Rollup merge of #146313 - nnethercote:rustc_middle-ty-cleanups-2, r=lcnr

Some `rustc_middle` cleanups

Minor improvements I found while looking through this code.

r? `@BoxyUwU`

1 files changed, 41 insertions, 2 deletions

diff --git a/compiler/rustc_infer/src/infer/relate/generalize.rs b/compiler/rustc_infer/src/infer/relate/generalize.rs
index a000bb1123c..a75fd8dfa18 100644
--- a/compiler/rustc_infer/src/infer/relate/generalize.rs
+++ b/compiler/rustc_infer/src/infer/relate/generalize.rs
@@ -6,8 +6,8 @@ use rustc_hir::def_id::DefId;
 use rustc_middle::bug;
 use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::{
-    self, AliasRelationDirection, InferConst, MaxUniverse, Term, Ty, TyCtxt, TypeVisitable,
-    TypeVisitableExt, TypingMode,
+    self, AliasRelationDirection, InferConst, Term, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable,
+    TypeVisitableExt, TypeVisitor, TypingMode,
 };
 use rustc_span::Span;
 use tracing::{debug, instrument, warn};
@@ -290,6 +290,45 @@ impl<'tcx> InferCtxt<'tcx> {
     }
 }
 
+/// Finds the max universe present
+struct MaxUniverse {
+    max_universe: ty::UniverseIndex,
+}
+
+impl MaxUniverse {
+    fn new() -> Self {
+        MaxUniverse { max_universe: ty::UniverseIndex::ROOT }
+    }
+
+    fn max_universe(self) -> ty::UniverseIndex {
+        self.max_universe
+    }
+}
+
+impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for MaxUniverse {
+    fn visit_ty(&mut self, t: Ty<'tcx>) {
+        if let ty::Placeholder(placeholder) = t.kind() {
+            self.max_universe = self.max_universe.max(placeholder.universe);
+        }
+
+        t.super_visit_with(self)
+    }
+
+    fn visit_const(&mut self, c: ty::Const<'tcx>) {
+        if let ty::ConstKind::Placeholder(placeholder) = c.kind() {
+            self.max_universe = self.max_universe.max(placeholder.universe);
+        }
+
+        c.super_visit_with(self)
+    }
+
+    fn visit_region(&mut self, r: ty::Region<'tcx>) {
+        if let ty::RePlaceholder(placeholder) = r.kind() {
+            self.max_universe = self.max_universe.max(placeholder.universe);
+        }
+    }
+}
+
 /// The "generalizer" is used when handling inference variables.
 ///
 /// The basic strategy for handling a constraint like `?A <: B` is to