Uplift PredicateEmittingRelation first

compiler/rustc_next_trait_solver/src/lib.rs

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

compiler/rustc_next_trait_solver/src/relate.rs

@@ -0,0 +1,15 @@
+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

@@ -0,0 +1,34 @@
+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);
+}