Rollup merge of #57045 - RalfJung:kill-more-uninit, r=SimonSapin

Kill remaining uses of mem::uninitialized in libcore, liballoc

Kill remaining uses of mem::uninitialized in libcore and liballoc, and enable a lint that will warn when uses are added again in the future.

To avoid casting raw pointers around (which is always very dangerous because it is not typechecked at all -- it doesn't even get the "same size" sanity check that `transmute` gets), I also added two new functions to `MaybeUninit`:

```rust
    /// Get a pointer to the first contained values.
    pub fn first_ptr(this: &[MaybeUninit<T>]) -> *const T {
        this as *const [MaybeUninit<T>] as *const T
    }

    /// Get a mutable pointer to the first contained values.
    pub fn first_mut_ptr(this: &mut [MaybeUninit<T>]) -> *mut T {
        this as *mut [MaybeUninit<T>] as *mut T
    }
```

I changed some of the existing code to use array-of-`MaybeUninit` instead of `MaybeUninit`-of-array, successfully removing raw pointer casts there as well.

src/etc/gdb_rust_pretty_printing.py

@@ -330,19 +330,20 @@ def children_of_node(boxed_node, height, want_values):
         leaf = node_ptr['data']
     else:
         leaf = node_ptr.dereference()
-    keys = leaf['keys']['value']['value']
+    keys = leaf['keys']
     if want_values:
-        values = leaf['vals']['value']['value']
+        values = leaf['vals']
     length = int(leaf['len'])
     for i in xrange(0, length + 1):
         if height > 0:
-            for child in children_of_node(node_ptr['edges'][i], height - 1, want_values):
+            child_ptr = node_ptr['edges'][i]['value']['value']
+            for child in children_of_node(child_ptr, height - 1, want_values):
                 yield child
         if i < length:
             if want_values:
-                yield (keys[i], values[i])
+                yield (keys[i]['value']['value'], values[i]['value']['value'])
             else:
-                yield keys[i]
+                yield keys[i]['value']['value']
 
 class RustStdBTreeSetPrinter(object):
     def __init__(self, val):

src/liballoc/borrow.rs

@@ -380,7 +380,6 @@ impl<'a, B: ?Sized> Hash for Cow<'a, B>
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-#[allow(deprecated)]
 impl<'a, T: ?Sized + ToOwned> AsRef<T> for Cow<'a, T> {
     fn as_ref(&self) -> &T {
         self

src/liballoc/collections/btree/node.rs

@@ -95,8 +95,8 @@ struct LeafNode<K, V> {
 
     /// The arrays storing the actual data of the node. Only the first `len` elements of each
     /// array are initialized and valid.
-    keys: MaybeUninit<[K; CAPACITY]>,
-    vals: MaybeUninit<[V; CAPACITY]>,
+    keys: [MaybeUninit<K>; CAPACITY],
+    vals: [MaybeUninit<V>; CAPACITY],
 }
 
 impl<K, V> LeafNode<K, V> {
@@ -106,8 +106,8 @@ impl<K, V> LeafNode<K, V> {
         LeafNode {
             // As a general policy, we leave fields uninitialized if they can be, as this should
             // be both slightly faster and easier to track in Valgrind.
-            keys: MaybeUninit::uninitialized(),
-            vals: MaybeUninit::uninitialized(),
+            keys: uninitialized_array![_; CAPACITY],
+            vals: uninitialized_array![_; CAPACITY],
             parent: ptr::null(),
             parent_idx: MaybeUninit::uninitialized(),
             len: 0
@@ -145,7 +145,7 @@ struct InternalNode<K, V> {
 
     /// The pointers to the children of this node. `len + 1` of these are considered
     /// initialized and valid.
-    edges: [BoxedNode<K, V>; 2 * B],
+    edges: [MaybeUninit<BoxedNode<K, V>>; 2 * B],
 }
 
 impl<K, V> InternalNode<K, V> {
@@ -159,7 +159,7 @@ impl<K, V> InternalNode<K, V> {
     unsafe fn new() -> Self {
         InternalNode {
             data: LeafNode::new(),
-            edges: mem::uninitialized()
+            edges: uninitialized_array![_; 2*B],
         }
     }
 }
@@ -261,7 +261,7 @@ impl<K, V> Root<K, V> {
             -> NodeRef<marker::Mut, K, V, marker::Internal> {
         debug_assert!(!self.is_shared_root());
         let mut new_node = Box::new(unsafe { InternalNode::new() });
-        new_node.edges[0] = unsafe { BoxedNode::from_ptr(self.node.as_ptr()) };
+        new_node.edges[0].set(unsafe { BoxedNode::from_ptr(self.node.as_ptr()) });
 
         self.node = BoxedNode::from_internal(new_node);
         self.height += 1;
@@ -623,7 +623,7 @@ impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Immut<'a>, K, V, Type> {
         // We cannot be the root, so `as_leaf` is okay
         unsafe {
             slice::from_raw_parts(
-                self.as_leaf().vals.as_ptr() as *const V,
+                MaybeUninit::first_ptr(&self.as_leaf().vals),
                 self.len()
             )
         }
@@ -650,7 +650,7 @@ impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
         } else {
             unsafe {
                 slice::from_raw_parts_mut(
-                    (*self.as_leaf_mut()).keys.as_mut_ptr() as *mut K,
+                    MaybeUninit::first_ptr_mut(&mut (*self.as_leaf_mut()).keys),
                     self.len()
                 )
             }
@@ -661,7 +661,7 @@ impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
         debug_assert!(!self.is_shared_root());
         unsafe {
             slice::from_raw_parts_mut(
-                (*self.as_leaf_mut()).vals.as_mut_ptr() as *mut V,
+                MaybeUninit::first_ptr_mut(&mut (*self.as_leaf_mut()).vals),
                 self.len()
             )
         }
@@ -718,7 +718,7 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
         unsafe {
             ptr::write(self.keys_mut().get_unchecked_mut(idx), key);
             ptr::write(self.vals_mut().get_unchecked_mut(idx), val);
-            ptr::write(self.as_internal_mut().edges.get_unchecked_mut(idx + 1), edge.node);
+            self.as_internal_mut().edges.get_unchecked_mut(idx + 1).set(edge.node);
 
             (*self.as_leaf_mut()).len += 1;
 
@@ -749,7 +749,7 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
             slice_insert(self.vals_mut(), 0, val);
             slice_insert(
                 slice::from_raw_parts_mut(
-                    self.as_internal_mut().edges.as_mut_ptr(),
+                    MaybeUninit::first_ptr_mut(&mut self.as_internal_mut().edges),
                     self.len()+1
                 ),
                 0,
@@ -778,7 +778,9 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
             let edge = match self.reborrow_mut().force() {
                 ForceResult::Leaf(_) => None,
                 ForceResult::Internal(internal) => {
-                    let edge = ptr::read(internal.as_internal().edges.get_unchecked(idx + 1));
+                    let edge = ptr::read(
+                        internal.as_internal().edges.get_unchecked(idx + 1).as_ptr()
+                    );
                     let mut new_root = Root { node: edge, height: internal.height - 1 };
                     (*new_root.as_mut().as_leaf_mut()).parent = ptr::null();
                     Some(new_root)
@@ -806,7 +808,7 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
                 ForceResult::Internal(mut internal) => {
                     let edge = slice_remove(
                         slice::from_raw_parts_mut(
-                            internal.as_internal_mut().edges.as_mut_ptr(),
+                            MaybeUninit::first_ptr_mut(&mut internal.as_internal_mut().edges),
                             old_len+1
                         ),
                         0
@@ -1085,7 +1087,7 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
 
             slice_insert(
                 slice::from_raw_parts_mut(
-                    self.node.as_internal_mut().edges.as_mut_ptr(),
+                    MaybeUninit::first_ptr_mut(&mut self.node.as_internal_mut().edges),
                     self.node.len()
                 ),
                 self.idx + 1,
@@ -1140,7 +1142,9 @@ impl<BorrowType, K, V>
     pub fn descend(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
         NodeRef {
             height: self.node.height - 1,
-            node: unsafe { self.node.as_internal().edges.get_unchecked(self.idx).as_ptr() },
+            node: unsafe {
+                self.node.as_internal().edges.get_unchecked(self.idx).get_ref().as_ptr()
+            },
             root: self.node.root,
             _marker: PhantomData
         }

src/liballoc/lib.rs

@@ -63,8 +63,9 @@
 #![no_std]
 #![needs_allocator]
 
-#![deny(intra_doc_link_resolution_failure)]
-#![deny(missing_debug_implementations)]
+#![warn(deprecated_in_future)]
+#![warn(intra_doc_link_resolution_failure)]
+#![warn(missing_debug_implementations)]
 
 #![cfg_attr(not(test), feature(fn_traits))]
 #![cfg_attr(not(test), feature(generator_trait))]

src/liballoc/rc.rs

@@ -1,5 +1,3 @@
-#![allow(deprecated)]
-
 //! Single-threaded reference-counting pointers. 'Rc' stands for 'Reference
 //! Counted'.
 //!

src/libcore/fmt/mod.rs

@@ -2048,7 +2048,7 @@ macro_rules! tuple {
     ( $($name:ident,)+ ) => (
         #[stable(feature = "rust1", since = "1.0.0")]
         impl<$($name:Debug),*> Debug for ($($name,)*) where last_type!($($name,)+): ?Sized {
-            #[allow(non_snake_case, unused_assignments, deprecated)]
+            #[allow(non_snake_case, unused_assignments)]
             fn fmt(&self, f: &mut Formatter) -> Result {
                 let mut builder = f.debug_tuple("");
                 let ($(ref $name,)*) = *self;

src/libcore/fmt/num.rs

@@ -1,14 +1,12 @@
 //! Integer and floating-point number formatting
 
-#![allow(deprecated)]
-
 
 use fmt;
 use ops::{Div, Rem, Sub};
 use str;
 use slice;
 use ptr;
-use mem;
+use mem::MaybeUninit;
 
 #[doc(hidden)]
 trait Int: PartialEq + PartialOrd + Div<Output=Self> + Rem<Output=Self> +
@@ -53,7 +51,7 @@ trait GenericRadix {
         // characters for a base 2 number.
         let zero = T::zero();
         let is_nonnegative = x >= zero;
-        let mut buf: [u8; 128] = unsafe { mem::uninitialized() };
+        let mut buf = uninitialized_array![u8; 128];
         let mut curr = buf.len();
         let base = T::from_u8(Self::BASE);
         if is_nonnegative {
@@ -62,7 +60,7 @@ trait GenericRadix {
             for byte in buf.iter_mut().rev() {
                 let n = x % base;               // Get the current place value.
                 x = x / base;                   // Deaccumulate the number.
-                *byte = Self::digit(n.to_u8()); // Store the digit in the buffer.
+                byte.set(Self::digit(n.to_u8())); // Store the digit in the buffer.
                 curr -= 1;
                 if x == zero {
                     // No more digits left to accumulate.
@@ -74,7 +72,7 @@ trait GenericRadix {
             for byte in buf.iter_mut().rev() {
                 let n = zero - (x % base);      // Get the current place value.
                 x = x / base;                   // Deaccumulate the number.
-                *byte = Self::digit(n.to_u8()); // Store the digit in the buffer.
+                byte.set(Self::digit(n.to_u8())); // Store the digit in the buffer.
                 curr -= 1;
                 if x == zero {
                     // No more digits left to accumulate.
@@ -82,7 +80,11 @@ trait GenericRadix {
                 };
             }
         }
-        let buf = unsafe { str::from_utf8_unchecked(&buf[curr..]) };
+        let buf = &buf[curr..];
+        let buf = unsafe { str::from_utf8_unchecked(slice::from_raw_parts(
+            MaybeUninit::first_ptr(buf),
+            buf.len()
+        )) };
         f.pad_integral(is_nonnegative, Self::PREFIX, buf)
     }
 }
@@ -196,9 +198,9 @@ macro_rules! impl_Display {
                 // convert the negative num to positive by summing 1 to it's 2 complement
                 (!self.$conv_fn()).wrapping_add(1)
             };
-            let mut buf: [u8; 39] = unsafe { mem::uninitialized() };
+            let mut buf = uninitialized_array![u8; 39];
             let mut curr = buf.len() as isize;
-            let buf_ptr = buf.as_mut_ptr();
+            let buf_ptr = MaybeUninit::first_ptr_mut(&mut buf);
             let lut_ptr = DEC_DIGITS_LUT.as_ptr();
 
             unsafe {

src/libcore/hash/sip.rs

@@ -1,6 +1,6 @@
 //! An implementation of SipHash.
 
-#![allow(deprecated)]
+#![allow(deprecated)] // the types in this module are deprecated
 
 use marker::PhantomData;
 use ptr;

src/libcore/lib.rs

@@ -58,11 +58,12 @@
        issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
        test(no_crate_inject, attr(deny(warnings))),
        test(attr(allow(dead_code, deprecated, unused_variables, unused_mut))))]
-
 #![no_core]
-#![deny(missing_docs)]
-#![deny(intra_doc_link_resolution_failure)]
-#![deny(missing_debug_implementations)]
+
+#![warn(deprecated_in_future)]
+#![warn(missing_docs)]
+#![warn(intra_doc_link_resolution_failure)]
+#![warn(missing_debug_implementations)]
 
 #![feature(allow_internal_unstable)]
 #![feature(arbitrary_self_types)]
@@ -122,6 +123,7 @@
 #![feature(structural_match)]
 #![feature(abi_unadjusted)]
 #![feature(adx_target_feature)]
+#![feature(maybe_uninit)]
 
 #[prelude_import]
 #[allow(unused)]

src/libcore/macros.rs

@@ -547,6 +547,23 @@ macro_rules! unimplemented {
     ($($arg:tt)+) => (panic!("not yet implemented: {}", format_args!($($arg)*)));
 }
 
+/// A macro to create an array of [`MaybeUninit`]
+///
+/// This macro constructs and uninitialized array of the type `[MaybeUninit<K>; N]`.
+///
+/// [`MaybeUninit`]: mem/union.MaybeUninit.html
+#[macro_export]
+#[unstable(feature = "maybe_uninit", issue = "53491")]
+macro_rules! uninitialized_array {
+    // This `into_inner` is safe because an array of `MaybeUninit` does not
+    // require initialization.
+    // FIXME(#49147): Could be replaced by an array initializer, once those can
+    // be any const expression.
+    ($t:ty; $size:expr) => (unsafe {
+        MaybeUninit::<[MaybeUninit<$t>; $size]>::uninitialized().into_inner()
+    });
+}
+
 /// Built-in macros to the compiler itself.
 ///
 /// These macros do not have any corresponding definition with a `macro_rules!`

src/libcore/mem.rs

@@ -1148,4 +1148,18 @@ impl<T> MaybeUninit<T> {
     pub fn as_mut_ptr(&mut self) -> *mut T {
         unsafe { &mut *self.value as *mut T }
     }
+
+    /// Get a pointer to the first element of the array.
+    #[unstable(feature = "maybe_uninit", issue = "53491")]
+    #[inline(always)]
+    pub fn first_ptr(this: &[MaybeUninit<T>]) -> *const T {
+        this as *const [MaybeUninit<T>] as *const T
+    }
+
+    /// Get a mutable pointer to the first element of the array.
+    #[unstable(feature = "maybe_uninit", issue = "53491")]
+    #[inline(always)]
+    pub fn first_ptr_mut(this: &mut [MaybeUninit<T>]) -> *mut T {
+        this as *mut [MaybeUninit<T>] as *mut T
+    }
 }

src/libcore/slice/sort.rs

@@ -216,14 +216,14 @@ fn partition_in_blocks<T, F>(v: &mut [T], pivot: &T, is_less: &mut F) -> usize
     let mut block_l = BLOCK;
     let mut start_l = ptr::null_mut();
     let mut end_l = ptr::null_mut();
-    let mut offsets_l = MaybeUninit::<[u8; BLOCK]>::uninitialized();
+    let mut offsets_l: [MaybeUninit<u8>; BLOCK] = uninitialized_array![u8; BLOCK];
 
     // The current block on the right side (from `r.sub(block_r)` to `r`).
     let mut r = unsafe { l.add(v.len()) };
     let mut block_r = BLOCK;
     let mut start_r = ptr::null_mut();
     let mut end_r = ptr::null_mut();
-    let mut offsets_r = MaybeUninit::<[u8; BLOCK]>::uninitialized();
+    let mut offsets_r: [MaybeUninit<u8>; BLOCK] = uninitialized_array![u8; BLOCK];
 
     // FIXME: When we get VLAs, try creating one array of length `min(v.len(), 2 * BLOCK)` rather
     // than two fixed-size arrays of length `BLOCK`. VLAs might be more cache-efficient.
@@ -262,8 +262,8 @@ fn partition_in_blocks<T, F>(v: &mut [T], pivot: &T, is_less: &mut F) -> usize
 
         if start_l == end_l {
             // Trace `block_l` elements from the left side.
-            start_l = offsets_l.as_mut_ptr() as *mut u8;
-            end_l = offsets_l.as_mut_ptr() as *mut u8;
+            start_l = MaybeUninit::first_ptr_mut(&mut offsets_l);
+            end_l = MaybeUninit::first_ptr_mut(&mut offsets_l);
             let mut elem = l;
 
             for i in 0..block_l {
@@ -278,8 +278,8 @@ fn partition_in_blocks<T, F>(v: &mut [T], pivot: &T, is_less: &mut F) -> usize
 
         if start_r == end_r {
             // Trace `block_r` elements from the right side.
-            start_r = offsets_r.as_mut_ptr() as *mut u8;
-            end_r = offsets_r.as_mut_ptr() as *mut u8;
+            start_r = MaybeUninit::first_ptr_mut(&mut offsets_r);
+            end_r = MaybeUninit::first_ptr_mut(&mut offsets_r);
             let mut elem = r;
 
             for i in 0..block_r {