Rollup of 8 pull requests

src/etc/lldb_rust_formatters.py

@@ -290,6 +290,8 @@ def render_element(i):
 
 
 def read_utf8_string(ptr_val, byte_count):
+    if byte_count == 0:
+        return '""'
     error = lldb.SBError()
     process = ptr_val.get_wrapped_value().GetProcess()
     data = process.ReadMemory(ptr_val.as_integer(), byte_count, error)

src/libcore/benches/iter.rs

@@ -185,13 +185,13 @@ bench_sums! {
 bench_sums! {
     bench_filter_sum,
     bench_filter_ref_sum,
-    (0i64..1000000).filter(|x| x % 2 == 0)
+    (0i64..1000000).filter(|x| x % 3 == 0)
 }
 
 bench_sums! {
     bench_filter_chain_sum,
     bench_filter_chain_ref_sum,
-    (0i64..1000000).chain(0..1000000).filter(|x| x % 2 == 0)
+    (0i64..1000000).chain(0..1000000).filter(|x| x % 3 == 0)
 }
 
 bench_sums! {
@@ -306,3 +306,31 @@ fn bench_skip_then_zip(b: &mut Bencher) {
         assert_eq!(s, 2009900);
     });
 }
+
+#[bench]
+fn bench_filter_count(b: &mut Bencher) {
+    b.iter(|| {
+        (0i64..1000000).map(black_box).filter(|x| x % 3 == 0).count()
+    })
+}
+
+#[bench]
+fn bench_filter_ref_count(b: &mut Bencher) {
+    b.iter(|| {
+        (0i64..1000000).map(black_box).by_ref().filter(|x| x % 3 == 0).count()
+    })
+}
+
+#[bench]
+fn bench_filter_chain_count(b: &mut Bencher) {
+    b.iter(|| {
+        (0i64..1000000).chain(0..1000000).map(black_box).filter(|x| x % 3 == 0).count()
+    })
+}
+
+#[bench]
+fn bench_filter_chain_ref_count(b: &mut Bencher) {
+    b.iter(|| {
+        (0i64..1000000).chain(0..1000000).map(black_box).by_ref().filter(|x| x % 3 == 0).count()
+    })
+}

src/libcore/convert.rs

@@ -361,11 +361,17 @@ pub trait From<T>: Sized {
 /// An attempted conversion that consumes `self`, which may or may not be
 /// expensive.
 ///
-/// Library authors should not directly implement this trait, but should prefer
-/// implementing the [`TryFrom`] trait, which offers greater flexibility and
-/// provides an equivalent `TryInto` implementation for free, thanks to a
-/// blanket implementation in the standard library. For more information on this,
-/// see the documentation for [`Into`].
+/// Library authors should usually not directly implement this trait,
+/// but should prefer implementing the [`TryFrom`] trait, which offers
+/// greater flexibility and provides an equivalent `TryInto`
+/// implementation for free, thanks to a blanket implementation in the
+/// standard library. For more information on this, see the
+/// documentation for [`Into`].
+///
+/// # Implementing `TryInto`
+///
+/// This suffers the same restrictions and reasoning as implementing
+/// [`Into`], see there for details.
 ///
 /// [`TryFrom`]: trait.TryFrom.html
 /// [`Into`]: trait.Into.html
@@ -380,7 +386,56 @@ pub trait TryInto<T>: Sized {
     fn try_into(self) -> Result<T, Self::Error>;
 }
 
-/// Attempt to construct `Self` via a conversion.
+/// Simple and safe type conversions that may fail in a controlled
+/// way under some circumstances. It is the reciprocal of [`TryInto`].
+///
+/// This is useful when you are doing a type conversion that may
+/// trivially succeed but may also need special handling.
+/// For example, there is no way to convert an `i64` into an `i32`
+/// using the [`From`] trait, because an `i64` may contain a value
+/// that an `i32` cannot represent and so the conversion would lose data.
+/// This might be handled by truncating the `i64` to an `i32` (essentially
+/// giving the `i64`'s value modulo `i32::MAX`) or by simply returning
+/// `i32::MAX`, or by some other method.  The `From` trait is intended
+/// for perfect conversions, so the `TryFrom` trait informs the
+/// programmer when a type conversion could go bad and lets them
+/// decide how to handle it.
+///
+/// # Generic Implementations
+///
+/// - `TryFrom<T> for U` implies [`TryInto<U>`]` for T`
+/// - [`try_from`] is reflexive, which means that `TryFrom<T> for T`
+/// is implemented and cannot fail -- the associated `Error` type for
+/// calling `T::try_from()` on a value of type `T` is `Infallible`.
+/// When the `!` type is stablized `Infallible` and `!` will be
+/// equivalent.
+///
+/// # Examples
+///
+/// As described, [`i32`] implements `TryFrom<i64>`:
+///
+/// ```
+/// #![feature(try_from)]
+/// use std::convert::TryFrom;
+///
+/// let big_number = 1_000_000_000_000i64;
+/// // Silently truncates `big_number`, requires detecting
+/// // and handling the truncation after the fact.
+/// let smaller_number = big_number as i32;
+/// assert_eq!(smaller_number, -727379968);
+///
+/// // Returns an error because `big_number` is too big to
+/// // fit in an `i32`.
+/// let try_smaller_number = i32::try_from(big_number);
+/// assert!(try_smaller_number.is_err());
+///
+/// // Returns `Ok(3)`.
+/// let try_successful_smaller_number = i32::try_from(3);
+/// assert!(try_successful_smaller_number.is_ok());
+/// ```
+///
+/// [`try_from`]: trait.TryFrom.html#tymethod.try_from
+/// [`TryInto`]: trait.TryInto.html
 #[stable(feature = "try_from", since = "1.34.0")]
 pub trait TryFrom<T>: Sized {
     /// The type returned in the event of a conversion error.

src/libcore/iter/adapters/mod.rs

@@ -681,12 +681,7 @@ impl<I: Iterator, P> Iterator for Filter<I, P> where P: FnMut(&I::Item) -> bool
 
     #[inline]
     fn next(&mut self) -> Option<I::Item> {
-        for x in &mut self.iter {
-            if (self.predicate)(&x) {
-                return Some(x);
-            }
-        }
-        None
+        self.try_for_each(Err).err()
     }
 
     #[inline]
@@ -707,12 +702,9 @@ impl<I: Iterator, P> Iterator for Filter<I, P> where P: FnMut(&I::Item) -> bool
     // Using the branchless version will also simplify the LLVM byte code, thus
     // leaving more budget for LLVM optimizations.
     #[inline]
-    fn count(mut self) -> usize {
-        let mut count = 0;
-        for x in &mut self.iter {
-            count += (self.predicate)(&x) as usize;
-        }
-        count
+    fn count(self) -> usize {
+        let mut predicate = self.predicate;
+        self.iter.map(|x| predicate(&x) as usize).sum()
     }
 
     #[inline]
@@ -746,12 +738,7 @@ impl<I: DoubleEndedIterator, P> DoubleEndedIterator for Filter<I, P>
 {
     #[inline]
     fn next_back(&mut self) -> Option<I::Item> {
-        for x in self.iter.by_ref().rev() {
-            if (self.predicate)(&x) {
-                return Some(x);
-            }
-        }
-        None
+        self.try_rfold((), |_, x| Err(x)).err()
     }
 
     #[inline]
@@ -820,12 +807,7 @@ impl<B, I: Iterator, F> Iterator for FilterMap<I, F>
 
     #[inline]
     fn next(&mut self) -> Option<B> {
-        for x in self.iter.by_ref() {
-            if let Some(y) = (self.f)(x) {
-                return Some(y);
-            }
-        }
-        None
+        self.try_for_each(Err).err()
     }
 
     #[inline]
@@ -863,12 +845,7 @@ impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for FilterMap<I, F>
 {
     #[inline]
     fn next_back(&mut self) -> Option<B> {
-        for x in self.iter.by_ref().rev() {
-            if let Some(y) = (self.f)(x) {
-                return Some(y);
-            }
-        }
-        None
+        self.try_rfold((), |_, x| Err(x)).err()
     }
 
     #[inline]

src/libcore/mem.rs

@@ -900,10 +900,16 @@ pub fn discriminant<T>(v: &T) -> Discriminant<T> {
     }
 }
 
+// FIXME: Reference `MaybeUninit` from these docs, once that is stable.
 /// A wrapper to inhibit compiler from automatically calling `T`’s destructor.
 ///
 /// This wrapper is 0-cost.
 ///
+/// `ManuallyDrop<T>` is subject to the same layout optimizations as `T`.
+/// As a consequence, it has *no effect* on the assumptions that the compiler makes
+/// about all values being initialized at their type.  In particular, initializing
+/// a `ManuallyDrop<&mut T>` with [`mem::zeroed`] is undefined behavior.
+///
 /// # Examples
 ///
 /// This wrapper helps with explicitly documenting the drop order dependencies between fields of
@@ -935,6 +941,8 @@ pub fn discriminant<T>(v: &T) -> Discriminant<T> {
 ///     }
 /// }
 /// ```
+///
+/// [`mem::zeroed']: fn.zeroed.html
 #[stable(feature = "manually_drop", since = "1.20.0")]
 #[lang = "manually_drop"]
 #[derive(Copy, Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]

src/libcore/num/mod.rs

@@ -4544,6 +4544,9 @@ macro_rules! try_from_unbounded {
         impl TryFrom<$source> for $target {
             type Error = TryFromIntError;
 
+            /// Try to create the target number type from a source
+            /// number type. This returns an error if the source value
+            /// is outside of the range of the target type.
             #[inline]
             fn try_from(value: $source) -> Result<Self, Self::Error> {
                 Ok(value as $target)
@@ -4559,6 +4562,9 @@ macro_rules! try_from_lower_bounded {
         impl TryFrom<$source> for $target {
             type Error = TryFromIntError;
 
+            /// Try to create the target number type from a source
+            /// number type. This returns an error if the source value
+            /// is outside of the range of the target type.
             #[inline]
             fn try_from(u: $source) -> Result<$target, TryFromIntError> {
                 if u >= 0 {
@@ -4578,6 +4584,9 @@ macro_rules! try_from_upper_bounded {
         impl TryFrom<$source> for $target {
             type Error = TryFromIntError;
 
+            /// Try to create the target number type from a source
+            /// number type. This returns an error if the source value
+            /// is outside of the range of the target type.
             #[inline]
             fn try_from(u: $source) -> Result<$target, TryFromIntError> {
                 if u > (<$target>::max_value() as $source) {
@@ -4597,6 +4606,9 @@ macro_rules! try_from_both_bounded {
         impl TryFrom<$source> for $target {
             type Error = TryFromIntError;
 
+            /// Try to create the target number type from a source
+            /// number type. This returns an error if the source value
+            /// is outside of the range of the target type.
             #[inline]
             fn try_from(u: $source) -> Result<$target, TryFromIntError> {
                 let min = <$target>::min_value() as $source;

src/libcore/str/mod.rs

@@ -3965,7 +3965,7 @@ impl str {
         me.make_ascii_lowercase()
     }
 
-    /// Return an iterator that escapes each char in `s` with [`char::escape_debug`].
+    /// Return an iterator that escapes each char in `self` with [`char::escape_debug`].
     ///
     /// Note: only extended grapheme codepoints that begin the string will be
     /// escaped.
@@ -4013,7 +4013,7 @@ impl str {
         }
     }
 
-    /// Return an iterator that escapes each char in `s` with [`char::escape_default`].
+    /// Return an iterator that escapes each char in `self` with [`char::escape_default`].
     ///
     /// [`char::escape_default`]: ../std/primitive.char.html#method.escape_default
     ///
@@ -4051,7 +4051,7 @@ impl str {
         EscapeDefault { inner: self.chars().flat_map(CharEscapeDefault) }
     }
 
-    /// Return an iterator that escapes each char in `s` with [`char::escape_unicode`].
+    /// Return an iterator that escapes each char in `self` with [`char::escape_unicode`].
     ///
     /// [`char::escape_unicode`]: ../std/primitive.char.html#method.escape_unicode
     ///

src/librustc/ich/impls_mir.rs

@@ -209,13 +209,13 @@ impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for mir::Place<'gcx> {
                                           hasher: &mut StableHasher<W>) {
         mem::discriminant(self).hash_stable(hcx, hasher);
         match *self {
-            mir::Place::Local(ref local) => {
+            mir::Place::Base(mir::PlaceBase::Local(ref local)) => {
                 local.hash_stable(hcx, hasher);
             }
-            mir::Place::Static(ref statik) => {
+            mir::Place::Base(mir::PlaceBase::Static(ref statik)) => {
                 statik.hash_stable(hcx, hasher);
             }
-            mir::Place::Promoted(ref promoted) => {
+            mir::Place::Base(mir::PlaceBase::Promoted(ref promoted)) => {
                 promoted.hash_stable(hcx, hasher);
             }
             mir::Place::Projection(ref place_projection) => {

src/librustc/lint/mod.rs

@@ -132,14 +132,22 @@ macro_rules! declare_lint {
 
 #[macro_export]
 macro_rules! declare_tool_lint {
-    ($vis: vis $tool: ident ::$NAME: ident, $Level: ident, $desc: expr) => (
-        declare_tool_lint!{$vis $tool::$NAME, $Level, $desc, false}
+    (
+        $(#[$attr:meta])* $vis:vis $tool:ident ::$NAME:ident, $Level: ident, $desc: expr
+    ) => (
+        declare_tool_lint!{$(#[$attr])* $vis $tool::$NAME, $Level, $desc, false}
     );
-    ($vis: vis $tool: ident ::$NAME: ident, $Level: ident, $desc: expr,
-     report_in_external_macro: $rep: expr) => (
-         declare_tool_lint!{$vis $tool::$NAME, $Level, $desc, $rep}
+    (
+        $(#[$attr:meta])* $vis:vis $tool:ident ::$NAME:ident, $Level:ident, $desc:expr,
+        report_in_external_macro: $rep:expr
+    ) => (
+         declare_tool_lint!{$(#[$attr])* $vis $tool::$NAME, $Level, $desc, $rep}
     );
-    ($vis: vis $tool: ident ::$NAME: ident, $Level: ident, $desc: expr, $external: expr) => (
+    (
+        $(#[$attr:meta])* $vis:vis $tool:ident ::$NAME:ident, $Level:ident, $desc:expr,
+        $external:expr
+    ) => (
+        $(#[$attr])*
         $vis static $NAME: &$crate::lint::Lint = &$crate::lint::Lint {
             name: &concat!(stringify!($tool), "::", stringify!($NAME)),
             default_level: $crate::lint::$Level,