Auto merge of #60949 - Centril:rollup-f918e1v, r=Centril

Rollup of 8 pull requests

Successful merges:

 - #60370 (Mark core::alloc::Layout::from_size_align_unchecked const)
 - #60678 (Stabilize vecdeque_rotate)
 - #60924 (Explain that ? converts the error type using From)
 - #60931 (Use iter() for iterating arrays by slice)
 - #60934 (Declare DefIndex with the newtype_index macro)
 - #60943 (fix copy-paste typo in docs for ptr::read_volatile)
 - #60945 (Simplify BufRead::fill_buf doc example using NLL)
 - #60947 (Fix typos in docs of GlobalAlloc)

Failed merges:

r? @ghost

31 files changed, 108 insertions, 101 deletions

diff --git a/src/liballoc/collections/vec_deque.rs b/src/liballoc/collections/vec_deque.rs
index 9a8d48083e6..31e49d06a7b 100644
--- a/src/liballoc/collections/vec_deque.rs
+++ b/src/liballoc/collections/vec_deque.rs
@@ -1948,8 +1948,6 @@ impl<T> VecDeque<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(vecdeque_rotate)]
-    ///
     /// use std::collections::VecDeque;
     ///
     /// let mut buf: VecDeque<_> = (0..10).collect();
@@ -1963,7 +1961,7 @@ impl<T> VecDeque<T> {
     /// }
     /// assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
     /// ```
-    #[unstable(feature = "vecdeque_rotate", issue = "56686")]
+    #[stable(feature = "vecdeque_rotate", since = "1.36.0")]
     pub fn rotate_left(&mut self, mid: usize) {
         assert!(mid <= self.len());
         let k = self.len() - mid;
@@ -1993,8 +1991,6 @@ impl<T> VecDeque<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(vecdeque_rotate)]
-    ///
     /// use std::collections::VecDeque;
     ///
     /// let mut buf: VecDeque<_> = (0..10).collect();
@@ -2008,7 +2004,7 @@ impl<T> VecDeque<T> {
     /// }
     /// assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
     /// ```
-    #[unstable(feature = "vecdeque_rotate", issue = "56686")]
+    #[stable(feature = "vecdeque_rotate", since = "1.36.0")]
     pub fn rotate_right(&mut self, k: usize) {
         assert!(k <= self.len());
         let mid = self.len() - k;
diff --git a/src/liballoc/tests/btree/set.rs b/src/liballoc/tests/btree/set.rs
index d52814118b3..989beb3b1bf 100644
--- a/src/liballoc/tests/btree/set.rs
+++ b/src/liballoc/tests/btree/set.rs
@@ -143,8 +143,8 @@ fn test_union() {
 #[test]
 // Only tests the simple function definition with respect to intersection
 fn test_is_disjoint() {
-    let one = [1].into_iter().collect::<BTreeSet<_>>();
-    let two = [2].into_iter().collect::<BTreeSet<_>>();
+    let one = [1].iter().collect::<BTreeSet<_>>();
+    let two = [2].iter().collect::<BTreeSet<_>>();
     assert!(one.is_disjoint(&two));
 }
 
diff --git a/src/liballoc/tests/lib.rs b/src/liballoc/tests/lib.rs
index b736750c576..ddb3120e89d 100644
--- a/src/liballoc/tests/lib.rs
+++ b/src/liballoc/tests/lib.rs
@@ -6,7 +6,6 @@
 #![feature(repeat_generic_slice)]
 #![feature(try_reserve)]
 #![feature(unboxed_closures)]
-#![feature(vecdeque_rotate)]
 #![deny(rust_2018_idioms)]
 
 use std::hash::{Hash, Hasher};
diff --git a/src/libcore/alloc.rs b/src/libcore/alloc.rs
index c124457118c..f25631e028e 100644
--- a/src/libcore/alloc.rs
+++ b/src/libcore/alloc.rs
@@ -99,7 +99,7 @@ impl Layout {
     /// [`Layout::from_size_align`](#method.from_size_align).
     #[stable(feature = "alloc_layout", since = "1.28.0")]
     #[inline]
-    pub unsafe fn from_size_align_unchecked(size: usize, align: usize) -> Self {
+    pub const unsafe fn from_size_align_unchecked(size: usize, align: usize) -> Self {
         Layout { size_: size, align_: NonZeroUsize::new_unchecked(align) }
     }
 
@@ -480,7 +480,7 @@ pub unsafe trait GlobalAlloc {
     ///   this allocator,
     ///
     /// * `layout` must be the same layout that was used
-    ///   to allocated that block of memory,
+    ///   to allocate that block of memory,
     #[stable(feature = "global_alloc", since = "1.28.0")]
     unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout);
 
@@ -535,7 +535,7 @@ pub unsafe trait GlobalAlloc {
     /// * `ptr` must be currently allocated via this allocator,
     ///
     /// * `layout` must be the same layout that was used
-    ///   to allocated that block of memory,
+    ///   to allocate that block of memory,
     ///
     /// * `new_size` must be greater than zero.
     ///
diff --git a/src/libcore/iter/traits/iterator.rs b/src/libcore/iter/traits/iterator.rs
index 403f3358105..38c7c9bc4d0 100644
--- a/src/libcore/iter/traits/iterator.rs
+++ b/src/libcore/iter/traits/iterator.rs
@@ -356,7 +356,7 @@ pub trait Iterator {
     ///
     /// ```
     /// let a = [0, 1, 2, 3, 4, 5];
-    /// let mut iter = a.into_iter().step_by(2);
+    /// let mut iter = a.iter().step_by(2);
     ///
     /// assert_eq!(iter.next(), Some(&0));
     /// assert_eq!(iter.next(), Some(&2));
@@ -531,7 +531,7 @@ pub trait Iterator {
     /// ```
     /// let a = [1, 2, 3];
     ///
-    /// let mut iter = a.into_iter().map(|x| 2 * x);
+    /// let mut iter = a.iter().map(|x| 2 * x);
     ///
     /// assert_eq!(iter.next(), Some(2));
     /// assert_eq!(iter.next(), Some(4));
@@ -620,7 +620,7 @@ pub trait Iterator {
     /// ```
     /// let a = [0i32, 1, 2];
     ///
-    /// let mut iter = a.into_iter().filter(|x| x.is_positive());
+    /// let mut iter = a.iter().filter(|x| x.is_positive());
     ///
     /// assert_eq!(iter.next(), Some(&1));
     /// assert_eq!(iter.next(), Some(&2));
@@ -634,7 +634,7 @@ pub trait Iterator {
     /// ```
     /// let a = [0, 1, 2];
     ///
-    /// let mut iter = a.into_iter().filter(|x| **x > 1); // need two *s!
+    /// let mut iter = a.iter().filter(|x| **x > 1); // need two *s!
     ///
     /// assert_eq!(iter.next(), Some(&2));
     /// assert_eq!(iter.next(), None);
@@ -646,7 +646,7 @@ pub trait Iterator {
     /// ```
     /// let a = [0, 1, 2];
     ///
-    /// let mut iter = a.into_iter().filter(|&x| *x > 1); // both & and *
+    /// let mut iter = a.iter().filter(|&x| *x > 1); // both & and *
     ///
     /// assert_eq!(iter.next(), Some(&2));
     /// assert_eq!(iter.next(), None);
@@ -657,7 +657,7 @@ pub trait Iterator {
     /// ```
     /// let a = [0, 1, 2];
     ///
-    /// let mut iter = a.into_iter().filter(|&&x| x > 1); // two &s
+    /// let mut iter = a.iter().filter(|&&x| x > 1); // two &s
     ///
     /// assert_eq!(iter.next(), Some(&2));
     /// assert_eq!(iter.next(), None);
@@ -837,7 +837,7 @@ pub trait Iterator {
     /// ```
     /// let a = [-1i32, 0, 1];
     ///
-    /// let mut iter = a.into_iter().skip_while(|x| x.is_negative());
+    /// let mut iter = a.iter().skip_while(|x| x.is_negative());
     ///
     /// assert_eq!(iter.next(), Some(&0));
     /// assert_eq!(iter.next(), Some(&1));
@@ -851,7 +851,7 @@ pub trait Iterator {
     /// ```
     /// let a = [-1, 0, 1];
     ///
-    /// let mut iter = a.into_iter().skip_while(|x| **x < 0); // need two *s!
+    /// let mut iter = a.iter().skip_while(|x| **x < 0); // need two *s!
     ///
     /// assert_eq!(iter.next(), Some(&0));
     /// assert_eq!(iter.next(), Some(&1));
@@ -863,7 +863,7 @@ pub trait Iterator {
     /// ```
     /// let a = [-1, 0, 1, -2];
     ///
-    /// let mut iter = a.into_iter().skip_while(|x| **x < 0);
+    /// let mut iter = a.iter().skip_while(|x| **x < 0);
     ///
     /// assert_eq!(iter.next(), Some(&0));
     /// assert_eq!(iter.next(), Some(&1));
@@ -898,7 +898,7 @@ pub trait Iterator {
     /// ```
     /// let a = [-1i32, 0, 1];
     ///
-    /// let mut iter = a.into_iter().take_while(|x| x.is_negative());
+    /// let mut iter = a.iter().take_while(|x| x.is_negative());
     ///
     /// assert_eq!(iter.next(), Some(&-1));
     /// assert_eq!(iter.next(), None);
@@ -911,7 +911,7 @@ pub trait Iterator {
     /// ```
     /// let a = [-1, 0, 1];
     ///
-    /// let mut iter = a.into_iter().take_while(|x| **x < 0); // need two *s!
+    /// let mut iter = a.iter().take_while(|x| **x < 0); // need two *s!
     ///
     /// assert_eq!(iter.next(), Some(&-1));
     /// assert_eq!(iter.next(), None);
@@ -922,7 +922,7 @@ pub trait Iterator {
     /// ```
     /// let a = [-1, 0, 1, -2];
     ///
-    /// let mut iter = a.into_iter().take_while(|x| **x < 0);
+    /// let mut iter = a.iter().take_while(|x| **x < 0);
     ///
     /// assert_eq!(iter.next(), Some(&-1));
     ///
@@ -937,7 +937,7 @@ pub trait Iterator {
     ///
     /// ```
     /// let a = [1, 2, 3, 4];
-    /// let mut iter = a.into_iter();
+    /// let mut iter = a.iter();
     ///
     /// let result: Vec<i32> = iter.by_ref()
     ///                            .take_while(|n| **n != 3)
@@ -1321,7 +1321,7 @@ pub trait Iterator {
     /// ```
     /// let a = [1, 2, 3];
     ///
-    /// let iter = a.into_iter();
+    /// let iter = a.iter();
     ///
     /// let sum: i32 = iter.take(5).fold(0, |acc, i| acc + i );
     ///
@@ -1334,7 +1334,7 @@ pub trait Iterator {
     /// // let's try that again
     /// let a = [1, 2, 3];
     ///
-    /// let mut iter = a.into_iter();
+    /// let mut iter = a.iter();
     ///
     /// // instead, we add in a .by_ref()
     /// let sum: i32 = iter.by_ref().take(2).fold(0, |acc, i| acc + i );
@@ -1479,7 +1479,7 @@ pub trait Iterator {
     /// let a = [1, 2, 3];
     ///
     /// let (even, odd): (Vec<i32>, Vec<i32>) = a
-    ///     .into_iter()
+    ///     .iter()
     ///     .partition(|&n| n % 2 == 0);
     ///
     /// assert_eq!(even, vec![2]);
diff --git a/src/libcore/ptr.rs b/src/libcore/ptr.rs
index b6de9f57b01..ada784e9ce7 100644
--- a/src/libcore/ptr.rs
+++ b/src/libcore/ptr.rs
@@ -837,7 +837,7 @@ pub unsafe fn write_unaligned<T>(dst: *mut T, src: T) {
 ///
 /// * `src` must be properly aligned.
 ///
-/// Like [`read`], `read_unaligned` creates a bitwise copy of `T`, regardless of
+/// Like [`read`], `read_volatile` creates a bitwise copy of `T`, regardless of
 /// whether `T` is [`Copy`]. If `T` is not [`Copy`], using both the returned
 /// value and the value at `*src` can [violate memory safety][read-ownership].
 /// However, storing non-[`Copy`] types in volatile memory is almost certainly
diff --git a/src/libcore/tests/alloc.rs b/src/libcore/tests/alloc.rs
new file mode 100644
index 00000000000..63537ba23d8
--- /dev/null
+++ b/src/libcore/tests/alloc.rs
@@ -0,0 +1,10 @@
+use core::alloc::Layout;
+
+#[test]
+fn const_unchecked_layout() {
+    const SIZE: usize = 0x2000;
+    const ALIGN: usize = 0x1000;
+    const LAYOUT: Layout = unsafe { Layout::from_size_align_unchecked(SIZE, ALIGN) };
+    assert_eq!(LAYOUT.size(), SIZE);
+    assert_eq!(LAYOUT.align(), ALIGN);
+}
diff --git a/src/libcore/tests/lib.rs b/src/libcore/tests/lib.rs
index b8075ef2942..c617596aba8 100644
--- a/src/libcore/tests/lib.rs
+++ b/src/libcore/tests/lib.rs
@@ -31,10 +31,12 @@
 #![feature(slice_partition_dedup)]
 #![feature(copy_within)]
 #![feature(int_error_matching)]
+#![feature(const_fn)]
 #![warn(rust_2018_idioms)]
 
 extern crate test;
 
+mod alloc;
 mod any;
 mod array;
 mod ascii;
diff --git a/src/librustc/hir/def_id.rs b/src/librustc/hir/def_id.rs
index b268a1a494d..0c4f5fb3fc1 100644
--- a/src/librustc/hir/def_id.rs
+++ b/src/librustc/hir/def_id.rs
@@ -96,34 +96,20 @@ impl fmt::Display for CrateNum {
 impl serialize::UseSpecializedEncodable for CrateNum {}
 impl serialize::UseSpecializedDecodable for CrateNum {}
 
-/// A DefIndex is an index into the hir-map for a crate, identifying a
-/// particular definition. It should really be considered an interned
-/// shorthand for a particular DefPath.
-#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Copy)]
-pub struct DefIndex(u32);
-
-/// The crate root is always assigned index 0 by the AST Map code,
-/// thanks to `NodeCollector::new`.
-pub const CRATE_DEF_INDEX: DefIndex = DefIndex(0);
+newtype_index! {
+    /// A DefIndex is an index into the hir-map for a crate, identifying a
+    /// particular definition. It should really be considered an interned
+    /// shorthand for a particular DefPath.
+    pub struct DefIndex {
+        DEBUG_FORMAT = "DefIndex({})",
 
-impl fmt::Debug for DefIndex {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "DefIndex({})", self.as_array_index())
+        /// The crate root is always assigned index 0 by the AST Map code,
+        /// thanks to `NodeCollector::new`.
+        const CRATE_DEF_INDEX = 0,
     }
 }
 
 impl DefIndex {
-    /// Converts this DefIndex into a zero-based array index.
-    #[inline]
-    pub fn as_array_index(&self) -> usize {
-        self.0 as usize
-    }
-
-    #[inline]
-    pub fn from_array_index(i: usize) -> DefIndex {
-        DefIndex(i as u32)
-    }
-
     // Proc macros from a proc-macro crate have a kind of virtual DefIndex. This
     // function maps the index of the macro within the crate (which is also the
     // index of the macro in the CrateMetadata::proc_macros array) to the
@@ -132,7 +118,7 @@ impl DefIndex {
         // DefIndex for proc macros start from FIRST_FREE_DEF_INDEX,
         // because the first FIRST_FREE_DEF_INDEX indexes are reserved
         // for internal use.
-        let def_index = DefIndex::from_array_index(
+        let def_index = DefIndex::from(
             proc_macro_index.checked_add(FIRST_FREE_DEF_INDEX)
                 .expect("integer overflow adding `proc_macro_index`"));
         assert!(def_index != CRATE_DEF_INDEX);
@@ -141,19 +127,11 @@ impl DefIndex {
 
     // This function is the reverse of from_proc_macro_index() above.
     pub fn to_proc_macro_index(self: DefIndex) -> usize {
-        self.as_array_index().checked_sub(FIRST_FREE_DEF_INDEX)
+        self.index().checked_sub(FIRST_FREE_DEF_INDEX)
             .unwrap_or_else(|| {
                 bug!("using local index {:?} as proc-macro index", self)
             })
     }
-
-    pub fn from_raw_u32(x: u32) -> DefIndex {
-        DefIndex(x)
-    }
-
-    pub fn as_raw_u32(&self) -> u32 {
-        self.0
-    }
 }
 
 impl serialize::UseSpecializedEncodable for DefIndex {}
@@ -169,7 +147,7 @@ pub struct DefId {
 
 impl fmt::Debug for DefId {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "DefId({}:{}", self.krate, self.index.as_array_index())?;
+        write!(f, "DefId({}:{}", self.krate, self.index.index())?;
 
         ty::tls::with_opt(|opt_tcx| {
             if let Some(tcx) = opt_tcx {
diff --git a/src/librustc/hir/map/collector.rs b/src/librustc/hir/map/collector.rs
index a1cf338bf12..eeba628b3bf 100644
--- a/src/librustc/hir/map/collector.rs
+++ b/src/librustc/hir/map/collector.rs
@@ -226,7 +226,7 @@ impl<'a, 'hir> NodeCollector<'a, 'hir> {
 
     fn insert_entry(&mut self, id: HirId, entry: Entry<'hir>) {
         debug!("hir_map: {:?} => {:?}", id, entry);
-        let local_map = &mut self.map[id.owner.as_array_index()];
+        let local_map = &mut self.map[id.owner.index()];
         let i = id.local_id.as_u32() as usize;
         if local_map.is_none() {
             *local_map = Some(IndexVec::with_capacity(i + 1));
diff --git a/src/librustc/hir/map/definitions.rs b/src/librustc/hir/map/definitions.rs
index 9cb85c4db47..1cc9a2c0e8a 100644
--- a/src/librustc/hir/map/definitions.rs
+++ b/src/librustc/hir/map/definitions.rs
@@ -38,7 +38,7 @@ impl DefPathTable {
                 def_path_hash: DefPathHash)
                 -> DefIndex {
         let index = {
-            let index = DefIndex::from_array_index(self.index_to_key.len());
+            let index = DefIndex::from(self.index_to_key.len());
             debug!("DefPathTable::insert() - {:?} <-> {:?}", key, index);
             self.index_to_key.push(key);
             index
@@ -49,17 +49,17 @@ impl DefPathTable {
     }
 
     pub fn next_id(&self) -> DefIndex {
-        DefIndex::from_array_index(self.index_to_key.len())
+        DefIndex::from(self.index_to_key.len())
     }
 
     #[inline(always)]
     pub fn def_key(&self, index: DefIndex) -> DefKey {
-        self.index_to_key[index.as_array_index()].clone()
+        self.index_to_key[index.index()].clone()
     }
 
     #[inline(always)]
     pub fn def_path_hash(&self, index: DefIndex) -> DefPathHash {
-        let ret = self.def_path_hashes[index.as_array_index()];
+        let ret = self.def_path_hashes[index.index()];
         debug!("def_path_hash({:?}) = {:?}", index, ret);
         return ret
     }
@@ -74,7 +74,7 @@ impl DefPathTable {
                 .map(|(index, &hash)| {
                     let def_id = DefId {
                         krate: cnum,
-                        index: DefIndex::from_array_index(index),
+                        index: DefIndex::from(index),
                     };
                     (hash, def_id)
                 })
@@ -387,7 +387,7 @@ impl Definitions {
     #[inline]
     pub fn as_local_node_id(&self, def_id: DefId) -> Option<ast::NodeId> {
         if def_id.krate == LOCAL_CRATE {
-            let node_id = self.def_index_to_node[def_id.index.as_array_index()];
+            let node_id = self.def_index_to_node[def_id.index.index()];
             if node_id != ast::DUMMY_NODE_ID {
                 return Some(node_id);
             }
@@ -417,7 +417,7 @@ impl Definitions {
 
     #[inline]
     pub fn def_index_to_hir_id(&self, def_index: DefIndex) -> hir::HirId {
-        let node_id = self.def_index_to_node[def_index.as_array_index()];
+        let node_id = self.def_index_to_node[def_index.index()];
         self.node_to_hir_id[node_id]
     }
 
@@ -508,7 +508,7 @@ impl Definitions {
 
         // Create the definition.
         let index = self.table.allocate(key, def_path_hash);
-        assert_eq!(index.as_array_index(), self.def_index_to_node.len());
+        assert_eq!(index.index(), self.def_index_to_node.len());
         self.def_index_to_node.push(node_id);
 
         // Some things for which we allocate DefIndices don't correspond to
@@ -653,7 +653,7 @@ macro_rules! define_global_metadata_kind {
                                           .position(|k| *k == def_key)
                                           .unwrap();
 
-                DefIndex::from_array_index(index)
+                DefIndex::from(index)
             }
 
             fn name(&self) -> Symbol {
diff --git a/src/librustc/hir/map/mod.rs b/src/librustc/hir/map/mod.rs
index b8ee98551a2..4b94f772554 100644
--- a/src/librustc/hir/map/mod.rs
+++ b/src/librustc/hir/map/mod.rs
@@ -189,7 +189,7 @@ pub struct Map<'hir> {
 impl<'hir> Map<'hir> {
     #[inline]
     fn lookup(&self, id: HirId) -> Option<&Entry<'hir>> {
-        let local_map = self.map.get(id.owner.as_array_index())?;
+        let local_map = self.map.get(id.owner.index())?;
         local_map.as_ref()?.get(id.local_id)?.as_ref()
     }
 
@@ -1023,7 +1023,7 @@ impl<'hir> Map<'hir> {
             local_map.iter_enumerated().filter_map(move |(i, entry)| entry.map(move |_| {
                 // Reconstruct the HirId based on the 3 indices we used to find it
                 HirId {
-                    owner: DefIndex::from_array_index(array_index),
+                    owner: DefIndex::from(array_index),
                     local_id: i,
                 }
             }))
diff --git a/src/librustc/infer/lexical_region_resolve/graphviz.rs b/src/librustc/infer/lexical_region_resolve/graphviz.rs
index 073a3f74422..1878afd581d 100644
--- a/src/librustc/infer/lexical_region_resolve/graphviz.rs
+++ b/src/librustc/infer/lexical_region_resolve/graphviz.rs
@@ -56,7 +56,7 @@ pub fn maybe_print_constraints_for<'a, 'gcx, 'tcx>(
     }
 
     let requested_node = env::var("RUST_REGION_GRAPH_NODE")
-        .ok().and_then(|s| s.parse().map(DefIndex::from_raw_u32).ok());
+        .ok().and_then(|s| s.parse().map(DefIndex::from_u32).ok());
 
     if requested_node.is_some() && requested_node != Some(context.index) {
         return;
@@ -90,7 +90,7 @@ pub fn maybe_print_constraints_for<'a, 'gcx, 'tcx>(
             let mut new_str = String::new();
             for c in output_template.chars() {
                 if c == '%' {
-                    new_str.push_str(&context.index.as_raw_u32().to_string());
+                    new_str.push_str(&context.index.as_u32().to_string());
                 } else {
                     new_str.push(c);
                 }
diff --git a/src/librustc/traits/error_reporting.rs b/src/librustc/traits/error_reporting.rs
index df268839710..9019c4a0575 100644
--- a/src/librustc/traits/error_reporting.rs
+++ b/src/librustc/traits/error_reporting.rs
@@ -643,13 +643,16 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                             .map(|s| &s == "?")
                             .unwrap_or(false);
                         let is_from = format!("{}", trait_ref).starts_with("std::convert::From<");
-                        let message = if is_try && is_from {
-                            Some(format!(
+                        let (message, note) = if is_try && is_from {
+                            (Some(format!(
                                 "`?` couldn't convert the error to `{}`",
                                 trait_ref.self_ty(),
+                            )), Some(
+                                "the question mark operation (`?`) implicitly performs a \
+                                 conversion on the error value using the `From` trait".to_owned()
                             ))
                         } else {
-                            message
+                            (message, note)
                         };
 
                         let mut err = struct_span_err!(
diff --git a/src/librustc/traits/specialize/mod.rs b/src/librustc/traits/specialize/mod.rs
index fc20735eb0f..fdd1a821e31 100644
--- a/src/librustc/traits/specialize/mod.rs
+++ b/src/librustc/traits/specialize/mod.rs
@@ -298,7 +298,7 @@ pub(super) fn specialization_graph_provider<'a, 'tcx>(
     // negated `CrateNum` (so remote definitions are visited first) and then
     // by a flattened version of the `DefIndex`.
     trait_impls.sort_unstable_by_key(|def_id| {
-        (-(def_id.krate.as_u32() as i64), def_id.index.as_array_index())
+        (-(def_id.krate.as_u32() as i64), def_id.index.index())
     });
 
     for impl_def_id in trait_impls {
diff --git a/src/librustc_driver/pretty.rs b/src/librustc_driver/pretty.rs
index c74ed5ec30c..812321ff5e6 100644
--- a/src/librustc_driver/pretty.rs
+++ b/src/librustc_driver/pretty.rs
@@ -648,7 +648,7 @@ fn print_flowgraph<'a, 'tcx, W: Write>(variants: Vec<borrowck_dot::Variant>,
     // have to be user friendly.
     let name = format!(
         "hir_id_{}_{}",
-        hir_id.owner.as_array_index(),
+        hir_id.owner.index(),
         hir_id.local_id.index(),
     );
     let lcfg = LabelledCFG {
diff --git a/src/librustc_metadata/decoder.rs b/src/librustc_metadata/decoder.rs
index e950c2815e9..d882fe6f27e 100644
--- a/src/librustc_metadata/decoder.rs
+++ b/src/librustc_metadata/decoder.rs
@@ -264,7 +264,7 @@ impl<'a, 'tcx> SpecializedDecoder<DefId> for DecodeContext<'a, 'tcx> {
 impl<'a, 'tcx> SpecializedDecoder<DefIndex> for DecodeContext<'a, 'tcx> {
     #[inline]
     fn specialized_decode(&mut self) -> Result<DefIndex, Self::Error> {
-        Ok(DefIndex::from_raw_u32(self.read_u32()?))
+        Ok(DefIndex::from_u32(self.read_u32()?))
     }
 }
 
diff --git a/src/librustc_metadata/encoder.rs b/src/librustc_metadata/encoder.rs
index 0ac03526832..939aadcc9ec 100644
--- a/src/librustc_metadata/encoder.rs
+++ b/src/librustc_metadata/encoder.rs
@@ -134,7 +134,7 @@ impl<'a, 'tcx> SpecializedEncoder<DefId> for EncodeContext<'a, 'tcx> {
 impl<'a, 'tcx> SpecializedEncoder<DefIndex> for EncodeContext<'a, 'tcx> {
     #[inline]
     fn specialized_encode(&mut self, def_index: &DefIndex) -> Result<(), Self::Error> {
-        self.emit_u32(def_index.as_raw_u32())
+        self.emit_u32(def_index.as_u32())
     }
 }
 
diff --git a/src/librustc_metadata/index.rs b/src/librustc_metadata/index.rs
index 4c1e39cd0a9..934e871559c 100644
--- a/src/librustc_metadata/index.rs
+++ b/src/librustc_metadata/index.rs
@@ -93,7 +93,7 @@ impl Index {
     pub fn record_index(&mut self, item: DefIndex, entry: Lazy<Entry<'_>>) {
         assert!(entry.position < (u32::MAX as usize));
         let position = entry.position as u32;
-        let array_index = item.as_array_index();
+        let array_index = item.index();
 
         let positions = &mut self.positions;
         assert!(u32::read_from_bytes_at(positions, array_index) == u32::MAX,
@@ -126,7 +126,7 @@ impl<'tcx> LazySeq<Index> {
                def_index,
                self.len);
 
-        let position = u32::read_from_bytes_at(bytes, 1 + def_index.as_array_index());
+        let position = u32::read_from_bytes_at(bytes, 1 + def_index.index());
         if position == u32::MAX {
             debug!("Index::lookup: position=u32::MAX");
             None
diff --git a/src/librustc_mir/util/graphviz.rs b/src/librustc_mir/util/graphviz.rs
index 188da9a82dc..fc4c6b3fd3f 100644
--- a/src/librustc_mir/util/graphviz.rs
+++ b/src/librustc_mir/util/graphviz.rs
@@ -27,7 +27,7 @@ pub fn graphviz_safe_def_name(def_id: DefId) -> String {
     format!(
         "{}_{}",
         def_id.krate.index(),
-        def_id.index.as_array_index(),
+        def_id.index.index(),
     )
 }
 
diff --git a/src/librustc_resolve/macros.rs b/src/librustc_resolve/macros.rs
index 9f3e1c308f6..e34a33ef8fa 100644
--- a/src/librustc_resolve/macros.rs
+++ b/src/librustc_resolve/macros.rs
@@ -172,7 +172,7 @@ impl<'a> base::Resolver for Resolver<'a> {
     fn add_builtin(&mut self, ident: ast::Ident, ext: Lrc<SyntaxExtension>) {
         let def_id = DefId {
             krate: CrateNum::BuiltinMacros,
-            index: DefIndex::from_array_index(self.macro_map.len()),
+            index: DefIndex::from(self.macro_map.len()),
         };
         let kind = ext.kind();
         self.macro_map.insert(def_id, ext);
diff --git a/src/librustc_save_analysis/lib.rs b/src/librustc_save_analysis/lib.rs
index e03da2ed608..d34f5633946 100644
--- a/src/librustc_save_analysis/lib.rs
+++ b/src/librustc_save_analysis/lib.rs
@@ -1170,7 +1170,7 @@ fn generated_code(span: Span) -> bool {
 fn id_from_def_id(id: DefId) -> rls_data::Id {
     rls_data::Id {
         krate: id.krate.as_u32(),
-        index: id.index.as_raw_u32(),
+        index: id.index.as_u32(),
     }
 }
 
diff --git a/src/librustdoc/config.rs b/src/librustdoc/config.rs
index 72421c9decc..4fae7e080b1 100644
--- a/src/librustdoc/config.rs
+++ b/src/librustdoc/config.rs
@@ -538,7 +538,7 @@ fn check_deprecated_options(matches: &getopts::Matches, diag: &errors::Handler)
        "passes",
     ];
 
-    for flag in deprecated_flags.into_iter() {
+    for flag in deprecated_flags.iter() {
         if matches.opt_present(flag) {
             let mut err = diag.struct_warn(&format!("the '{}' flag is considered deprecated",
                                                     flag));
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index 428f4f328b9..2a3bc5e9961 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -143,7 +143,7 @@ impl<'tcx> DocContext<'tcx> {
             crate_num,
             DefId {
                 krate: crate_num,
-                index: DefIndex::from_array_index(def_id.index.as_array_index() + 1),
+                index: DefIndex::from(def_id.index.index() + 1),
             },
         );
 
diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index 3978f10367d..36ce89558db 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -506,7 +506,7 @@ pub fn initial_ids() -> Vec<String> {
      "methods",
      "deref-methods",
      "implementations",
-    ].into_iter().map(|id| (String::from(*id))).collect()
+    ].iter().map(|id| (String::from(*id))).collect()
 }
 
 /// Generates the documentation for `crate` into the directory `dst`
diff --git a/src/libstd/io/mod.rs b/src/libstd/io/mod.rs
index 8fea6251e65..917199f8ea8 100644
--- a/src/libstd/io/mod.rs
+++ b/src/libstd/io/mod.rs
@@ -1579,18 +1579,13 @@ pub trait BufRead: Read {
     /// let stdin = io::stdin();
     /// let mut stdin = stdin.lock();
     ///
-    /// // we can't have two `&mut` references to `stdin`, so use a block
-    /// // to end the borrow early.
-    /// let length = {
-    ///     let buffer = stdin.fill_buf().unwrap();
+    /// let buffer = stdin.fill_buf().unwrap();
     ///
-    ///     // work with buffer
-    ///     println!("{:?}", buffer);
-    ///
-    ///     buffer.len()
-    /// };
+    /// // work with buffer
+    /// println!("{:?}", buffer);
     ///
     /// // ensure the bytes we worked with aren't returned again later
+    /// let length = buffer.len();
     /// stdin.consume(length);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/test/ui/consts/std/alloc.rs b/src/test/ui/consts/std/alloc.rs
new file mode 100644
index 00000000000..65ac7e44926
--- /dev/null
+++ b/src/test/ui/consts/std/alloc.rs
@@ -0,0 +1,10 @@
+use std::alloc::Layout;
+
+// ok
+const LAYOUT_VALID: Layout = unsafe { Layout::from_size_align_unchecked(0x1000, 0x08) };
+
+// not ok, since alignment needs to be non-zero.
+const LAYOUT_INVALID: Layout = unsafe { Layout::from_size_align_unchecked(0x1000, 0x00) };
+//~^ ERROR it is undefined behavior to use this value
+
+fn main() {}
diff --git a/src/test/ui/consts/std/alloc.stderr b/src/test/ui/consts/std/alloc.stderr
new file mode 100644
index 00000000000..74a8f3daf6a
--- /dev/null
+++ b/src/test/ui/consts/std/alloc.stderr
@@ -0,0 +1,11 @@
+error[E0080]: it is undefined behavior to use this value
+  --> $DIR/alloc.rs:7:1
+   |
+LL | const LAYOUT_INVALID: Layout = unsafe { Layout::from_size_align_unchecked(0x1000, 0x00) };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 0 at .align_, but expected something greater or equal to 1
+   |
+   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.
diff --git a/src/test/ui/issues/issue-32709.stderr b/src/test/ui/issues/issue-32709.stderr
index 84cca5b20af..04b8c3aa353 100644
--- a/src/test/ui/issues/issue-32709.stderr
+++ b/src/test/ui/issues/issue-32709.stderr
@@ -4,6 +4,7 @@ error[E0277]: `?` couldn't convert the error to `()`
 LL |     Err(5)?;
    |           ^ the trait `std::convert::From<{integer}>` is not implemented for `()`
    |
+   = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
    = note: required by `std::convert::From::from`
 
 error: aborting due to previous error
diff --git a/src/test/ui/try-block/try-block-bad-type.stderr b/src/test/ui/try-block/try-block-bad-type.stderr
index 7c7366df1dc..e1c2c6b675e 100644
--- a/src/test/ui/try-block/try-block-bad-type.stderr
+++ b/src/test/ui/try-block/try-block-bad-type.stderr
@@ -4,6 +4,7 @@ error[E0277]: `?` couldn't convert the error to `i32`
 LL |         Err("")?;
    |                ^ the trait `std::convert::From<&str>` is not implemented for `i32`
    |
+   = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
    = help: the following implementations were found:
              <i32 as std::convert::From<bool>>
              <i32 as std::convert::From<i16>>
diff --git a/src/test/ui/try-on-option.stderr b/src/test/ui/try-on-option.stderr
index 4465fbe14b7..db5046f8c15 100644
--- a/src/test/ui/try-on-option.stderr
+++ b/src/test/ui/try-on-option.stderr
@@ -4,6 +4,7 @@ error[E0277]: `?` couldn't convert the error to `()`
 LL |     x?;
    |      ^ the trait `std::convert::From<std::option::NoneError>` is not implemented for `()`
    |
+   = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
    = note: required by `std::convert::From::from`
 
 error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `std::ops::Try`)