
+                            == result
                     } else {
                         false
                     };
@@ -452,7 +449,7 @@ impl<'tcx> SearchGraph<'tcx> {
                 debug!("canonical cycle overflow");
                 let current_entry = self.pop_stack();
                 debug_assert!(current_entry.has_been_used.is_empty());
-                let result = Self::response_no_constraints(tcx, input, Certainty::OVERFLOW);
+                let result = Self::response_no_constraints(tcx, input, Certainty::overflow(false));
                 (current_entry, result)
             });
 

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -22,7 +22,7 @@ use rustc_errors::{Diag, EmissionGuarantee};
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, TyCtxtInferExt};
-use rustc_infer::traits::{util, TraitEngine, TraitEngineExt};
+use rustc_infer::traits::{util, FulfillmentErrorCode, TraitEngine, TraitEngineExt};
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::solve::{CandidateSource, Certainty, Goal};
 use rustc_middle::traits::specialization_graph::OverlapMode;
@@ -35,6 +35,8 @@ use rustc_span::DUMMY_SP;
 use std::fmt::Debug;
 use std::ops::ControlFlow;
 
+use super::error_reporting::suggest_new_overflow_limit;
+
 /// Whether we do the orphan check relative to this crate or
 /// to some remote crate.
 #[derive(Copy, Clone, Debug)]
@@ -56,6 +58,9 @@ pub struct OverlapResult<'tcx> {
     /// `true` if the overlap might've been permitted before the shift
     /// to universes.
     pub involves_placeholder: bool,
+
+    /// Used in the new solver to suggest increasing the recursion limit.
+    pub overflowing_predicates: Vec<ty::Predicate<'tcx>>,
 }
 
 pub fn add_placeholder_note<G: EmissionGuarantee>(err: &mut Diag<'_, G>) {
@@ -65,6 +70,18 @@ pub fn add_placeholder_note<G: EmissionGuarantee>(err: &mut Diag<'_, G>) {
     );
 }
 
+pub fn suggest_increasing_recursion_limit<'tcx, G: EmissionGuarantee>(
+    tcx: TyCtxt<'tcx>,
+    err: &mut Diag<'_, G>,
+    overflowing_predicates: &[ty::Predicate<'tcx>],
+) {
+    for pred in overflowing_predicates {
+        err.note(format!("overflow evaluating the requirement `{}`", pred));
+    }
+
+    suggest_new_overflow_limit(tcx, err);
+}
+
 #[derive(Debug, Clone, Copy)]
 enum TrackAmbiguityCauses {
     Yes,
@@ -221,11 +238,13 @@ fn overlap<'tcx>(
         ),
     );
 
+    let mut overflowing_predicates = Vec::new();
     if overlap_mode.use_implicit_negative() {
-        if let Some(_failing_obligation) =
+        match impl_intersection_has_impossible_obligation(selcx, &obligations) {
-            impl_intersection_has_impossible_obligation(selcx, &obligations)
+            IntersectionHasImpossibleObligations::Yes => return None,
-        {
+            IntersectionHasImpossibleObligations::No { overflowing_predicates: p } => {
-            return None;
+                overflowing_predicates = p
+            }
         }
     }
 
@@ -261,7 +280,12 @@ fn overlap<'tcx>(
         impl_header = deeply_normalize_for_diagnostics(&infcx, param_env, impl_header);
     }
 
-    Some(OverlapResult { impl_header, intercrate_ambiguity_causes, involves_placeholder })
+    Some(OverlapResult {
+        impl_header,
+        intercrate_ambiguity_causes,
+        involves_placeholder,
+        overflowing_predicates,
+    })
 }
 
 #[instrument(level = "debug", skip(infcx), ret)]
@@ -287,6 +311,19 @@ fn equate_impl_headers<'tcx>(
     result.map(|infer_ok| infer_ok.obligations).ok()
 }
 
+/// The result of [fn impl_intersection_has_impossible_obligation].
+enum IntersectionHasImpossibleObligations<'tcx> {
+    Yes,
+    No {
+        /// With `-Znext-solver=coherence`, some obligations may
+        /// fail if only the user increased the recursion limit.
+        ///
+        /// We return those obligations here and mention them in the
+        /// error message.
+        overflowing_predicates: Vec<ty::Predicate<'tcx>>,
+    },
+}
+
 /// Check if both impls can be satisfied by a common type by considering whether
 /// any of either impl's obligations is not known to hold.
 ///
@@ -308,7 +345,7 @@ fn equate_impl_headers<'tcx>(
 fn impl_intersection_has_impossible_obligation<'a, 'cx, 'tcx>(
     selcx: &mut SelectionContext<'cx, 'tcx>,
     obligations: &'a [PredicateObligation<'tcx>],
-) -> Option<PredicateObligation<'tcx>> {
+) -> IntersectionHasImpossibleObligations<'tcx> {
     let infcx = selcx.infcx;
 
     if infcx.next_trait_solver() {
@@ -317,28 +354,42 @@ fn impl_intersection_has_impossible_obligation<'a, 'cx, 'tcx>(
 
         // We only care about the obligations that are *definitely* true errors.
         // Ambiguities do not prove the disjointness of two impls.
-        let mut errors = fulfill_cx.select_where_possible(infcx);
+        let errors = fulfill_cx.select_where_possible(infcx);
-        errors.pop().map(|err| err.obligation)
+        if errors.is_empty() {
+            let overflow_errors = fulfill_cx.collect_remaining_errors(infcx);
+            let overflowing_predicates = overflow_errors
+                .into_iter()
+                .filter(|e| match e.code {
+                    FulfillmentErrorCode::Ambiguity { overflow: Some(true) } => true,
+                    _ => false,
+                })
+                .map(|e| infcx.resolve_vars_if_possible(e.obligation.predicate))
+                .collect();
+            IntersectionHasImpossibleObligations::No { overflowing_predicates }
         } else {
-        obligations
+            IntersectionHasImpossibleObligations::Yes
-            .iter()
+        }
-            .find(|obligation| {
+    } else {
+        for obligation in obligations {
             // We use `evaluate_root_obligation` to correctly track intercrate
-                // ambiguity clauses. We cannot use this in the new solver.
+            // ambiguity clauses.
             let evaluation_result = selcx.evaluate_root_obligation(obligation);
 
             match evaluation_result {
-                    Ok(result) => !result.may_apply(),
+                Ok(result) => {
+                    if !result.may_apply() {
+                        return IntersectionHasImpossibleObligations::Yes;
+                    }
+                }
                 // If overflow occurs, we need to conservatively treat the goal as possibly holding,
                 // since there can be instantiations of this goal that don't overflow and result in
-                    // success. This isn't much of a problem in the old solver, since we treat overflow
+                // success. While this isn't much of a problem in the old solver, since we treat overflow
-                    // fatally (this still can be encountered: <https://github.com/rust-lang/rust/issues/105231>),
+                // fatally, this still can be encountered: <https://github.com/rust-lang/rust/issues/105231>.
-                    // but in the new solver, this is very important for correctness, since overflow
+                Err(_overflow) => {}
-                    // *must* be treated as ambiguity for completeness.
-                    Err(_overflow) => false,
             }
-            })
+        }
-            .cloned()
+
+        IntersectionHasImpossibleObligations::No { overflowing_predicates: Vec::new() }
     }
 }
 

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -20,10 +20,9 @@ use crate::traits::{
     SelectionError, SignatureMismatch, TraitNotObjectSafe,
 };
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
-use rustc_errors::{
+use rustc_errors::codes::*;
-    codes::*, pluralize, struct_span_code_err, Applicability, Diag, ErrorGuaranteed, FatalError,
+use rustc_errors::{pluralize, struct_span_code_err, Applicability, MultiSpan, StringPart};
-    MultiSpan, StashKey, StringPart,
+use rustc_errors::{Diag, EmissionGuarantee, ErrorGuaranteed, FatalError, StashKey};
-};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Namespace, Res};
 use rustc_hir::def_id::{DefId, LocalDefId};
@@ -62,6 +61,22 @@ pub enum OverflowCause<'tcx> {
     TraitSolver(ty::Predicate<'tcx>),
 }
 
+pub fn suggest_new_overflow_limit<'tcx, G: EmissionGuarantee>(
+    tcx: TyCtxt<'tcx>,
+    err: &mut Diag<'_, G>,
+) {
+    let suggested_limit = match tcx.recursion_limit() {
+        Limit(0) => Limit(2),
+        limit => limit * 2,
+    };
+    err.help(format!(
+        "consider increasing the recursion limit by adding a \
+         `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)",
+        suggested_limit,
+        tcx.crate_name(LOCAL_CRATE),
+    ));
+}
+
 #[extension(pub trait TypeErrCtxtExt<'tcx>)]
 impl<'tcx> TypeErrCtxt<'_, 'tcx> {
     fn report_fulfillment_errors(
@@ -263,7 +278,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         };
 
         if suggest_increasing_limit {
-            self.suggest_new_overflow_limit(&mut err);
+            suggest_new_overflow_limit(self.tcx, &mut err);
         }
 
         err
@@ -303,19 +318,6 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         );
     }
 
-    fn suggest_new_overflow_limit(&self, err: &mut Diag<'_>) {
-        let suggested_limit = match self.tcx.recursion_limit() {
-            Limit(0) => Limit(2),
-            limit => limit * 2,
-        };
-        err.help(format!(
-            "consider increasing the recursion limit by adding a \
-             `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)",
-            suggested_limit,
-            self.tcx.crate_name(LOCAL_CRATE),
-        ));
-    }
-
     /// Reports that a cycle was detected which led to overflow and halts
     /// compilation. This is equivalent to `report_overflow_obligation` except
     /// that we can give a more helpful error message (and, in particular,
@@ -335,12 +337,16 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         );
     }
 
-    fn report_overflow_no_abort(&self, obligation: PredicateObligation<'tcx>) -> ErrorGuaranteed {
+    fn report_overflow_no_abort(
+        &self,
+        obligation: PredicateObligation<'tcx>,
+        suggest_increasing_limit: bool,
+    ) -> ErrorGuaranteed {
         let obligation = self.resolve_vars_if_possible(obligation);
         let mut err = self.build_overflow_error(
             OverflowCause::TraitSolver(obligation.predicate),
             obligation.cause.span,
-            true,
+            suggest_increasing_limit,
         );
         self.note_obligation_cause(&mut err, &obligation);
         self.point_at_returns_when_relevant(&mut err, &obligation);
@@ -1422,11 +1428,11 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             FulfillmentErrorCode::ProjectionError(ref e) => {
                 self.report_projection_error(&error.obligation, e)
             }
-            FulfillmentErrorCode::Ambiguity { overflow: false } => {
+            FulfillmentErrorCode::Ambiguity { overflow: None } => {
                 self.maybe_report_ambiguity(&error.obligation)
             }
-            FulfillmentErrorCode::Ambiguity { overflow: true } => {
+            FulfillmentErrorCode::Ambiguity { overflow: Some(suggest_increasing_limit) } => {
-                self.report_overflow_no_abort(error.obligation.clone())
+                self.report_overflow_no_abort(error.obligation.clone(), suggest_increasing_limit)
             }
             FulfillmentErrorCode::SubtypeError(ref expected_found, ref err) => self
                 .report_mismatched_types(

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -138,7 +138,7 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentContext<'tcx> {
         _infcx: &InferCtxt<'tcx>,
     ) -> Vec<FulfillmentError<'tcx>> {
         self.predicates
-            .to_errors(FulfillmentErrorCode::Ambiguity { overflow: false })
+            .to_errors(FulfillmentErrorCode::Ambiguity { overflow: None })
             .into_iter()
             .map(to_fulfillment_error)
             .collect()

compiler/rustc_trait_selection/src/traits/specialize/mod.rs

@@ -39,6 +39,7 @@ pub struct OverlapError<'tcx> {
     pub self_ty: Option<Ty<'tcx>>,
     pub intercrate_ambiguity_causes: FxIndexSet<IntercrateAmbiguityCause<'tcx>>,
     pub involves_placeholder: bool,
+    pub overflowing_predicates: Vec<ty::Predicate<'tcx>>,
 }
 
 /// Given the generic parameters for the requested impl, translate it to the generic parameters
@@ -435,6 +436,14 @@ fn report_conflicting_impls<'tcx>(
         if overlap.involves_placeholder {
             coherence::add_placeholder_note(err);
         }
+
+        if !overlap.overflowing_predicates.is_empty() {
+            coherence::suggest_increasing_recursion_limit(
+                tcx,
+                err,
+                &overlap.overflowing_predicates,
+            );
+        }
     }
 
     let msg = DelayDm(|| {

compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs

@@ -103,6 +103,7 @@ impl<'tcx> Children {
                     self_ty: self_ty.has_concrete_skeleton().then_some(self_ty),
                     intercrate_ambiguity_causes: overlap.intercrate_ambiguity_causes,
                     involves_placeholder: overlap.involves_placeholder,
+                    overflowing_predicates: overlap.overflowing_predicates,
                 }
             };
 

tests/ui/higher-ranked/trait-bounds/issue-95230.next.stderr

@@ -4,7 +4,6 @@ error[E0275]: overflow evaluating the requirement `for<'a> &'a mut Bar well-form
 LL |     for<'a> &'a mut Self:;
    |             ^^^^^^^^^^^^
    |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`issue_95230`)
 note: required by a bound in `Bar`
   --> $DIR/issue-95230.rs:9:13
    |

tests/ui/lazy-type-alias/inherent-impls-overflow.next.stderr

@@ -3,8 +3,6 @@ error[E0275]: overflow evaluating the requirement `Loop == _`
    |
 LL | impl Loop {}
    |      ^^^^
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`inherent_impls_overflow`)
 
 error[E0392]: type parameter `T` is never used
   --> $DIR/inherent-impls-overflow.rs:13:12

tests/ui/traits/next-solver/alias-bound-unsound.stderr

@@ -4,7 +4,6 @@ error[E0275]: overflow evaluating the requirement `String: Copy`
 LL |     type Item = String where String: Copy;
    |                                      ^^^^
    |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`alias_bound_unsound`)
 note: the requirement `String: Copy` appears on the `impl`'s associated type `Item` but not on the corresponding trait's associated type
   --> $DIR/alias-bound-unsound.rs:8:10
    |
@@ -18,32 +17,24 @@ error[E0275]: overflow evaluating the requirement `String <: <() as Foo>::Item`
    |
 LL |     drop(<() as Foo>::copy_me(&x));
    |                               ^^
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`alias_bound_unsound`)
 
 error[E0275]: overflow evaluating the requirement `<() as Foo>::Item == _`
   --> $DIR/alias-bound-unsound.rs:24:10
    |
 LL |     drop(<() as Foo>::copy_me(&x));
    |          ^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`alias_bound_unsound`)
 
 error[E0275]: overflow evaluating the requirement `&<() as Foo>::Item well-formed`
   --> $DIR/alias-bound-unsound.rs:24:31
    |
 LL |     drop(<() as Foo>::copy_me(&x));
    |                               ^^
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`alias_bound_unsound`)
 
 error[E0275]: overflow evaluating the requirement `<() as Foo>::Item well-formed`
   --> $DIR/alias-bound-unsound.rs:24:10
    |
 LL |     drop(<() as Foo>::copy_me(&x));
    |          ^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`alias_bound_unsound`)
 
 error[E0275]: overflow evaluating the requirement `<() as Foo>::Item == _`
   --> $DIR/alias-bound-unsound.rs:24:10
@@ -51,7 +42,6 @@ error[E0275]: overflow evaluating the requirement `<() as Foo>::Item == _`
 LL |     drop(<() as Foo>::copy_me(&x));
    |          ^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`alias_bound_unsound`)
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: aborting due to 6 previous errors

tests/ui/traits/next-solver/coherence-fulfill-overflow.stderr

@@ -5,6 +5,9 @@ LL | impl<T: ?Sized + TwoW> Trait for W<T> {}
    | ------------------------------------- first implementation here
 LL | impl<T: ?Sized + TwoW> Trait for T {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<_>>>>>>>>>>>>>>>>>>>>>`
+   |
+   = note: overflow evaluating the requirement `W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<W<_>>>>>>>>>>>>>>>>>>>>>: TwoW`
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "20"]` attribute to your crate (`coherence_fulfill_overflow`)
 
 error: aborting due to 1 previous error
 

tests/ui/traits/next-solver/coherence/trait_ref_is_knowable-norm-overflow.stderr

@@ -6,6 +6,9 @@ LL | impl<T: Copy> Trait for T {}
 LL | struct LocalTy;
 LL | impl Trait for <LocalTy as Overflow>::Assoc {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation
+   |
+   = note: overflow evaluating the requirement `_ == <LocalTy as Overflow>::Assoc`
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`trait_ref_is_knowable_norm_overflow`)
 
 error[E0275]: overflow evaluating the requirement `<T as Overflow>::Assoc: Sized`
   --> $DIR/trait_ref_is_knowable-norm-overflow.rs:10:18

tests/ui/traits/next-solver/cycles/coinduction/fixpoint-exponential-growth.stderr

@@ -4,7 +4,6 @@ error[E0275]: overflow evaluating the requirement `W<_>: Trait`
 LL |     impls::<W<_>>();
    |             ^^^^
    |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`fixpoint_exponential_growth`)
 note: required by a bound in `impls`
   --> $DIR/fixpoint-exponential-growth.rs:30:13
    |

tests/ui/traits/next-solver/cycles/double-cycle-inductive-coinductive.stderr

@@ -4,7 +4,6 @@ error[E0275]: overflow evaluating the requirement `(): Trait`
 LL |     impls_trait::<()>();
    |                   ^^
    |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`double_cycle_inductive_coinductive`)
 note: required by a bound in `impls_trait`
   --> $DIR/double-cycle-inductive-coinductive.rs:17:19
    |
@@ -17,7 +16,6 @@ error[E0275]: overflow evaluating the requirement `(): TraitRev`
 LL |     impls_trait_rev::<()>();
    |                       ^^
    |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`double_cycle_inductive_coinductive`)
 note: required by a bound in `impls_trait_rev`
   --> $DIR/double-cycle-inductive-coinductive.rs:29:23
    |

tests/ui/traits/next-solver/cycles/inductive-fixpoint-hang.stderr

@@ -4,7 +4,6 @@ error[E0275]: overflow evaluating the requirement `W<_>: Trait`
 LL |     impls_trait::<W<_>>();
    |                   ^^^^
    |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`inductive_fixpoint_hang`)
 note: required by a bound in `impls_trait`
   --> $DIR/inductive-fixpoint-hang.rs:28:19
    |

tests/ui/traits/next-solver/cycles/inductive-not-on-stack.stderr

@@ -4,7 +4,6 @@ error[E0275]: overflow evaluating the requirement `(): A`
 LL |     impls_a::<()>();
    |               ^^
    |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`inductive_not_on_stack`)
 note: required by a bound in `impls_a`
   --> $DIR/inductive-not-on-stack.rs:25:15
    |
@@ -17,7 +16,6 @@ error[E0275]: overflow evaluating the requirement `(): AR`
 LL |     impls_ar::<()>();
    |                ^^
    |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`inductive_not_on_stack`)
 note: required by a bound in `impls_ar`
   --> $DIR/inductive-not-on-stack.rs:38:16
    |

tests/ui/traits/next-solver/cycles/mixed-cycles-1.stderr

@@ -4,7 +4,6 @@ error[E0275]: overflow evaluating the requirement `(): A`
 LL |     impls_a::<()>();
    |               ^^
    |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`mixed_cycles_1`)
 note: required by a bound in `impls_a`
   --> $DIR/mixed-cycles-1.rs:34:15
    |

tests/ui/traits/next-solver/cycles/mixed-cycles-2.stderr

@@ -4,7 +4,6 @@ error[E0275]: overflow evaluating the requirement `(): A`
 LL |     impls_a::<()>();
    |               ^^
    |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`mixed_cycles_2`)
 note: required by a bound in `impls_a`
   --> $DIR/mixed-cycles-2.rs:27:15
    |

tests/ui/traits/next-solver/normalize-param-env-2.stderr

@@ -4,7 +4,6 @@ error[E0275]: overflow evaluating the requirement `<() as A<T>>::Assoc: A<T>`
 LL |         Self::Assoc: A<T>,
    |                      ^^^^
    |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`normalize_param_env_2`)
 note: the requirement `<() as A<T>>::Assoc: A<T>` appears on the `impl`'s method `f` but not on the corresponding trait's method
   --> $DIR/normalize-param-env-2.rs:12:8
    |
@@ -19,24 +18,18 @@ error[E0275]: overflow evaluating the requirement `<() as A<T>>::Assoc: A<T>`
    |
 LL |         Self::Assoc: A<T>,
    |                      ^^^^
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`normalize_param_env_2`)
 
 error[E0275]: overflow evaluating the requirement `<() as A<T>>::Assoc well-formed`
   --> $DIR/normalize-param-env-2.rs:24:22
    |
 LL |         Self::Assoc: A<T>,
    |                      ^^^^
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`normalize_param_env_2`)
 
 error[E0275]: overflow evaluating the requirement `(): A<T>`
   --> $DIR/normalize-param-env-2.rs:27:10
    |
 LL |         <() as A<T>>::f();
    |          ^^
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`normalize_param_env_2`)
 
 error[E0275]: overflow evaluating the requirement `<() as A<T>>::Assoc: A<T>`
   --> $DIR/normalize-param-env-2.rs:27:9
@@ -44,7 +37,6 @@ error[E0275]: overflow evaluating the requirement `<() as A<T>>::Assoc: A<T>`
 LL |         <() as A<T>>::f();
    |         ^^^^^^^^^^^^^^^^^
    |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`normalize_param_env_2`)
 note: required by a bound in `A::f`
   --> $DIR/normalize-param-env-2.rs:14:22
    |

tests/ui/traits/next-solver/normalize-param-env-4.next.stderr

@@ -3,16 +3,12 @@ error[E0275]: overflow evaluating the requirement `<T as Trait>::Assoc: Trait`
    |
 LL |     <T as Trait>::Assoc: Trait,
    |                          ^^^^^
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`normalize_param_env_4`)
 
 error[E0275]: overflow evaluating the requirement `<T as Trait>::Assoc well-formed`
   --> $DIR/normalize-param-env-4.rs:18:26
    |
 LL |     <T as Trait>::Assoc: Trait,
    |                          ^^^^^
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`normalize_param_env_4`)
 
 error[E0275]: overflow evaluating the requirement `T: Trait`
   --> $DIR/normalize-param-env-4.rs:31:19
@@ -20,7 +16,6 @@ error[E0275]: overflow evaluating the requirement `T: Trait`
 LL |     impls_trait::<T>();
    |                   ^
    |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`normalize_param_env_4`)
 note: required by a bound in `impls_trait`
   --> $DIR/normalize-param-env-4.rs:14:19
    |

tests/ui/traits/next-solver/overflow/exponential-trait-goals.stderr

@@ -4,7 +4,6 @@ error[E0275]: overflow evaluating the requirement `W<_>: Trait`
 LL |     impls::<W<_>>();
    |             ^^^^
    |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`exponential_trait_goals`)
 note: required by a bound in `impls`
   --> $DIR/exponential-trait-goals.rs:14:13
    |

tests/ui/traits/next-solver/overflow/recursion-limit-zero-issue-115351.rs

@@ -1,12 +1,7 @@
-//~ ERROR overflow evaluating the requirement `Self well-formed`
-//~| ERROR overflow evaluating the requirement `Self: Trait`
-
 // This is a non-regression test for issue #115351, where a recursion limit of 0 caused an ICE.
 //@ compile-flags: -Znext-solver --crate-type=lib
-//@ check-fail
+//@ check-pass
 
 #![recursion_limit = "0"]
 trait Trait {}
 impl Trait for u32 {}
-//~^ ERROR overflow evaluating the requirement `u32: Trait`
-//~| ERROR overflow evaluating the requirement `u32 well-formed`

tests/ui/traits/next-solver/overflow/recursion-limit-zero-issue-115351.stderr

@@ -1,27 +0,0 @@
-error[E0275]: overflow evaluating the requirement `Self: Trait`
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "2"]` attribute to your crate (`recursion_limit_zero_issue_115351`)
-
-error[E0275]: overflow evaluating the requirement `Self well-formed`
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "2"]` attribute to your crate (`recursion_limit_zero_issue_115351`)
-
-error[E0275]: overflow evaluating the requirement `u32: Trait`
-  --> $DIR/recursion-limit-zero-issue-115351.rs:10:16
-   |
-LL | impl Trait for u32 {}
-   |                ^^^
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "2"]` attribute to your crate (`recursion_limit_zero_issue_115351`)
-
-error[E0275]: overflow evaluating the requirement `u32 well-formed`
-  --> $DIR/recursion-limit-zero-issue-115351.rs:10:16
-   |
-LL | impl Trait for u32 {}
-   |                ^^^
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "2"]` attribute to your crate (`recursion_limit_zero_issue_115351`)
-
-error: aborting due to 4 previous errors
-
-For more information about this error, try `rustc --explain E0275`.