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.)

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)]

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>();

src/libarena/lib.rs

@@ -38,8 +38,14 @@
 #![feature(ptr_as_ref)]
 #![feature(raw)]
 #![feature(staged_api)]
+#![feature(dropck_parametricity)]
 #![cfg_attr(test, feature(test))]
 
+// SNAP 1af31d4
+#![allow(unused_features)]
+// SNAP 1af31d4
+#![allow(unused_attributes)]
+
 extern crate alloc;
 
 use std::cell::{Cell, RefCell};
@@ -510,6 +516,7 @@ impl<T> TypedArena<T> {
 }
 
 impl<T> Drop for TypedArena<T> {
+    #[unsafe_destructor_blind_to_params]
     fn drop(&mut self) {
         unsafe {
             // Determine how much was filled.

src/libcollections/btree/node.rs

@@ -275,12 +275,14 @@ impl<T> DoubleEndedIterator for RawItems<T> {
 }
 
 impl<T> Drop for RawItems<T> {
+    #[unsafe_destructor_blind_to_params]
     fn drop(&mut self) {
         for _ in self {}
     }
 }
 
 impl<K, V> Drop for Node<K, V> {
+    #[unsafe_destructor_blind_to_params]
     fn drop(&mut self) {
         if self.keys.is_null() ||
             (unsafe { self.keys.get() as *const K as usize == mem::POST_DROP_USIZE })
@@ -1419,6 +1421,7 @@ impl<K, V> TraversalImpl for MoveTraversalImpl<K, V> {
 }
 
 impl<K, V> Drop for MoveTraversalImpl<K, V> {
+    #[unsafe_destructor_blind_to_params]
     fn drop(&mut self) {
         // We need to cleanup the stored values manually, as the RawItems destructor would run
         // after our deallocation.

src/libcollections/lib.rs

@@ -32,6 +32,11 @@
 #![allow(trivial_casts)]
 #![cfg_attr(test, allow(deprecated))] // rand
 
+// SNAP 1af31d4
+#![allow(unused_features)]
+// SNAP 1af31d4
+#![allow(unused_attributes)]
+
 #![feature(alloc)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
@@ -59,6 +64,7 @@
 #![feature(unboxed_closures)]
 #![feature(unicode)]
 #![feature(unique)]
+#![feature(dropck_parametricity)]
 #![feature(unsafe_no_drop_flag, filling_drop)]
 #![feature(decode_utf16)]
 #![feature(utf8_error)]

src/libcollections/linked_list.rs

@@ -655,6 +655,7 @@ impl<T> LinkedList<T> {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> Drop for LinkedList<T> {
+    #[unsafe_destructor_blind_to_params]
     fn drop(&mut self) {
         // Dissolve the linked_list in a loop.
         // Just dropping the list_head can lead to stack exhaustion

src/libcollections/vec.rs

@@ -1385,6 +1385,7 @@ impl<T: Ord> Ord for Vec<T> {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> Drop for Vec<T> {
+    #[unsafe_destructor_blind_to_params]
     fn drop(&mut self) {
         // NOTE: this is currently abusing the fact that ZSTs can't impl Drop.
         // Or rather, that impl'ing Drop makes them not zero-sized. This is

src/libcollections/vec_deque.rs

@@ -64,6 +64,7 @@ impl<T: Clone> Clone for VecDeque<T> {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> Drop for VecDeque<T> {
+    #[unsafe_destructor_blind_to_params]
     fn drop(&mut self) {
         self.clear();
         // RawVec handles deallocation

src/libstd/collections/hash/table.rs

@@ -999,6 +999,7 @@ impl<K: Clone, V: Clone> Clone for RawTable<K, V> {
 }
 
 impl<K, V> Drop for RawTable<K, V> {
+    #[unsafe_destructor_blind_to_params]
     fn drop(&mut self) {
         if self.capacity == 0 || self.capacity == mem::POST_DROP_USIZE {
             return;

src/libstd/lib.rs

@@ -199,6 +199,11 @@
        test(no_crate_inject, attr(deny(warnings))),
        test(attr(allow(dead_code, deprecated, unused_variables, unused_mut))))]
 
+// SNAP 1af31d4
+#![allow(unused_features)]
+// SNAP 1af31d4
+#![allow(unused_attributes)]
+
 #![feature(alloc)]
 #![feature(allow_internal_unstable)]
 #![feature(associated_consts)]
@@ -241,6 +246,7 @@
 #![feature(unboxed_closures)]
 #![feature(unicode)]
 #![feature(unique)]
+#![feature(dropck_parametricity)]
 #![feature(unsafe_no_drop_flag, filling_drop)]
 #![feature(decode_utf16)]
 #![feature(unwind_attributes)]

src/libsyntax/feature_gate.rs

@@ -136,9 +136,9 @@ const KNOWN_FEATURES: &'static [(&'static str, &'static str, Option<u32>, Status
     // switch to Accepted; see RFC 320)
     ("unsafe_no_drop_flag", "1.0.0", None, Active),
 
-    // Allows using the unsafe_destructor_blind_to_params attribute
-    // (Needs an RFC link)
-    ("unsafe_destructor_blind_to_params", "1.3.0", Some(28498), Active),
+    // Allows using the unsafe_destructor_blind_to_params attribute;
+    // RFC 1238
+    ("dropck_parametricity", "1.3.0", Some(28498), Active),
 
     // Allows the use of custom attributes; RFC 572
     ("custom_attribute", "1.0.0", None, Active),
@@ -345,7 +345,7 @@ pub const KNOWN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeGat
                                                 and may be removed in the future")),
     ("unsafe_destructor_blind_to_params",
      Normal,
-     Gated("unsafe_destructor_blind_to_params",
+     Gated("dropck_parametricity",
            "unsafe_destructor_blind_to_params has unstable semantics \
             and may be removed in the future")),
     ("unwind", Whitelisted, Gated("unwind_attributes", "#[unwind] is experimental")),

src/test/run-pass/issue-24805-dropck-itemless.rs

@@ -13,6 +13,8 @@
 
 #![allow(non_camel_case_types)]
 
+#![feature(dropck_parametricity)]
+
 trait UserDefined { }
 
 impl UserDefined for i32 { }
@@ -26,7 +28,10 @@ impl<'a, T> UserDefined for &'a T { }
 macro_rules! impl_drop {
     ($Bound:ident, $Id:ident) => {
         struct $Id<T:$Bound>(T);
-        impl <T:$Bound> Drop for $Id<T> { fn drop(&mut self) { } }
+        impl <T:$Bound> Drop for $Id<T> {
+            #[unsafe_destructor_blind_to_params]
+            fn drop(&mut self) { }
+        }
     }
 }