Add RFC 1238's `unsafe_destructor_blind_to_params` (UGEH) where needed.

I needed it in `RawVec`, `Vec`, and `TypedArena` for `rustc` to
bootstrap; but of course that alone was not sufficient for `make
check`.

Later I added `unsafe_destructor_blind_to_params` to collections, in
particular `LinkedList` and `RawTable` (the backing representation for
`HashMap` and `HashSet`), to get the regression tests exercising
cyclic structure from PR #27185 building.

----

Note that the feature is `dropck_parametricity` (which is not the same
as the attribute's name). We will almost certainly vary our strategy
here in the future, so it makes some sense to have a not-as-ugly name
for the feature gate. (The attribute name was deliberately selected to
be ugly looking.)

2 files changed, 6 insertions, 0 deletions

diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index 98c729aaba4..8ecc78a231e 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -94,6 +94,11 @@
 #![feature(unboxed_closures)]
 #![feature(unique)]
 #![feature(unsafe_no_drop_flag, filling_drop)]
+// SNAP 1af31d4
+#![allow(unused_features)]
+// SNAP 1af31d4
+#![allow(unused_attributes)]
+#![feature(dropck_parametricity)]
 #![feature(unsize)]
 #![feature(core_slice_ext)]
 #![feature(core_str_ext)]
diff --git a/src/liballoc/raw_vec.rs b/src/liballoc/raw_vec.rs
index dd2db6fab08..49d37698154 100644
--- a/src/liballoc/raw_vec.rs
+++ b/src/liballoc/raw_vec.rs
@@ -445,6 +445,7 @@ impl<T> RawVec<T> {
 }
 
 impl<T> Drop for RawVec<T> {
+    #[unsafe_destructor_blind_to_params]
     /// Frees the memory owned by the RawVec *without* trying to Drop its contents.
     fn drop(&mut self) {
         let elem_size = mem::size_of::<T>();