Auto merge of #125230 - compiler-errors:uplift-query-stuff, r=lcnr

Uplift more query stuff

- Uplift various query input/response internals
- Uplift the `ProofTree` structures and make the `ProofTreeBuilder` stuff (mostly) generic over `Interner`
- Stop using `TyCtxt::def_kind` in favor of `AliasTerm::kind`

r? lcnr

Cargo.lock

@@ -4343,6 +4343,7 @@ dependencies = [
  "rustc_hir_pretty",
  "rustc_index",
  "rustc_macros",
+ "rustc_next_trait_solver",
  "rustc_query_system",
  "rustc_serialize",
  "rustc_session",
@@ -4451,7 +4452,13 @@ dependencies = [
 name = "rustc_next_trait_solver"
 version = "0.0.0"
 dependencies = [
+ "derivative",
+ "rustc_ast_ir",
+ "rustc_data_structures",
+ "rustc_macros",
+ "rustc_serialize",
  "rustc_type_ir",
+ "rustc_type_ir_macros",
 ]
 
 [[package]]
@@ -4752,6 +4759,7 @@ name = "rustc_trait_selection"
 version = "0.0.0"
 dependencies = [
  "bitflags 2.5.0",
+ "derivative",
  "itertools 0.12.1",
  "rustc_ast",
  "rustc_ast_ir",
@@ -4767,10 +4775,13 @@ dependencies = [
  "rustc_next_trait_solver",
  "rustc_parse_format",
  "rustc_query_system",
+ "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",
  "rustc_transmute",
+ "rustc_type_ir",
+ "rustc_type_ir_macros",
  "smallvec",
  "tracing",
 ]

compiler/rustc_infer/src/infer/at.rs

@@ -385,19 +385,31 @@ impl<'tcx> ToTrace<'tcx> for ty::GenericArg<'tcx> {
         a: Self,
         b: Self,
     ) -> TypeTrace<'tcx> {
-        use GenericArgKind::*;
         TypeTrace {
             cause: cause.clone(),
             values: match (a.unpack(), b.unpack()) {
-                (Lifetime(a), Lifetime(b)) => Regions(ExpectedFound::new(a_is_expected, a, b)),
+                (GenericArgKind::Lifetime(a), GenericArgKind::Lifetime(b)) => {
-                (Type(a), Type(b)) => Terms(ExpectedFound::new(a_is_expected, a.into(), b.into())),
+                    Regions(ExpectedFound::new(a_is_expected, a, b))
-                (Const(a), Const(b)) => {
+                }
+                (GenericArgKind::Type(a), GenericArgKind::Type(b)) => {
+                    Terms(ExpectedFound::new(a_is_expected, a.into(), b.into()))
+                }
+                (GenericArgKind::Const(a), GenericArgKind::Const(b)) => {
                     Terms(ExpectedFound::new(a_is_expected, a.into(), b.into()))
                 }
 
-                (Lifetime(_), Type(_) | Const(_))
+                (
-                | (Type(_), Lifetime(_) | Const(_))
+                    GenericArgKind::Lifetime(_),
-                | (Const(_), Lifetime(_) | Type(_)) => {
+                    GenericArgKind::Type(_) | GenericArgKind::Const(_),
+                )
+                | (
+                    GenericArgKind::Type(_),
+                    GenericArgKind::Lifetime(_) | GenericArgKind::Const(_),
+                )
+                | (
+                    GenericArgKind::Const(_),
+                    GenericArgKind::Lifetime(_) | GenericArgKind::Type(_),
+                ) => {
                     bug!("relating different kinds: {a:?} {b:?}")
                 }
             },

compiler/rustc_infer/src/traits/mod.rs

@@ -78,9 +78,9 @@ impl<T: Hash> Hash for Obligation<'_, T> {
     }
 }
 
-impl<'tcx, P> From<Obligation<'tcx, P>> for ty::Goal<'tcx, P> {
+impl<'tcx, P> From<Obligation<'tcx, P>> for solve::Goal<'tcx, P> {
     fn from(value: Obligation<'tcx, P>) -> Self {
-        ty::Goal { param_env: value.param_env, predicate: value.predicate }
+        solve::Goal { param_env: value.param_env, predicate: value.predicate }
     }
 }
 

compiler/rustc_middle/Cargo.toml

@@ -28,6 +28,7 @@ rustc_hir = { path = "../rustc_hir" }
 rustc_hir_pretty = { path = "../rustc_hir_pretty" }
 rustc_index = { path = "../rustc_index" }
 rustc_macros = { path = "../rustc_macros" }
+rustc_next_trait_solver = { path = "../rustc_next_trait_solver" }
 rustc_query_system = { path = "../rustc_query_system" }
 rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }

compiler/rustc_middle/src/arena.rs

@@ -61,7 +61,7 @@ macro_rules! arena_types {
             [] dtorck_constraint: rustc_middle::traits::query::DropckConstraint<'tcx>,
             [] candidate_step: rustc_middle::traits::query::CandidateStep<'tcx>,
             [] autoderef_bad_ty: rustc_middle::traits::query::MethodAutoderefBadTy<'tcx>,
-            [] canonical_goal_evaluation: rustc_middle::traits::solve::inspect::GoalEvaluationStep<'tcx>,
+            [] canonical_goal_evaluation: rustc_next_trait_solver::solve::inspect::GoalEvaluationStep<rustc_middle::ty::TyCtxt<'tcx>>,
             [] query_region_constraints: rustc_middle::infer::canonical::QueryRegionConstraints<'tcx>,
             [] type_op_subtype:
                 rustc_middle::infer::canonical::Canonical<'tcx,

compiler/rustc_middle/src/infer/canonical.rs

@@ -23,23 +23,20 @@
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::Lock;
-use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable};
+use rustc_macros::{HashStable, TypeFoldable, TypeVisitable};
-use rustc_type_ir::Canonical as IrCanonical;
+pub use rustc_type_ir as ir;
-use rustc_type_ir::CanonicalVarInfo as IrCanonicalVarInfo;
 pub use rustc_type_ir::{CanonicalTyVarKind, CanonicalVarKind};
 use smallvec::SmallVec;
 use std::collections::hash_map::Entry;
-use std::ops::Index;
 
 use crate::infer::MemberConstraint;
 use crate::mir::ConstraintCategory;
 use crate::ty::GenericArg;
-use crate::ty::{self, BoundVar, List, Region, Ty, TyCtxt, TypeFlags, TypeVisitableExt};
+use crate::ty::{self, List, Region, Ty, TyCtxt, TypeFlags, TypeVisitableExt};
-
-pub type Canonical<'tcx, V> = IrCanonical<TyCtxt<'tcx>, V>;
-
-pub type CanonicalVarInfo<'tcx> = IrCanonicalVarInfo<TyCtxt<'tcx>>;
 
+pub type Canonical<'tcx, V> = ir::Canonical<TyCtxt<'tcx>, V>;
+pub type CanonicalVarInfo<'tcx> = ir::CanonicalVarInfo<TyCtxt<'tcx>>;
+pub type CanonicalVarValues<'tcx> = ir::CanonicalVarValues<TyCtxt<'tcx>>;
 pub type CanonicalVarInfos<'tcx> = &'tcx List<CanonicalVarInfo<'tcx>>;
 
 impl<'tcx> ty::TypeFoldable<TyCtxt<'tcx>> for CanonicalVarInfos<'tcx> {
@@ -51,74 +48,6 @@ impl<'tcx> ty::TypeFoldable<TyCtxt<'tcx>> for CanonicalVarInfos<'tcx> {
     }
 }
 
-/// A set of values corresponding to the canonical variables from some
-/// `Canonical`. You can give these values to
-/// `canonical_value.instantiate` to instantiate them into the canonical
-/// value at the right places.
-///
-/// When you canonicalize a value `V`, you get back one of these
-/// vectors with the original values that were replaced by canonical
-/// variables. You will need to supply it later to instantiate the
-/// canonicalized query response.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyDecodable, TyEncodable)]
-#[derive(HashStable, TypeFoldable, TypeVisitable)]
-pub struct CanonicalVarValues<'tcx> {
-    pub var_values: ty::GenericArgsRef<'tcx>,
-}
-
-impl CanonicalVarValues<'_> {
-    pub fn is_identity(&self) -> bool {
-        self.var_values.iter().enumerate().all(|(bv, arg)| match arg.unpack() {
-            ty::GenericArgKind::Lifetime(r) => {
-                matches!(*r, ty::ReBound(ty::INNERMOST, br) if br.var.as_usize() == bv)
-            }
-            ty::GenericArgKind::Type(ty) => {
-                matches!(*ty.kind(), ty::Bound(ty::INNERMOST, bt) if bt.var.as_usize() == bv)
-            }
-            ty::GenericArgKind::Const(ct) => {
-                matches!(ct.kind(), ty::ConstKind::Bound(ty::INNERMOST, bc) if bc.as_usize() == bv)
-            }
-        })
-    }
-
-    pub fn is_identity_modulo_regions(&self) -> bool {
-        let mut var = ty::BoundVar::ZERO;
-        for arg in self.var_values {
-            match arg.unpack() {
-                ty::GenericArgKind::Lifetime(r) => {
-                    if let ty::ReBound(ty::INNERMOST, br) = *r
-                        && var == br.var
-                    {
-                        var = var + 1;
-                    } else {
-                        // It's ok if this region var isn't unique
-                    }
-                }
-                ty::GenericArgKind::Type(ty) => {
-                    if let ty::Bound(ty::INNERMOST, bt) = *ty.kind()
-                        && var == bt.var
-                    {
-                        var = var + 1;
-                    } else {
-                        return false;
-                    }
-                }
-                ty::GenericArgKind::Const(ct) => {
-                    if let ty::ConstKind::Bound(ty::INNERMOST, bc) = ct.kind()
-                        && var == bc
-                    {
-                        var = var + 1;
-                    } else {
-                        return false;
-                    }
-                }
-            }
-        }
-
-        true
-    }
-}
-
 /// When we canonicalize a value to form a query, we wind up replacing
 /// various parts of it with canonical variables. This struct stores
 /// those replaced bits to remember for when we process the query
@@ -218,78 +147,6 @@ TrivialTypeTraversalImpls! {
     crate::infer::canonical::Certainty,
 }
 
-impl<'tcx> CanonicalVarValues<'tcx> {
-    // Given a list of canonical variables, construct a set of values which are
-    // the identity response.
-    pub fn make_identity(
-        tcx: TyCtxt<'tcx>,
-        infos: CanonicalVarInfos<'tcx>,
-    ) -> CanonicalVarValues<'tcx> {
-        CanonicalVarValues {
-            var_values: tcx.mk_args_from_iter(infos.iter().enumerate().map(
-                |(i, info)| -> ty::GenericArg<'tcx> {
-                    match info.kind {
-                        CanonicalVarKind::Ty(_) | CanonicalVarKind::PlaceholderTy(_) => {
-                            Ty::new_bound(tcx, ty::INNERMOST, ty::BoundVar::from_usize(i).into())
-                                .into()
-                        }
-                        CanonicalVarKind::Region(_) | CanonicalVarKind::PlaceholderRegion(_) => {
-                            let br = ty::BoundRegion {
-                                var: ty::BoundVar::from_usize(i),
-                                kind: ty::BrAnon,
-                            };
-                            ty::Region::new_bound(tcx, ty::INNERMOST, br).into()
-                        }
-                        CanonicalVarKind::Effect => ty::Const::new_bound(
-                            tcx,
-                            ty::INNERMOST,
-                            ty::BoundVar::from_usize(i),
-                            tcx.types.bool,
-                        )
-                        .into(),
-                        CanonicalVarKind::Const(_, ty)
-                        | CanonicalVarKind::PlaceholderConst(_, ty) => ty::Const::new_bound(
-                            tcx,
-                            ty::INNERMOST,
-                            ty::BoundVar::from_usize(i),
-                            ty,
-                        )
-                        .into(),
-                    }
-                },
-            )),
-        }
-    }
-
-    /// Creates dummy var values which should not be used in a
-    /// canonical response.
-    pub fn dummy() -> CanonicalVarValues<'tcx> {
-        CanonicalVarValues { var_values: ty::List::empty() }
-    }
-
-    #[inline]
-    pub fn len(&self) -> usize {
-        self.var_values.len()
-    }
-}
-
-impl<'a, 'tcx> IntoIterator for &'a CanonicalVarValues<'tcx> {
-    type Item = GenericArg<'tcx>;
-    type IntoIter = ::std::iter::Copied<::std::slice::Iter<'a, GenericArg<'tcx>>>;
-
-    fn into_iter(self) -> Self::IntoIter {
-        self.var_values.iter()
-    }
-}
-
-impl<'tcx> Index<BoundVar> for CanonicalVarValues<'tcx> {
-    type Output = GenericArg<'tcx>;
-
-    fn index(&self, value: BoundVar) -> &GenericArg<'tcx> {
-        &self.var_values[value.as_usize()]
-    }
-}
-
 #[derive(Default)]
 pub struct CanonicalParamEnvCache<'tcx> {
     map: Lock<

compiler/rustc_middle/src/traits/mod.rs

@@ -9,7 +9,6 @@ pub mod specialization_graph;
 mod structural_impls;
 pub mod util;
 
-use crate::infer::canonical::Canonical;
 use crate::mir::ConstraintCategory;
 use crate::ty::abstract_const::NotConstEvaluatable;
 use crate::ty::GenericArgsRef;
@@ -32,6 +31,8 @@ use std::borrow::Cow;
 use std::hash::{Hash, Hasher};
 
 pub use self::select::{EvaluationCache, EvaluationResult, OverflowError, SelectionCache};
+// FIXME: Remove this import and import via `solve::`
+pub use rustc_next_trait_solver::solve::BuiltinImplSource;
 
 /// Depending on the stage of compilation, we want projection to be
 /// more or less conservative.
@@ -736,32 +737,6 @@ pub struct ImplSourceUserDefinedData<'tcx, N> {
     pub nested: Vec<N>,
 }
 
-#[derive(Copy, Clone, PartialEq, Eq, TyEncodable, TyDecodable, HashStable, Debug)]
-pub enum BuiltinImplSource {
-    /// Some builtin impl we don't need to differentiate. This should be used
-    /// unless more specific information is necessary.
-    Misc,
-    /// A builtin impl for trait objects.
-    ///
-    /// The vtable is formed by concatenating together the method lists of
-    /// the base object trait and all supertraits, pointers to supertrait vtable will
-    /// be provided when necessary; this is the start of `upcast_trait_ref`'s methods
-    /// in that vtable.
-    Object { vtable_base: usize },
-    /// The vtable is formed by concatenating together the method lists of
-    /// the base object trait and all supertraits, pointers to supertrait vtable will
-    /// be provided when necessary; this is the position of `upcast_trait_ref`'s vtable
-    /// within that vtable.
-    TraitUpcasting { vtable_vptr_slot: Option<usize> },
-    /// Unsizing a tuple like `(A, B, ..., X)` to `(A, B, ..., Y)` if `X` unsizes to `Y`.
-    ///
-    /// This needs to be a separate variant as it is still unstable and we need to emit
-    /// a feature error when using it on stable.
-    TupleUnsizing,
-}
-
-TrivialTypeTraversalImpls! { BuiltinImplSource }
-
 #[derive(Clone, Debug, PartialEq, Eq, Hash, HashStable, PartialOrd, Ord)]
 pub enum ObjectSafetyViolation {
     /// `Self: Sized` declared on the trait.

compiler/rustc_middle/src/traits/query.rs

@@ -12,6 +12,8 @@ use crate::ty::GenericArg;
 use crate::ty::{self, Ty, TyCtxt};
 use rustc_macros::{HashStable, TypeFoldable, TypeVisitable};
 use rustc_span::Span;
+// FIXME: Remove this import and import via `traits::solve`.
+pub use rustc_next_trait_solver::solve::NoSolution;
 
 pub mod type_op {
     use crate::ty::fold::TypeFoldable;
@@ -89,9 +91,6 @@ pub type CanonicalTypeOpProvePredicateGoal<'tcx> =
 pub type CanonicalTypeOpNormalizeGoal<'tcx, T> =
     Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::Normalize<T>>>;
 
-#[derive(Copy, Clone, Debug, Hash, HashStable, PartialEq, Eq)]
-pub struct NoSolution;
-
 impl<'tcx> From<TypeError<'tcx>> for NoSolution {
     fn from(_: TypeError<'tcx>) -> NoSolution {
         NoSolution

compiler/rustc_middle/src/traits/solve.rs

@@ -1,97 +1,24 @@
 use rustc_ast_ir::try_visit;
 use rustc_data_structures::intern::Interned;
 use rustc_macros::{HashStable, TypeFoldable, TypeVisitable};
-use rustc_span::def_id::DefId;
+use rustc_next_trait_solver as ir;
+pub use rustc_next_trait_solver::solve::*;
 
-use crate::infer::canonical::{CanonicalVarValues, QueryRegionConstraints};
+use crate::infer::canonical::QueryRegionConstraints;
-use crate::traits::query::NoSolution;
-use crate::traits::Canonical;
 use crate::ty::{
     self, FallibleTypeFolder, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeVisitable, TypeVisitor,
 };
-// FIXME(compiler-errors): remove this import in favor of `use rustc_middle::ty::Goal`.
-pub use crate::ty::Goal;
-
-use super::BuiltinImplSource;
 
 mod cache;
-pub mod inspect;
 
 pub use cache::{CacheData, EvaluationCache};
 
-#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, HashStable, TypeFoldable, TypeVisitable)]
+pub type Goal<'tcx, P> = ir::solve::Goal<TyCtxt<'tcx>, P>;
-pub struct Response<'tcx> {
+pub type QueryInput<'tcx, P> = ir::solve::QueryInput<TyCtxt<'tcx>, P>;
-    pub certainty: Certainty,
+pub type QueryResult<'tcx> = ir::solve::QueryResult<TyCtxt<'tcx>>;
-    pub var_values: CanonicalVarValues<'tcx>,
+pub type CandidateSource<'tcx> = ir::solve::CandidateSource<TyCtxt<'tcx>>;
-    /// Additional constraints returned by this query.
+pub type CanonicalInput<'tcx, P = ty::Predicate<'tcx>> = ir::solve::CanonicalInput<TyCtxt<'tcx>, P>;
-    pub external_constraints: ExternalConstraints<'tcx>,
+pub type CanonicalResponse<'tcx> = ir::solve::CanonicalResponse<TyCtxt<'tcx>>;
-}
-
-#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, HashStable, TypeFoldable, TypeVisitable)]
-pub enum Certainty {
-    Yes,
-    Maybe(MaybeCause),
-}
-
-impl Certainty {
-    pub const AMBIGUOUS: Certainty = Certainty::Maybe(MaybeCause::Ambiguity);
-
-    /// Use this function to merge the certainty of multiple nested subgoals.
-    ///
-    /// Given an impl like `impl<T: Foo + Bar> Baz for T {}`, we have 2 nested
-    /// subgoals whenever we use the impl as a candidate: `T: Foo` and `T: Bar`.
-    /// If evaluating `T: Foo` results in ambiguity and `T: Bar` results in
-    /// success, we merge these two responses. This results in ambiguity.
-    ///
-    /// If we unify ambiguity with overflow, we return overflow. This doesn't matter
-    /// inside of the solver as we do not distinguish ambiguity from overflow. It does
-    /// however matter for diagnostics. If `T: Foo` resulted in overflow and `T: Bar`
-    /// in ambiguity without changing the inference state, we still want to tell the
-    /// user that `T: Baz` results in overflow.
-    pub fn unify_with(self, other: Certainty) -> Certainty {
-        match (self, other) {
-            (Certainty::Yes, Certainty::Yes) => Certainty::Yes,
-            (Certainty::Yes, Certainty::Maybe(_)) => other,
-            (Certainty::Maybe(_), Certainty::Yes) => self,
-            (Certainty::Maybe(a), Certainty::Maybe(b)) => Certainty::Maybe(a.unify_with(b)),
-        }
-    }
-
-    pub const fn overflow(suggest_increasing_limit: bool) -> Certainty {
-        Certainty::Maybe(MaybeCause::Overflow { suggest_increasing_limit })
-    }
-}
-
-/// Why we failed to evaluate a goal.
-#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, HashStable, TypeFoldable, TypeVisitable)]
-pub enum MaybeCause {
-    /// We failed due to ambiguity. This ambiguity can either
-    /// be a true ambiguity, i.e. there are multiple different answers,
-    /// 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 { 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)]
-pub struct QueryInput<'tcx, T> {
-    pub goal: Goal<'tcx, T>,
-    pub predefined_opaques_in_body: PredefinedOpaques<'tcx>,
-}
 
 /// Additional constraints returned on success.
 #[derive(Debug, PartialEq, Eq, Clone, Hash, HashStable, Default)]
@@ -110,18 +37,6 @@ impl<'tcx> std::ops::Deref for PredefinedOpaques<'tcx> {
     }
 }
 
-pub type CanonicalInput<'tcx, T = ty::Predicate<'tcx>> = Canonical<'tcx, QueryInput<'tcx, T>>;
-
-pub type CanonicalResponse<'tcx> = Canonical<'tcx, Response<'tcx>>;
-
-/// The result of evaluating a canonical query.
-///
-/// FIXME: We use a different type than the existing canonical queries. This is because
-/// we need to add a `Certainty` for `overflow` and may want to restructure this code without
-/// having to worry about changes to currently used code. Once we've made progress on this
-/// solver, merge the two responses again.
-pub type QueryResult<'tcx> = Result<CanonicalResponse<'tcx>, NoSolution>;
-
 #[derive(Debug, PartialEq, Eq, Copy, Clone, Hash, HashStable)]
 pub struct ExternalConstraints<'tcx>(pub(crate) Interned<'tcx, ExternalConstraintsData<'tcx>>);
 
@@ -228,91 +143,3 @@ impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for PredefinedOpaques<'tcx> {
         self.opaque_types.visit_with(visitor)
     }
 }
-
-/// Why a specific goal has to be proven.
-///
-/// This is necessary as we treat nested goals different depending on
-/// their source.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable, TypeVisitable, TypeFoldable)]
-pub enum GoalSource {
-    Misc,
-    /// We're proving a where-bound of an impl.
-    ///
-    /// FIXME(-Znext-solver=coinductive): Explain how and why this
-    /// changes whether cycles are coinductive.
-    ///
-    /// This also impacts whether we erase constraints on overflow.
-    /// Erasing constraints is generally very useful for perf and also
-    /// results in better error messages by avoiding spurious errors.
-    /// We do not erase overflow constraints in `normalizes-to` goals unless
-    /// they are from an impl where-clause. This is necessary due to
-    /// backwards compatability, cc trait-system-refactor-initiatitive#70.
-    ImplWhereBound,
-    /// Instantiating a higher-ranked goal and re-proving it.
-    InstantiateHigherRanked,
-}
-
-/// 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,
-    /// A candidate that is registered only during coherence to represent some
-    /// yet-unknown impl that could be produced downstream without violating orphan
-    /// rules.
-    // FIXME: Merge this with the forced ambiguity candidates, so those don't use `Misc`.
-    CoherenceUnknowable,
-}

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

@@ -17,7 +17,7 @@ pub struct EvaluationCache<'tcx> {
 #[derive(PartialEq, Eq)]
 pub struct CacheData<'tcx> {
     pub result: QueryResult<'tcx>,
-    pub proof_tree: Option<&'tcx [inspect::GoalEvaluationStep<'tcx>]>,
+    pub proof_tree: Option<&'tcx [inspect::GoalEvaluationStep<TyCtxt<'tcx>>]>,
     pub reached_depth: usize,
     pub encountered_overflow: bool,
 }
@@ -28,7 +28,7 @@ impl<'tcx> EvaluationCache<'tcx> {
         &self,
         tcx: TyCtxt<'tcx>,
         key: CanonicalInput<'tcx>,
-        proof_tree: Option<&'tcx [inspect::GoalEvaluationStep<'tcx>]>,
+        proof_tree: Option<&'tcx [inspect::GoalEvaluationStep<TyCtxt<'tcx>>]>,
         reached_depth: usize,
         encountered_overflow: bool,
         cycle_participants: FxHashSet<CanonicalInput<'tcx>>,
@@ -105,7 +105,7 @@ struct Success<'tcx> {
 #[derive(Clone, Copy)]
 pub struct QueryData<'tcx> {
     pub result: QueryResult<'tcx>,
-    pub proof_tree: Option<&'tcx [inspect::GoalEvaluationStep<'tcx>]>,
+    pub proof_tree: Option<&'tcx [inspect::GoalEvaluationStep<TyCtxt<'tcx>>]>,
 }
 
 /// The cache entry for a goal `CanonicalInput`.

compiler/rustc_middle/src/ty/context.rs

@@ -89,18 +89,23 @@ use std::ops::{Bound, Deref};
 #[allow(rustc::usage_of_ty_tykind)]
 impl<'tcx> Interner for TyCtxt<'tcx> {
     type DefId = DefId;
-    type DefiningOpaqueTypes = &'tcx ty::List<LocalDefId>;
     type AdtDef = ty::AdtDef<'tcx>;
+
     type GenericArgs = ty::GenericArgsRef<'tcx>;
     type OwnItemArgs = &'tcx [ty::GenericArg<'tcx>];
     type GenericArg = ty::GenericArg<'tcx>;
-
     type Term = ty::Term<'tcx>;
+
     type Binder<T: TypeVisitable<TyCtxt<'tcx>>> = Binder<'tcx, T>;
     type BoundVars = &'tcx List<ty::BoundVariableKind>;
     type BoundVar = ty::BoundVariableKind;
 
     type CanonicalVars = CanonicalVarInfos<'tcx>;
+    type PredefinedOpaques = solve::PredefinedOpaques<'tcx>;
+    type DefiningOpaqueTypes = &'tcx ty::List<LocalDefId>;
+    type ExternalConstraints = ExternalConstraints<'tcx>;
+    type GoalEvaluationSteps = &'tcx [solve::inspect::GoalEvaluationStep<TyCtxt<'tcx>>];
+
     type Ty = Ty<'tcx>;
     type Tys = &'tcx List<Ty<'tcx>>;
     type FnInputTys = &'tcx [Ty<'tcx>];

compiler/rustc_middle/src/ty/generic_args.rs

@@ -11,6 +11,7 @@ use rustc_ast_ir::walk_visitable_list;
 use rustc_data_structures::intern::Interned;
 use rustc_errors::{DiagArgValue, IntoDiagArg};
 use rustc_hir::def_id::DefId;
+use rustc_macros::extension;
 use rustc_macros::{
     Decodable, Encodable, HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable,
 };
@@ -25,6 +26,8 @@ use std::num::NonZero;
 use std::ops::Deref;
 use std::ptr::NonNull;
 
+pub type GenericArgKind<'tcx> = rustc_type_ir::GenericArgKind<TyCtxt<'tcx>>;
+
 /// An entity in the Rust type system, which can be one of
 /// several kinds (types, lifetimes, and consts).
 /// To reduce memory usage, a `GenericArg` is an interned pointer,
@@ -49,6 +52,14 @@ impl<'tcx> rustc_type_ir::inherent::GenericArgs<TyCtxt<'tcx>> for ty::GenericArg
     }
 }
 
+impl<'tcx> rustc_type_ir::inherent::IntoKind for GenericArg<'tcx> {
+    type Kind = GenericArgKind<'tcx>;
+
+    fn kind(self) -> Self::Kind {
+        self.unpack()
+    }
+}
+
 #[cfg(parallel_compiler)]
 unsafe impl<'tcx> rustc_data_structures::sync::DynSend for GenericArg<'tcx> where
     &'tcx (Ty<'tcx>, ty::Region<'tcx>, ty::Const<'tcx>): rustc_data_structures::sync::DynSend
@@ -79,13 +90,7 @@ const TYPE_TAG: usize = 0b00;
 const REGION_TAG: usize = 0b01;
 const CONST_TAG: usize = 0b10;
 
-#[derive(Debug, TyEncodable, TyDecodable, PartialEq, Eq, HashStable)]
+#[extension(trait GenericArgPackExt<'tcx>)]
-pub enum GenericArgKind<'tcx> {
-    Lifetime(ty::Region<'tcx>),
-    Type(Ty<'tcx>),
-    Const(ty::Const<'tcx>),
-}
-
 impl<'tcx> GenericArgKind<'tcx> {
     #[inline]
     fn pack(self) -> GenericArg<'tcx> {

compiler/rustc_middle/src/ty/mod.rs

@@ -28,7 +28,7 @@ use crate::ty::fast_reject::SimplifiedType;
 use crate::ty::util::Discr;
 pub use adt::*;
 pub use assoc::*;
-pub use generic_args::*;
+pub use generic_args::{GenericArgKind, *};
 pub use generics::*;
 pub use intrinsic::IntrinsicDef;
 use rustc_ast as ast;
@@ -97,13 +97,12 @@ pub use self::parameterized::ParameterizedOverTcx;
 pub use self::pattern::{Pattern, PatternKind};
 pub use self::predicate::{
     AliasTerm, Clause, ClauseKind, CoercePredicate, ExistentialPredicate,
-    ExistentialPredicateStableCmpExt, ExistentialProjection, ExistentialTraitRef, Goal,
+    ExistentialPredicateStableCmpExt, ExistentialProjection, ExistentialTraitRef, NormalizesTo,
-    NormalizesTo, OutlivesPredicate, PolyCoercePredicate, PolyExistentialPredicate,
+    OutlivesPredicate, PolyCoercePredicate, PolyExistentialPredicate, PolyExistentialProjection,
-    PolyExistentialProjection, PolyExistentialTraitRef, PolyProjectionPredicate,
+    PolyExistentialTraitRef, PolyProjectionPredicate, PolyRegionOutlivesPredicate,
-    PolyRegionOutlivesPredicate, PolySubtypePredicate, PolyTraitPredicate, PolyTraitRef,
+    PolySubtypePredicate, PolyTraitPredicate, PolyTraitRef, PolyTypeOutlivesPredicate, Predicate,
-    PolyTypeOutlivesPredicate, Predicate, PredicateKind, ProjectionPredicate,
+    PredicateKind, ProjectionPredicate, RegionOutlivesPredicate, SubtypePredicate, ToPolyTraitRef,
-    RegionOutlivesPredicate, SubtypePredicate, ToPolyTraitRef, TraitPredicate, TraitRef,
+    TraitPredicate, TraitRef, TypeOutlivesPredicate,
-    TypeOutlivesPredicate,
 };
 pub use self::region::{
     BoundRegion, BoundRegionKind, BoundRegionKind::*, EarlyParamRegion, LateParamRegion, Region,

compiler/rustc_middle/src/ty/predicate.rs

@@ -12,7 +12,6 @@ use crate::ty::{
     Upcast, UpcastFrom, WithCachedTypeInfo,
 };
 
-pub type Goal<'tcx, P> = ir::Goal<TyCtxt<'tcx>, P>;
 pub type TraitRef<'tcx> = ir::TraitRef<TyCtxt<'tcx>>;
 pub type AliasTerm<'tcx> = ir::AliasTerm<TyCtxt<'tcx>>;
 pub type ProjectionPredicate<'tcx> = ir::ProjectionPredicate<TyCtxt<'tcx>>;

compiler/rustc_middle/src/ty/region.rs

@@ -396,6 +396,12 @@ pub struct BoundRegion {
     pub kind: BoundRegionKind,
 }
 
+impl<'tcx> rustc_type_ir::inherent::BoundVarLike<TyCtxt<'tcx>> for BoundRegion {
+    fn var(self) -> BoundVar {
+        self.var
+    }
+}
+
 impl core::fmt::Debug for BoundRegion {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self.kind {

compiler/rustc_middle/src/ty/sty.rs

@@ -1199,6 +1199,12 @@ pub struct BoundTy {
     pub kind: BoundTyKind,
 }
 
+impl<'tcx> rustc_type_ir::inherent::BoundVarLike<TyCtxt<'tcx>> for BoundTy {
+    fn var(self) -> BoundVar {
+        self.var
+    }
+}
+
 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, TyEncodable, TyDecodable)]
 #[derive(HashStable)]
 pub enum BoundTyKind {
@@ -1601,6 +1607,10 @@ impl<'tcx> Ty<'tcx> {
 }
 
 impl<'tcx> rustc_type_ir::inherent::Ty<TyCtxt<'tcx>> for Ty<'tcx> {
+    fn new_bool(tcx: TyCtxt<'tcx>) -> Self {
+        tcx.types.bool
+    }
+
     fn new_anon_bound(tcx: TyCtxt<'tcx>, debruijn: ty::DebruijnIndex, var: ty::BoundVar) -> Self {
         Ty::new_bound(tcx, debruijn, ty::BoundTy { var, kind: ty::BoundTyKind::Anon })
     }

compiler/rustc_next_trait_solver/Cargo.toml

@@ -5,9 +5,19 @@ edition = "2021"
 
 [dependencies]
 rustc_type_ir = { path = "../rustc_type_ir", default-features = false }
+derivative = "2.2.0"
+rustc_macros = { path = "../rustc_macros", optional = true }
+rustc_type_ir_macros = { path = "../rustc_type_ir_macros" }
+rustc_serialize = { path = "../rustc_serialize", optional = true }
+rustc_data_structures = { path = "../rustc_data_structures", optional = true }
+rustc_ast_ir = { path = "../rustc_ast_ir", default-features = false }
 
 [features]
 default = ["nightly"]
 nightly = [
     "rustc_type_ir/nightly",
-]
+    "rustc_macros",
+    "rustc_serialize",
+    "rustc_data_structures",
+    "rustc_ast_ir/nightly",
+]

compiler/rustc_next_trait_solver/src/lib.rs

@@ -1 +1,2 @@
 pub mod canonicalizer;
+pub mod solve;

compiler/rustc_next_trait_solver/src/solve.rs

@@ -0,0 +1 @@
+pub use rustc_type_ir::solve::*;

compiler/rustc_trait_selection/Cargo.toml

@@ -6,6 +6,7 @@ edition = "2021"
 [dependencies]
 # tidy-alphabetical-start
 bitflags = "2.4.1"
+derivative = "2.2.0"
 itertools = "0.12"
 rustc_ast = { path = "../rustc_ast" }
 rustc_ast_ir = { path = "../rustc_ast_ir" }
@@ -21,10 +22,13 @@ rustc_middle = { path = "../rustc_middle" }
 rustc_next_trait_solver = { path = "../rustc_next_trait_solver" }
 rustc_parse_format = { path = "../rustc_parse_format" }
 rustc_query_system = { path = "../rustc_query_system" }
+rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
 rustc_transmute = { path = "../rustc_transmute", features = ["rustc"] }
+rustc_type_ir = { path = "../rustc_type_ir" }
+rustc_type_ir_macros = { path = "../rustc_type_ir_macros" }
 smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
 tracing = "0.1"
 # tidy-alphabetical-end

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

@@ -25,7 +25,7 @@ pub(super) mod structural_traits;
 /// and the `result` when using the given `source`.
 #[derive(Debug, Clone)]
 pub(super) struct Candidate<'tcx> {
-    pub(super) source: CandidateSource,
+    pub(super) source: CandidateSource<'tcx>,
     pub(super) result: CanonicalResponse<'tcx>,
 }
 
@@ -47,7 +47,7 @@ pub(super) trait GoalKind<'tcx>:
     /// [`EvalCtxt::evaluate_added_goals_and_make_canonical_response`]).
     fn probe_and_match_goal_against_assumption(
         ecx: &mut EvalCtxt<'_, 'tcx>,
-        source: CandidateSource,
+        source: CandidateSource<'tcx>,
         goal: Goal<'tcx, Self>,
         assumption: ty::Clause<'tcx>,
         then: impl FnOnce(&mut EvalCtxt<'_, 'tcx>) -> QueryResult<'tcx>,
@@ -58,7 +58,7 @@ pub(super) trait GoalKind<'tcx>:
     /// goal by equating it with the assumption.
     fn probe_and_consider_implied_clause(
         ecx: &mut EvalCtxt<'_, 'tcx>,
-        parent_source: CandidateSource,
+        parent_source: CandidateSource<'tcx>,
         goal: Goal<'tcx, Self>,
         assumption: ty::Clause<'tcx>,
         requirements: impl IntoIterator<Item = (GoalSource, Goal<'tcx, ty::Predicate<'tcx>>)>,
@@ -76,7 +76,7 @@ pub(super) trait GoalKind<'tcx>:
     /// since they're not implied by the well-formedness of the object type.
     fn probe_and_consider_object_bound_candidate(
         ecx: &mut EvalCtxt<'_, 'tcx>,
-        source: CandidateSource,
+        source: CandidateSource<'tcx>,
         goal: Goal<'tcx, Self>,
         assumption: ty::Clause<'tcx>,
     ) -> Result<Candidate<'tcx>, NoSolution> {

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

@@ -6,9 +6,8 @@ use rustc_hir::{def_id::DefId, Movability, Mutability};
 use rustc_infer::traits::query::NoSolution;
 use rustc_macros::{TypeFoldable, TypeVisitable};
 use rustc_middle::bug;
-use rustc_middle::ty::{
+use rustc_middle::traits::solve::Goal;
-    self, Goal, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable, Upcast,
+use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable, Upcast};
-};
 use rustc_span::sym;
 
 use crate::solve::EvalCtxt;

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

@@ -40,13 +40,13 @@ trait ResponseT<'tcx> {
     fn var_values(&self) -> CanonicalVarValues<'tcx>;
 }
 
-impl<'tcx> ResponseT<'tcx> for Response<'tcx> {
+impl<'tcx> ResponseT<'tcx> for Response<TyCtxt<'tcx>> {
     fn var_values(&self) -> CanonicalVarValues<'tcx> {
         self.var_values
     }
 }
 
-impl<'tcx, T> ResponseT<'tcx> for inspect::State<'tcx, T> {
+impl<'tcx, T> ResponseT<'tcx> for inspect::State<TyCtxt<'tcx>, T> {
     fn var_values(&self) -> CanonicalVarValues<'tcx> {
         self.var_values
     }
@@ -384,7 +384,7 @@ pub(in crate::solve) fn make_canonical_state<'tcx, T: TypeFoldable<TyCtxt<'tcx>>
     var_values: &[ty::GenericArg<'tcx>],
     max_input_universe: ty::UniverseIndex,
     data: T,
-) -> inspect::CanonicalState<'tcx, T> {
+) -> inspect::CanonicalState<TyCtxt<'tcx>, T> {
     let var_values = CanonicalVarValues { var_values: infcx.tcx.mk_args(var_values) };
     let state = inspect::State { var_values, data };
     let state = state.fold_with(&mut EagerResolver::new(infcx));
@@ -414,7 +414,7 @@ pub(in crate::solve) fn instantiate_canonical_state<'tcx, T: TypeFoldable<TyCtxt
     span: Span,
     param_env: ty::ParamEnv<'tcx>,
     orig_values: &mut Vec<ty::GenericArg<'tcx>>,
-    state: inspect::CanonicalState<'tcx, T>,
+    state: inspect::CanonicalState<TyCtxt<'tcx>, T>,
 ) -> T {
     // In case any fresh inference variables have been created between `state`
     // and the previous instantiation, extend `orig_values` for it.

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

@@ -1,3 +1,6 @@
+use std::io::Write;
+use std::ops::ControlFlow;
+
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::at::ToTrace;
@@ -8,13 +11,12 @@ use rustc_infer::infer::{
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::solve::{MaybeCause, NestedNormalizationGoals};
 use rustc_infer::traits::ObligationCause;
-use rustc_macros::{extension, HashStable};
+use rustc_macros::{extension, HashStable, HashStable_NoContext, TyDecodable, TyEncodable};
 use rustc_middle::bug;
 use rustc_middle::infer::canonical::CanonicalVarInfos;
-use rustc_middle::traits::solve::inspect;
 use rustc_middle::traits::solve::{
-    CanonicalInput, CanonicalResponse, Certainty, PredefinedOpaques, PredefinedOpaquesData,
+    inspect, CanonicalInput, CanonicalResponse, Certainty, PredefinedOpaques,
-    QueryResult,
+    PredefinedOpaquesData, QueryResult,
 };
 use rustc_middle::traits::specialization_graph;
 use rustc_middle::ty::{
@@ -23,8 +25,8 @@ use rustc_middle::ty::{
 };
 use rustc_session::config::DumpSolverProofTree;
 use rustc_span::DUMMY_SP;
-use std::io::Write;
+use rustc_type_ir::{self as ir, Interner};
-use std::ops::ControlFlow;
+use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Generic};
 
 use crate::traits::coherence;
 use crate::traits::vtable::{count_own_vtable_entries, prepare_vtable_segments, VtblSegment};
@@ -85,7 +87,7 @@ pub struct EvalCtxt<'a, 'tcx> {
 
     pub(super) search_graph: &'a mut SearchGraph<'tcx>,
 
-    nested_goals: NestedGoals<'tcx>,
+    nested_goals: NestedGoals<TyCtxt<'tcx>>,
 
     // Has this `EvalCtxt` errored out with `NoSolution` in `try_evaluate_added_goals`?
     //
@@ -95,11 +97,15 @@ pub struct EvalCtxt<'a, 'tcx> {
     // evaluation code.
     tainted: Result<(), NoSolution>,
 
-    pub(super) inspect: ProofTreeBuilder<'tcx>,
+    pub(super) inspect: ProofTreeBuilder<TyCtxt<'tcx>>,
 }
 
-#[derive(Default, Debug, Clone)]
+#[derive(derivative::Derivative)]
-pub(super) struct NestedGoals<'tcx> {
+#[derivative(Clone(bound = ""), Debug(bound = ""), Default(bound = ""))]
+#[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
+#[derive(TyDecodable, TyEncodable, HashStable_NoContext)]
+// FIXME: This can be made crate-private once `EvalCtxt` also lives in this crate.
+pub struct NestedGoals<I: Interner> {
     /// These normalizes-to goals are treated specially during the evaluation
     /// loop. In each iteration we take the RHS of the projection, replace it with
     /// a fresh inference variable, and only after evaluating that goal do we
@@ -110,17 +116,17 @@ pub(super) struct NestedGoals<'tcx> {
     ///
     /// Forgetting to replace the RHS with a fresh inference variable when we evaluate
     /// this goal results in an ICE..
-    pub(super) normalizes_to_goals: Vec<Goal<'tcx, ty::NormalizesTo<'tcx>>>,
+    pub normalizes_to_goals: Vec<ir::solve::Goal<I, ir::NormalizesTo<I>>>,
     /// The rest of the goals which have not yet processed or remain ambiguous.
-    pub(super) goals: Vec<(GoalSource, Goal<'tcx, ty::Predicate<'tcx>>)>,
+    pub goals: Vec<(GoalSource, ir::solve::Goal<I, I::Predicate>)>,
 }
 
-impl<'tcx> NestedGoals<'tcx> {
+impl<I: Interner> NestedGoals<I> {
-    pub(super) fn new() -> Self {
+    pub fn new() -> Self {
         Self { normalizes_to_goals: Vec::new(), goals: Vec::new() }
     }
 
-    pub(super) fn is_empty(&self) -> bool {
+    pub fn is_empty(&self) -> bool {
         self.normalizes_to_goals.is_empty() && self.goals.is_empty()
     }
 }
@@ -143,7 +149,8 @@ impl<'tcx> InferCtxt<'tcx> {
         &self,
         goal: Goal<'tcx, ty::Predicate<'tcx>>,
         generate_proof_tree: GenerateProofTree,
-    ) -> (Result<(bool, Certainty), NoSolution>, Option<inspect::GoalEvaluation<'tcx>>) {
+    ) -> (Result<(bool, Certainty), NoSolution>, Option<inspect::GoalEvaluation<TyCtxt<'tcx>>>)
+    {
         EvalCtxt::enter_root(self, generate_proof_tree, |ecx| {
             ecx.evaluate_goal(GoalEvaluationKind::Root, GoalSource::Misc, goal)
         })
@@ -166,7 +173,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
         infcx: &InferCtxt<'tcx>,
         generate_proof_tree: GenerateProofTree,
         f: impl FnOnce(&mut EvalCtxt<'_, 'tcx>) -> R,
-    ) -> (R, Option<inspect::GoalEvaluation<'tcx>>) {
+    ) -> (R, Option<inspect::GoalEvaluation<TyCtxt<'tcx>>>) {
         let mode = if infcx.intercrate { SolverMode::Coherence } else { SolverMode::Normal };
         let mut search_graph = search_graph::SearchGraph::new(mode);
 
@@ -220,7 +227,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
         tcx: TyCtxt<'tcx>,
         search_graph: &'a mut search_graph::SearchGraph<'tcx>,
         canonical_input: CanonicalInput<'tcx>,
-        canonical_goal_evaluation: &mut ProofTreeBuilder<'tcx>,
+        canonical_goal_evaluation: &mut ProofTreeBuilder<TyCtxt<'tcx>>,
         f: impl FnOnce(&mut EvalCtxt<'_, 'tcx>, Goal<'tcx, ty::Predicate<'tcx>>) -> R,
     ) -> R {
         let intercrate = match search_graph.solver_mode() {
@@ -282,7 +289,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
         tcx: TyCtxt<'tcx>,
         search_graph: &'a mut search_graph::SearchGraph<'tcx>,
         canonical_input: CanonicalInput<'tcx>,
-        goal_evaluation: &mut ProofTreeBuilder<'tcx>,
+        goal_evaluation: &mut ProofTreeBuilder<TyCtxt<'tcx>>,
     ) -> QueryResult<'tcx> {
         let mut canonical_goal_evaluation =
             goal_evaluation.new_canonical_goal_evaluation(canonical_input);

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

@@ -2,10 +2,9 @@ use crate::solve::assembly::Candidate;
 
 use super::EvalCtxt;
 use rustc_infer::traits::BuiltinImplSource;
-use rustc_middle::traits::{
+use rustc_middle::traits::query::NoSolution;
-    query::NoSolution,
+use rustc_middle::traits::solve::{inspect, CandidateSource, QueryResult};
-    solve::{inspect, CandidateSource, QueryResult},
+use rustc_middle::ty::TyCtxt;
-};
 use std::marker::PhantomData;
 
 pub(in crate::solve) struct ProbeCtxt<'me, 'a, 'tcx, F, T> {
@@ -16,7 +15,7 @@ pub(in crate::solve) struct ProbeCtxt<'me, 'a, 'tcx, F, T> {
 
 impl<'tcx, F, T> ProbeCtxt<'_, '_, 'tcx, F, T>
 where
-    F: FnOnce(&T) -> inspect::ProbeKind<'tcx>,
+    F: FnOnce(&T) -> inspect::ProbeKind<TyCtxt<'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;
@@ -51,12 +50,12 @@ where
 
 pub(in crate::solve) struct TraitProbeCtxt<'me, 'a, 'tcx, F> {
     cx: ProbeCtxt<'me, 'a, 'tcx, F, QueryResult<'tcx>>,
-    source: CandidateSource,
+    source: CandidateSource<'tcx>,
 }
 
 impl<'tcx, F> TraitProbeCtxt<'_, '_, 'tcx, F>
 where
-    F: FnOnce(&QueryResult<'tcx>) -> inspect::ProbeKind<'tcx>,
+    F: FnOnce(&QueryResult<'tcx>) -> inspect::ProbeKind<TyCtxt<'tcx>>,
 {
     #[instrument(level = "debug", skip_all, fields(source = ?self.source))]
     pub(in crate::solve) fn enter(
@@ -72,7 +71,7 @@ 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::ProbeKind<'tcx>,
+        F: FnOnce(&T) -> inspect::ProbeKind<TyCtxt<'tcx>>,
     {
         ProbeCtxt { ecx: self, probe_kind, _result: PhantomData }
     }
@@ -80,16 +79,24 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
     pub(in crate::solve) fn probe_builtin_trait_candidate(
         &mut self,
         source: BuiltinImplSource,
-    ) -> TraitProbeCtxt<'_, 'a, 'tcx, impl FnOnce(&QueryResult<'tcx>) -> inspect::ProbeKind<'tcx>>
+    ) -> TraitProbeCtxt<
-    {
+        '_,
+        'a,
+        'tcx,
+        impl FnOnce(&QueryResult<'tcx>) -> inspect::ProbeKind<TyCtxt<'tcx>>,
+    > {
         self.probe_trait_candidate(CandidateSource::BuiltinImpl(source))
     }
 
     pub(in crate::solve) fn probe_trait_candidate(
         &mut self,
-        source: CandidateSource,
+        source: CandidateSource<'tcx>,
-    ) -> TraitProbeCtxt<'_, 'a, 'tcx, impl FnOnce(&QueryResult<'tcx>) -> inspect::ProbeKind<'tcx>>
+    ) -> TraitProbeCtxt<
-    {
+        '_,
+        'a,
+        'tcx,
+        impl FnOnce(&QueryResult<'tcx>) -> inspect::ProbeKind<TyCtxt<'tcx>>,
+    > {
         TraitProbeCtxt {
             cx: ProbeCtxt {
                 ecx: self,

compiler/rustc_trait_selection/src/solve/fulfill.rs

@@ -3,7 +3,6 @@ use std::ops::ControlFlow;
 
 use rustc_infer::infer::InferCtxt;
 use rustc_infer::traits::query::NoSolution;
-use rustc_infer::traits::solve::inspect::ProbeKind;
 use rustc_infer::traits::solve::{CandidateSource, GoalSource, MaybeCause};
 use rustc_infer::traits::{
     self, FulfillmentError, FulfillmentErrorCode, MismatchedProjectionTypes, Obligation,
@@ -15,7 +14,7 @@ use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::symbol::sym;
 
 use super::eval_ctxt::GenerateProofTree;
-use super::inspect::{InspectCandidate, InspectGoal, ProofTreeInferCtxtExt, ProofTreeVisitor};
+use super::inspect::{self, ProofTreeInferCtxtExt, ProofTreeVisitor};
 use super::{Certainty, InferCtxtEvalExt};
 
 /// A trait engine using the new trait solver.
@@ -319,8 +318,8 @@ impl<'tcx> BestObligation<'tcx> {
     /// *don't* hold and which have impl-where clauses that also don't hold.
     fn non_trivial_candidates<'a>(
         &self,
-        goal: &'a InspectGoal<'a, 'tcx>,
+        goal: &'a inspect::InspectGoal<'a, 'tcx>,
-    ) -> Vec<InspectCandidate<'a, 'tcx>> {
+    ) -> Vec<inspect::InspectCandidate<'a, 'tcx>> {
         let mut candidates = goal.candidates();
         match self.consider_ambiguities {
             true => {
@@ -370,15 +369,17 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
         self.obligation.cause.span
     }
 
-    fn visit_goal(&mut self, goal: &super::inspect::InspectGoal<'_, 'tcx>) -> Self::Result {
+    fn visit_goal(&mut self, goal: &inspect::InspectGoal<'_, 'tcx>) -> Self::Result {
         let candidates = self.non_trivial_candidates(goal);
         let [candidate] = candidates.as_slice() else {
             return ControlFlow::Break(self.obligation.clone());
         };
 
         // Don't walk into impls that have `do_not_recommend`.
-        if let ProbeKind::TraitCandidate { source: CandidateSource::Impl(impl_def_id), result: _ } =
+        if let inspect::ProbeKind::TraitCandidate {
-            candidate.kind()
+            source: CandidateSource::Impl(impl_def_id),
+            result: _,
+        } = candidate.kind()
             && goal.infcx().tcx.has_attr(impl_def_id, sym::do_not_recommend)
         {
             return ControlFlow::Break(self.obligation.clone());
@@ -475,13 +476,16 @@ enum ChildMode<'tcx> {
 
 fn derive_cause<'tcx>(
     tcx: TyCtxt<'tcx>,
-    candidate_kind: ProbeKind<'tcx>,
+    candidate_kind: inspect::ProbeKind<TyCtxt<'tcx>>,
     mut cause: ObligationCause<'tcx>,
     idx: usize,
     parent_trait_pred: ty::PolyTraitPredicate<'tcx>,
 ) -> ObligationCause<'tcx> {
     match candidate_kind {
-        ProbeKind::TraitCandidate { source: CandidateSource::Impl(impl_def_id), result: _ } => {
+        inspect::ProbeKind::TraitCandidate {
+            source: CandidateSource::Impl(impl_def_id),
+            result: _,
+        } => {
             if let Some((_, span)) =
                 tcx.predicates_of(impl_def_id).instantiate_identity(tcx).iter().nth(idx)
             {
@@ -495,7 +499,10 @@ fn derive_cause<'tcx>(
                 })
             }
         }
-        ProbeKind::TraitCandidate { source: CandidateSource::BuiltinImpl(..), result: _ } => {
+        inspect::ProbeKind::TraitCandidate {
+            source: CandidateSource::BuiltinImpl(..),
+            result: _,
+        } => {
             cause = cause.derived_cause(parent_trait_pred, ObligationCauseCode::BuiltinDerived);
         }
         _ => {}

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

@@ -18,7 +18,7 @@ use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::solve::{inspect, QueryResult};
 use rustc_middle::traits::solve::{Certainty, Goal};
 use rustc_middle::traits::ObligationCause;
-use rustc_middle::ty::TypeFoldable;
+use rustc_middle::ty::{TyCtxt, TypeFoldable};
 use rustc_middle::{bug, ty};
 use rustc_span::{Span, DUMMY_SP};
 
@@ -37,7 +37,7 @@ pub struct InspectGoal<'a, 'tcx> {
     orig_values: Vec<ty::GenericArg<'tcx>>,
     goal: Goal<'tcx, ty::Predicate<'tcx>>,
     result: Result<Certainty, NoSolution>,
-    evaluation_kind: inspect::CanonicalGoalEvaluationKind<'tcx>,
+    evaluation_kind: inspect::CanonicalGoalEvaluationKind<TyCtxt<'tcx>>,
     normalizes_to_term_hack: Option<NormalizesToTermHack<'tcx>>,
     source: GoalSource,
 }
@@ -88,16 +88,17 @@ impl<'tcx> NormalizesToTermHack<'tcx> {
 
 pub struct InspectCandidate<'a, 'tcx> {
     goal: &'a InspectGoal<'a, 'tcx>,
-    kind: inspect::ProbeKind<'tcx>,
+    kind: inspect::ProbeKind<TyCtxt<'tcx>>,
-    nested_goals: Vec<(GoalSource, inspect::CanonicalState<'tcx, Goal<'tcx, ty::Predicate<'tcx>>>)>,
+    nested_goals:
-    final_state: inspect::CanonicalState<'tcx, ()>,
+        Vec<(GoalSource, inspect::CanonicalState<TyCtxt<'tcx>, Goal<'tcx, ty::Predicate<'tcx>>>)>,
-    impl_args: Option<inspect::CanonicalState<'tcx, ty::GenericArgsRef<'tcx>>>,
+    final_state: inspect::CanonicalState<TyCtxt<'tcx>, ()>,
+    impl_args: Option<inspect::CanonicalState<TyCtxt<'tcx>, ty::GenericArgsRef<'tcx>>>,
     result: QueryResult<'tcx>,
     shallow_certainty: Certainty,
 }
 
 impl<'a, 'tcx> InspectCandidate<'a, 'tcx> {
-    pub fn kind(&self) -> inspect::ProbeKind<'tcx> {
+    pub fn kind(&self) -> inspect::ProbeKind<TyCtxt<'tcx>> {
         self.kind
     }
 
@@ -280,9 +281,9 @@ impl<'a, 'tcx> InspectGoal<'a, 'tcx> {
         candidates: &mut Vec<InspectCandidate<'a, 'tcx>>,
         nested_goals: &mut Vec<(
             GoalSource,
-            inspect::CanonicalState<'tcx, Goal<'tcx, ty::Predicate<'tcx>>>,
+            inspect::CanonicalState<TyCtxt<'tcx>, Goal<'tcx, ty::Predicate<'tcx>>>,
         )>,
-        probe: &inspect::Probe<'tcx>,
+        probe: &inspect::Probe<TyCtxt<'tcx>>,
     ) {
         let mut shallow_certainty = None;
         let mut impl_args = None;
@@ -387,7 +388,7 @@ impl<'a, 'tcx> InspectGoal<'a, 'tcx> {
     fn new(
         infcx: &'a InferCtxt<'tcx>,
         depth: usize,
-        root: inspect::GoalEvaluation<'tcx>,
+        root: inspect::GoalEvaluation<TyCtxt<'tcx>>,
         normalizes_to_term_hack: Option<NormalizesToTermHack<'tcx>>,
         source: GoalSource,
     ) -> Self {

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

@@ -9,11 +9,12 @@ use rustc_infer::infer::InferCtxt;
 use rustc_middle::bug;
 use rustc_middle::infer::canonical::CanonicalVarValues;
 use rustc_middle::traits::query::NoSolution;
-use rustc_middle::traits::solve::{
+use rustc_middle::ty::{self, TyCtxt};
+use rustc_next_trait_solver::solve::{
     CanonicalInput, Certainty, Goal, GoalSource, QueryInput, QueryResult,
 };
-use rustc_middle::ty::{self, TyCtxt};
 use rustc_session::config::DumpSolverProofTree;
+use rustc_type_ir::Interner;
 
 use crate::solve::eval_ctxt::canonical;
 use crate::solve::{self, inspect, GenerateProofTree};
@@ -38,49 +39,51 @@ use crate::solve::{self, inspect, GenerateProofTree};
 /// trees. At the end of trait solving `ProofTreeBuilder::finalize`
 /// is called to recursively convert the whole structure to a
 /// finished proof tree.
-pub(in crate::solve) struct ProofTreeBuilder<'tcx> {
+pub(in crate::solve) struct ProofTreeBuilder<I: Interner> {
-    state: Option<Box<DebugSolver<'tcx>>>,
+    state: Option<Box<DebugSolver<I>>>,
 }
 
 /// The current state of the proof tree builder, at most places
 /// in the code, only one or two variants are actually possible.
 ///
 /// We simply ICE in case that assumption is broken.
-#[derive(Debug)]
+#[derive(derivative::Derivative)]
-enum DebugSolver<'tcx> {
+#[derivative(Debug(bound = ""))]
+enum DebugSolver<I: Interner> {
     Root,
-    GoalEvaluation(WipGoalEvaluation<'tcx>),
+    GoalEvaluation(WipGoalEvaluation<I>),
-    CanonicalGoalEvaluation(WipCanonicalGoalEvaluation<'tcx>),
+    CanonicalGoalEvaluation(WipCanonicalGoalEvaluation<I>),
-    GoalEvaluationStep(WipGoalEvaluationStep<'tcx>),
+    GoalEvaluationStep(WipGoalEvaluationStep<I>),
 }
 
-impl<'tcx> From<WipGoalEvaluation<'tcx>> for DebugSolver<'tcx> {
+impl<I: Interner> From<WipGoalEvaluation<I>> for DebugSolver<I> {
-    fn from(g: WipGoalEvaluation<'tcx>) -> DebugSolver<'tcx> {
+    fn from(g: WipGoalEvaluation<I>) -> DebugSolver<I> {
         DebugSolver::GoalEvaluation(g)
     }
 }
 
-impl<'tcx> From<WipCanonicalGoalEvaluation<'tcx>> for DebugSolver<'tcx> {
+impl<I: Interner> From<WipCanonicalGoalEvaluation<I>> for DebugSolver<I> {
-    fn from(g: WipCanonicalGoalEvaluation<'tcx>) -> DebugSolver<'tcx> {
+    fn from(g: WipCanonicalGoalEvaluation<I>) -> DebugSolver<I> {
         DebugSolver::CanonicalGoalEvaluation(g)
     }
 }
 
-impl<'tcx> From<WipGoalEvaluationStep<'tcx>> for DebugSolver<'tcx> {
+impl<I: Interner> From<WipGoalEvaluationStep<I>> for DebugSolver<I> {
-    fn from(g: WipGoalEvaluationStep<'tcx>) -> DebugSolver<'tcx> {
+    fn from(g: WipGoalEvaluationStep<I>) -> DebugSolver<I> {
         DebugSolver::GoalEvaluationStep(g)
     }
 }
 
-#[derive(Eq, PartialEq, Debug)]
+#[derive(derivative::Derivative)]
-struct WipGoalEvaluation<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""), Debug(bound = ""))]
-    pub uncanonicalized_goal: Goal<'tcx, ty::Predicate<'tcx>>,
+struct WipGoalEvaluation<I: Interner> {
-    pub kind: WipGoalEvaluationKind<'tcx>,
+    pub uncanonicalized_goal: Goal<I, I::Predicate>,
-    pub evaluation: Option<WipCanonicalGoalEvaluation<'tcx>>,
+    pub kind: WipGoalEvaluationKind<I>,
+    pub evaluation: Option<WipCanonicalGoalEvaluation<I>>,
 }
 
-impl<'tcx> WipGoalEvaluation<'tcx> {
+impl<I: Interner> WipGoalEvaluation<I> {
-    fn finalize(self) -> inspect::GoalEvaluation<'tcx> {
+    fn finalize(self) -> inspect::GoalEvaluation<I> {
         inspect::GoalEvaluation {
             uncanonicalized_goal: self.uncanonicalized_goal,
             kind: match self.kind {
@@ -94,21 +97,23 @@ impl<'tcx> WipGoalEvaluation<'tcx> {
     }
 }
 
-#[derive(Eq, PartialEq, Debug)]
+#[derive(derivative::Derivative)]
-pub(in crate::solve) enum WipGoalEvaluationKind<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""), Debug(bound = ""))]
-    Root { orig_values: Vec<ty::GenericArg<'tcx>> },
+pub(in crate::solve) enum WipGoalEvaluationKind<I: Interner> {
+    Root { orig_values: Vec<I::GenericArg> },
     Nested,
 }
 
-#[derive(Eq, PartialEq)]
+#[derive(derivative::Derivative)]
-pub(in crate::solve) enum WipCanonicalGoalEvaluationKind<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""))]
+pub(in crate::solve) enum WipCanonicalGoalEvaluationKind<I: Interner> {
     Overflow,
     CycleInStack,
     ProvisionalCacheHit,
-    Interned { revisions: &'tcx [inspect::GoalEvaluationStep<'tcx>] },
+    Interned { revisions: I::GoalEvaluationSteps },
 }
 
-impl std::fmt::Debug for WipCanonicalGoalEvaluationKind<'_> {
+impl<I: Interner> std::fmt::Debug for WipCanonicalGoalEvaluationKind<I> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
             Self::Overflow => write!(f, "Overflow"),
@@ -119,18 +124,19 @@ impl std::fmt::Debug for WipCanonicalGoalEvaluationKind<'_> {
     }
 }
 
-#[derive(Eq, PartialEq, Debug)]
+#[derive(derivative::Derivative)]
-struct WipCanonicalGoalEvaluation<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""), Debug(bound = ""))]
-    goal: CanonicalInput<'tcx>,
+struct WipCanonicalGoalEvaluation<I: Interner> {
-    kind: Option<WipCanonicalGoalEvaluationKind<'tcx>>,
+    goal: CanonicalInput<I>,
+    kind: Option<WipCanonicalGoalEvaluationKind<I>>,
     /// Only used for uncached goals. After we finished evaluating
     /// the goal, this is interned and moved into `kind`.
-    revisions: Vec<WipGoalEvaluationStep<'tcx>>,
+    revisions: Vec<WipGoalEvaluationStep<I>>,
-    result: Option<QueryResult<'tcx>>,
+    result: Option<QueryResult<I>>,
 }
 
-impl<'tcx> WipCanonicalGoalEvaluation<'tcx> {
+impl<I: Interner> WipCanonicalGoalEvaluation<I> {
-    fn finalize(self) -> inspect::CanonicalGoalEvaluation<'tcx> {
+    fn finalize(self) -> inspect::CanonicalGoalEvaluation<I> {
         assert!(self.revisions.is_empty());
         let kind = match self.kind.unwrap() {
             WipCanonicalGoalEvaluationKind::Overflow => {
@@ -151,14 +157,15 @@ impl<'tcx> WipCanonicalGoalEvaluation<'tcx> {
     }
 }
 
-#[derive(Eq, PartialEq, Debug)]
+#[derive(derivative::Derivative)]
-struct WipAddedGoalsEvaluation<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""), Debug(bound = ""))]
-    evaluations: Vec<Vec<WipGoalEvaluation<'tcx>>>,
+struct WipAddedGoalsEvaluation<I: Interner> {
+    evaluations: Vec<Vec<WipGoalEvaluation<I>>>,
     result: Option<Result<Certainty, NoSolution>>,
 }
 
-impl<'tcx> WipAddedGoalsEvaluation<'tcx> {
+impl<I: Interner> WipAddedGoalsEvaluation<I> {
-    fn finalize(self) -> inspect::AddedGoalsEvaluation<'tcx> {
+    fn finalize(self) -> inspect::AddedGoalsEvaluation<I> {
         inspect::AddedGoalsEvaluation {
             evaluations: self
                 .evaluations
@@ -172,22 +179,23 @@ impl<'tcx> WipAddedGoalsEvaluation<'tcx> {
     }
 }
 
-#[derive(Eq, PartialEq, Debug)]
+#[derive(derivative::Derivative)]
-struct WipGoalEvaluationStep<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""), Debug(bound = ""))]
+struct WipGoalEvaluationStep<I: Interner> {
     /// Unlike `EvalCtxt::var_values`, we append a new
     /// generic arg here whenever we create a new inference
     /// variable.
     ///
     /// This is necessary as we otherwise don't unify these
     /// vars when instantiating multiple `CanonicalState`.
-    var_values: Vec<ty::GenericArg<'tcx>>,
+    var_values: Vec<I::GenericArg>,
-    instantiated_goal: QueryInput<'tcx, ty::Predicate<'tcx>>,
+    instantiated_goal: QueryInput<I, I::Predicate>,
     probe_depth: usize,
-    evaluation: WipProbe<'tcx>,
+    evaluation: WipProbe<I>,
 }
 
-impl<'tcx> WipGoalEvaluationStep<'tcx> {
+impl<I: Interner> WipGoalEvaluationStep<I> {
-    fn current_evaluation_scope(&mut self) -> &mut WipProbe<'tcx> {
+    fn current_evaluation_scope(&mut self) -> &mut WipProbe<I> {
         let mut current = &mut self.evaluation;
         for _ in 0..self.probe_depth {
             match current.steps.last_mut() {
@@ -198,7 +206,7 @@ impl<'tcx> WipGoalEvaluationStep<'tcx> {
         current
     }
 
-    fn added_goals_evaluation(&mut self) -> &mut WipAddedGoalsEvaluation<'tcx> {
+    fn added_goals_evaluation(&mut self) -> &mut WipAddedGoalsEvaluation<I> {
         let mut current = &mut self.evaluation;
         loop {
             match current.steps.last_mut() {
@@ -209,7 +217,7 @@ impl<'tcx> WipGoalEvaluationStep<'tcx> {
         }
     }
 
-    fn finalize(self) -> inspect::GoalEvaluationStep<'tcx> {
+    fn finalize(self) -> inspect::GoalEvaluationStep<I> {
         let evaluation = self.evaluation.finalize();
         match evaluation.kind {
             inspect::ProbeKind::Root { .. } => (),
@@ -219,16 +227,17 @@ impl<'tcx> WipGoalEvaluationStep<'tcx> {
     }
 }
 
-#[derive(Eq, PartialEq, Debug)]
+#[derive(derivative::Derivative)]
-struct WipProbe<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""), Debug(bound = ""))]
+struct WipProbe<I: Interner> {
     initial_num_var_values: usize,
-    steps: Vec<WipProbeStep<'tcx>>,
+    steps: Vec<WipProbeStep<I>>,
-    kind: Option<inspect::ProbeKind<'tcx>>,
+    kind: Option<inspect::ProbeKind<I>>,
-    final_state: Option<inspect::CanonicalState<'tcx, ()>>,
+    final_state: Option<inspect::CanonicalState<I, ()>>,
 }
 
-impl<'tcx> WipProbe<'tcx> {
+impl<I: Interner> WipProbe<I> {
-    fn finalize(self) -> inspect::Probe<'tcx> {
+    fn finalize(self) -> inspect::Probe<I> {
         inspect::Probe {
             steps: self.steps.into_iter().map(WipProbeStep::finalize).collect(),
             kind: self.kind.unwrap(),
@@ -237,17 +246,18 @@ impl<'tcx> WipProbe<'tcx> {
     }
 }
 
-#[derive(Eq, PartialEq, Debug)]
+#[derive(derivative::Derivative)]
-enum WipProbeStep<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""), Debug(bound = ""))]
-    AddGoal(GoalSource, inspect::CanonicalState<'tcx, Goal<'tcx, ty::Predicate<'tcx>>>),
+enum WipProbeStep<I: Interner> {
-    EvaluateGoals(WipAddedGoalsEvaluation<'tcx>),
+    AddGoal(GoalSource, inspect::CanonicalState<I, Goal<I, I::Predicate>>),
-    NestedProbe(WipProbe<'tcx>),
+    EvaluateGoals(WipAddedGoalsEvaluation<I>),
+    NestedProbe(WipProbe<I>),
     MakeCanonicalResponse { shallow_certainty: Certainty },
-    RecordImplArgs { impl_args: inspect::CanonicalState<'tcx, ty::GenericArgsRef<'tcx>> },
+    RecordImplArgs { impl_args: inspect::CanonicalState<I, I::GenericArgs> },
 }
 
-impl<'tcx> WipProbeStep<'tcx> {
+impl<I: Interner> WipProbeStep<I> {
-    fn finalize(self) -> inspect::ProbeStep<'tcx> {
+    fn finalize(self) -> inspect::ProbeStep<I> {
         match self {
             WipProbeStep::AddGoal(source, goal) => inspect::ProbeStep::AddGoal(source, goal),
             WipProbeStep::EvaluateGoals(eval) => inspect::ProbeStep::EvaluateGoals(eval.finalize()),
@@ -262,26 +272,27 @@ impl<'tcx> WipProbeStep<'tcx> {
     }
 }
 
-impl<'tcx> ProofTreeBuilder<'tcx> {
+// FIXME: Genericize this impl.
-    fn new(state: impl Into<DebugSolver<'tcx>>) -> ProofTreeBuilder<'tcx> {
+impl<'tcx> ProofTreeBuilder<TyCtxt<'tcx>> {
+    fn new(state: impl Into<DebugSolver<TyCtxt<'tcx>>>) -> ProofTreeBuilder<TyCtxt<'tcx>> {
         ProofTreeBuilder { state: Some(Box::new(state.into())) }
     }
 
-    fn nested<T: Into<DebugSolver<'tcx>>>(&self, state: impl FnOnce() -> T) -> Self {
+    fn nested<T: Into<DebugSolver<TyCtxt<'tcx>>>>(&self, state: impl FnOnce() -> T) -> Self {
         ProofTreeBuilder { state: self.state.as_ref().map(|_| Box::new(state().into())) }
     }
 
-    fn as_mut(&mut self) -> Option<&mut DebugSolver<'tcx>> {
+    fn as_mut(&mut self) -> Option<&mut DebugSolver<TyCtxt<'tcx>>> {
         self.state.as_deref_mut()
     }
 
-    pub fn take_and_enter_probe(&mut self) -> ProofTreeBuilder<'tcx> {
+    pub fn take_and_enter_probe(&mut self) -> ProofTreeBuilder<TyCtxt<'tcx>> {
         let mut nested = ProofTreeBuilder { state: self.state.take() };
         nested.enter_probe();
         nested
     }
 
-    pub fn finalize(self) -> Option<inspect::GoalEvaluation<'tcx>> {
+    pub fn finalize(self) -> Option<inspect::GoalEvaluation<TyCtxt<'tcx>>> {
         match *self.state? {
             DebugSolver::GoalEvaluation(wip_goal_evaluation) => {
                 Some(wip_goal_evaluation.finalize())
@@ -293,7 +304,7 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
     pub fn new_maybe_root(
         tcx: TyCtxt<'tcx>,
         generate_proof_tree: GenerateProofTree,
-    ) -> ProofTreeBuilder<'tcx> {
+    ) -> ProofTreeBuilder<TyCtxt<'tcx>> {
         match generate_proof_tree {
             GenerateProofTree::Never => ProofTreeBuilder::new_noop(),
             GenerateProofTree::IfEnabled => {
@@ -311,11 +322,11 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
         }
     }
 
-    pub fn new_root() -> ProofTreeBuilder<'tcx> {
+    pub fn new_root() -> ProofTreeBuilder<TyCtxt<'tcx>> {
         ProofTreeBuilder::new(DebugSolver::Root)
     }
 
-    pub fn new_noop() -> ProofTreeBuilder<'tcx> {
+    pub fn new_noop() -> ProofTreeBuilder<TyCtxt<'tcx>> {
         ProofTreeBuilder { state: None }
     }
 
@@ -325,10 +336,10 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
 
     pub(in crate::solve) fn new_goal_evaluation(
         &mut self,
-        goal: Goal<'tcx, ty::Predicate<'tcx>>,
+        goal: Goal<TyCtxt<'tcx>, ty::Predicate<'tcx>>,
         orig_values: &[ty::GenericArg<'tcx>],
         kind: solve::GoalEvaluationKind,
-    ) -> ProofTreeBuilder<'tcx> {
+    ) -> ProofTreeBuilder<TyCtxt<'tcx>> {
         self.nested(|| WipGoalEvaluation {
             uncanonicalized_goal: goal,
             kind: match kind {
@@ -343,8 +354,8 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
 
     pub fn new_canonical_goal_evaluation(
         &mut self,
-        goal: CanonicalInput<'tcx>,
+        goal: CanonicalInput<TyCtxt<'tcx>>,
-    ) -> ProofTreeBuilder<'tcx> {
+    ) -> ProofTreeBuilder<TyCtxt<'tcx>> {
         self.nested(|| WipCanonicalGoalEvaluation {
             goal,
             kind: None,
@@ -356,7 +367,7 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
     pub fn finalize_evaluation(
         &mut self,
         tcx: TyCtxt<'tcx>,
-    ) -> Option<&'tcx [inspect::GoalEvaluationStep<'tcx>]> {
+    ) -> Option<&'tcx [inspect::GoalEvaluationStep<TyCtxt<'tcx>>]> {
         self.as_mut().map(|this| match this {
             DebugSolver::CanonicalGoalEvaluation(evaluation) => {
                 let revisions = mem::take(&mut evaluation.revisions)
@@ -371,7 +382,10 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
         })
     }
 
-    pub fn canonical_goal_evaluation(&mut self, canonical_goal_evaluation: ProofTreeBuilder<'tcx>) {
+    pub fn canonical_goal_evaluation(
+        &mut self,
+        canonical_goal_evaluation: ProofTreeBuilder<TyCtxt<'tcx>>,
+    ) {
         if let Some(this) = self.as_mut() {
             match (this, *canonical_goal_evaluation.state.unwrap()) {
                 (
@@ -386,7 +400,7 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
         }
     }
 
-    pub fn goal_evaluation_kind(&mut self, kind: WipCanonicalGoalEvaluationKind<'tcx>) {
+    pub fn goal_evaluation_kind(&mut self, kind: WipCanonicalGoalEvaluationKind<TyCtxt<'tcx>>) {
         if let Some(this) = self.as_mut() {
             match this {
                 DebugSolver::CanonicalGoalEvaluation(canonical_goal_evaluation) => {
@@ -397,7 +411,7 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
         }
     }
 
-    pub fn goal_evaluation(&mut self, goal_evaluation: ProofTreeBuilder<'tcx>) {
+    pub fn goal_evaluation(&mut self, goal_evaluation: ProofTreeBuilder<TyCtxt<'tcx>>) {
         if let Some(this) = self.as_mut() {
             match (this, *goal_evaluation.state.unwrap()) {
                 (
@@ -418,8 +432,8 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
     pub fn new_goal_evaluation_step(
         &mut self,
         var_values: CanonicalVarValues<'tcx>,
-        instantiated_goal: QueryInput<'tcx, ty::Predicate<'tcx>>,
+        instantiated_goal: QueryInput<TyCtxt<'tcx>, ty::Predicate<'tcx>>,
-    ) -> ProofTreeBuilder<'tcx> {
+    ) -> ProofTreeBuilder<TyCtxt<'tcx>> {
         self.nested(|| WipGoalEvaluationStep {
             var_values: var_values.var_values.to_vec(),
             instantiated_goal,
@@ -433,7 +447,7 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
         })
     }
 
-    pub fn goal_evaluation_step(&mut self, goal_evaluation_step: ProofTreeBuilder<'tcx>) {
+    pub fn goal_evaluation_step(&mut self, goal_evaluation_step: ProofTreeBuilder<TyCtxt<'tcx>>) {
         if let Some(this) = self.as_mut() {
             match (this, *goal_evaluation_step.state.unwrap()) {
                 (
@@ -474,7 +488,7 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
         }
     }
 
-    pub fn probe_kind(&mut self, probe_kind: inspect::ProbeKind<'tcx>) {
+    pub fn probe_kind(&mut self, probe_kind: inspect::ProbeKind<TyCtxt<'tcx>>) {
         match self.as_mut() {
             None => {}
             Some(DebugSolver::GoalEvaluationStep(state)) => {
@@ -510,7 +524,7 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
         &mut self,
         infcx: &InferCtxt<'tcx>,
         max_input_universe: ty::UniverseIndex,
-        goal: Goal<'tcx, ty::NormalizesTo<'tcx>>,
+        goal: Goal<TyCtxt<'tcx>, ty::NormalizesTo<'tcx>>,
     ) {
         self.add_goal(
             infcx,
@@ -525,7 +539,7 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
         infcx: &InferCtxt<'tcx>,
         max_input_universe: ty::UniverseIndex,
         source: GoalSource,
-        goal: Goal<'tcx, ty::Predicate<'tcx>>,
+        goal: Goal<TyCtxt<'tcx>, ty::Predicate<'tcx>>,
     ) {
         match self.as_mut() {
             None => {}
@@ -579,7 +593,7 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
         }
     }
 
-    pub fn finish_probe(mut self) -> ProofTreeBuilder<'tcx> {
+    pub fn finish_probe(mut self) -> ProofTreeBuilder<TyCtxt<'tcx>> {
         match self.as_mut() {
             None => {}
             Some(DebugSolver::GoalEvaluationStep(state)) => {
@@ -627,7 +641,7 @@ impl<'tcx> ProofTreeBuilder<'tcx> {
         }
     }
 
-    pub fn query_result(&mut self, result: QueryResult<'tcx>) {
+    pub fn query_result(&mut self, result: QueryResult<TyCtxt<'tcx>>) {
         if let Some(this) = self.as_mut() {
             match this {
                 DebugSolver::CanonicalGoalEvaluation(canonical_goal_evaluation) => {

compiler/rustc_trait_selection/src/solve/mod.rs

@@ -20,11 +20,11 @@ use rustc_macros::extension;
 use rustc_middle::bug;
 use rustc_middle::infer::canonical::CanonicalVarInfos;
 use rustc_middle::traits::solve::{
-    CanonicalResponse, Certainty, ExternalConstraintsData, GoalSource, QueryResult, Response,
+    CanonicalResponse, Certainty, ExternalConstraintsData, Goal, GoalSource, QueryResult, Response,
 };
 use rustc_middle::ty::{
-    self, AliasRelationDirection, CoercePredicate, Goal, RegionOutlivesPredicate, SubtypePredicate,
+    self, AliasRelationDirection, CoercePredicate, RegionOutlivesPredicate, SubtypePredicate, Ty,
-    Ty, TyCtxt, TypeOutlivesPredicate, UniverseIndex,
+    TyCtxt, TypeOutlivesPredicate, UniverseIndex,
 };
 
 mod alias_relate;
@@ -74,7 +74,7 @@ enum GoalEvaluationKind {
 }
 
 #[extension(trait CanonicalResponseExt)]
-impl<'tcx> Canonical<'tcx, Response<'tcx>> {
+impl<'tcx> Canonical<'tcx, Response<TyCtxt<'tcx>>> {
     fn has_no_inference_or_external_constraints(&self) -> bool {
         self.value.external_constraints.region_constraints.is_empty()
             && self.value.var_values.is_identity()

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

@@ -3,7 +3,6 @@ use crate::traits::specialization_graph;
 use super::assembly::structural_traits::AsyncCallableRelevantTypes;
 use super::assembly::{self, structural_traits, Candidate};
 use super::{EvalCtxt, GoalSource};
-use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
 use rustc_hir::LangItem;
 use rustc_infer::traits::query::NoSolution;
@@ -54,23 +53,15 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         &mut self,
         goal: Goal<'tcx, NormalizesTo<'tcx>>,
     ) -> QueryResult<'tcx> {
-        let def_id = goal.predicate.def_id();
+        match goal.predicate.alias.kind(self.tcx()) {
-        match self.tcx().def_kind(def_id) {
+            ty::AliasTermKind::ProjectionTy | ty::AliasTermKind::ProjectionConst => {
-            DefKind::AssocTy | DefKind::AssocConst => {
+                let candidates = self.assemble_and_evaluate_candidates(goal);
-                match self.tcx().associated_item(def_id).container {
+                self.merge_candidates(candidates)
-                    ty::AssocItemContainer::TraitContainer => {
-                        let candidates = self.assemble_and_evaluate_candidates(goal);
-                        self.merge_candidates(candidates)
-                    }
-                    ty::AssocItemContainer::ImplContainer => {
-                        self.normalize_inherent_associated_type(goal)
-                    }
-                }
             }
-            DefKind::AnonConst => self.normalize_anon_const(goal),
+            ty::AliasTermKind::InherentTy => self.normalize_inherent_associated_type(goal),
-            DefKind::TyAlias => self.normalize_weak_type(goal),
+            ty::AliasTermKind::OpaqueTy => self.normalize_opaque_type(goal),
-            DefKind::OpaqueTy => self.normalize_opaque_type(goal),
+            ty::AliasTermKind::WeakTy => self.normalize_weak_type(goal),
-            kind => bug!("unknown DefKind {} in normalizes-to goal: {goal:#?}", kind.descr(def_id)),
+            ty::AliasTermKind::UnevaluatedConst => self.normalize_anon_const(goal),
         }
     }
 
@@ -108,7 +99,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for NormalizesTo<'tcx> {
 
     fn probe_and_match_goal_against_assumption(
         ecx: &mut EvalCtxt<'_, 'tcx>,
-        source: CandidateSource,
+        source: CandidateSource<'tcx>,
         goal: Goal<'tcx, Self>,
         assumption: ty::Clause<'tcx>,
         then: impl FnOnce(&mut EvalCtxt<'_, 'tcx>) -> QueryResult<'tcx>,

compiler/rustc_trait_selection/src/solve/search_graph.rs

@@ -253,8 +253,8 @@ impl<'tcx> SearchGraph<'tcx> {
         &mut self,
         tcx: TyCtxt<'tcx>,
         input: CanonicalInput<'tcx>,
-        inspect: &mut ProofTreeBuilder<'tcx>,
+        inspect: &mut ProofTreeBuilder<TyCtxt<'tcx>>,
-        mut prove_goal: impl FnMut(&mut Self, &mut ProofTreeBuilder<'tcx>) -> QueryResult<'tcx>,
+        mut prove_goal: impl FnMut(&mut Self, &mut ProofTreeBuilder<TyCtxt<'tcx>>) -> QueryResult<'tcx>,
     ) -> QueryResult<'tcx> {
         // Check for overflow.
         let Some(available_depth) = Self::allowed_depth_for_nested(tcx, &self.stack) else {

compiler/rustc_trait_selection/src/solve/trait_goals.rs

@@ -103,7 +103,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
 
     fn probe_and_match_goal_against_assumption(
         ecx: &mut EvalCtxt<'_, 'tcx>,
-        source: CandidateSource,
+        source: CandidateSource<'tcx>,
         goal: Goal<'tcx, Self>,
         assumption: ty::Clause<'tcx>,
         then: impl FnOnce(&mut EvalCtxt<'_, 'tcx>) -> QueryResult<'tcx>,
@@ -821,7 +821,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
     fn consider_builtin_upcast_to_principal(
         &mut self,
         goal: Goal<'tcx, (Ty<'tcx>, Ty<'tcx>)>,
-        source: CandidateSource,
+        source: CandidateSource<'tcx>,
         a_data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
         a_region: ty::Region<'tcx>,
         b_data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
@@ -1149,7 +1149,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
     /// wrapped in one.
     fn probe_and_evaluate_goal_for_constituent_tys(
         &mut self,
-        source: CandidateSource,
+        source: CandidateSource<'tcx>,
         goal: Goal<'tcx, TraitPredicate<'tcx>>,
         constituent_tys: impl Fn(
             &EvalCtxt<'_, 'tcx>,

compiler/rustc_type_ir/src/canonical.rs

@@ -1,11 +1,12 @@
 #[cfg(feature = "nightly")]
 use rustc_macros::{HashStable_NoContext, TyDecodable, TyEncodable};
-use rustc_type_ir_macros::{TypeFoldable_Generic, TypeVisitable_Generic};
+use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Generic};
 use std::fmt;
 use std::hash::Hash;
+use std::ops::Index;
 
 use crate::inherent::*;
-use crate::{Interner, UniverseIndex};
+use crate::{self as ty, Interner, UniverseIndex};
 
 /// A "canonicalized" type `V` is one where all free inference
 /// variables have been rewritten to "canonical vars". These are
@@ -257,3 +258,139 @@ pub enum CanonicalTyVarKind {
     /// Floating-point type variable `?F` (that can only be unified with float types).
     Float,
 }
+
+/// A set of values corresponding to the canonical variables from some
+/// `Canonical`. You can give these values to
+/// `canonical_value.instantiate` to instantiate them into the canonical
+/// value at the right places.
+///
+/// When you canonicalize a value `V`, you get back one of these
+/// vectors with the original values that were replaced by canonical
+/// variables. You will need to supply it later to instantiate the
+/// canonicalized query response.
+#[derive(derivative::Derivative)]
+#[derivative(
+    Clone(bound = ""),
+    Copy(bound = ""),
+    PartialEq(bound = ""),
+    Eq(bound = ""),
+    Hash(bound = ""),
+    Debug(bound = "")
+)]
+#[cfg_attr(feature = "nightly", derive(TyEncodable, TyDecodable, HashStable_NoContext))]
+#[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
+pub struct CanonicalVarValues<I: Interner> {
+    pub var_values: I::GenericArgs,
+}
+
+impl<I: Interner> CanonicalVarValues<I> {
+    pub fn is_identity(&self) -> bool {
+        self.var_values.into_iter().enumerate().all(|(bv, arg)| match arg.kind() {
+            ty::GenericArgKind::Lifetime(r) => {
+                matches!(r.kind(), ty::ReBound(ty::INNERMOST, br) if br.var().as_usize() == bv)
+            }
+            ty::GenericArgKind::Type(ty) => {
+                matches!(ty.kind(), ty::Bound(ty::INNERMOST, bt) if bt.var().as_usize() == bv)
+            }
+            ty::GenericArgKind::Const(ct) => {
+                matches!(ct.kind(), ty::ConstKind::Bound(ty::INNERMOST, bc) if bc.var().as_usize() == bv)
+            }
+        })
+    }
+
+    pub fn is_identity_modulo_regions(&self) -> bool {
+        let mut var = ty::BoundVar::ZERO;
+        for arg in self.var_values {
+            match arg.kind() {
+                ty::GenericArgKind::Lifetime(r) => {
+                    if matches!(r.kind(), ty::ReBound(ty::INNERMOST, br) if var == br.var()) {
+                        var = var + 1;
+                    } else {
+                        // It's ok if this region var isn't an identity variable
+                    }
+                }
+                ty::GenericArgKind::Type(ty) => {
+                    if matches!(ty.kind(), ty::Bound(ty::INNERMOST, bt) if var == bt.var()) {
+                        var = var + 1;
+                    } else {
+                        return false;
+                    }
+                }
+                ty::GenericArgKind::Const(ct) => {
+                    if matches!(ct.kind(), ty::ConstKind::Bound(ty::INNERMOST, bc) if var == bc.var())
+                    {
+                        var = var + 1;
+                    } else {
+                        return false;
+                    }
+                }
+            }
+        }
+
+        true
+    }
+
+    // Given a list of canonical variables, construct a set of values which are
+    // the identity response.
+    pub fn make_identity(tcx: I, infos: I::CanonicalVars) -> CanonicalVarValues<I> {
+        CanonicalVarValues {
+            var_values: tcx.mk_args_from_iter(infos.into_iter().enumerate().map(
+                |(i, info)| -> I::GenericArg {
+                    match info.kind {
+                        CanonicalVarKind::Ty(_) | CanonicalVarKind::PlaceholderTy(_) => {
+                            Ty::new_anon_bound(tcx, ty::INNERMOST, ty::BoundVar::from_usize(i))
+                                .into()
+                        }
+                        CanonicalVarKind::Region(_) | CanonicalVarKind::PlaceholderRegion(_) => {
+                            Region::new_anon_bound(tcx, ty::INNERMOST, ty::BoundVar::from_usize(i))
+                                .into()
+                        }
+                        CanonicalVarKind::Effect => Const::new_anon_bound(
+                            tcx,
+                            ty::INNERMOST,
+                            ty::BoundVar::from_usize(i),
+                            Ty::new_bool(tcx),
+                        )
+                        .into(),
+                        CanonicalVarKind::Const(_, ty)
+                        | CanonicalVarKind::PlaceholderConst(_, ty) => Const::new_anon_bound(
+                            tcx,
+                            ty::INNERMOST,
+                            ty::BoundVar::from_usize(i),
+                            ty,
+                        )
+                        .into(),
+                    }
+                },
+            )),
+        }
+    }
+
+    /// Creates dummy var values which should not be used in a
+    /// canonical response.
+    pub fn dummy() -> CanonicalVarValues<I> {
+        CanonicalVarValues { var_values: Default::default() }
+    }
+
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.var_values.len()
+    }
+}
+
+impl<'a, I: Interner> IntoIterator for &'a CanonicalVarValues<I> {
+    type Item = I::GenericArg;
+    type IntoIter = <I::GenericArgs as IntoIterator>::IntoIter;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.var_values.into_iter()
+    }
+}
+
+impl<I: Interner> Index<ty::BoundVar> for CanonicalVarValues<I> {
+    type Output = I::GenericArg;
+
+    fn index(&self, value: ty::BoundVar) -> &I::GenericArg {
+        &self.var_values[value.as_usize()]
+    }
+}

compiler/rustc_type_ir/src/generic_arg.rs

@@ -0,0 +1,18 @@
+use rustc_macros::{HashStable_NoContext, TyDecodable, TyEncodable};
+
+use crate::Interner;
+
+#[derive(derivative::Derivative)]
+#[derivative(
+    Clone(bound = ""),
+    Copy(bound = ""),
+    Debug(bound = ""),
+    Eq(bound = ""),
+    PartialEq(bound = "")
+)]
+#[cfg_attr(feature = "nightly", derive(TyDecodable, TyEncodable, HashStable_NoContext))]
+pub enum GenericArgKind<I: Interner> {
+    Lifetime(I::Region),
+    Type(I::Ty),
+    Const(I::Const),
+}

compiler/rustc_type_ir/src/inherent.rs

@@ -1,3 +1,8 @@
+//! Set of traits which are used to emulate the inherent impls that are present in `rustc_middle`.
+//! It is customary to glob-import `rustc_type_ir::inherent::*` to bring all of these traits into
+//! scope when programming in interner-agnostic settings, and to avoid importing any of these
+//! directly elsewhere (i.e. specify the full path for an implementation downstream).
+
 use std::fmt::Debug;
 use std::hash::Hash;
 use std::ops::Deref;
@@ -21,6 +26,8 @@ pub trait Ty<I: Interner<Ty = Self>>:
     + TypeSuperFoldable<I>
     + Flags
 {
+    fn new_bool(interner: I) -> Self;
+
     fn new_anon_bound(interner: I, debruijn: DebruijnIndex, var: BoundVar) -> Self;
 
     fn new_alias(interner: I, kind: AliasTyKind, alias_ty: AliasTy<I>) -> Self;
@@ -79,6 +86,7 @@ pub trait GenericArgs<I: Interner<GenericArgs = Self>>:
     + Eq
     + IntoIterator<Item = I::GenericArg>
     + Deref<Target: Deref<Target = [I::GenericArg]>>
+    + Default
 {
     fn type_at(self, i: usize) -> I::Ty;
 
@@ -111,3 +119,7 @@ pub trait BoundVars<I: Interner> {
 
     fn has_no_bound_vars(&self) -> bool;
 }
+
+pub trait BoundVarLike<I: Interner> {
+    fn var(self) -> BoundVar;
+}

compiler/rustc_type_ir/src/interner.rs

@@ -5,11 +5,12 @@ use std::ops::Deref;
 
 use crate::inherent::*;
 use crate::ir_print::IrPrint;
+use crate::solve::inspect::GoalEvaluationStep;
 use crate::visit::{Flags, TypeSuperVisitable, TypeVisitable};
 use crate::{
     AliasTerm, AliasTermKind, AliasTy, AliasTyKind, CanonicalVarInfo, CoercePredicate,
-    DebugWithInfcx, ExistentialProjection, ExistentialTraitRef, FnSig, NormalizesTo,
+    DebugWithInfcx, ExistentialProjection, ExistentialTraitRef, FnSig, GenericArgKind,
-    ProjectionPredicate, SubtypePredicate, TraitPredicate, TraitRef,
+    NormalizesTo, ProjectionPredicate, SubtypePredicate, TraitPredicate, TraitRef,
 };
 
 pub trait Interner:
@@ -28,14 +29,13 @@ pub trait Interner:
     + IrPrint<FnSig<Self>>
 {
     type DefId: Copy + Debug + Hash + Eq;
-    type DefiningOpaqueTypes: Copy + Debug + Hash + Default + Eq + TypeVisitable<Self>;
     type AdtDef: Copy + Debug + Hash + Eq;
 
     type GenericArgs: GenericArgs<Self>;
     /// The slice of args for a specific item. For a GAT like `type Foo<'a>`, it will be `['a]`,
     /// not including the args from the parent item (trait or impl).
     type OwnItemArgs: Copy + Debug + Hash + Eq;
-    type GenericArg: Copy + DebugWithInfcx<Self> + Hash + Eq;
+    type GenericArg: Copy + DebugWithInfcx<Self> + Hash + Eq + IntoKind<Kind = GenericArgKind<Self>>;
     type Term: Copy + Debug + Hash + Eq;
 
     type Binder<T: TypeVisitable<Self>>: BoundVars<Self> + TypeSuperVisitable<Self>;
@@ -43,13 +43,17 @@ pub trait Interner:
     type BoundVar;
 
     type CanonicalVars: Copy + Debug + Hash + Eq + IntoIterator<Item = CanonicalVarInfo<Self>>;
+    type PredefinedOpaques: Copy + Debug + Hash + Eq;
+    type DefiningOpaqueTypes: Copy + Debug + Hash + Default + Eq + TypeVisitable<Self>;
+    type ExternalConstraints: Copy + Debug + Hash + Eq;
+    type GoalEvaluationSteps: Copy + Debug + Hash + Eq + Deref<Target = [GoalEvaluationStep<Self>]>;
 
     // Kinds of tys
     type Ty: Ty<Self>;
     type Tys: Tys<Self>;
     type FnInputTys: Copy + Debug + Hash + Eq + Deref<Target = [Self::Ty]>;
     type ParamTy: Copy + Debug + Hash + Eq;
-    type BoundTy: Copy + Debug + Hash + Eq;
+    type BoundTy: Copy + Debug + Hash + Eq + BoundVarLike<Self>;
     type PlaceholderTy: PlaceholderLike;
 
     // Things stored inside of tys
@@ -66,7 +70,7 @@ pub trait Interner:
     type AliasConst: Copy + DebugWithInfcx<Self> + Hash + Eq;
     type PlaceholderConst: PlaceholderLike;
     type ParamConst: Copy + Debug + Hash + Eq;
-    type BoundConst: Copy + Debug + Hash + Eq;
+    type BoundConst: Copy + Debug + Hash + Eq + BoundVarLike<Self>;
     type ValueConst: Copy + Debug + Hash + Eq;
     type ExprConst: Copy + DebugWithInfcx<Self> + Hash + Eq;
 
@@ -74,7 +78,7 @@ pub trait Interner:
     type Region: Region<Self>;
     type EarlyParamRegion: Copy + Debug + Hash + Eq;
     type LateParamRegion: Copy + Debug + Hash + Eq;
-    type BoundRegion: Copy + Debug + Hash + Eq;
+    type BoundRegion: Copy + Debug + Hash + Eq + BoundVarLike<Self>;
     type InferRegion: Copy + DebugWithInfcx<Self> + Hash + Eq;
     type PlaceholderRegion: PlaceholderLike;
 

compiler/rustc_type_ir/src/lib.rs

@@ -19,13 +19,13 @@ use std::sync::Arc as Lrc;
 
 #[macro_use]
 pub mod visit;
-
 #[cfg(feature = "nightly")]
 pub mod codec;
 pub mod fold;
 pub mod inherent;
 pub mod ir_print;
 pub mod lift;
+pub mod solve;
 pub mod ty_info;
 pub mod ty_kind;
 
@@ -35,6 +35,7 @@ mod canonical;
 mod const_kind;
 mod debug;
 mod flags;
+mod generic_arg;
 mod infcx;
 mod interner;
 mod predicate;
@@ -48,6 +49,7 @@ pub use codec::*;
 pub use const_kind::*;
 pub use debug::{DebugWithInfcx, WithInfcx};
 pub use flags::*;
+pub use generic_arg::*;
 pub use infcx::InferCtxtLike;
 pub use interner::*;
 pub use predicate::*;
@@ -368,6 +370,12 @@ rustc_index::newtype_index! {
     pub struct BoundVar {}
 }
 
+impl<I: Interner> inherent::BoundVarLike<I> for BoundVar {
+    fn var(self) -> BoundVar {
+        self
+    }
+}
+
 /// Represents the various closure traits in the language. This
 /// will determine the type of the environment (`self`, in the
 /// desugaring) argument that the closure expects.

compiler/rustc_type_ir/src/predicate.rs

@@ -8,42 +8,9 @@ use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Gen
 use crate::inherent::*;
 use crate::visit::TypeVisitableExt as _;
 use crate::{
-    AliasTy, AliasTyKind, DebugWithInfcx, InferCtxtLike, Interner, UnevaluatedConst, Upcast,
+    AliasTy, AliasTyKind, DebugWithInfcx, InferCtxtLike, Interner, UnevaluatedConst, WithInfcx,
-    WithInfcx,
 };
 
-/// A goal is a statement, i.e. `predicate`, we want to prove
-/// given some assumptions, i.e. `param_env`.
-///
-/// Most of the time the `param_env` contains the `where`-bounds of the function
-/// we're currently typechecking while the `predicate` is some trait bound.
-#[derive(derivative::Derivative)]
-#[derivative(
-    Clone(bound = "P: Clone"),
-    Copy(bound = "P: Copy"),
-    Hash(bound = "P: Hash"),
-    PartialEq(bound = "P: PartialEq"),
-    Eq(bound = "P: Eq"),
-    Debug(bound = "P: fmt::Debug")
-)]
-#[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
-#[cfg_attr(feature = "nightly", derive(TyDecodable, TyEncodable, HashStable_NoContext))]
-pub struct Goal<I: Interner, P> {
-    pub param_env: I::ParamEnv,
-    pub predicate: P,
-}
-
-impl<I: Interner, P> Goal<I, P> {
-    pub fn new(tcx: I, param_env: I::ParamEnv, predicate: impl Upcast<I, P>) -> Goal<I, P> {
-        Goal { param_env, predicate: predicate.upcast(tcx) }
-    }
-
-    /// Updates the goal to one with a different `predicate` but the same `param_env`.
-    pub fn with<Q>(self, tcx: I, predicate: impl Upcast<I, Q>) -> Goal<I, Q> {
-        Goal { param_env: self.param_env, predicate: predicate.upcast(tcx) }
-    }
-}
-
 /// A complete reference to a trait. These take numerous guises in syntax,
 /// but perhaps the most recognizable form is in a where-clause:
 /// ```ignore (illustrative)

compiler/rustc_type_ir/src/solve.rs

@@ -0,0 +1,278 @@
+pub mod inspect;
+
+use std::fmt;
+use std::hash::Hash;
+
+#[cfg(feature = "nightly")]
+use rustc_macros::{HashStable_NoContext, TyDecodable, TyEncodable};
+use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Generic};
+
+use crate::{Canonical, CanonicalVarValues, Interner, Upcast};
+
+pub type CanonicalInput<I, T = <I as Interner>::Predicate> = Canonical<I, QueryInput<I, T>>;
+pub type CanonicalResponse<I> = Canonical<I, Response<I>>;
+/// The result of evaluating a canonical query.
+///
+/// FIXME: We use a different type than the existing canonical queries. This is because
+/// we need to add a `Certainty` for `overflow` and may want to restructure this code without
+/// having to worry about changes to currently used code. Once we've made progress on this
+/// solver, merge the two responses again.
+pub type QueryResult<I> = Result<CanonicalResponse<I>, NoSolution>;
+
+#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+#[derive(TypeFoldable_Generic, TypeVisitable_Generic)]
+#[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
+pub struct NoSolution;
+
+/// A goal is a statement, i.e. `predicate`, we want to prove
+/// given some assumptions, i.e. `param_env`.
+///
+/// Most of the time the `param_env` contains the `where`-bounds of the function
+/// we're currently typechecking while the `predicate` is some trait bound.
+#[derive(derivative::Derivative)]
+#[derivative(
+    Clone(bound = "P: Clone"),
+    Copy(bound = "P: Copy"),
+    Hash(bound = "P: Hash"),
+    PartialEq(bound = "P: PartialEq"),
+    Eq(bound = "P: Eq"),
+    Debug(bound = "P: fmt::Debug")
+)]
+#[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
+#[cfg_attr(feature = "nightly", derive(TyDecodable, TyEncodable, HashStable_NoContext))]
+pub struct Goal<I: Interner, P> {
+    pub param_env: I::ParamEnv,
+    pub predicate: P,
+}
+
+impl<I: Interner, P> Goal<I, P> {
+    pub fn new(tcx: I, param_env: I::ParamEnv, predicate: impl Upcast<I, P>) -> Goal<I, P> {
+        Goal { param_env, predicate: predicate.upcast(tcx) }
+    }
+
+    /// Updates the goal to one with a different `predicate` but the same `param_env`.
+    pub fn with<Q>(self, tcx: I, predicate: impl Upcast<I, Q>) -> Goal<I, Q> {
+        Goal { param_env: self.param_env, predicate: predicate.upcast(tcx) }
+    }
+}
+
+/// Why a specific goal has to be proven.
+///
+/// This is necessary as we treat nested goals different depending on
+/// their source.
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TypeVisitable_Generic, TypeFoldable_Generic)]
+#[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
+pub enum GoalSource {
+    Misc,
+    /// We're proving a where-bound of an impl.
+    ///
+    /// FIXME(-Znext-solver=coinductive): Explain how and why this
+    /// changes whether cycles are coinductive.
+    ///
+    /// This also impacts whether we erase constraints on overflow.
+    /// Erasing constraints is generally very useful for perf and also
+    /// results in better error messages by avoiding spurious errors.
+    /// We do not erase overflow constraints in `normalizes-to` goals unless
+    /// they are from an impl where-clause. This is necessary due to
+    /// backwards compatability, cc trait-system-refactor-initiatitive#70.
+    ImplWhereBound,
+    /// Instantiating a higher-ranked goal and re-proving it.
+    InstantiateHigherRanked,
+}
+
+#[derive(derivative::Derivative)]
+#[derivative(
+    Clone(bound = "Goal<I, P>: Clone"),
+    Copy(bound = "Goal<I, P>: Copy"),
+    Hash(bound = "Goal<I, P>: Hash"),
+    PartialEq(bound = "Goal<I, P>: PartialEq"),
+    Eq(bound = "Goal<I, P>: Eq"),
+    Debug(bound = "Goal<I, P>: fmt::Debug")
+)]
+#[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
+#[cfg_attr(feature = "nightly", derive(TyDecodable, TyEncodable, HashStable_NoContext))]
+pub struct QueryInput<I: Interner, P> {
+    pub goal: Goal<I, P>,
+    pub predefined_opaques_in_body: I::PredefinedOpaques,
+}
+
+/// Possible ways the given goal can be proven.
+#[derive(derivative::Derivative)]
+#[derivative(
+    Clone(bound = ""),
+    Copy(bound = ""),
+    Hash(bound = ""),
+    PartialEq(bound = ""),
+    Eq(bound = ""),
+    Debug(bound = "")
+)]
+pub enum CandidateSource<I: Interner> {
+    /// 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(I::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,
+    /// A candidate that is registered only during coherence to represent some
+    /// yet-unknown impl that could be produced downstream without violating orphan
+    /// rules.
+    // FIXME: Merge this with the forced ambiguity candidates, so those don't use `Misc`.
+    CoherenceUnknowable,
+}
+
+#[derive(Clone, Copy, Hash, PartialEq, Eq, Debug)]
+#[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
+#[cfg_attr(feature = "nightly", derive(HashStable_NoContext, TyEncodable, TyDecodable))]
+pub enum BuiltinImplSource {
+    /// Some builtin impl we don't need to differentiate. This should be used
+    /// unless more specific information is necessary.
+    Misc,
+    /// A builtin impl for trait objects.
+    ///
+    /// The vtable is formed by concatenating together the method lists of
+    /// the base object trait and all supertraits, pointers to supertrait vtable will
+    /// be provided when necessary; this is the start of `upcast_trait_ref`'s methods
+    /// in that vtable.
+    Object { vtable_base: usize },
+    /// The vtable is formed by concatenating together the method lists of
+    /// the base object trait and all supertraits, pointers to supertrait vtable will
+    /// be provided when necessary; this is the position of `upcast_trait_ref`'s vtable
+    /// within that vtable.
+    TraitUpcasting { vtable_vptr_slot: Option<usize> },
+    /// Unsizing a tuple like `(A, B, ..., X)` to `(A, B, ..., Y)` if `X` unsizes to `Y`.
+    ///
+    /// This needs to be a separate variant as it is still unstable and we need to emit
+    /// a feature error when using it on stable.
+    TupleUnsizing,
+}
+
+#[derive(derivative::Derivative)]
+#[derivative(
+    Clone(bound = ""),
+    Copy(bound = ""),
+    Hash(bound = ""),
+    PartialEq(bound = ""),
+    Eq(bound = ""),
+    Debug(bound = "")
+)]
+#[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
+#[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
+pub struct Response<I: Interner> {
+    pub certainty: Certainty,
+    pub var_values: CanonicalVarValues<I>,
+    /// Additional constraints returned by this query.
+    pub external_constraints: I::ExternalConstraints,
+}
+
+#[derive(Clone, Copy, Hash, PartialEq, Eq, Debug)]
+#[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
+#[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
+pub enum Certainty {
+    Yes,
+    Maybe(MaybeCause),
+}
+
+impl Certainty {
+    pub const AMBIGUOUS: Certainty = Certainty::Maybe(MaybeCause::Ambiguity);
+
+    /// Use this function to merge the certainty of multiple nested subgoals.
+    ///
+    /// Given an impl like `impl<T: Foo + Bar> Baz for T {}`, we have 2 nested
+    /// subgoals whenever we use the impl as a candidate: `T: Foo` and `T: Bar`.
+    /// If evaluating `T: Foo` results in ambiguity and `T: Bar` results in
+    /// success, we merge these two responses. This results in ambiguity.
+    ///
+    /// If we unify ambiguity with overflow, we return overflow. This doesn't matter
+    /// inside of the solver as we do not distinguish ambiguity from overflow. It does
+    /// however matter for diagnostics. If `T: Foo` resulted in overflow and `T: Bar`
+    /// in ambiguity without changing the inference state, we still want to tell the
+    /// user that `T: Baz` results in overflow.
+    pub fn unify_with(self, other: Certainty) -> Certainty {
+        match (self, other) {
+            (Certainty::Yes, Certainty::Yes) => Certainty::Yes,
+            (Certainty::Yes, Certainty::Maybe(_)) => other,
+            (Certainty::Maybe(_), Certainty::Yes) => self,
+            (Certainty::Maybe(a), Certainty::Maybe(b)) => Certainty::Maybe(a.unify_with(b)),
+        }
+    }
+
+    pub const fn overflow(suggest_increasing_limit: bool) -> Certainty {
+        Certainty::Maybe(MaybeCause::Overflow { suggest_increasing_limit })
+    }
+}
+
+/// Why we failed to evaluate a goal.
+#[derive(Clone, Copy, Hash, PartialEq, Eq, Debug)]
+#[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
+#[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
+pub enum MaybeCause {
+    /// We failed due to ambiguity. This ambiguity can either
+    /// be a true ambiguity, i.e. there are multiple different answers,
+    /// 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 { 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 },
+        }
+    }
+}

compiler/rustc_type_ir/src/solve/inspect.rs

@@ -18,113 +18,133 @@
 //!
 //! [canonicalized]: https://rustc-dev-guide.rust-lang.org/solve/canonicalization.html
 
-use super::{
-    CandidateSource, Canonical, CanonicalInput, Certainty, Goal, GoalSource, NoSolution,
-    QueryInput, QueryResult,
-};
-use crate::{infer::canonical::CanonicalVarValues, ty};
-use format::ProofTreeFormatter;
-use rustc_macros::{TypeFoldable, TypeVisitable};
-use std::fmt::{Debug, Write};
-
 mod format;
 
+use std::fmt::{Debug, Write};
+use std::hash::Hash;
+
+use rustc_type_ir_macros::{TypeFoldable_Generic, TypeVisitable_Generic};
+
+use self::format::ProofTreeFormatter;
+use crate::solve::{
+    CandidateSource, CanonicalInput, Certainty, Goal, GoalSource, NoSolution, QueryInput,
+    QueryResult,
+};
+use crate::{Canonical, CanonicalVarValues, Interner};
+
 /// Some `data` together with information about how they relate to the input
 /// of the canonical query.
 ///
 /// This is only ever used as [CanonicalState]. Any type information in proof
 /// trees used mechanically has to be canonicalized as we otherwise leak
 /// inference variables from a nested `InferCtxt`.
-#[derive(Debug, Clone, Copy, Eq, PartialEq, TypeFoldable, TypeVisitable)]
+#[derive(derivative::Derivative)]
-pub struct State<'tcx, T> {
+#[derivative(
-    pub var_values: CanonicalVarValues<'tcx>,
+    Clone(bound = "T: Clone"),
+    Copy(bound = "T: Copy"),
+    PartialEq(bound = "T: PartialEq"),
+    Eq(bound = "T: Eq"),
+    Hash(bound = "T: Hash"),
+    Debug(bound = "T: Debug")
+)]
+#[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
+pub struct State<I: Interner, T> {
+    pub var_values: CanonicalVarValues<I>,
     pub data: T,
 }
 
-pub type CanonicalState<'tcx, T> = Canonical<'tcx, State<'tcx, T>>;
+pub type CanonicalState<I, T> = Canonical<I, State<I, T>>;
 
 /// When evaluating the root goals we also store the
 /// original values for the `CanonicalVarValues` of the
 /// canonicalized goal. We use this to map any [CanonicalState]
 /// from the local `InferCtxt` of the solver query to
 /// the `InferCtxt` of the caller.
-#[derive(Eq, PartialEq)]
+#[derive(derivative::Derivative)]
-pub enum GoalEvaluationKind<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""), Hash(bound = ""), Debug(bound = ""))]
-    Root { orig_values: Vec<ty::GenericArg<'tcx>> },
+pub enum GoalEvaluationKind<I: Interner> {
+    Root { orig_values: Vec<I::GenericArg> },
     Nested,
 }
 
-#[derive(Eq, PartialEq)]
+#[derive(derivative::Derivative)]
-pub struct GoalEvaluation<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""), Hash(bound = ""))]
-    pub uncanonicalized_goal: Goal<'tcx, ty::Predicate<'tcx>>,
+pub struct GoalEvaluation<I: Interner> {
-    pub kind: GoalEvaluationKind<'tcx>,
+    pub uncanonicalized_goal: Goal<I, I::Predicate>,
-    pub evaluation: CanonicalGoalEvaluation<'tcx>,
+    pub kind: GoalEvaluationKind<I>,
+    pub evaluation: CanonicalGoalEvaluation<I>,
 }
 
-#[derive(Eq, PartialEq, Debug)]
+#[derive(derivative::Derivative)]
-pub struct CanonicalGoalEvaluation<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""), Hash(bound = ""), Debug(bound = ""))]
-    pub goal: CanonicalInput<'tcx>,
+pub struct CanonicalGoalEvaluation<I: Interner> {
-    pub kind: CanonicalGoalEvaluationKind<'tcx>,
+    pub goal: CanonicalInput<I>,
-    pub result: QueryResult<'tcx>,
+    pub kind: CanonicalGoalEvaluationKind<I>,
+    pub result: QueryResult<I>,
 }
 
-#[derive(Eq, PartialEq, Debug)]
+#[derive(derivative::Derivative)]
-pub enum CanonicalGoalEvaluationKind<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""), Hash(bound = ""), Debug(bound = ""))]
+pub enum CanonicalGoalEvaluationKind<I: Interner> {
     Overflow,
     CycleInStack,
     ProvisionalCacheHit,
-    Evaluation { revisions: &'tcx [GoalEvaluationStep<'tcx>] },
+    Evaluation { revisions: I::GoalEvaluationSteps },
 }
-impl Debug for GoalEvaluation<'_> {
+impl<I: Interner> Debug for GoalEvaluation<I> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         ProofTreeFormatter::new(f).format_goal_evaluation(self)
     }
 }
 
-#[derive(Eq, PartialEq)]
+#[derive(derivative::Derivative)]
-pub struct AddedGoalsEvaluation<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""), Hash(bound = ""), Debug(bound = ""))]
-    pub evaluations: Vec<Vec<GoalEvaluation<'tcx>>>,
+pub struct AddedGoalsEvaluation<I: Interner> {
+    pub evaluations: Vec<Vec<GoalEvaluation<I>>>,
     pub result: Result<Certainty, NoSolution>,
 }
 
-#[derive(Eq, PartialEq, Debug)]
+#[derive(derivative::Derivative)]
-pub struct GoalEvaluationStep<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""), Hash(bound = ""), Debug(bound = ""))]
-    pub instantiated_goal: QueryInput<'tcx, ty::Predicate<'tcx>>,
+pub struct GoalEvaluationStep<I: Interner> {
+    pub instantiated_goal: QueryInput<I, I::Predicate>,
 
     /// The actual evaluation of the goal, always `ProbeKind::Root`.
-    pub evaluation: Probe<'tcx>,
+    pub evaluation: Probe<I>,
 }
 
 /// A self-contained computation during trait solving. This either
 /// corresponds to a `EvalCtxt::probe(_X)` call or the root evaluation
 /// of a goal.
-#[derive(Eq, PartialEq)]
+#[derive(derivative::Derivative)]
-pub struct Probe<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""), Hash(bound = ""))]
+pub struct Probe<I: Interner> {
     /// What happened inside of this probe in chronological order.
-    pub steps: Vec<ProbeStep<'tcx>>,
+    pub steps: Vec<ProbeStep<I>>,
-    pub kind: ProbeKind<'tcx>,
+    pub kind: ProbeKind<I>,
-    pub final_state: CanonicalState<'tcx, ()>,
+    pub final_state: CanonicalState<I, ()>,
 }
 
-impl Debug for Probe<'_> {
+impl<I: Interner> Debug for Probe<I> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         ProofTreeFormatter::new(f).format_probe(self)
     }
 }
 
-#[derive(Eq, PartialEq)]
+#[derive(derivative::Derivative)]
-pub enum ProbeStep<'tcx> {
+#[derivative(PartialEq(bound = ""), Eq(bound = ""), Hash(bound = ""), Debug(bound = ""))]
+pub enum ProbeStep<I: Interner> {
     /// We added a goal to the `EvalCtxt` which will get proven
     /// the next time `EvalCtxt::try_evaluate_added_goals` is called.
-    AddGoal(GoalSource, CanonicalState<'tcx, Goal<'tcx, ty::Predicate<'tcx>>>),
+    AddGoal(GoalSource, CanonicalState<I, Goal<I, I::Predicate>>),
     /// The inside of a `EvalCtxt::try_evaluate_added_goals` call.
-    EvaluateGoals(AddedGoalsEvaluation<'tcx>),
+    EvaluateGoals(AddedGoalsEvaluation<I>),
     /// A call to `probe` while proving the current goal. This is
     /// used whenever there are multiple candidates to prove the
     /// current goalby .
-    NestedProbe(Probe<'tcx>),
+    NestedProbe(Probe<I>),
     /// A trait goal was satisfied by an impl candidate.
-    RecordImplArgs { impl_args: CanonicalState<'tcx, ty::GenericArgsRef<'tcx>> },
+    RecordImplArgs { impl_args: CanonicalState<I, I::GenericArgs> },
     /// A call to `EvalCtxt::evaluate_added_goals_make_canonical_response` with
     /// `Certainty` was made. This is the certainty passed in, so it's not unified
     /// with the certainty of the `try_evaluate_added_goals` that is done within;
@@ -136,16 +156,25 @@ pub enum ProbeStep<'tcx> {
 /// What kind of probe we're in. In case the probe represents a candidate, or
 /// the final result of the current goal - via [ProbeKind::Root] - we also
 /// store the [QueryResult].
-#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+#[derive(derivative::Derivative)]
-pub enum ProbeKind<'tcx> {
+#[derivative(
+    Clone(bound = ""),
+    Copy(bound = ""),
+    PartialEq(bound = ""),
+    Eq(bound = ""),
+    Hash(bound = ""),
+    Debug(bound = "")
+)]
+#[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
+pub enum ProbeKind<I: Interner> {
     /// The root inference context while proving a goal.
-    Root { result: QueryResult<'tcx> },
+    Root { result: QueryResult<I> },
     /// Trying to normalize an alias by at least one step in `NormalizesTo`.
-    TryNormalizeNonRigid { result: QueryResult<'tcx> },
+    TryNormalizeNonRigid { result: QueryResult<I> },
     /// Probe entered when normalizing the self ty during candidate assembly
     NormalizedSelfTyAssembly,
     /// A candidate for proving a trait or alias-relate goal.
-    TraitCandidate { source: CandidateSource, result: QueryResult<'tcx> },
+    TraitCandidate { source: CandidateSource<I>, result: QueryResult<I> },
     /// Used in the probe that wraps normalizing the non-self type for the unsize
     /// trait, which is also structurally matched on.
     UnsizeAssembly,
@@ -156,5 +185,5 @@ pub enum ProbeKind<'tcx> {
     /// Looking for param-env candidates that satisfy the trait ref for a projection.
     ShadowedEnvProbing,
     /// Try to unify an opaque type with an existing key in the storage.
-    OpaqueTypeStorageLookup { result: QueryResult<'tcx> },
+    OpaqueTypeStorageLookup { result: QueryResult<I> },
 }

compiler/rustc_type_ir/src/solve/inspect/format.rs

@@ -1,7 +1,10 @@
+use std::marker::PhantomData;
+
 use super::*;
 
-pub(super) struct ProofTreeFormatter<'a, 'b> {
+pub(super) struct ProofTreeFormatter<'a, 'b, I> {
     f: &'a mut (dyn Write + 'b),
+    _interner: PhantomData<I>,
 }
 
 enum IndentorState {
@@ -36,23 +39,24 @@ impl Write for Indentor<'_, '_> {
     }
 }
 
-impl<'a, 'b> ProofTreeFormatter<'a, 'b> {
+impl<'a, 'b, I: Interner> ProofTreeFormatter<'a, 'b, I> {
     pub(super) fn new(f: &'a mut (dyn Write + 'b)) -> Self {
-        ProofTreeFormatter { f }
+        ProofTreeFormatter { f, _interner: PhantomData }
     }
 
     fn nested<F>(&mut self, func: F) -> std::fmt::Result
     where
-        F: FnOnce(&mut ProofTreeFormatter<'_, '_>) -> std::fmt::Result,
+        F: FnOnce(&mut ProofTreeFormatter<'_, '_, I>) -> std::fmt::Result,
     {
         write!(self.f, " {{")?;
         func(&mut ProofTreeFormatter {
             f: &mut Indentor { f: self.f, state: IndentorState::StartWithNewline },
+            _interner: PhantomData,
         })?;
         writeln!(self.f, "}}")
     }
 
-    pub(super) fn format_goal_evaluation(&mut self, eval: &GoalEvaluation<'_>) -> std::fmt::Result {
+    pub(super) fn format_goal_evaluation(&mut self, eval: &GoalEvaluation<I>) -> std::fmt::Result {
         let goal_text = match eval.kind {
             GoalEvaluationKind::Root { orig_values: _ } => "ROOT GOAL",
             GoalEvaluationKind::Nested => "GOAL",
@@ -63,7 +67,7 @@ impl<'a, 'b> ProofTreeFormatter<'a, 'b> {
 
     pub(super) fn format_canonical_goal_evaluation(
         &mut self,
-        eval: &CanonicalGoalEvaluation<'_>,
+        eval: &CanonicalGoalEvaluation<I>,
     ) -> std::fmt::Result {
         writeln!(self.f, "GOAL: {:?}", eval.goal)?;
 
@@ -89,13 +93,13 @@ impl<'a, 'b> ProofTreeFormatter<'a, 'b> {
 
     pub(super) fn format_evaluation_step(
         &mut self,
-        evaluation_step: &GoalEvaluationStep<'_>,
+        evaluation_step: &GoalEvaluationStep<I>,
     ) -> std::fmt::Result {
         writeln!(self.f, "INSTANTIATED: {:?}", evaluation_step.instantiated_goal)?;
         self.format_probe(&evaluation_step.evaluation)
     }
 
-    pub(super) fn format_probe(&mut self, probe: &Probe<'_>) -> std::fmt::Result {
+    pub(super) fn format_probe(&mut self, probe: &Probe<I>) -> std::fmt::Result {
         match &probe.kind {
             ProbeKind::Root { result } => {
                 write!(self.f, "ROOT RESULT: {result:?}")
@@ -150,7 +154,7 @@ impl<'a, 'b> ProofTreeFormatter<'a, 'b> {
 
     pub(super) fn format_added_goals_evaluation(
         &mut self,
-        added_goals_evaluation: &AddedGoalsEvaluation<'_>,
+        added_goals_evaluation: &AddedGoalsEvaluation<I>,
     ) -> std::fmt::Result {
         writeln!(self.f, "TRY_EVALUATE_ADDED_GOALS: {:?}", added_goals_evaluation.result)?;