Switch drop-flag to `u8` to allow special tags to instrument state.

Refactored code so that the drop-flag values for initialized
(`DTOR_NEEDED`) versus dropped (`DTOR_DONE`) are given explicit names.

Add `mem::dropped()` (which with `DTOR_DONE == 0` is semantically the
same as `mem::zeroed`, but the point is that it abstracts away from
the particular choice of value for `DTOR_DONE`).

Filling-drop needs to use something other than `ptr::read_and_zero`,
so I added such a function: `ptr::read_and_drop`.  But, libraries
should not use it if they can otherwise avoid it.

Fixes to tests to accommodate filling-drop.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libstd/collections/hash/table.rs b/src/libstd/collections/hash/table.rs
index 052bcfd7e16..710f0fe19db 100644
--- a/src/libstd/collections/hash/table.rs
+++ b/src/libstd/collections/hash/table.rs
@@ -985,7 +985,7 @@ impl<K: Clone, V: Clone> Clone for RawTable<K, V> {
 #[unsafe_destructor]
 impl<K, V> Drop for RawTable<K, V> {
     fn drop(&mut self) {
-        if self.capacity == 0 {
+        if self.capacity == 0 || self.capacity == mem::POST_DROP_USIZE {
             return;
         }