Auto merge of #131263 - compiler-errors:solver-relating, r=lcnr

Introduce SolverRelating type relation to the new solver

Redux of #128744.

Splits out relate for the new solver so that implementors don't need to implement it themselves.

r? lcnr

compiler/rustc_next_trait_solver/src/lib.rs

@@ -12,6 +12,5 @@
 pub mod canonicalizer;
 pub mod coherence;
 pub mod delegate;
-pub mod relate;
 pub mod resolve;
 pub mod solve;

compiler/rustc_next_trait_solver/src/relate.rs

@@ -1,15 +0,0 @@
-pub use rustc_type_ir::relate::*;
-
-pub mod combine;
-
-/// Whether aliases should be related structurally or not. Used
-/// to adjust the behavior of generalization and combine.
-///
-/// This should always be `No` unless in a few special-cases when
-/// instantiating canonical responses and in the new solver. Each
-/// such case should have a comment explaining why it is used.
-#[derive(Debug, Copy, Clone)]
-pub enum StructurallyRelateAliases {
-    Yes,
-    No,
-}

compiler/rustc_next_trait_solver/src/relate/combine.rs

@@ -1,34 +0,0 @@
-pub use rustc_type_ir::relate::*;
-use rustc_type_ir::solve::Goal;
-use rustc_type_ir::{InferCtxtLike, Interner, Upcast};
-
-use super::StructurallyRelateAliases;
-
-pub trait PredicateEmittingRelation<Infcx, I = <Infcx as InferCtxtLike>::Interner>:
-    TypeRelation<I>
-where
-    Infcx: InferCtxtLike<Interner = I>,
-    I: Interner,
-{
-    fn span(&self) -> I::Span;
-
-    fn param_env(&self) -> I::ParamEnv;
-
-    /// Whether aliases should be related structurally. This is pretty much
-    /// always `No` unless you're equating in some specific locations of the
-    /// new solver. See the comments in these use-cases for more details.
-    fn structurally_relate_aliases(&self) -> StructurallyRelateAliases;
-
-    /// Register obligations that must hold in order for this relation to hold
-    fn register_goals(&mut self, obligations: impl IntoIterator<Item = Goal<I, I::Predicate>>);
-
-    /// Register predicates that must hold in order for this relation to hold.
-    /// This uses the default `param_env` of the obligation.
-    fn register_predicates(
-        &mut self,
-        obligations: impl IntoIterator<Item: Upcast<I, I::Predicate>>,
-    );
-
-    /// Register `AliasRelate` obligation(s) that both types must be related to each other.
-    fn register_alias_relate_predicate(&mut self, a: I::Ty, b: I::Ty);
-}

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

@@ -14,6 +14,7 @@ use std::iter;
 use rustc_index::IndexVec;
 use rustc_type_ir::fold::TypeFoldable;
 use rustc_type_ir::inherent::*;
+use rustc_type_ir::relate::solver_relating::RelateExt;
 use rustc_type_ir::{self as ty, Canonical, CanonicalVarValues, InferCtxtLike, Interner};
 use tracing::{instrument, trace};
 

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

@@ -7,6 +7,7 @@ use rustc_type_ir::data_structures::{HashMap, HashSet, ensure_sufficient_stack};
 use rustc_type_ir::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
 use rustc_type_ir::inherent::*;
 use rustc_type_ir::relate::Relate;
+use rustc_type_ir::relate::solver_relating::RelateExt;
 use rustc_type_ir::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor};
 use rustc_type_ir::{self as ty, CanonicalVarValues, InferCtxtLike, Interner};
 use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Generic};
@@ -871,7 +872,7 @@ where
         lhs: T,
         rhs: T,
     ) -> Result<Vec<Goal<I, I::Predicate>>, NoSolution> {
-        self.delegate.relate(param_env, lhs, ty::Variance::Invariant, rhs)
+        Ok(self.delegate.relate(param_env, lhs, ty::Variance::Invariant, rhs)?)
     }
 
     pub(super) fn instantiate_binder_with_infer<T: TypeFoldable<I> + Copy>(