Rollup of 19 pull requests

Cargo.lock

@@ -1,3 +1,5 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
 [[package]]
 name = "adler32"
 version = "1.0.3"

src/libcore/convert.rs

@@ -17,7 +17,10 @@
 //! [`TryFrom<T>`][`TryFrom`] rather than [`Into<U>`][`Into`] or [`TryInto<U>`][`TryInto`],
 //! as [`From`] and [`TryFrom`] provide greater flexibility and offer
 //! equivalent [`Into`] or [`TryInto`] implementations for free, thanks to a
-//! blanket implementation in the standard library.
+//! blanket implementation in the standard library.  However, there are some cases
+//! where this is not possible, such as creating conversions into a type defined
+//! outside your library, so implementing [`Into`] instead of [`From`] is
+//! sometimes necessary.
 //!
 //! # Generic Implementations
 //!

src/libcore/lib.rs

@@ -24,7 +24,7 @@
 //!   often generated by LLVM. Additionally, this library can make explicit
 //!   calls to these functions. Their signatures are the same as found in C.
 //!   These functions are often provided by the system libc, but can also be
-//!   provided by the [rlibc crate](https://crates.io/crates/rlibc).
+//!   provided by the [compiler-builtins crate](https://crates.io/crates/compiler_builtins).
 //!
 //! * `rust_begin_panic` - This function takes four arguments, a
 //!   `fmt::Arguments`, a `&'static str`, and two `u32`'s. These four arguments

src/libcore/macros.rs

@@ -555,12 +555,12 @@ macro_rules! unimplemented {
 #[macro_export]
 #[unstable(feature = "maybe_uninit", issue = "53491")]
 macro_rules! uninitialized_array {
-    // This `into_inner` is safe because an array of `MaybeUninit` does not
+    // This `into_initialized` 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>; $size]>::uninitialized().into_inner()
+        MaybeUninit::<[MaybeUninit<$t>; $size]>::uninitialized().into_initialized()
     });
 }
 

src/libcore/mem.rs

@@ -1035,7 +1035,42 @@ impl<T: ?Sized> DerefMut for ManuallyDrop<T> {
     }
 }
 
-/// A newtype to construct uninitialized instances of `T`
+/// A newtype to construct uninitialized instances of `T`.
+///
+/// The compiler, in general, assumes that variables are properly initialized
+/// at their respective type.  For example, a variable of reference type must
+/// be aligned and non-NULL.  This is an invariant that must *always* be upheld,
+/// even in unsafe code.  As a consequence, 0-initializing a variable of reference
+/// type causes instantaneous undefined behavior, no matter whether that reference
+/// ever gets used to access memory:
+/// ```rust,no_run
+/// use std::mem;
+///
+/// let x: &i32 = unsafe { mem::zeroed() }; // undefined behavior!
+/// ```
+/// This is exploited by the compiler for various optimizations, such as eliding
+/// run-time checks and optimizing `enum` layout.
+///
+/// Not initializing memory at all (instead of 0-initializing it) causes the same
+/// issue: after all, the initial value of the variable might just happen to be
+/// one that violates the invariant.
+///
+/// `MaybeUninit` serves to enable unsafe code to deal with uninitialized data:
+/// it is a signal to the compiler indicating that the data here might *not*
+/// be initialized:
+/// ```rust
+/// #![feature(maybe_uninit)]
+/// use std::mem::MaybeUninit;
+///
+/// // Create an explicitly uninitialized reference.
+/// let mut x = MaybeUninit::<&i32>::uninitialized();
+/// // Set it to a valid value.
+/// x.set(&0);
+/// // Extract the initialized data -- this is only allowed *after* properly
+/// // initializing `x`!
+/// let x = unsafe { x.into_initialized() };
+/// ```
+/// The compiler then knows to not optimize this code.
 #[allow(missing_debug_implementations)]
 #[unstable(feature = "maybe_uninit", issue = "53491")]
 // NOTE after stabilizing `MaybeUninit` proceed to deprecate `mem::{uninitialized,zeroed}`
@@ -1084,11 +1119,14 @@ impl<T> MaybeUninit<T> {
     }
 
     /// Set the value of the `MaybeUninit`. This overwrites any previous value without dropping it.
+    /// For your convenience, this also returns a mutable reference to the (now
+    /// safely initialized) content of `self`.
     #[unstable(feature = "maybe_uninit", issue = "53491")]
     #[inline(always)]
-    pub fn set(&mut self, val: T) {
+    pub fn set(&mut self, val: T) -> &mut T {
         unsafe {
             self.value = ManuallyDrop::new(val);
+            self.get_mut()
         }
     }
 
@@ -1102,11 +1140,18 @@ impl<T> MaybeUninit<T> {
     /// state, otherwise this will immediately cause undefined behavior.
     #[unstable(feature = "maybe_uninit", issue = "53491")]
     #[inline(always)]
-    pub unsafe fn into_inner(self) -> T {
+    pub unsafe fn into_initialized(self) -> T {
         intrinsics::panic_if_uninhabited::<T>();
         ManuallyDrop::into_inner(self.value)
     }
 
+    /// Deprecated alternative to `into_initialized`.  Will never get stabilized.
+    /// Exists only to transition stdsimd to `into_initialized`.
+    #[inline(always)]
+    pub(crate) unsafe fn into_inner(self) -> T {
+        self.into_initialized()
+    }
+
     /// Get a reference to the contained value.
     ///
     /// # Unsafety
@@ -1134,16 +1179,16 @@ impl<T> MaybeUninit<T> {
         &mut *self.value
     }
 
-    /// Get a pointer to the contained value. Reading from this pointer will be undefined
-    /// behavior unless the `MaybeUninit` is initialized.
+    /// Get a pointer to the contained value. Reading from this pointer or turning it
+    /// into a reference will be undefined behavior unless the `MaybeUninit` is initialized.
     #[unstable(feature = "maybe_uninit", issue = "53491")]
     #[inline(always)]
     pub fn as_ptr(&self) -> *const T {
         unsafe { &*self.value as *const T }
     }
 
-    /// Get a mutable pointer to the contained value. Reading from this pointer will be undefined
-    /// behavior unless the `MaybeUninit` is initialized.
+    /// Get a mutable pointer to the contained value. Reading from this pointer or turning it
+    /// into a reference will be undefined behavior unless the `MaybeUninit` is initialized.
     #[unstable(feature = "maybe_uninit", issue = "53491")]
     #[inline(always)]
     pub fn as_mut_ptr(&mut self) -> *mut T {

src/libcore/ops/function.rs

@@ -62,7 +62,7 @@
     label="expected an `Fn<{Args}>` closure, found `{Self}`",
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
-#[must_use]
+#[must_use = "closures are lazy and do nothing unless called"]
 pub trait Fn<Args> : FnMut<Args> {
     /// Performs the call operation.
     #[unstable(feature = "fn_traits", issue = "29625")]
@@ -141,7 +141,7 @@ pub trait Fn<Args> : FnMut<Args> {
     label="expected an `FnMut<{Args}>` closure, found `{Self}`",
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
-#[must_use]
+#[must_use = "closures are lazy and do nothing unless called"]
 pub trait FnMut<Args> : FnOnce<Args> {
     /// Performs the call operation.
     #[unstable(feature = "fn_traits", issue = "29625")]
@@ -220,7 +220,7 @@ pub trait FnMut<Args> : FnOnce<Args> {
     label="expected an `FnOnce<{Args}>` closure, found `{Self}`",
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
-#[must_use]
+#[must_use = "closures are lazy and do nothing unless called"]
 pub trait FnOnce<Args> {
     /// The returned type after the call operator is used.
     #[stable(feature = "fn_once_output", since = "1.12.0")]

src/libcore/ptr.rs

@@ -573,7 +573,7 @@ pub unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
 pub unsafe fn read<T>(src: *const T) -> T {
     let mut tmp = MaybeUninit::<T>::uninitialized();
     copy_nonoverlapping(src, tmp.as_mut_ptr(), 1);
-    tmp.into_inner()
+    tmp.into_initialized()
 }
 
 /// Reads the value from `src` without moving it. This leaves the
@@ -642,7 +642,7 @@ pub unsafe fn read_unaligned<T>(src: *const T) -> T {
     copy_nonoverlapping(src as *const u8,
                         tmp.as_mut_ptr() as *mut u8,
                         mem::size_of::<T>());
-    tmp.into_inner()
+    tmp.into_initialized()
 }
 
 /// Overwrites a memory location with the given value without reading or

src/librustc/hir/map/mod.rs

@@ -934,7 +934,9 @@ impl<'hir> Map<'hir> {
         }
     }
 
-    pub fn expect_variant_data(&self, id: NodeId) -> &'hir VariantData {
+    pub fn expect_variant_data(&self, id: HirId) -> &'hir VariantData {
+        let id = self.hir_to_node_id(id); // FIXME(@ljedrz): remove when possible
+
         match self.find(id) {
             Some(Node::Item(i)) => {
                 match i.node {
@@ -949,7 +951,9 @@ impl<'hir> Map<'hir> {
         }
     }
 
-    pub fn expect_variant(&self, id: NodeId) -> &'hir Variant {
+    pub fn expect_variant(&self, id: HirId) -> &'hir Variant {
+        let id = self.hir_to_node_id(id); // FIXME(@ljedrz): remove when possible
+
         match self.find(id) {
             Some(Node::Variant(variant)) => variant,
             _ => bug!("expected variant, found {}", self.node_to_string(id)),

src/librustc/infer/error_reporting/mod.rs

@@ -56,7 +56,6 @@ use crate::hir::def_id::DefId;
 use crate::hir::Node;
 use crate::middle::region;
 use std::{cmp, fmt};
-use syntax::ast::DUMMY_NODE_ID;
 use syntax_pos::{Pos, Span};
 use crate::traits::{ObligationCause, ObligationCauseCode};
 use crate::ty::error::TypeError;
@@ -182,8 +181,8 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         let cm = self.sess.source_map();
 
         let scope = region.free_region_binding_scope(self);
-        let node = self.hir().as_local_node_id(scope).unwrap_or(DUMMY_NODE_ID);
-        let tag = match self.hir().find(node) {
+        let node = self.hir().as_local_hir_id(scope).unwrap_or(hir::DUMMY_HIR_ID);
+        let tag = match self.hir().find_by_hir_id(node) {
             Some(Node::Block(_)) | Some(Node::Expr(_)) => "body",
             Some(Node::Item(it)) => Self::item_scope_tag(&it),
             Some(Node::TraitItem(it)) => Self::trait_item_scope_tag(&it),
@@ -192,7 +191,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         };
         let (prefix, span) = match *region {
             ty::ReEarlyBound(ref br) => {
-                let mut sp = cm.def_span(self.hir().span(node));
+                let mut sp = cm.def_span(self.hir().span_by_hir_id(node));
                 if let Some(param) = self.hir()
                     .get_generics(scope)
                     .and_then(|generics| generics.get_named(&br.name))
@@ -205,7 +204,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                 bound_region: ty::BoundRegion::BrNamed(_, ref name),
                 ..
             }) => {
-                let mut sp = cm.def_span(self.hir().span(node));
+                let mut sp = cm.def_span(self.hir().span_by_hir_id(node));
                 if let Some(param) = self.hir()
                     .get_generics(scope)
                     .and_then(|generics| generics.get_named(&name))
@@ -217,15 +216,15 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             ty::ReFree(ref fr) => match fr.bound_region {
                 ty::BrAnon(idx) => (
                     format!("the anonymous lifetime #{} defined on", idx + 1),
-                    self.hir().span(node),
+                    self.hir().span_by_hir_id(node),
                 ),
                 ty::BrFresh(_) => (
                     "an anonymous lifetime defined on".to_owned(),
-                    self.hir().span(node),
+                    self.hir().span_by_hir_id(node),
                 ),
                 _ => (
                     format!("the lifetime {} as defined on", fr.bound_region),
-                    cm.def_span(self.hir().span(node)),
+                    cm.def_span(self.hir().span_by_hir_id(node)),
                 ),
             },
             _ => bug!(),
@@ -1451,8 +1450,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                 format!(" for lifetime parameter `{}` in coherence check", name)
             }
             infer::UpvarRegion(ref upvar_id, _) => {
-                let var_node_id = self.tcx.hir().hir_to_node_id(upvar_id.var_path.hir_id);
-                let var_name = self.tcx.hir().name(var_node_id);
+                let var_name = self.tcx.hir().name_by_hir_id(upvar_id.var_path.hir_id);
                 format!(" for capture of `{}` by closure", var_name)
             }
             infer::NLL(..) => bug!("NLL variable found in lexical phase"),

src/librustc/infer/error_reporting/note.rs

@@ -31,8 +31,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                               "...so that reference does not outlive borrowed content");
             }
             infer::ReborrowUpvar(span, ref upvar_id) => {
-                let var_node_id = self.tcx.hir().hir_to_node_id(upvar_id.var_path.hir_id);
-                let var_name = self.tcx.hir().name(var_node_id);
+                let var_name = self.tcx.hir().name_by_hir_id(upvar_id.var_path.hir_id);
                 err.span_note(span,
                               &format!("...so that closure can access `{}`", var_name));
             }
@@ -164,8 +163,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                 err
             }
             infer::ReborrowUpvar(span, ref upvar_id) => {
-                let var_node_id = self.tcx.hir().hir_to_node_id(upvar_id.var_path.hir_id);
-                let var_name = self.tcx.hir().name(var_node_id);
+                let var_name = self.tcx.hir().name_by_hir_id(upvar_id.var_path.hir_id);
                 let mut err = struct_span_err!(self.tcx.sess,
                                                span,
                                                E0313,