some inspect improvements

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

@@ -1,32 +1,37 @@
 use super::{
-    CanonicalInput, Certainty, Goal, IsNormalizesToHack, NoSolution, QueryInput, QueryResult,
+    CandidateSource, CanonicalInput, Certainty, Goal, IsNormalizesToHack, NoSolution, QueryInput,
+    QueryResult,
 };
 use crate::ty;
 use format::ProofTreeFormatter;
 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 canonicalized_goal: CanonicalInput<'tcx>,
-
-    pub kind: GoalEvaluationKind<'tcx>,
     pub is_normalizes_to_hack: IsNormalizesToHack,
+    pub evaluation: CanonicalGoalEvaluation<'tcx>,
     pub returned_goals: Vec<Goal<'tcx, ty::Predicate<'tcx>>>,
+}
 
+#[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> {
+    Overflow,
     CacheHit(CacheHit),
     Uncached { revisions: Vec<GoalEvaluationStep<'tcx>> },
 }
@@ -36,55 +41,50 @@ 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>,
 }
-impl Debug for AddedGoalsEvaluation<'_> {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        ProofTreeFormatter::new(f).format_nested_goal_evaluation(self)
-    }
-}
 
-#[derive(Eq, PartialEq, Hash, HashStable)]
+#[derive(Eq, PartialEq)]
 pub struct GoalEvaluationStep<'tcx> {
     pub instantiated_goal: QueryInput<'tcx, ty::Predicate<'tcx>>,
 
-    pub nested_goal_evaluations: Vec<AddedGoalsEvaluation<'tcx>>,
-    pub candidates: Vec<GoalCandidate<'tcx>>,
-
-    pub result: QueryResult<'tcx>,
-}
-impl Debug for GoalEvaluationStep<'_> {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        ProofTreeFormatter::new(f).format_evaluation_step(self)
-    }
+    /// The actual evaluation of the goal, always `ProbeKind::Root`.
+    pub evaluation: GoalCandidate<'tcx>,
 }
 
-#[derive(Eq, PartialEq, Hash, HashStable)]
+#[derive(Eq, PartialEq)]
 pub struct GoalCandidate<'tcx> {
-    pub nested_goal_evaluations: Vec<AddedGoalsEvaluation<'tcx>>,
+    pub added_goals_evaluations: Vec<AddedGoalsEvaluation<'tcx>>,
     pub candidates: Vec<GoalCandidate<'tcx>>,
-    pub kind: CandidateKind<'tcx>,
+    pub kind: ProbeKind<'tcx>,
+}
+
+impl Debug for GoalCandidate<'_> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        ProofTreeFormatter::new(f).format_candidate(self)
+    }
 }
 
-#[derive(Eq, PartialEq, Debug, Hash, HashStable)]
-pub enum CandidateKind<'tcx> {
+#[derive(Debug, PartialEq, Eq)]
+pub enum ProbeKind<'tcx> {
+    /// The root inference context while proving a goal.
+    Root { result: QueryResult<'tcx> },
     /// Probe entered when normalizing the self ty during candidate assembly
     NormalizedSelfTyAssembly,
-    /// A normal candidate for proving a goal
-    Candidate { name: String, result: QueryResult<'tcx> },
+    /// Some candidate to prove the current goal.
+    ///
+    /// 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,
-}
-impl Debug for GoalCandidate<'_> {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        ProofTreeFormatter::new(f).format_candidate(self)
-    }
+    UpcastProjectionCompatibility,
 }

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

@@ -39,99 +39,105 @@ impl<'a, 'b> ProofTreeFormatter<'a, 'b> {
         func(&mut ProofTreeFormatter { f: &mut Indentor { f: self.f, on_newline: true } })
     }
 
-    pub(super) fn format_goal_evaluation(&mut self, goal: &GoalEvaluation<'_>) -> std::fmt::Result {
-        let goal_text = match goal.is_normalizes_to_hack {
+    pub(super) fn format_goal_evaluation(&mut self, eval: &GoalEvaluation<'_>) -> std::fmt::Result {
+        let goal_text = match eval.is_normalizes_to_hack {
             IsNormalizesToHack::Yes => "NORMALIZES-TO HACK GOAL",
             IsNormalizesToHack::No => "GOAL",
         };
+        writeln!(self.f, "{}: {:?}", goal_text, eval.uncanonicalized_goal)?;
+        self.nested(|this| this.format_canonical_goal_evaluation(&eval.evaluation))?;
+        if eval.returned_goals.len() > 0 {
+            writeln!(self.f, "NESTED GOALS ADDED TO CALLER: [")?;
+            self.nested(|this| {
+                for goal in eval.returned_goals.iter() {
+                    writeln!(this.f, "ADDED GOAL: {goal:?},")?;
+                }
+                Ok(())
+            })?;
+
+            writeln!(self.f, "]")
+        } else {
+            Ok(())
+        }
+    }
 
-        writeln!(self.f, "{}: {:?}", goal_text, goal.uncanonicalized_goal)?;
-        writeln!(self.f, "CANONICALIZED: {:?}", goal.canonicalized_goal)?;
+    pub(super) fn format_canonical_goal_evaluation(
+        &mut self,
+        eval: &CanonicalGoalEvaluation<'_>,
+    ) -> std::fmt::Result {
+        writeln!(self.f, "GOAL: {:?}", eval.goal)?;
 
-        match &goal.kind {
+        match &eval.kind {
+            GoalEvaluationKind::Overflow => {
+                writeln!(self.f, "OVERFLOW: {:?}", eval.result)
+            }
             GoalEvaluationKind::CacheHit(CacheHit::Global) => {
-                writeln!(self.f, "GLOBAL CACHE HIT: {:?}", goal.result)
+                writeln!(self.f, "GLOBAL CACHE HIT: {:?}", eval.result)
             }
             GoalEvaluationKind::CacheHit(CacheHit::Provisional) => {
-                writeln!(self.f, "PROVISIONAL CACHE HIT: {:?}", goal.result)
+                writeln!(self.f, "PROVISIONAL CACHE HIT: {:?}", eval.result)
             }
             GoalEvaluationKind::Uncached { revisions } => {
                 for (n, step) in revisions.iter().enumerate() {
-                    writeln!(self.f, "REVISION {n}: {:?}", step.result)?;
+                    writeln!(self.f, "REVISION {n}")?;
                     self.nested(|this| this.format_evaluation_step(step))?;
                 }
-                writeln!(self.f, "RESULT: {:?}", goal.result)
+                writeln!(self.f, "RESULT: {:?}", eval.result)
             }
-        }?;
-
-        if goal.returned_goals.len() > 0 {
-            writeln!(self.f, "NESTED GOALS ADDED TO CALLER: [")?;
-            self.nested(|this| {
-                for goal in goal.returned_goals.iter() {
-                    writeln!(this.f, "ADDED GOAL: {goal:?},")?;
-                }
-                Ok(())
-            })?;
-
-            writeln!(self.f, "]")?;
         }
-
-        Ok(())
     }
 
     pub(super) fn format_evaluation_step(
         &mut self,
         evaluation_step: &GoalEvaluationStep<'_>,
     ) -> std::fmt::Result {
         writeln!(self.f, "INSTANTIATED: {:?}", evaluation_step.instantiated_goal)?;
-
-        for candidate in &evaluation_step.candidates {
-            self.nested(|this| this.format_candidate(candidate))?;
-        }
-        for nested in &evaluation_step.nested_goal_evaluations {
-            self.nested(|this| this.format_nested_goal_evaluation(nested))?;
-        }
-
-        Ok(())
+        self.format_candidate(&evaluation_step.evaluation)
     }
 
     pub(super) fn format_candidate(&mut self, candidate: &GoalCandidate<'_>) -> std::fmt::Result {
         match &candidate.kind {
-            CandidateKind::NormalizedSelfTyAssembly => {
+            ProbeKind::Root { result } => {
+                writeln!(self.f, "ROOT RESULT: {result:?}")
+            }
+            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| {
             for candidate in &candidate.candidates {
                 this.format_candidate(candidate)?;
             }
-            for nested in &candidate.nested_goal_evaluations {
-                this.format_nested_goal_evaluation(nested)?;
+            for nested in &candidate.added_goals_evaluations {
+                this.format_added_goals_evaluation(nested)?;
             }
             Ok(())
         })
     }
 
-    pub(super) fn format_nested_goal_evaluation(
+    pub(super) fn format_added_goals_evaluation(
         &mut self,
-        nested_goal_evaluation: &AddedGoalsEvaluation<'_>,
+        added_goals_evaluation: &AddedGoalsEvaluation<'_>,
     ) -> std::fmt::Result {
-        writeln!(self.f, "TRY_EVALUATE_ADDED_GOALS: {:?}", nested_goal_evaluation.result)?;
+        writeln!(self.f, "TRY_EVALUATE_ADDED_GOALS: {:?}", added_goals_evaluation.result)?;
 
-        for (n, revision) in nested_goal_evaluation.evaluations.iter().enumerate() {
-            writeln!(self.f, "REVISION {n}")?;
+        for (n, iterations) in added_goals_evaluation.evaluations.iter().enumerate() {
+            writeln!(self.f, "ITERATION {n}")?;
             self.nested(|this| {
-                for goal_evaluation in revision {
+                for goal_evaluation in iterations {
                     this.format_goal_evaluation(goal_evaluation)?;
                 }
                 Ok(())

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(),