Use try_normalize_erasing_regions in needs_drop

compiler/rustc_middle/src/ty/util.rs

@@ -788,10 +788,14 @@ impl<'tcx> ty::TyS<'tcx> {
                     [component_ty] => component_ty,
                     _ => self,
                 };
+
                 // This doesn't depend on regions, so try to minimize distinct
                 // query keys used.
-                let erased = tcx.normalize_erasing_regions(param_env, query_ty);
-                tcx.needs_drop_raw(param_env.and(erased))
+                // If normalization fails, we just use `query_ty`.
+                let query_ty =
+                    tcx.try_normalize_erasing_regions(param_env, query_ty).unwrap_or(query_ty);
+
+                tcx.needs_drop_raw(param_env.and(query_ty))
             }
         }
     }

compiler/rustc_ty_utils/src/needs_drop.rs

@@ -147,8 +147,10 @@ where
                             Ok(tys) => tys,
                         };
                         for required_ty in tys {
-                            let required =
-                                tcx.normalize_erasing_regions(self.param_env, required_ty);
+                            let required = tcx
+                                .try_normalize_erasing_regions(self.param_env, required_ty)
+                                .unwrap_or(required_ty);
+
                             queue_type(self, required);
                         }
                     }

src/test/ui/union/issue-81199.rs

@@ -0,0 +1,21 @@
+#[repr(C)]
+union PtrRepr<T: ?Sized> {
+    const_ptr: *const T,
+    mut_ptr: *mut T,
+    components: PtrComponents<T>,
+    //~^ ERROR the trait bound
+}
+
+#[repr(C)]
+struct PtrComponents<T: Pointee + ?Sized> {
+    data_address: *const (),
+    metadata: <T as Pointee>::Metadata,
+}
+
+
+
+pub trait Pointee {
+   type Metadata;
+}
+
+fn main() {}

src/test/ui/union/issue-81199.stderr

@@ -0,0 +1,29 @@
+error[E0277]: the trait bound `T: Pointee` is not satisfied in `PtrComponents<T>`
+  --> $DIR/issue-81199.rs:5:17
+   |
+LL |     components: PtrComponents<T>,
+   |                 ^^^^^^^^^^^^^^^^ within `PtrComponents<T>`, the trait `Pointee` is not implemented for `T`
+   |
+note: required because it appears within the type `PtrComponents<T>`
+  --> $DIR/issue-81199.rs:10:8
+   |
+LL | struct PtrComponents<T: Pointee + ?Sized> {
+   |        ^^^^^^^^^^^^^
+   = note: no field of a union may have a dynamically sized type
+   = help: change the field's type to have a statically known size
+help: consider further restricting this bound
+   |
+LL | union PtrRepr<T: ?Sized + Pointee> {
+   |                         +++++++++
+help: borrowed types always have a statically known size
+   |
+LL |     components: &PtrComponents<T>,
+   |                 +
+help: the `Box` type always has a statically known size and allocates its contents in the heap
+   |
+LL |     components: Box<PtrComponents<T>>,
+   |                 ++++                +
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.