Rollup merge of #142079 - lcnr:opaque-types-universes, r=BoxyUwU

nll-relate: improve hr opaque types support

This should currently not be user-facing outside of diagnostics as even if we successfully relate the opaque types, we don't support opaque types with non-param arguments and also require all member regions to be equal to the arguments or `'static`. This means there's no way to end up with a placeholder in the hidden type.

r? types

2 files changed, 22 insertions, 9 deletions

diff --git a/compiler/rustc_borrowck/src/type_check/relate_tys.rs b/compiler/rustc_borrowck/src/type_check/relate_tys.rs
index 84ca9bad2c1..7ac2dff12f7 100644
--- a/compiler/rustc_borrowck/src/type_check/relate_tys.rs
+++ b/compiler/rustc_borrowck/src/type_check/relate_tys.rs
@@ -124,8 +124,13 @@ impl<'a, 'b, 'tcx> NllTypeRelating<'a, 'b, 'tcx> {
         // by using `ty_vid rel B` and then finally and end by equating `ty_vid` to
         // the opaque.
         let mut enable_subtyping = |ty, opaque_is_expected| {
-            let ty_vid = infcx.next_ty_var_id_in_universe(self.span(), ty::UniverseIndex::ROOT);
-
+            // We create the fresh inference variable in the highest universe.
+            // In theory we could limit it to the highest universe in the args of
+            // the opaque but that isn't really worth the effort.
+            //
+            // We'll make sure that the opaque type can actually name everything
+            // in its hidden type later on.
+            let ty_vid = infcx.next_ty_vid(self.span());
             let variance = if opaque_is_expected {
                 self.ambient_variance
             } else {
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index 82d4856df39..9ff06bda89b 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -782,22 +782,30 @@ impl<'tcx> InferCtxt<'tcx> {
         self.inner.borrow_mut().type_variables().num_vars()
     }
 
-    pub fn next_ty_var(&self, span: Span) -> Ty<'tcx> {
-        self.next_ty_var_with_origin(TypeVariableOrigin { span, param_def_id: None })
+    pub fn next_ty_vid(&self, span: Span) -> TyVid {
+        self.next_ty_vid_with_origin(TypeVariableOrigin { span, param_def_id: None })
     }
 
-    pub fn next_ty_var_with_origin(&self, origin: TypeVariableOrigin) -> Ty<'tcx> {
-        let vid = self.inner.borrow_mut().type_variables().new_var(self.universe(), origin);
-        Ty::new_var(self.tcx, vid)
+    pub fn next_ty_vid_with_origin(&self, origin: TypeVariableOrigin) -> TyVid {
+        self.inner.borrow_mut().type_variables().new_var(self.universe(), origin)
     }
 
-    pub fn next_ty_var_id_in_universe(&self, span: Span, universe: ty::UniverseIndex) -> TyVid {
+    pub fn next_ty_vid_in_universe(&self, span: Span, universe: ty::UniverseIndex) -> TyVid {
         let origin = TypeVariableOrigin { span, param_def_id: None };
         self.inner.borrow_mut().type_variables().new_var(universe, origin)
     }
 
+    pub fn next_ty_var(&self, span: Span) -> Ty<'tcx> {
+        self.next_ty_var_with_origin(TypeVariableOrigin { span, param_def_id: None })
+    }
+
+    pub fn next_ty_var_with_origin(&self, origin: TypeVariableOrigin) -> Ty<'tcx> {
+        let vid = self.next_ty_vid_with_origin(origin);
+        Ty::new_var(self.tcx, vid)
+    }
+
     pub fn next_ty_var_in_universe(&self, span: Span, universe: ty::UniverseIndex) -> Ty<'tcx> {
-        let vid = self.next_ty_var_id_in_universe(span, universe);
+        let vid = self.next_ty_vid_in_universe(span, universe);
         Ty::new_var(self.tcx, vid)
     }