Auto merge of #41237 - frewsxcv:rollup, r=frewsxcv

Rollup of 8 pull requests

- Successful merges: #40377, #40559, #41173, #41202, #41204, #41209, #41216, #41231
- Failed merges:

2 files changed, 9 insertions, 29 deletions

diff --git a/src/librustc_data_structures/array_vec.rs b/src/librustc_data_structures/array_vec.rs
index 29fbcb70756..adb22197226 100644
--- a/src/librustc_data_structures/array_vec.rs
+++ b/src/librustc_data_structures/array_vec.rs
@@ -20,10 +20,11 @@ use std::fmt;
 use std::mem;
 use std::collections::range::RangeArgument;
 use std::collections::Bound::{Excluded, Included, Unbounded};
+use std::mem::ManuallyDrop;
 
 pub unsafe trait Array {
     type Element;
-    type PartialStorage: Default + Unsize<[ManuallyDrop<Self::Element>]>;
+    type PartialStorage: Unsize<[ManuallyDrop<Self::Element>]>;
     const LEN: usize;
 }
 
@@ -66,7 +67,7 @@ impl<A: Array> ArrayVec<A> {
     pub fn new() -> Self {
         ArrayVec {
             count: 0,
-            values: Default::default(),
+            values: unsafe { ::std::mem::uninitialized() },
         }
     }
 
@@ -81,7 +82,7 @@ impl<A: Array> ArrayVec<A> {
     /// Panics when the stack vector is full.
     pub fn push(&mut self, el: A::Element) {
         let arr = &mut self.values as &mut [ManuallyDrop<_>];
-        arr[self.count] = ManuallyDrop { value: el };
+        arr[self.count] = ManuallyDrop::new(el);
         self.count += 1;
     }
 
@@ -90,8 +91,8 @@ impl<A: Array> ArrayVec<A> {
             let arr = &mut self.values as &mut [ManuallyDrop<_>];
             self.count -= 1;
             unsafe {
-                let value = ptr::read(&arr[self.count]);
-                Some(value.value)
+                let value = ptr::read(&*arr[self.count]);
+                Some(value)
             }
         } else {
             None
@@ -210,7 +211,7 @@ impl<A: Array> Iterator for Iter<A> {
     fn next(&mut self) -> Option<A::Element> {
         let arr = &self.store as &[ManuallyDrop<_>];
         unsafe {
-            self.indices.next().map(|i| ptr::read(&arr[i]).value)
+            self.indices.next().map(|i| ptr::read(&*arr[i]))
         }
     }
 
@@ -233,7 +234,7 @@ impl<'a, A: Array> Iterator for Drain<'a, A> {
 
     #[inline]
     fn next(&mut self) -> Option<A::Element> {
-        self.iter.next().map(|elt| unsafe { ptr::read(elt as *const ManuallyDrop<_>).value })
+        self.iter.next().map(|elt| unsafe { ptr::read(&**elt) })
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
@@ -295,25 +296,3 @@ impl<'a, A: Array> IntoIterator for &'a mut ArrayVec<A> {
         self.iter_mut()
     }
 }
-
-// FIXME: This should use repr(transparent) from rust-lang/rfcs#1758.
-#[allow(unions_with_drop_fields)]
-pub union ManuallyDrop<T> {
-    value: T,
-    #[allow(dead_code)]
-    empty: (),
-}
-
-impl<T> ManuallyDrop<T> {
-    fn new() -> ManuallyDrop<T> {
-        ManuallyDrop {
-            empty: ()
-        }
-    }
-}
-
-impl<T> Default for ManuallyDrop<T> {
-    fn default() -> Self {
-        ManuallyDrop::new()
-    }
-}
diff --git a/src/librustc_data_structures/lib.rs b/src/librustc_data_structures/lib.rs
index c1735b4a4ec..72c533a7461 100644
--- a/src/librustc_data_structures/lib.rs
+++ b/src/librustc_data_structures/lib.rs
@@ -39,6 +39,7 @@
 #![feature(conservative_impl_trait)]
 #![feature(discriminant_value)]
 #![feature(specialization)]
+#![feature(manually_drop)]
 
 #![cfg_attr(unix, feature(libc))]
 #![cfg_attr(test, feature(test))]