inspect: strongly typed CandidateKind

compiler/rustc_middle/src/traits/solve.rs

@@ -9,6 +9,9 @@ use crate::ty::{
     self, FallibleTypeFolder, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeVisitable,
     TypeVisitor,
 };
+use rustc_span::def_id::DefId;
+
+use super::BuiltinImplSource;
 
 mod cache;
 pub mod inspect;
@@ -235,3 +238,63 @@ pub enum IsNormalizesToHack {
     Yes,
     No,
 }
+
+/// Possible ways the given goal can be proven.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CandidateSource {
+    /// A user written impl.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// fn main() {
+    ///     let x: Vec<u32> = Vec::new();
+    ///     // This uses the impl from the standard library to prove `Vec<T>: Clone`.
+    ///     let y = x.clone();
+    /// }
+    /// ```
+    Impl(DefId),
+    /// A builtin impl generated by the compiler. When adding a new special
+    /// trait, try to use actual impls whenever possible. Builtin impls should
+    /// only be used in cases where the impl cannot be manually be written.
+    ///
+    /// Notable examples are auto traits, `Sized`, and `DiscriminantKind`.
+    /// For a list of all traits with builtin impls, check out the
+    /// `EvalCtxt::assemble_builtin_impl_candidates` method.
+    BuiltinImpl(BuiltinImplSource),
+    /// An assumption from the environment.
+    ///
+    /// More precisely we've used the `n-th` assumption in the `param_env`.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// fn is_clone<T: Clone>(x: T) -> (T, T) {
+    ///     // This uses the assumption `T: Clone` from the `where`-bounds
+    ///     // to prove `T: Clone`.
+    ///     (x.clone(), x)
+    /// }
+    /// ```
+    ParamEnv(usize),
+    /// If the self type is an alias type, e.g. an opaque type or a projection,
+    /// we know the bounds on that alias to hold even without knowing its concrete
+    /// underlying type.
+    ///
+    /// More precisely this candidate is using the `n-th` bound in the `item_bounds` of
+    /// the self type.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// trait Trait {
+    ///     type Assoc: Clone;
+    /// }
+    ///
+    /// fn foo<T: Trait>(x: <T as Trait>::Assoc) {
+    ///     // We prove `<T as Trait>::Assoc` by looking at the bounds on `Assoc` in
+    ///     // in the trait definition.
+    ///     let _y = x.clone();
+    /// }
+    /// ```
+    AliasBound,
+}

compiler/rustc_middle/src/traits/solve/inspect.rs

@@ -1,5 +1,6 @@
 use super::{
-    CanonicalInput, Certainty, Goal, IsNormalizesToHack, NoSolution, QueryInput, QueryResult,
+    CandidateSource, CanonicalInput, Certainty, Goal, IsNormalizesToHack, NoSolution, QueryInput,
+    QueryResult,
 };
 use crate::ty;
 use format::ProofTreeFormatter;
@@ -7,13 +8,13 @@ use std::fmt::{Debug, Write};
 
 mod format;
 
-#[derive(Eq, PartialEq, Debug, Hash, HashStable)]
+#[derive(Debug, Eq, PartialEq)]
 pub enum CacheHit {
     Provisional,
     Global,
 }
 
-#[derive(Eq, PartialEq, Hash, HashStable)]
+#[derive(Eq, PartialEq)]
 pub struct GoalEvaluation<'tcx> {
     pub uncanonicalized_goal: Goal<'tcx, ty::Predicate<'tcx>>,
     pub is_normalizes_to_hack: IsNormalizesToHack,
@@ -21,14 +22,14 @@ pub struct GoalEvaluation<'tcx> {
     pub returned_goals: Vec<Goal<'tcx, ty::Predicate<'tcx>>>,
 }
 
-#[derive(Eq, PartialEq, Hash, HashStable)]
+#[derive(Eq, PartialEq)]
 pub struct CanonicalGoalEvaluation<'tcx> {
     pub goal: CanonicalInput<'tcx>,
     pub kind: GoalEvaluationKind<'tcx>,
     pub result: QueryResult<'tcx>,
 }
 
-#[derive(Eq, PartialEq, Hash, HashStable)]
+#[derive(Eq, PartialEq)]
 pub enum GoalEvaluationKind<'tcx> {
     CacheHit(CacheHit),
     Uncached { revisions: Vec<GoalEvaluationStep<'tcx>> },
@@ -39,13 +40,13 @@ impl Debug for GoalEvaluation<'_> {
     }
 }
 
-#[derive(Eq, PartialEq, Hash, HashStable)]
+#[derive(Eq, PartialEq)]
 pub struct AddedGoalsEvaluation<'tcx> {
     pub evaluations: Vec<Vec<GoalEvaluation<'tcx>>>,
     pub result: Result<Certainty, NoSolution>,
 }
 
-#[derive(Eq, PartialEq, Hash, HashStable)]
+#[derive(Eq, PartialEq)]
 pub struct GoalEvaluationStep<'tcx> {
     pub instantiated_goal: QueryInput<'tcx, ty::Predicate<'tcx>>,
 
@@ -55,24 +56,28 @@ pub struct GoalEvaluationStep<'tcx> {
     pub result: QueryResult<'tcx>,
 }
 
-#[derive(Eq, PartialEq, Hash, HashStable)]
+#[derive(Eq, PartialEq)]
 pub struct GoalCandidate<'tcx> {
     pub added_goals_evaluations: Vec<AddedGoalsEvaluation<'tcx>>,
     pub candidates: Vec<GoalCandidate<'tcx>>,
-    pub kind: CandidateKind<'tcx>,
+    pub kind: ProbeKind<'tcx>,
 }
 
-#[derive(Eq, PartialEq, Debug, Hash, HashStable)]
+#[derive(Debug, PartialEq, Eq)]
-pub enum CandidateKind<'tcx> {
+pub enum ProbeKind<'tcx> {
     /// Probe entered when normalizing the self ty during candidate assembly
     NormalizedSelfTyAssembly,
-    /// A normal candidate for proving a goal
+    /// Some candidate to prove the current goal.
-    Candidate { name: String, result: QueryResult<'tcx> },
+    ///
+    /// FIXME: Remove this in favor of always using more strongly typed variants.
+    MiscCandidate { name: &'static str, result: QueryResult<'tcx> },
+    /// A candidate for proving a trait or alias-relate goal.
+    TraitCandidate { source: CandidateSource, result: QueryResult<'tcx> },
     /// Used in the probe that wraps normalizing the non-self type for the unsize
     /// trait, which is also structurally matched on.
     UnsizeAssembly,
     /// During upcasting from some source object to target object type, used to
     /// do a probe to find out what projection type(s) may be used to prove that
     /// the source type upholds all of the target type's object bounds.
-    UpcastProbe,
+    UpcastProjectionCompatibility,
 }

compiler/rustc_middle/src/traits/solve/inspect/format.rs

@@ -102,18 +102,21 @@ impl<'a, 'b> ProofTreeFormatter<'a, 'b> {
 
     pub(super) fn format_candidate(&mut self, candidate: &GoalCandidate<'_>) -> std::fmt::Result {
         match &candidate.kind {
-            CandidateKind::NormalizedSelfTyAssembly => {
+            ProbeKind::NormalizedSelfTyAssembly => {
                 writeln!(self.f, "NORMALIZING SELF TY FOR ASSEMBLY:")
             }
-            CandidateKind::UnsizeAssembly => {
+            ProbeKind::UnsizeAssembly => {
                 writeln!(self.f, "ASSEMBLING CANDIDATES FOR UNSIZING:")
             }
-            CandidateKind::UpcastProbe => {
+            ProbeKind::UpcastProjectionCompatibility => {
                 writeln!(self.f, "PROBING FOR PROJECTION COMPATIBILITY FOR UPCASTING:")
             }
-            CandidateKind::Candidate { name, result } => {
+            ProbeKind::MiscCandidate { name, result } => {
                 writeln!(self.f, "CANDIDATE {name}: {result:?}")
             }
+            ProbeKind::TraitCandidate { source, result } => {
+                writeln!(self.f, "CANDIDATE {source:?}: {result:?}")
+            }
         }?;
 
         self.nested(|this| {

compiler/rustc_trait_selection/src/solve/alias_relate.rs

@@ -125,7 +125,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         direction: ty::AliasRelationDirection,
         invert: Invert,
     ) -> QueryResult<'tcx> {
-        self.probe_candidate("normalizes-to").enter(|ecx| {
+        self.probe_misc_candidate("normalizes-to").enter(|ecx| {
             ecx.normalizes_to_inner(param_env, alias, other, direction, invert)?;
             ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
         })
@@ -175,7 +175,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         alias_rhs: ty::AliasTy<'tcx>,
         direction: ty::AliasRelationDirection,
     ) -> QueryResult<'tcx> {
-        self.probe_candidate("args relate").enter(|ecx| {
+        self.probe_misc_candidate("args relate").enter(|ecx| {
             match direction {
                 ty::AliasRelationDirection::Equate => {
                     ecx.eq(param_env, alias_lhs, alias_rhs)?;
@@ -196,7 +196,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         rhs: ty::Term<'tcx>,
         direction: ty::AliasRelationDirection,
     ) -> QueryResult<'tcx> {
-        self.probe_candidate("bidir normalizes-to").enter(|ecx| {
+        self.probe_misc_candidate("bidir normalizes-to").enter(|ecx| {
             ecx.normalizes_to_inner(
                 param_env,
                 lhs.to_alias_ty(ecx.tcx()).unwrap(),

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

@@ -5,8 +5,10 @@ use crate::traits::coherence;
 use rustc_hir::def_id::DefId;
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::Reveal;
-use rustc_middle::traits::solve::inspect::CandidateKind;
+use rustc_middle::traits::solve::inspect::ProbeKind;
-use rustc_middle::traits::solve::{CanonicalResponse, Certainty, Goal, QueryResult};
+use rustc_middle::traits::solve::{
+    CandidateSource, CanonicalResponse, Certainty, Goal, QueryResult,
+};
 use rustc_middle::traits::BuiltinImplSource;
 use rustc_middle::ty::fast_reject::{SimplifiedType, TreatParams};
 use rustc_middle::ty::{self, Ty, TyCtxt};
@@ -27,66 +29,6 @@ pub(super) struct Candidate<'tcx> {
     pub(super) result: CanonicalResponse<'tcx>,
 }
 
-/// Possible ways the given goal can be proven.
-#[derive(Debug, Clone, Copy)]
-pub(super) enum CandidateSource {
-    /// A user written impl.
-    ///
-    /// ## Examples
-    ///
-    /// ```rust
-    /// fn main() {
-    ///     let x: Vec<u32> = Vec::new();
-    ///     // This uses the impl from the standard library to prove `Vec<T>: Clone`.
-    ///     let y = x.clone();
-    /// }
-    /// ```
-    Impl(DefId),
-    /// A builtin impl generated by the compiler. When adding a new special
-    /// trait, try to use actual impls whenever possible. Builtin impls should
-    /// only be used in cases where the impl cannot be manually be written.
-    ///
-    /// Notable examples are auto traits, `Sized`, and `DiscriminantKind`.
-    /// For a list of all traits with builtin impls, check out the
-    /// [`EvalCtxt::assemble_builtin_impl_candidates`] method. Not
-    BuiltinImpl(BuiltinImplSource),
-    /// An assumption from the environment.
-    ///
-    /// More precisely we've used the `n-th` assumption in the `param_env`.
-    ///
-    /// ## Examples
-    ///
-    /// ```rust
-    /// fn is_clone<T: Clone>(x: T) -> (T, T) {
-    ///     // This uses the assumption `T: Clone` from the `where`-bounds
-    ///     // to prove `T: Clone`.
-    ///     (x.clone(), x)
-    /// }
-    /// ```
-    ParamEnv(usize),
-    /// If the self type is an alias type, e.g. an opaque type or a projection,
-    /// we know the bounds on that alias to hold even without knowing its concrete
-    /// underlying type.
-    ///
-    /// More precisely this candidate is using the `n-th` bound in the `item_bounds` of
-    /// the self type.
-    ///
-    /// ## Examples
-    ///
-    /// ```rust
-    /// trait Trait {
-    ///     type Assoc: Clone;
-    /// }
-    ///
-    /// fn foo<T: Trait>(x: <T as Trait>::Assoc) {
-    ///     // We prove `<T as Trait>::Assoc` by looking at the bounds on `Assoc` in
-    ///     // in the trait definition.
-    ///     let _y = x.clone();
-    /// }
-    /// ```
-    AliasBound,
-}
-
 /// Methods used to assemble candidates for either trait or projection goals.
 pub(super) trait GoalKind<'tcx>:
     TypeFoldable<TyCtxt<'tcx>> + Copy + Eq + std::fmt::Display
@@ -399,7 +341,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         let tcx = self.tcx();
         let &ty::Alias(_, projection_ty) = goal.predicate.self_ty().kind() else { return };
 
-        candidates.extend(self.probe(|_| CandidateKind::NormalizedSelfTyAssembly).enter(|ecx| {
+        candidates.extend(self.probe(|_| ProbeKind::NormalizedSelfTyAssembly).enter(|ecx| {
             if num_steps < ecx.local_overflow_limit() {
                 let normalized_ty = ecx.next_ty_infer();
                 let normalizes_to_goal = goal.with(
@@ -910,7 +852,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
             SolverMode::Coherence => {}
         };
 
-        let result = self.probe_candidate("coherence unknowable").enter(|ecx| {
+        let result = self.probe_misc_candidate("coherence unknowable").enter(|ecx| {
             let trait_ref = goal.predicate.trait_ref(tcx);
 
             #[derive(Debug)]

compiler/rustc_trait_selection/src/solve/eval_ctxt.rs

@@ -920,7 +920,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
             if candidate_key.def_id != key.def_id {
                 continue;
             }
-            values.extend(self.probe_candidate("opaque type storage").enter(|ecx| {
+            values.extend(self.probe_misc_candidate("opaque type storage").enter(|ecx| {
                 for (a, b) in std::iter::zip(candidate_key.args, key.args) {
                     ecx.eq(param_env, a, b)?;
                 }

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

@@ -1,5 +1,5 @@
 use super::EvalCtxt;
-use rustc_middle::traits::solve::{inspect, QueryResult};
+use rustc_middle::traits::solve::{inspect, CandidateSource, QueryResult};
 use std::marker::PhantomData;
 
 pub(in crate::solve) struct ProbeCtxt<'me, 'a, 'tcx, F, T> {
@@ -10,7 +10,7 @@ pub(in crate::solve) struct ProbeCtxt<'me, 'a, 'tcx, F, T> {
 
 impl<'tcx, F, T> ProbeCtxt<'_, '_, 'tcx, F, T>
 where
-    F: FnOnce(&T) -> inspect::CandidateKind<'tcx>,
+    F: FnOnce(&T) -> inspect::ProbeKind<'tcx>,
 {
     pub(in crate::solve) fn enter(self, f: impl FnOnce(&mut EvalCtxt<'_, 'tcx>) -> T) -> T {
         let ProbeCtxt { ecx: outer_ecx, probe_kind, _result } = self;
@@ -28,8 +28,8 @@ where
         };
         let r = nested_ecx.infcx.probe(|_| f(&mut nested_ecx));
         if !outer_ecx.inspect.is_noop() {
-            let cand_kind = probe_kind(&r);
+            let probe_kind = probe_kind(&r);
-            nested_ecx.inspect.candidate_kind(cand_kind);
+            nested_ecx.inspect.probe_kind(probe_kind);
             outer_ecx.inspect.goal_candidate(nested_ecx.inspect);
         }
         r
@@ -41,25 +41,45 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
     /// as expensive as necessary to output the desired information.
     pub(in crate::solve) fn probe<F, T>(&mut self, probe_kind: F) -> ProbeCtxt<'_, 'a, 'tcx, F, T>
     where
-        F: FnOnce(&T) -> inspect::CandidateKind<'tcx>,
+        F: FnOnce(&T) -> inspect::ProbeKind<'tcx>,
     {
         ProbeCtxt { ecx: self, probe_kind, _result: PhantomData }
     }
 
-    pub(in crate::solve) fn probe_candidate(
+    pub(in crate::solve) fn probe_misc_candidate(
         &mut self,
         name: &'static str,
     ) -> ProbeCtxt<
         '_,
         'a,
         'tcx,
-        impl FnOnce(&QueryResult<'tcx>) -> inspect::CandidateKind<'tcx>,
+        impl FnOnce(&QueryResult<'tcx>) -> inspect::ProbeKind<'tcx>,
         QueryResult<'tcx>,
     > {
         ProbeCtxt {
             ecx: self,
-            probe_kind: move |result: &QueryResult<'tcx>| inspect::CandidateKind::Candidate {
+            probe_kind: move |result: &QueryResult<'tcx>| inspect::ProbeKind::MiscCandidate {
-                name: name.to_string(),
+                name,
+                result: *result,
+            },
+            _result: PhantomData,
+        }
+    }
+
+    pub(in crate::solve) fn probe_trait_candidate(
+        &mut self,
+        source: CandidateSource,
+    ) -> ProbeCtxt<
+        '_,
+        'a,
+        'tcx,
+        impl FnOnce(&QueryResult<'tcx>) -> inspect::ProbeKind<'tcx>,
+        QueryResult<'tcx>,
+    > {
+        ProbeCtxt {
+            ecx: self,
+            probe_kind: move |result: &QueryResult<'tcx>| inspect::ProbeKind::TraitCandidate {
+                source,
                 result: *result,
             },
             _result: PhantomData,

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

@@ -4,14 +4,14 @@ use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt};
 use rustc_infer::traits::{
     Obligation, PolyTraitObligation, PredicateObligation, Selection, SelectionResult, TraitEngine,
 };
-use rustc_middle::traits::solve::{CanonicalInput, Certainty, Goal};
+use rustc_middle::traits::solve::{CandidateSource, CanonicalInput, Certainty, Goal};
 use rustc_middle::traits::{
     BuiltinImplSource, ImplSource, ImplSourceUserDefinedData, ObligationCause, SelectionError,
 };
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::DUMMY_SP;
 
-use crate::solve::assembly::{Candidate, CandidateSource};
+use crate::solve::assembly::Candidate;
 use crate::solve::eval_ctxt::{EvalCtxt, GenerateProofTree};
 use crate::solve::inspect::ProofTreeBuilder;
 use crate::traits::StructurallyNormalizeExt;

compiler/rustc_trait_selection/src/solve/inspect.rs

@@ -1,5 +1,5 @@
 use rustc_middle::traits::query::NoSolution;
-use rustc_middle::traits::solve::inspect::{self, CacheHit, CandidateKind};
+use rustc_middle::traits::solve::inspect::{self, CacheHit, ProbeKind};
 use rustc_middle::traits::solve::{
     CanonicalInput, Certainty, Goal, IsNormalizesToHack, QueryInput, QueryResult,
 };
@@ -9,7 +9,7 @@ use rustc_session::config::DumpSolverProofTree;
 use super::eval_ctxt::UseGlobalCache;
 use super::GenerateProofTree;
 
-#[derive(Eq, PartialEq, Debug, Hash, HashStable)]
+#[derive(Eq, PartialEq, Debug)]
 pub struct WipGoalEvaluation<'tcx> {
     pub uncanonicalized_goal: Goal<'tcx, ty::Predicate<'tcx>>,
     pub evaluation: Option<WipCanonicalGoalEvaluation<'tcx>>,
@@ -28,7 +28,7 @@ impl<'tcx> WipGoalEvaluation<'tcx> {
     }
 }
 
-#[derive(Eq, PartialEq, Debug, Hash, HashStable)]
+#[derive(Eq, PartialEq, Debug)]
 pub struct WipCanonicalGoalEvaluation<'tcx> {
     pub goal: CanonicalInput<'tcx>,
     pub cache_hit: Option<CacheHit>,
@@ -56,7 +56,7 @@ impl<'tcx> WipCanonicalGoalEvaluation<'tcx> {
     }
 }
 
-#[derive(Eq, PartialEq, Debug, Hash, HashStable)]
+#[derive(Eq, PartialEq, Debug)]
 pub struct WipAddedGoalsEvaluation<'tcx> {
     pub evaluations: Vec<Vec<WipGoalEvaluation<'tcx>>>,
     pub result: Option<Result<Certainty, NoSolution>>,
@@ -77,7 +77,7 @@ impl<'tcx> WipAddedGoalsEvaluation<'tcx> {
     }
 }
 
-#[derive(Eq, PartialEq, Debug, Hash, HashStable)]
+#[derive(Eq, PartialEq, Debug)]
 pub struct WipGoalEvaluationStep<'tcx> {
     pub instantiated_goal: QueryInput<'tcx, ty::Predicate<'tcx>>,
 
@@ -102,11 +102,11 @@ impl<'tcx> WipGoalEvaluationStep<'tcx> {
     }
 }
 
-#[derive(Eq, PartialEq, Debug, Hash, HashStable)]
+#[derive(Eq, PartialEq, Debug)]
 pub struct WipGoalCandidate<'tcx> {
     pub added_goals_evaluations: Vec<WipAddedGoalsEvaluation<'tcx>>,
     pub candidates: Vec<WipGoalCandidate<'tcx>>,
-    pub kind: Option<CandidateKind<'tcx>>,
+    pub kind: Option<ProbeKind<'tcx>>,
 }
 
 impl<'tcx> WipGoalCandidate<'tcx> {
@@ -357,11 +357,11 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
         })
     }
 
-    pub fn candidate_kind(&mut self, candidate_kind: CandidateKind<'tcx>) {
+    pub fn probe_kind(&mut self, probe_kind: ProbeKind<'tcx>) {
         if let Some(this) = self.as_mut() {
             match this {
                 DebugSolver::GoalCandidate(this) => {
-                    assert_eq!(this.kind.replace(candidate_kind), None)
+                    assert_eq!(this.kind.replace(probe_kind), None)
                 }
                 _ => unreachable!(),
             }

compiler/rustc_trait_selection/src/solve/project_goals.rs

@@ -8,8 +8,9 @@ use rustc_hir::LangItem;
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::specialization_graph::LeafDef;
 use rustc_infer::traits::Reveal;
-use rustc_middle::traits::solve::inspect::CandidateKind;
+use rustc_middle::traits::solve::{
-use rustc_middle::traits::solve::{CanonicalResponse, Certainty, Goal, QueryResult};
+    CandidateSource, CanonicalResponse, Certainty, Goal, QueryResult,
+};
 use rustc_middle::traits::BuiltinImplSource;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
 use rustc_middle::ty::ProjectionPredicate;
@@ -113,7 +114,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
         if let Some(projection_pred) = assumption.as_projection_clause() {
             if projection_pred.projection_def_id() == goal.predicate.def_id() {
                 let tcx = ecx.tcx();
-                ecx.probe_candidate("assumption").enter(|ecx| {
+                ecx.probe_misc_candidate("assumption").enter(|ecx| {
                     let assumption_projection_pred =
                         ecx.instantiate_binder_with_infer(projection_pred);
                     ecx.eq(
@@ -155,7 +156,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
             return Err(NoSolution);
         }
 
-        ecx.probe(|r| CandidateKind::Candidate { name: "impl".into(), result: *r }).enter(|ecx| {
+        ecx.probe_trait_candidate(CandidateSource::Impl(impl_def_id)).enter(|ecx| {
             let impl_args = ecx.fresh_args_for_item(impl_def_id);
             let impl_trait_ref = impl_trait_ref.instantiate(tcx, impl_args);
 
@@ -369,7 +370,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
         goal: Goal<'tcx, Self>,
     ) -> QueryResult<'tcx> {
         let tcx = ecx.tcx();
-        ecx.probe_candidate("builtin pointee").enter(|ecx| {
+        ecx.probe_misc_candidate("builtin pointee").enter(|ecx| {
             let metadata_ty = match goal.predicate.self_ty().kind() {
                 ty::Bool
                 | ty::Char
@@ -578,7 +579,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
             ),
         };
 
-        ecx.probe_candidate("builtin discriminant kind").enter(|ecx| {
+        ecx.probe_misc_candidate("builtin discriminant kind").enter(|ecx| {
             ecx.eq(goal.param_env, goal.predicate.term, discriminant_ty.into())
                 .expect("expected goal term to be fully unconstrained");
             ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)

compiler/rustc_trait_selection/src/solve/trait_goals.rs

@@ -5,7 +5,7 @@ use super::{EvalCtxt, SolverMode};
 use rustc_hir::def_id::DefId;
 use rustc_hir::{LangItem, Movability};
 use rustc_infer::traits::query::NoSolution;
-use rustc_middle::traits::solve::inspect::CandidateKind;
+use rustc_middle::traits::solve::inspect::ProbeKind;
 use rustc_middle::traits::solve::{CanonicalResponse, Certainty, Goal, QueryResult};
 use rustc_middle::traits::{BuiltinImplSource, Reveal};
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams, TreatProjections};
@@ -61,7 +61,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
             },
         };
 
-        ecx.probe_candidate("impl").enter(|ecx| {
+        ecx.probe_misc_candidate("impl").enter(|ecx| {
             let impl_args = ecx.fresh_args_for_item(impl_def_id);
             let impl_trait_ref = impl_trait_ref.instantiate(tcx, impl_args);
 
@@ -96,7 +96,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
                 && trait_clause.polarity() == goal.predicate.polarity
             {
                 // FIXME: Constness
-                ecx.probe_candidate("assumption").enter(|ecx| {
+                ecx.probe_misc_candidate("assumption").enter(|ecx| {
                     let assumption_trait_pred = ecx.instantiate_binder_with_infer(trait_clause);
                     ecx.eq(
                         goal.param_env,
@@ -167,7 +167,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
 
         let tcx = ecx.tcx();
 
-        ecx.probe_candidate("trait alias").enter(|ecx| {
+        ecx.probe_misc_candidate("trait alias").enter(|ecx| {
             let nested_obligations = tcx
                 .predicates_of(goal.predicate.def_id())
                 .instantiate(tcx, goal.predicate.trait_ref.args);
@@ -427,7 +427,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
         ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, Self>,
     ) -> QueryResult<'tcx> {
-        ecx.probe(|_| CandidateKind::UnsizeAssembly).enter(|ecx| {
+        ecx.probe(|_| ProbeKind::UnsizeAssembly).enter(|ecx| {
             let a_ty = goal.predicate.self_ty();
             // We need to normalize the b_ty since it's destructured as a `dyn Trait`.
             let Some(b_ty) =
@@ -491,7 +491,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
             Err(NoSolution) => vec![],
         };
 
-        ecx.probe(|_| CandidateKind::UnsizeAssembly).enter(|ecx| {
+        ecx.probe(|_| ProbeKind::UnsizeAssembly).enter(|ecx| {
             let a_ty = goal.predicate.self_ty();
             // We need to normalize the b_ty since it's matched structurally
             // in the other functions below.
@@ -597,7 +597,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
             self.walk_vtable(
                 a_principal.with_self_ty(tcx, a_ty),
                 |ecx, new_a_principal, _, vtable_vptr_slot| {
-                    if let Ok(resp) = ecx.probe_candidate("dyn upcast").enter(|ecx| {
+                    if let Ok(resp) = ecx.probe_misc_candidate("dyn upcast").enter(|ecx| {
                         ecx.consider_builtin_upcast_to_principal(
                             goal,
                             a_data,
@@ -640,7 +640,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
              target_projection: ty::PolyExistentialProjection<'tcx>| {
                 source_projection.item_def_id() == target_projection.item_def_id()
                     && ecx
-                        .probe(|_| CandidateKind::UpcastProbe)
+                        .probe(|_| ProbeKind::UpcastProjectionCompatibility)
                         .enter(|ecx| -> Result<(), NoSolution> {
                             ecx.eq(param_env, source_projection, target_projection)?;
                             let _ = ecx.try_evaluate_added_goals()?;
@@ -918,7 +918,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         goal: Goal<'tcx, TraitPredicate<'tcx>>,
         constituent_tys: impl Fn(&EvalCtxt<'_, 'tcx>, Ty<'tcx>) -> Result<Vec<Ty<'tcx>>, NoSolution>,
     ) -> QueryResult<'tcx> {
-        self.probe_candidate("constituent tys").enter(|ecx| {
+        self.probe_misc_candidate("constituent tys").enter(|ecx| {
             ecx.add_goals(
                 constituent_tys(ecx, goal.predicate.self_ty())?
                     .into_iter()