Revert "Fix stack overflow in exhaustiveness due to recursive HIR opaque type values"

This reverts commit b08e9c2.

Author: compiler-errors

compiler/rustc_pattern_analysis/src/rustc.rs

@@ -1,6 +1,5 @@
 use std::fmt;
 use std::iter::once;
-use std::ops::ControlFlow;
 
 use rustc_abi::{FIRST_VARIANT, FieldIdx, Integer, VariantIdx};
 use rustc_arena::DroplessArena;
@@ -12,8 +11,7 @@ use rustc_middle::mir::{self, Const};
 use rustc_middle::thir::{self, Pat, PatKind, PatRange, PatRangeBoundary};
 use rustc_middle::ty::layout::IntegerExt;
 use rustc_middle::ty::{
-    self, FieldDef, OpaqueTypeKey, ScalarInt, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable,
-    TypeVisitableExt, TypeVisitor, VariantDef,
+    self, FieldDef, OpaqueTypeKey, ScalarInt, Ty, TyCtxt, TypeVisitableExt, VariantDef,
 };
 use rustc_middle::{bug, span_bug};
 use rustc_session::lint;
@@ -137,22 +135,11 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
     /// Returns the hidden type corresponding to this key if the body under analysis is allowed to
     /// know it.
     fn reveal_opaque_key(&self, key: OpaqueTypeKey<'tcx>) -> Option<Ty<'tcx>> {
-        if let Some(hidden_ty) = self.typeck_results.concrete_opaque_types.get(&key.def_id) {
-            let ty = ty::EarlyBinder::bind(hidden_ty.ty).instantiate(self.tcx, key.args);
-            if ty.visit_with(&mut RecursiveOpaque { def_id: key.def_id.into() }).is_continue() {
-                Some(ty)
-            } else {
-                // HACK: We skip revealing opaque types which recursively expand
-                // to themselves. This is because we may infer hidden types like
-                // `Opaque<T> = Opaque<Opaque<T>>` or `Opaque<T> = Opaque<(T,)>`
-                // in hir typeck.
-                None
-            }
-        } else {
-            None
-        }
+        self.typeck_results
+            .concrete_opaque_types
+            .get(&key.def_id)
+            .map(|x| ty::EarlyBinder::bind(x.ty).instantiate(self.tcx, key.args))
     }
-
     // This can take a non-revealed `Ty` because it reveals opaques itself.
     pub fn is_uninhabited(&self, ty: Ty<'tcx>) -> bool {
         !ty.inhabited_predicate(self.tcx).apply_revealing_opaque(
@@ -1118,20 +1105,3 @@ pub fn analyze_match<'p, 'tcx>(
 
     Ok(report)
 }
-
-struct RecursiveOpaque {
-    def_id: DefId,
-}
-impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for RecursiveOpaque {
-    type Result = ControlFlow<()>;
-
-    fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result {
-        if let ty::Alias(ty::Opaque, alias_ty) = t.kind() {
-            if alias_ty.def_id == self.def_id {
-                return ControlFlow::Break(());
-            }
-        }
-
-        if t.has_opaque_types() { t.super_visit_with(self) } else { ControlFlow::Continue(()) }
-    }
-}