Opt-in diagnostics reporting to avoid doing extra work in the new solver

compiler/rustc_trait_selection/src/infer.rs

@@ -1,14 +1,16 @@
+use crate::solve::NextSolverError;
 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
-use crate::traits::{self, ObligationCtxt, SelectionContext};
+use crate::traits::{
+    self, FromSolverError, Obligation, ObligationCause, ObligationCtxt, OldSolverError,
+    SelectionContext,
+};
 
 use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
-use rustc_infer::traits::Obligation;
 use rustc_macros::extension;
 use rustc_middle::arena::ArenaAllocatable;
 use rustc_middle::infer::canonical::{Canonical, CanonicalQueryResponse, QueryResponse};
 use rustc_middle::traits::query::NoSolution;
-use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeVisitableExt};
 use rustc_middle::ty::{GenericArg, Upcast};
 use rustc_span::DUMMY_SP;
@@ -94,7 +96,7 @@ impl<'tcx> InferCtxt<'tcx> {
                 ty::TraitRef::new(self.tcx, trait_def_id, [ty]),
             )) {
                 Ok(Some(selection)) => {
-                    let ocx = ObligationCtxt::new(self);
+                    let ocx = ObligationCtxt::new_with_diagnostics(self);
                     ocx.register_obligations(selection.nested_obligations());
                     Some(ocx.select_all_or_error())
                 }
@@ -122,19 +124,21 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
     /// bound for the closure and in part because it is convenient to
     /// have `'tcx` be free on this function so that we can talk about
     /// `K: TypeFoldable<TyCtxt<'tcx>>`.)
-    fn enter_canonical_trait_query<K, R>(
+    fn enter_canonical_trait_query<K, R, E>(
         self,
         canonical_key: &Canonical<'tcx, K>,
-        operation: impl FnOnce(&ObligationCtxt<'_, 'tcx>, K) -> Result<R, NoSolution>,
+        operation: impl FnOnce(&ObligationCtxt<'_, 'tcx, E>, K) -> Result<R, NoSolution>,
     ) -> Result<CanonicalQueryResponse<'tcx, R>, NoSolution>
     where
         K: TypeFoldable<TyCtxt<'tcx>>,
         R: Debug + TypeFoldable<TyCtxt<'tcx>>,
         Canonical<'tcx, QueryResponse<'tcx, R>>: ArenaAllocatable<'tcx>,
+        E: FromSolverError<'tcx, NextSolverError<'tcx>>
+            + FromSolverError<'tcx, OldSolverError<'tcx>>,
     {
         let (infcx, key, canonical_inference_vars) =
             self.build_with_canonical(DUMMY_SP, canonical_key);
-        let ocx = ObligationCtxt::new(&infcx);
+        let ocx = ObligationCtxt::new_generic(&infcx);
         let value = operation(&ocx, key)?;
         ocx.make_canonicalized_query_response(canonical_inference_vars, value)
     }

compiler/rustc_trait_selection/src/solve/fulfill.rs

@@ -15,7 +15,7 @@ use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::symbol::sym;
 
-use crate::traits::FulfillmentError;
+use crate::traits::{FulfillmentError, ScrubbedTraitError};
 
 use super::eval_ctxt::GenerateProofTree;
 use super::inspect::{self, ProofTreeInferCtxtExt, ProofTreeVisitor};
@@ -226,6 +226,17 @@ impl<'tcx> FromSolverError<'tcx, NextSolverError<'tcx>> for FulfillmentError<'tc
     }
 }
 
+impl<'tcx> FromSolverError<'tcx, NextSolverError<'tcx>> for ScrubbedTraitError {
+    fn from_solver_error(_infcx: &InferCtxt<'tcx>, error: NextSolverError<'tcx>) -> Self {
+        match error {
+            NextSolverError::TrueError(_) => ScrubbedTraitError::TrueError,
+            NextSolverError::Ambiguity(_) | NextSolverError::Overflow(_) => {
+                ScrubbedTraitError::Ambiguity
+            }
+        }
+    }
+}
+
 fn fulfillment_error_for_no_solution<'tcx>(
     infcx: &InferCtxt<'tcx>,
     root_obligation: PredicateObligation<'tcx>,

compiler/rustc_trait_selection/src/solve/inspect/analyse.rs

@@ -12,6 +12,7 @@
 use rustc_ast_ir::try_visit;
 use rustc_ast_ir::visit::VisitorResult;
 use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, InferOk};
+use rustc_infer::traits::FulfillmentErrorLike as _;
 use rustc_macros::extension;
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::solve::{inspect, QueryResult};

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -360,7 +360,7 @@ fn impl_intersection_has_impossible_obligation<'a, 'cx, 'tcx>(
     let infcx = selcx.infcx;
 
     if infcx.next_trait_solver() {
-        let ocx = ObligationCtxt::new(infcx);
+        let ocx = ObligationCtxt::new_with_diagnostics(infcx);
         ocx.register_obligations(obligations.iter().cloned());
         let errors_and_ambiguities = ocx.select_all_or_error();
         // We only care about the obligations that are *definitely* true errors.

compiler/rustc_trait_selection/src/traits/engine.rs

@@ -1,8 +1,8 @@
 use std::cell::RefCell;
 use std::fmt::Debug;
 
-use super::FulfillmentContext;
 use super::{FromSolverError, TraitEngine};
+use super::{FulfillmentContext, ScrubbedTraitError};
 use crate::regions::InferCtxtRegionExt;
 use crate::solve::FulfillmentCtxt as NextFulfillmentCtxt;
 use crate::solve::NextSolverError;
@@ -21,6 +21,7 @@ use rustc_infer::infer::canonical::{
 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
 use rustc_infer::infer::RegionResolutionError;
 use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, InferOk};
+use rustc_infer::traits::FulfillmentErrorLike;
 use rustc_macros::extension;
 use rustc_middle::arena::ArenaAllocatable;
 use rustc_middle::traits::query::NoSolution;
@@ -53,20 +54,36 @@ impl<
 
 /// Used if you want to have pleasant experience when dealing
 /// with obligations outside of hir or mir typeck.
-pub struct ObligationCtxt<'a, 'tcx> {
+pub struct ObligationCtxt<'a, 'tcx, E = ScrubbedTraitError> {
     pub infcx: &'a InferCtxt<'tcx>,
-    engine: RefCell<Box<dyn TraitEngine<'tcx, FulfillmentError<'tcx>>>>,
+    engine: RefCell<Box<dyn TraitEngine<'tcx, E>>>,
 }
 
-impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
-    pub fn new(infcx: &'a InferCtxt<'tcx>) -> Self {
-        // TODO:
-        Self {
-            infcx,
-            engine: RefCell::new(<dyn TraitEngine<'tcx, FulfillmentError<'tcx>>>::new(infcx)),
-        }
+impl<'a, 'tcx> ObligationCtxt<'a, 'tcx, FulfillmentError<'tcx>> {
+    pub fn new_with_diagnostics(infcx: &'a InferCtxt<'tcx>) -> Self {
+        Self { infcx, engine: RefCell::new(<dyn TraitEngine<'tcx, _>>::new(infcx)) }
     }
+}
 
+impl<'a, 'tcx> ObligationCtxt<'a, 'tcx, ScrubbedTraitError> {
+    pub fn new(infcx: &'a InferCtxt<'tcx>) -> Self {
+        Self { infcx, engine: RefCell::new(<dyn TraitEngine<'tcx, _>>::new(infcx)) }
+    }
+}
+
+impl<'a, 'tcx, E> ObligationCtxt<'a, 'tcx, E>
+where
+    E: FromSolverError<'tcx, NextSolverError<'tcx>> + FromSolverError<'tcx, OldSolverError<'tcx>>,
+{
+    pub fn new_generic(infcx: &'a InferCtxt<'tcx>) -> Self {
+        Self { infcx, engine: RefCell::new(<dyn TraitEngine<'tcx, _>>::new(infcx)) }
+    }
+}
+
+impl<'a, 'tcx, E> ObligationCtxt<'a, 'tcx, E>
+where
+    E: FulfillmentErrorLike<'tcx>,
+{
     pub fn register_obligation(&self, obligation: PredicateObligation<'tcx>) {
         self.engine.borrow_mut().register_predicate_obligation(self.infcx, obligation);
     }
@@ -118,26 +135,6 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
         self.register_infer_ok_obligations(infer_ok)
     }
 
-    pub fn deeply_normalize<T: TypeFoldable<TyCtxt<'tcx>>>(
-        &self,
-        cause: &ObligationCause<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-        value: T,
-    ) -> Result<T, Vec<FulfillmentError<'tcx>>> {
-        self.infcx.at(cause, param_env).deeply_normalize(value, &mut **self.engine.borrow_mut())
-    }
-
-    pub fn structurally_normalize(
-        &self,
-        cause: &ObligationCause<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-        value: Ty<'tcx>,
-    ) -> Result<Ty<'tcx>, Vec<FulfillmentError<'tcx>>> {
-        self.infcx
-            .at(cause, param_env)
-            .structurally_normalize(value, &mut **self.engine.borrow_mut())
-    }
-
     pub fn eq<T: ToTrace<'tcx>>(
         &self,
         cause: &ObligationCause<'tcx>,
@@ -194,12 +191,12 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
     }
 
     #[must_use]
-    pub fn select_where_possible(&self) -> Vec<FulfillmentError<'tcx>> {
+    pub fn select_where_possible(&self) -> Vec<E> {
         self.engine.borrow_mut().select_where_possible(self.infcx)
     }
 
     #[must_use]
-    pub fn select_all_or_error(&self) -> Vec<FulfillmentError<'tcx>> {
+    pub fn select_all_or_error(&self) -> Vec<E> {
         self.engine.borrow_mut().select_all_or_error(self.infcx)
     }
 
@@ -244,6 +241,24 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
         self.infcx.resolve_regions(outlives_env)
     }
 
+    pub fn make_canonicalized_query_response<T>(
+        &self,
+        inference_vars: CanonicalVarValues<'tcx>,
+        answer: T,
+    ) -> Result<CanonicalQueryResponse<'tcx, T>, NoSolution>
+    where
+        T: Debug + TypeFoldable<TyCtxt<'tcx>>,
+        Canonical<'tcx, QueryResponse<'tcx, T>>: ArenaAllocatable<'tcx>,
+    {
+        self.infcx.make_canonicalized_query_response(
+            inference_vars,
+            answer,
+            &mut **self.engine.borrow_mut(),
+        )
+    }
+}
+
+impl<'tcx> ObligationCtxt<'_, 'tcx, FulfillmentError<'tcx>> {
     pub fn assumed_wf_types_and_report_errors(
         &self,
         param_env: ty::ParamEnv<'tcx>,
@@ -252,12 +267,17 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
         self.assumed_wf_types(param_env, def_id)
             .map_err(|errors| self.infcx.err_ctxt().report_fulfillment_errors(errors))
     }
+}
 
+impl<'tcx, E> ObligationCtxt<'_, 'tcx, E>
+where
+    E: FromSolverError<'tcx, NextSolverError<'tcx>>,
+{
     pub fn assumed_wf_types(
         &self,
         param_env: ty::ParamEnv<'tcx>,
         def_id: LocalDefId,
-    ) -> Result<FxIndexSet<Ty<'tcx>>, Vec<FulfillmentError<'tcx>>> {
+    ) -> Result<FxIndexSet<Ty<'tcx>>, Vec<E>> {
         let tcx = self.infcx.tcx;
         let mut implied_bounds = FxIndexSet::default();
         let mut errors = Vec::new();
@@ -289,19 +309,23 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
         if errors.is_empty() { Ok(implied_bounds) } else { Err(errors) }
     }
 
-    pub fn make_canonicalized_query_response<T>(
+    pub fn deeply_normalize<T: TypeFoldable<TyCtxt<'tcx>>>(
         &self,
-        inference_vars: CanonicalVarValues<'tcx>,
-        answer: T,
-    ) -> Result<CanonicalQueryResponse<'tcx, T>, NoSolution>
-    where
-        T: Debug + TypeFoldable<TyCtxt<'tcx>>,
-        Canonical<'tcx, QueryResponse<'tcx, T>>: ArenaAllocatable<'tcx>,
-    {
-        self.infcx.make_canonicalized_query_response(
-            inference_vars,
-            answer,
-            &mut **self.engine.borrow_mut(),
-        )
+        cause: &ObligationCause<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+        value: T,
+    ) -> Result<T, Vec<E>> {
+        self.infcx.at(cause, param_env).deeply_normalize(value, &mut **self.engine.borrow_mut())
+    }
+
+    pub fn structurally_normalize(
+        &self,
+        cause: &ObligationCause<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+        value: Ty<'tcx>,
+    ) -> Result<Ty<'tcx>, Vec<E>> {
+        self.infcx
+            .at(cause, param_env)
+            .structurally_normalize(value, &mut **self.engine.borrow_mut())
     }
 }

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -16,13 +16,13 @@ use rustc_middle::ty::GenericArgsRef;
 use rustc_middle::ty::{self, Binder, Const, TypeVisitableExt};
 use std::marker::PhantomData;
 
-use super::const_evaluatable;
 use super::project::{self, ProjectAndUnifyResult};
 use super::select::SelectionContext;
 use super::wf;
 use super::EvaluationResult;
 use super::PredicateObligation;
 use super::Unimplemented;
+use super::{const_evaluatable, ScrubbedTraitError};
 use super::{FulfillmentError, FulfillmentErrorCode};
 
 use crate::traits::project::PolyProjectionObligation;
@@ -855,3 +855,17 @@ impl<'tcx> FromSolverError<'tcx, OldSolverError<'tcx>> for FulfillmentError<'tcx
         FulfillmentError::new(obligation, error.error, root_obligation)
     }
 }
+
+impl<'tcx> FromSolverError<'tcx, OldSolverError<'tcx>> for ScrubbedTraitError {
+    fn from_solver_error(_infcx: &InferCtxt<'tcx>, error: OldSolverError<'tcx>) -> Self {
+        match error.error {
+            FulfillmentErrorCode::Select(_)
+            | FulfillmentErrorCode::Project(_)
+            | FulfillmentErrorCode::Subtype(_, _)
+            | FulfillmentErrorCode::ConstEquate(_, _) => ScrubbedTraitError::TrueError,
+            FulfillmentErrorCode::Cycle(_) | FulfillmentErrorCode::Ambiguity { overflow: _ } => {
+                ScrubbedTraitError::Ambiguity
+            }
+        }
+    }
+}

compiler/rustc_trait_selection/src/traits/misc.rs

@@ -137,7 +137,7 @@ pub fn all_fields_implement_trait<'tcx>(
         for field in &variant.fields {
             // Do this per-field to get better error messages.
             let infcx = tcx.infer_ctxt().build();
-            let ocx = traits::ObligationCtxt::new(&infcx);
+            let ocx = traits::ObligationCtxt::new_with_diagnostics(&infcx);
 
             let unnormalized_ty = field.ty(tcx, args);
             if unnormalized_ty.references_error() {

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -46,7 +46,7 @@ pub use self::coherence::{add_placeholder_note, orphan_check_trait_ref, overlapp
 pub use self::coherence::{InCrate, IsFirstInputType, UncoveredTyParams};
 pub use self::coherence::{OrphanCheckErr, OrphanCheckMode, OverlapResult};
 pub use self::engine::{ObligationCtxt, TraitEngineExt};
-pub use self::fulfill::{FulfillmentContext, PendingPredicateObligation};
+pub use self::fulfill::{FulfillmentContext, OldSolverError, PendingPredicateObligation};
 pub use self::normalize::NormalizeExt;
 pub use self::object_safety::hir_ty_lowering_object_safety_violations;
 pub use self::object_safety::is_vtable_safe_method;
@@ -70,6 +70,28 @@ pub use self::util::{with_replaced_escaping_bound_vars, BoundVarReplacer, Placeh
 
 pub use rustc_infer::traits::*;
 
+// A trait error without any information in it. You likely want to alternately use [`ObligationCtxt::new_with_diagnostics`] to get a [`FulfillmentError`].
+#[derive(Copy, Clone, Debug)]
+pub enum ScrubbedTraitError {
+    TrueError,
+    Ambiguity,
+}
+
+impl ScrubbedTraitError {
+    fn is_true_error(&self) -> bool {
+        match self {
+            ScrubbedTraitError::TrueError => true,
+            ScrubbedTraitError::Ambiguity => false,
+        }
+    }
+}
+
+impl<'tcx> FulfillmentErrorLike<'tcx> for ScrubbedTraitError {
+    fn is_true_error(&self) -> bool {
+        self.is_true_error()
+    }
+}
+
 pub struct FulfillmentError<'tcx> {
     pub obligation: PredicateObligation<'tcx>,
     pub code: FulfillmentErrorCode<'tcx>,
@@ -450,7 +472,7 @@ pub fn fully_normalize<'tcx, T>(
 where
     T: TypeFoldable<TyCtxt<'tcx>>,
 {
-    let ocx = ObligationCtxt::new(infcx);
+    let ocx = ObligationCtxt::new_with_diagnostics(infcx);
     debug!(?value);
     let normalized_value = ocx.normalize(&cause, param_env, value);
     debug!(?normalized_value);