Auto merge of #93285 - JulianKnodt:const_eq_2, r=oli-obk

Continue work on associated const equality

This actually implements some more complex logic for assigning associated consts to values.
Inside of projection candidates, it now defers to a separate function for either consts or
types. To reduce amount of code, projections are now generic over T, where T is either a Type or
a Const. I can add some comments back later, but this was the fastest way to implement it.

It also now finds the correct type of consts in type_of.

---

The current main TODO is finding the const of the def id for the LeafDef.

Right now it works if the function isn't called, but once you use the trait impl with the bound it fails inside projection.
I was hoping to get some help in getting the `&'tcx ty::Const<'tcx>`, in addition to a bunch of other `todo!()`s which I think may not be hit.

r? `@oli-obk`

Updates #92827

Author: bors

compiler/rustc_hir/src/hir.rs

@@ -2203,6 +2203,12 @@ impl TypeBinding<'_> {
             _ => panic!("expected equality type binding for parenthesized generic args"),
         }
     }
+    pub fn opt_const(&self) -> Option<&'_ AnonConst> {
+        match self.kind {
+            TypeBindingKind::Equality { term: Term::Const(ref c) } => Some(c),
+            _ => None,
+        }
+    }
 }
 
 #[derive(Debug)]

compiler/rustc_infer/src/infer/at.rs

@@ -286,6 +286,26 @@ impl<'tcx> ToTrace<'tcx> for &'tcx Const<'tcx> {
     }
 }
 
+impl<'tcx> ToTrace<'tcx> for ty::Term<'tcx> {
+    fn to_trace(
+        tcx: TyCtxt<'tcx>,
+        cause: &ObligationCause<'tcx>,
+        a_is_expected: bool,
+        a: Self,
+        b: Self,
+    ) -> TypeTrace<'tcx> {
+        match (a, b) {
+            (ty::Term::Ty(a), ty::Term::Ty(b)) => {
+                ToTrace::to_trace(tcx, cause, a_is_expected, a, b)
+            }
+            (ty::Term::Const(a), ty::Term::Const(b)) => {
+                ToTrace::to_trace(tcx, cause, a_is_expected, a, b)
+            }
+            (_, _) => todo!(),
+        }
+    }
+}
+
 impl<'tcx> ToTrace<'tcx> for ty::TraitRef<'tcx> {
     fn to_trace(
         _: TyCtxt<'tcx>,

compiler/rustc_infer/src/traits/project.rs

@@ -93,7 +93,7 @@ pub enum ProjectionCacheEntry<'tcx> {
     Recur,
     Error,
     NormalizedTy {
-        ty: NormalizedTy<'tcx>,
+        ty: Normalized<'tcx, ty::Term<'tcx>>,
         /// If we were able to successfully evaluate the
         /// corresponding cache entry key during predicate
         /// evaluation, then this field stores the final
@@ -174,7 +174,11 @@ impl<'tcx> ProjectionCache<'_, 'tcx> {
     }
 
     /// Indicates that `key` was normalized to `value`.
-    pub fn insert_ty(&mut self, key: ProjectionCacheKey<'tcx>, value: NormalizedTy<'tcx>) {
+    pub fn insert_term(
+        &mut self,
+        key: ProjectionCacheKey<'tcx>,
+        value: Normalized<'tcx, ty::Term<'tcx>>,
+    ) {
         debug!(
             "ProjectionCacheEntry::insert_ty: adding cache entry: key={:?}, value={:?}",
             key, value

compiler/rustc_middle/src/ty/mod.rs

@@ -867,6 +867,9 @@ impl<'tcx> Term<'tcx> {
     pub fn ty(&self) -> Option<Ty<'tcx>> {
         if let Term::Ty(ty) = self { Some(ty) } else { None }
     }
+    pub fn ct(&self) -> Option<&'tcx Const<'tcx>> {
+        if let Term::Const(c) = self { Some(c) } else { None }
+    }
 }
 
 /// This kind of predicate has no *direct* correspondent in the

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -1373,19 +1373,31 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
                         | ObligationCauseCode::ObjectCastObligation(_)
                         | ObligationCauseCode::OpaqueType
                 );
-                // FIXME(associated_const_equality): Handle Consts here
-                let data_ty = data.term.ty().unwrap();
                 if let Err(error) = self.at(&obligation.cause, obligation.param_env).eq_exp(
                     is_normalized_ty_expected,
                     normalized_ty,
-                    data_ty,
+                    data.term,
                 ) {
-                    values = Some(infer::ValuePairs::Types(ExpectedFound::new(
-                        is_normalized_ty_expected,
-                        normalized_ty,
-                        data_ty,
-                    )));
-
+                    values = Some(match (normalized_ty, data.term) {
+                        (ty::Term::Ty(normalized_ty), ty::Term::Ty(ty)) => {
+                            infer::ValuePairs::Types(ExpectedFound::new(
+                                is_normalized_ty_expected,
+                                normalized_ty,
+                                ty,
+                            ))
+                        }
+                        (ty::Term::Const(normalized_ct), ty::Term::Const(ct)) => {
+                            infer::ValuePairs::Consts(ExpectedFound::new(
+                                is_normalized_ty_expected,
+                                normalized_ct,
+                                ct,
+                            ))
+                        }
+                        (_, _) => span_bug!(
+                            obligation.cause.span,
+                            "found const or type where other expected"
+                        ),
+                    });
                     err_buf = error;
                     err = &err_buf;
                 }

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -2496,7 +2496,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 let try_obligation = self.mk_trait_obligation_with_new_self_ty(
                     obligation.param_env,
                     trait_pred,
-                    normalized_ty,
+                    normalized_ty.ty().unwrap(),
                 );
                 debug!("suggest_await_before_try: try_trait_obligation {:?}", try_obligation);
                 if self.predicate_may_hold(&try_obligation)

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -200,7 +200,7 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentContext<'tcx> {
 
         debug!(?normalized_ty);
 
-        normalized_ty
+        normalized_ty.ty().unwrap()
     }
 
     fn register_predicate_obligation(