Rollup merge of #41064 - Gankro:ptr-redux, r=alexcrichton

refactor NonZero, Shared, and Unique APIs

Major difference is that I removed Deref impls, as apparently LLVM has
trouble maintaining metadata with a `&ptr -> &ptr` API. This was cited
as a blocker for ever stabilizing this API. It wasn't that ergonomic
anyway.

* Added `get` to NonZero to replace Deref impl
* Added `ptr` getter to Shared/Unique to replace Deref impl
* Added Unique's `get` and `get_mut` conveniences to Shared
* Deprecated `as_mut_ptr` on Shared in favour of `ptr`

Note that Shared used to primarily expose only `*const` but there isn't
a good justification for that, so I made it `*mut`.

1 files changed, 13 insertions, 15 deletions

diff --git a/src/liballoc/raw_vec.rs b/src/liballoc/raw_vec.rs
index 6a53d3a9ca5..7edf07944ec 100644
--- a/src/liballoc/raw_vec.rs
+++ b/src/liballoc/raw_vec.rs
@@ -22,13 +22,13 @@ use core::cmp;
 /// involved. This type is excellent for building your own data structures like Vec and VecDeque.
 /// In particular:
 ///
-/// * Produces heap::EMPTY on zero-sized types
-/// * Produces heap::EMPTY on zero-length allocations
+/// * Produces Unique::empty() on zero-sized types
+/// * Produces Unique::empty() on zero-length allocations
 /// * Catches all overflows in capacity computations (promotes them to "capacity overflow" panics)
 /// * Guards against 32-bit systems allocating more than isize::MAX bytes
 /// * Guards against overflowing your length
 /// * Aborts on OOM
-/// * Avoids freeing heap::EMPTY
+/// * Avoids freeing Unique::empty()
 /// * Contains a ptr::Unique and thus endows the user with all related benefits
 ///
 /// This type does not in anyway inspect the memory that it manages. When dropped it *will*
@@ -55,15 +55,13 @@ impl<T> RawVec<T> {
     /// it makes a RawVec with capacity `usize::MAX`. Useful for implementing
     /// delayed allocation.
     pub fn new() -> Self {
-        unsafe {
-            // !0 is usize::MAX. This branch should be stripped at compile time.
-            let cap = if mem::size_of::<T>() == 0 { !0 } else { 0 };
+        // !0 is usize::MAX. This branch should be stripped at compile time.
+        let cap = if mem::size_of::<T>() == 0 { !0 } else { 0 };
 
-            // heap::EMPTY doubles as "unallocated" and "zero-sized allocation"
-            RawVec {
-                ptr: Unique::new(heap::EMPTY as *mut T),
-                cap: cap,
-            }
+        // Unique::empty() doubles as "unallocated" and "zero-sized allocation"
+        RawVec {
+            ptr: Unique::empty(),
+            cap: cap,
         }
     }
 
@@ -101,7 +99,7 @@ impl<T> RawVec<T> {
 
             // handles ZSTs and `cap = 0` alike
             let ptr = if alloc_size == 0 {
-                heap::EMPTY as *mut u8
+                mem::align_of::<T>() as *mut u8
             } else {
                 let align = mem::align_of::<T>();
                 let ptr = if zeroed {
@@ -148,10 +146,10 @@ impl<T> RawVec<T> {
 
 impl<T> RawVec<T> {
     /// Gets a raw pointer to the start of the allocation. Note that this is
-    /// heap::EMPTY if `cap = 0` or T is zero-sized. In the former case, you must
+    /// Unique::empty() if `cap = 0` or T is zero-sized. In the former case, you must
     /// be careful.
     pub fn ptr(&self) -> *mut T {
-        *self.ptr
+        self.ptr.as_ptr()
     }
 
     /// Gets the capacity of the allocation.
@@ -563,7 +561,7 @@ unsafe impl<#[may_dangle] T> Drop for RawVec<T> {
 
             let num_bytes = elem_size * self.cap;
             unsafe {
-                heap::deallocate(*self.ptr as *mut _, num_bytes, align);
+                heap::deallocate(self.ptr() as *mut u8, num_bytes, align);
             }
         }
     }