Add Destructible for replacing ~const Drop

Author: fee1-dead

compiler/rustc_hir/src/lang_items.rs

@@ -216,6 +216,7 @@ language_item_table! {
     Freeze,                  sym::freeze,              freeze_trait,               Target::Trait,          GenericRequirement::Exact(0);
 
     Drop,                    sym::drop,                drop_trait,                 Target::Trait,          GenericRequirement::None;
+    Destructible,            sym::destructible,        destructible_trait,         Target::Trait,          GenericRequirement::None;
 
     CoerceUnsized,           sym::coerce_unsized,      coerce_unsized_trait,       Target::Trait,          GenericRequirement::Minimum(1);
     DispatchFromDyn,         sym::dispatch_from_dyn,   dispatch_from_dyn_trait,    Target::Trait,          GenericRequirement::Minimum(1);

compiler/rustc_span/src/symbol.rs

@@ -571,6 +571,7 @@ symbols! {
         deref_target,
         derive,
         derive_default_enum,
+        destructible,
         destructuring_assignment,
         diagnostic,
         direct,

library/core/src/marker.rs

@@ -792,6 +792,13 @@ impl<T: ?Sized> Unpin for *const T {}
 #[stable(feature = "pin_raw", since = "1.38.0")]
 impl<T: ?Sized> Unpin for *mut T {}
 
+/// A marker for types that can be dropped.
+///
+/// The compiler logic for this trait is currently unimplemented.
+#[unstable(feature = "const_trait_impl", issue = "67792")]
+#[cfg_attr(not(bootstrap), lang = "destructible")]
+pub trait Destructible {}
+
 /// Implementations of `Copy` for primitive types.
 ///
 /// Implementations that cannot be described in Rust