Auto merge of #56549 - pietroalbini:rollup, r=pietroalbini

Rollup of 15 pull requests

Successful merges:

 - #51753 (Document `From` implementations)
 - #55563 (Improve no result found sentence in doc search)
 - #55987 (Add Weak.ptr_eq)
 - #56119 (Utilize `?` instead of `return None`.)
 - #56372 (Refer to the second borrow as the "second borrow" in E0501.rs)
 - #56388 (More MIR borrow check cleanup)
 - #56424 (Mention raw-ident syntax)
 - #56452 (Remove redundant clones)
 - #56456 (Handle existential types in dead code analysis)
 - #56466 (data_structures: remove tuple_slice)
 - #56476 (Fix invalid line number match)
 - #56497 (cleanup: remove static lifetimes from consts in libstd)
 - #56498 (Fix line numbers display)
 - #56523 (Added a bare-bones eslint config (removing jslint))
 - #56538 (Use inner iterator may_have_side_effect for Cloned)

Failed merges:

r? @ghost

59 files changed, 518 insertions, 418 deletions

diff --git a/src/liballoc/rc.rs b/src/liballoc/rc.rs
index 3ca6de191de..c0a947e7011 100644
--- a/src/liballoc/rc.rs
+++ b/src/liballoc/rc.rs
@@ -1187,8 +1187,9 @@ impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Weak<U>> for Weak<T> {}
 
 impl<T> Weak<T> {
     /// Constructs a new `Weak<T>`, without allocating any memory.
-    /// Calling [`upgrade`][Weak::upgrade] on the return value always gives [`None`].
+    /// Calling [`upgrade`] on the return value always gives [`None`].
     ///
+    /// [`upgrade`]: #method.upgrade
     /// [`None`]: ../../std/option/enum.Option.html
     ///
     /// # Examples
@@ -1260,6 +1261,52 @@ impl<T: ?Sized> Weak<T> {
             Some(unsafe { self.ptr.as_ref() })
         }
     }
+
+    /// Returns true if the two `Weak`s point to the same value (not just values
+    /// that compare as equal).
+    ///
+    /// # Notes
+    ///
+    /// Since this compares pointers it means that `Weak::new()` will equal each
+    /// other, even though they don't point to any value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(weak_ptr_eq)]
+    /// use std::rc::{Rc, Weak};
+    ///
+    /// let first_rc = Rc::new(5);
+    /// let first = Rc::downgrade(&first_rc);
+    /// let second = Rc::downgrade(&first_rc);
+    ///
+    /// assert!(Weak::ptr_eq(&first, &second));
+    ///
+    /// let third_rc = Rc::new(5);
+    /// let third = Rc::downgrade(&third_rc);
+    ///
+    /// assert!(!Weak::ptr_eq(&first, &third));
+    /// ```
+    ///
+    /// Comparing `Weak::new`.
+    ///
+    /// ```
+    /// #![feature(weak_ptr_eq)]
+    /// use std::rc::{Rc, Weak};
+    ///
+    /// let first = Weak::new();
+    /// let second = Weak::new();
+    /// assert!(Weak::ptr_eq(&first, &second));
+    ///
+    /// let third_rc = Rc::new(());
+    /// let third = Rc::downgrade(&third_rc);
+    /// assert!(!Weak::ptr_eq(&first, &third));
+    /// ```
+    #[inline]
+    #[unstable(feature = "weak_ptr_eq", issue = "55981")]
+    pub fn ptr_eq(this: &Self, other: &Self) -> bool {
+        this.ptr.as_ptr() == other.ptr.as_ptr()
+    }
 }
 
 #[stable(feature = "rc_weak", since = "1.4.0")]
diff --git a/src/liballoc/sync.rs b/src/liballoc/sync.rs
index 4f4031e3c4e..0a397f79103 100644
--- a/src/liballoc/sync.rs
+++ b/src/liballoc/sync.rs
@@ -1130,6 +1130,53 @@ impl<T: ?Sized> Weak<T> {
             Some(unsafe { self.ptr.as_ref() })
         }
     }
+
+    /// Returns true if the two `Weak`s point to the same value (not just values
+    /// that compare as equal).
+    ///
+    /// # Notes
+    ///
+    /// Since this compares pointers it means that `Weak::new()` will equal each
+    /// other, even though they don't point to any value.
+    ///
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(weak_ptr_eq)]
+    /// use std::sync::{Arc, Weak};
+    ///
+    /// let first_rc = Arc::new(5);
+    /// let first = Arc::downgrade(&first_rc);
+    /// let second = Arc::downgrade(&first_rc);
+    ///
+    /// assert!(Weak::ptr_eq(&first, &second));
+    ///
+    /// let third_rc = Arc::new(5);
+    /// let third = Arc::downgrade(&third_rc);
+    ///
+    /// assert!(!Weak::ptr_eq(&first, &third));
+    /// ```
+    ///
+    /// Comparing `Weak::new`.
+    ///
+    /// ```
+    /// #![feature(weak_ptr_eq)]
+    /// use std::sync::{Arc, Weak};
+    ///
+    /// let first = Weak::new();
+    /// let second = Weak::new();
+    /// assert!(Weak::ptr_eq(&first, &second));
+    ///
+    /// let third_rc = Arc::new(());
+    /// let third = Arc::downgrade(&third_rc);
+    /// assert!(!Weak::ptr_eq(&first, &third));
+    /// ```
+    #[inline]
+    #[unstable(feature = "weak_ptr_eq", issue = "55981")]
+    pub fn ptr_eq(this: &Self, other: &Self) -> bool {
+        this.ptr.as_ptr() == other.ptr.as_ptr()
+    }
 }
 
 #[stable(feature = "arc_weak", since = "1.4.0")]
diff --git a/src/libcore/iter/mod.rs b/src/libcore/iter/mod.rs
index 62e1f9fcb64..de7ab8843da 100644
--- a/src/libcore/iter/mod.rs
+++ b/src/libcore/iter/mod.rs
@@ -602,7 +602,9 @@ unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
     }
 
     #[inline]
-    fn may_have_side_effect() -> bool { false }
+    fn may_have_side_effect() -> bool {
+        I::may_have_side_effect()
+    }
 }
 
 #[unstable(feature = "trusted_len", issue = "37572")]
diff --git a/src/libcore/macros.rs b/src/libcore/macros.rs
index 8b1855800c2..5ba0e949483 100644
--- a/src/libcore/macros.rs
+++ b/src/libcore/macros.rs
@@ -238,6 +238,10 @@ macro_rules! debug_assert_ne {
 /// with converting downstream errors.
 ///
 /// The `?` operator was added to replace `try!` and should be used instead.
+/// Furthermore, `try` is a reserved word in Rust 2018, so if you must use
+/// it, you will need to use the [raw-identifier syntax][ris]: `r#try`.
+///
+/// [ris]: https://doc.rust-lang.org/nightly/rust-by-example/compatibility/raw_identifiers.html
 ///
 /// `try!` matches the given [`Result`]. In case of the `Ok` variant, the
 /// expression has the value of the wrapped value.
diff --git a/src/libcore/str/mod.rs b/src/libcore/str/mod.rs
index 89efa120a6f..6c953d1b9a0 100644
--- a/src/libcore/str/mod.rs
+++ b/src/libcore/str/mod.rs
@@ -536,10 +536,9 @@ fn next_code_point_reverse<'a, I>(bytes: &mut I) -> Option<u32>
     where I: DoubleEndedIterator<Item = &'a u8>,
 {
     // Decode UTF-8
-    let w = match bytes.next_back() {
-        None => return None,
-        Some(&next_byte) if next_byte < 128 => return Some(next_byte as u32),
-        Some(&back_byte) => back_byte,
+    let w = match *bytes.next_back()? {
+        next_byte if next_byte < 128 => return Some(next_byte as u32),
+        back_byte => back_byte,
     };
 
     // Multibyte case follows
diff --git a/src/libcore/tests/iter.rs b/src/libcore/tests/iter.rs
index 495483db555..19be1a07c5b 100644
--- a/src/libcore/tests/iter.rs
+++ b/src/libcore/tests/iter.rs
@@ -1250,6 +1250,23 @@ fn test_cloned() {
 }
 
 #[test]
+fn test_cloned_side_effects() {
+    let mut count = 0;
+    {
+        let iter = [1, 2, 3]
+            .iter()
+            .map(|x| {
+                count += 1;
+                x
+            })
+            .cloned()
+            .zip(&[1]);
+        for _ in iter {}
+    }
+    assert_eq!(count, 2);
+}
+
+#[test]
 fn test_double_ended_map() {
     let xs = [1, 2, 3, 4, 5, 6];
     let mut it = xs.iter().map(|&x| x * -1);
diff --git a/src/librustc/middle/dead.rs b/src/librustc/middle/dead.rs
index 282b5d13e2c..bb7a6a6ee7b 100644
--- a/src/librustc/middle/dead.rs
+++ b/src/librustc/middle/dead.rs
@@ -166,6 +166,7 @@ impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
                     hir::ItemKind::Fn(..)
                     | hir::ItemKind::Ty(..)
                     | hir::ItemKind::Static(..)
+                    | hir::ItemKind::Existential(..)
                     | hir::ItemKind::Const(..) => {
                         intravisit::walk_item(self, &item);
                     }
diff --git a/src/librustc/middle/region.rs b/src/librustc/middle/region.rs
index 35d1a4dd2cb..3c2551f5cd4 100644
--- a/src/librustc/middle/region.rs
+++ b/src/librustc/middle/region.rs
@@ -592,10 +592,7 @@ impl<'tcx> ScopeTree {
                 return Some(scope.item_local_id());
             }
 
-            match self.opt_encl_scope(scope) {
-                None => return None,
-                Some(parent) => scope = parent,
-            }
+            scope = self.opt_encl_scope(scope)?;
         }
     }
 
diff --git a/src/librustc/session/search_paths.rs b/src/librustc/session/search_paths.rs
index 768d4f1e5fb..6b0a8a0af2b 100644
--- a/src/librustc/session/search_paths.rs
+++ b/src/librustc/session/search_paths.rs
@@ -67,14 +67,13 @@ impl<'a> Iterator for Iter<'a> {
 
     fn next(&mut self) -> Option<(&'a Path, PathKind)> {
         loop {
-            match self.iter.next() {
-                Some(&(kind, ref p)) if self.kind == PathKind::All ||
-                                        kind == PathKind::All ||
-                                        kind == self.kind => {
+            match *self.iter.next()? {
+                (kind, ref p) if self.kind == PathKind::All ||
+                                  kind == PathKind::All ||
+                                  kind == self.kind => {
                     return Some((p, kind))
                 }
-                Some(..) => {}
-                None => return None,
+                _ => {}
             }
         }
     }
diff --git a/src/librustc_borrowck/borrowck/check_loans.rs b/src/librustc_borrowck/borrowck/check_loans.rs
index a802729e3fb..e47e95afb16 100644
--- a/src/librustc_borrowck/borrowck/check_loans.rs
+++ b/src/librustc_borrowck/borrowck/check_loans.rs
@@ -615,7 +615,7 @@ impl<'a, 'tcx> CheckLoanCtxt<'a, 'tcx> {
                     let new_loan_str = &new_loan.kind.to_user_str();
                     self.bccx.cannot_reborrow_already_uniquely_borrowed(
                         new_loan.span, "closure", &nl, &new_loan_msg, new_loan_str,
-                        old_loan.span, &old_loan_msg, previous_end_span, Origin::Ast)
+                        old_loan.span, &old_loan_msg, previous_end_span, "", Origin::Ast)
                 }
                 (..) =>
                     self.bccx.cannot_reborrow_already_borrowed(
diff --git a/src/librustc_data_structures/lib.rs b/src/librustc_data_structures/lib.rs
index 96cb235a933..8e0ecb70c68 100644
--- a/src/librustc_data_structures/lib.rs
+++ b/src/librustc_data_structures/lib.rs
@@ -81,7 +81,6 @@ pub mod sync;
 pub mod tiny_list;
 pub mod thin_vec;
 pub mod transitive_relation;
-pub mod tuple_slice;
 pub use ena::unify;
 pub mod vec_linked_list;
 pub mod work_queue;
diff --git a/src/librustc_data_structures/tuple_slice.rs b/src/librustc_data_structures/tuple_slice.rs
deleted file mode 100644
index b7c71dd3664..00000000000
--- a/src/librustc_data_structures/tuple_slice.rs
+++ /dev/null
@@ -1,70 +0,0 @@
-// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-use std::slice;
-
-/// Allows to view uniform tuples as slices
-pub trait TupleSlice<T> {
-    fn as_slice(&self) -> &[T];
-    fn as_mut_slice(&mut self) -> &mut [T];
-}
-
-macro_rules! impl_tuple_slice {
-    ($tuple_type:ty, $size:expr) => {
-        impl<T> TupleSlice<T> for $tuple_type {
-            fn as_slice(&self) -> &[T] {
-                unsafe {
-                    let ptr = &self.0 as *const T;
-                    slice::from_raw_parts(ptr, $size)
-                }
-            }
-
-            fn as_mut_slice(&mut self) -> &mut [T] {
-                unsafe {
-                    let ptr = &mut self.0 as *mut T;
-                    slice::from_raw_parts_mut(ptr, $size)
-                }
-            }
-        }
-    }
-}
-
-impl_tuple_slice!((T, T), 2);
-impl_tuple_slice!((T, T, T), 3);
-impl_tuple_slice!((T, T, T, T), 4);
-impl_tuple_slice!((T, T, T, T, T), 5);
-impl_tuple_slice!((T, T, T, T, T, T), 6);
-impl_tuple_slice!((T, T, T, T, T, T, T), 7);
-impl_tuple_slice!((T, T, T, T, T, T, T, T), 8);
-
-#[test]
-fn test_sliced_tuples() {
-    let t2 = (100, 101);
-    assert_eq!(t2.as_slice(), &[100, 101]);
-
-    let t3 = (102, 103, 104);
-    assert_eq!(t3.as_slice(), &[102, 103, 104]);
-
-    let t4 = (105, 106, 107, 108);
-    assert_eq!(t4.as_slice(), &[105, 106, 107, 108]);
-
-    let t5 = (109, 110, 111, 112, 113);
-    assert_eq!(t5.as_slice(), &[109, 110, 111, 112, 113]);
-
-    let t6 = (114, 115, 116, 117, 118, 119);
-    assert_eq!(t6.as_slice(), &[114, 115, 116, 117, 118, 119]);
-
-    let t7 = (120, 121, 122, 123, 124, 125, 126);
-    assert_eq!(t7.as_slice(), &[120, 121, 122, 123, 124, 125, 126]);
-
-    let t8 = (127, 128, 129, 130, 131, 132, 133, 134);
-    assert_eq!(t8.as_slice(), &[127, 128, 129, 130, 131, 132, 133, 134]);
-
-}
diff --git a/src/librustc_incremental/persist/work_product.rs b/src/librustc_incremental/persist/work_product.rs
index cfe59b1f672..ddd28eb5393 100644
--- a/src/librustc_incremental/persist/work_product.rs
+++ b/src/librustc_incremental/persist/work_product.rs
@@ -29,7 +29,7 @@ pub fn copy_cgu_workproducts_to_incr_comp_cache_dir(
         return None
     }
 
-    let saved_files: Option<Vec<_>> =
+    let saved_files =
         files.iter()
              .map(|&(kind, ref path)| {
                  let extension = match kind {
@@ -51,11 +51,7 @@ pub fn copy_cgu_workproducts_to_incr_comp_cache_dir(
                      }
                  }
              })
-             .collect();
-    let saved_files = match saved_files {
-        None => return None,
-        Some(v) => v,
-    };
+             .collect::<Option<Vec<_>>>()?;
 
     let work_product = WorkProduct {
         cgu_name: cgu_name.to_string(),
diff --git a/src/librustc_mir/borrow_check/borrow_set.rs b/src/librustc_mir/borrow_check/borrow_set.rs
index fd7dc7fc4bd..947c32df0f6 100644
--- a/src/librustc_mir/borrow_check/borrow_set.rs
+++ b/src/librustc_mir/borrow_check/borrow_set.rs
@@ -16,7 +16,7 @@ use rustc::mir::traversal;
 use rustc::mir::visit::{
     PlaceContext, Visitor, NonUseContext, MutatingUseContext, NonMutatingUseContext
 };
-use rustc::mir::{self, Location, Mir, Place, Local};
+use rustc::mir::{self, Location, Mir, Local};
 use rustc::ty::{RegionVid, TyCtxt};
 use rustc::util::nodemap::{FxHashMap, FxHashSet};
 use rustc_data_structures::indexed_vec::IndexVec;
@@ -41,10 +41,6 @@ crate struct BorrowSet<'tcx> {
     /// only need to store one borrow index
     crate activation_map: FxHashMap<Location, Vec<BorrowIndex>>,
 
-    /// Every borrow has a region; this maps each such regions back to
-    /// its borrow-indexes.
-    crate region_map: FxHashMap<RegionVid, FxHashSet<BorrowIndex>>,
-
     /// Map from local to all the borrows on that local
     crate local_map: FxHashMap<mir::Local, FxHashSet<BorrowIndex>>,
 
@@ -149,7 +145,6 @@ impl<'tcx> BorrowSet<'tcx> {
             idx_vec: IndexVec::new(),
             location_map: Default::default(),
             activation_map: Default::default(),
-            region_map: Default::default(),
             local_map: Default::default(),
             pending_activations: Default::default(),
             locals_state_at_exit:
@@ -164,7 +159,6 @@ impl<'tcx> BorrowSet<'tcx> {
             borrows: visitor.idx_vec,
             location_map: visitor.location_map,
             activation_map: visitor.activation_map,
-            region_map: visitor.region_map,
             local_map: visitor.local_map,
             locals_state_at_exit: visitor.locals_state_at_exit,
         }
@@ -184,7 +178,6 @@ struct GatherBorrows<'a, 'gcx: 'tcx, 'tcx: 'a> {
     idx_vec: IndexVec<BorrowIndex, BorrowData<'tcx>>,
     location_map: FxHashMap<Location, BorrowIndex>,
     activation_map: FxHashMap<Location, Vec<BorrowIndex>>,
-    region_map: FxHashMap<RegionVid, FxHashSet<BorrowIndex>>,
     local_map: FxHashMap<mir::Local, FxHashSet<BorrowIndex>>,
 
     /// When we encounter a 2-phase borrow statement, it will always
@@ -229,7 +222,6 @@ impl<'a, 'gcx, 'tcx> Visitor<'tcx> for GatherBorrows<'a, 'gcx, 'tcx> {
 
             self.insert_as_pending_if_two_phase(location, &assigned_place, kind, idx);
 
-            self.region_map.entry(region).or_default().insert(idx);
             if let Some(local) = borrowed_place.root_local() {
                 self.local_map.entry(local).or_default().insert(idx);
             }
@@ -238,68 +230,68 @@ impl<'a, 'gcx, 'tcx> Visitor<'tcx> for GatherBorrows<'a, 'gcx, 'tcx> {
         self.super_assign(block, assigned_place, rvalue, location)
     }
 
-    fn visit_place(
+    fn visit_local(
         &mut self,
-        place: &mir::Place<'tcx>,
+        temp: &Local,
         context: PlaceContext<'tcx>,
         location: Location,
     ) {
-        self.super_place(place, context, location);
-
-        // We found a use of some temporary TEMP...
-        if let Place::Local(temp) = place {
-            // ... check whether we (earlier) saw a 2-phase borrow like
-            //
-            //     TMP = &mut place
-            if let Some(&borrow_index) = self.pending_activations.get(temp) {
-                let borrow_data = &mut self.idx_vec[borrow_index];
-
-                // Watch out: the use of TMP in the borrow itself
-                // doesn't count as an activation. =)
-                if borrow_data.reserve_location == location &&
-                    context == PlaceContext::MutatingUse(MutatingUseContext::Store)
-                {
-                    return;
-                }
+        if !context.is_use() {
+            return;
+        }
 
-                if let TwoPhaseActivation::ActivatedAt(other_location) =
-                        borrow_data.activation_location {
-                    span_bug!(
-                        self.mir.source_info(location).span,
-                        "found two uses for 2-phase borrow temporary {:?}: \
-                         {:?} and {:?}",
-                        temp,
-                        location,
-                        other_location,
-                    );
-                }
+        // We found a use of some temporary TMP
+        // check whether we (earlier) saw a 2-phase borrow like
+        //
+        //     TMP = &mut place
+        if let Some(&borrow_index) = self.pending_activations.get(temp) {
+            let borrow_data = &mut self.idx_vec[borrow_index];
 
-                // Otherwise, this is the unique later use
-                // that we expect.
-                borrow_data.activation_location = match context {
-                    // The use of TMP in a shared borrow does not
-                    // count as an actual activation.
-                    PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow(..)) |
-                    PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow(..)) =>
-                        TwoPhaseActivation::NotActivated,
-                    _ => {
-                        // Double check: This borrow is indeed a two-phase borrow (that is,
-                        // we are 'transitioning' from `NotActivated` to `ActivatedAt`) and
-                        // we've not found any other activations (checked above).
-                        assert_eq!(
-                            borrow_data.activation_location,
-                            TwoPhaseActivation::NotActivated,
-                            "never found an activation for this borrow!",
-                        );
-
-                        self.activation_map
-                            .entry(location)
-                            .or_default()
-                            .push(borrow_index);
-                        TwoPhaseActivation::ActivatedAt(location)
-                    }
-                };
+            // Watch out: the use of TMP in the borrow itself
+            // doesn't count as an activation. =)
+            if borrow_data.reserve_location == location &&
+                context == PlaceContext::MutatingUse(MutatingUseContext::Store)
+            {
+                return;
+            }
+
+            if let TwoPhaseActivation::ActivatedAt(other_location) =
+                    borrow_data.activation_location {
+                span_bug!(
+                    self.mir.source_info(location).span,
+                    "found two uses for 2-phase borrow temporary {:?}: \
+                     {:?} and {:?}",
+                    temp,
+                    location,
+                    other_location,
+                );
             }
+
+            // Otherwise, this is the unique later use
+            // that we expect.
+            borrow_data.activation_location = match context {
+                // The use of TMP in a shared borrow does not
+                // count as an actual activation.
+                PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow(..)) |
+                PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow(..)) =>
+                    TwoPhaseActivation::NotActivated,
+                _ => {
+                    // Double check: This borrow is indeed a two-phase borrow (that is,
+                    // we are 'transitioning' from `NotActivated` to `ActivatedAt`) and
+                    // we've not found any other activations (checked above).
+                    assert_eq!(
+                        borrow_data.activation_location,
+                        TwoPhaseActivation::NotActivated,
+                        "never found an activation for this borrow!",
+                    );
+
+                    self.activation_map
+                        .entry(location)
+                        .or_default()
+                        .push(borrow_index);
+                    TwoPhaseActivation::ActivatedAt(location)
+                }
+            };
         }
     }
 
diff --git a/src/librustc_mir/borrow_check/error_reporting.rs b/src/librustc_mir/borrow_check/error_reporting.rs
index 4ccd26bee8b..ba26ed36c20 100644
--- a/src/librustc_mir/borrow_check/error_reporting.rs
+++ b/src/librustc_mir/borrow_check/error_reporting.rs
@@ -344,6 +344,13 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
 
         let first_borrow_desc;
 
+        let explanation = self.explain_why_borrow_contains_point(context, issued_borrow, None);
+        let second_borrow_desc = if explanation.is_explained() {
+            "second "
+        } else {
+            ""
+        };
+
         // FIXME: supply non-"" `opt_via` when appropriate
         let mut err = match (
             gen_borrow_kind,
@@ -454,6 +461,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                     issued_span,
                     "",
                     None,
+                    second_borrow_desc,
                     Origin::Mir,
                 )
             }
@@ -469,6 +477,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                     issued_span,
                     "",
                     None,
+                    second_borrow_desc,
                     Origin::Mir,
                 )
             }
@@ -513,7 +522,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
             );
         }
 
-        self.explain_why_borrow_contains_point(context, issued_borrow, None)
+        explanation
             .add_explanation_to_diagnostic(self.infcx.tcx, self.mir, &mut err, first_borrow_desc);
 
         err.buffer(&mut self.errors_buffer);
diff --git a/src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs b/src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs
index bb9a29b055b..477b7892608 100644
--- a/src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs
+++ b/src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs
@@ -52,6 +52,12 @@ pub(in borrow_check) enum LaterUseKind {
 }
 
 impl BorrowExplanation {
+    pub(in borrow_check) fn is_explained(&self) -> bool {
+        match self {
+            BorrowExplanation::Unexplained => false,
+            _ => true,
+        }
+    }
     pub(in borrow_check) fn add_explanation_to_diagnostic<'cx, 'gcx, 'tcx>(
         &self,
         tcx: TyCtxt<'cx, 'gcx, 'tcx>,
diff --git a/src/librustc_mir/borrow_check/prefixes.rs b/src/librustc_mir/borrow_check/prefixes.rs
index f73e08eb135..7d583b4f541 100644
--- a/src/librustc_mir/borrow_check/prefixes.rs
+++ b/src/librustc_mir/borrow_check/prefixes.rs
@@ -87,10 +87,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
 impl<'cx, 'gcx, 'tcx> Iterator for Prefixes<'cx, 'gcx, 'tcx> {
     type Item = &'cx Place<'tcx>;
     fn next(&mut self) -> Option<Self::Item> {
-        let mut cursor = match self.next {
-            None => return None,
-            Some(place) => place,
-        };
+        let mut cursor = self.next?;
 
         // Post-processing `place`: Enqueue any remaining
         // work. Also, `place` may not be a prefix itself, but
diff --git a/src/librustc_mir/dataflow/impls/borrows.rs b/src/librustc_mir/dataflow/impls/borrows.rs
index 27bc28ac81d..3a9e4fc9e4a 100644
--- a/src/librustc_mir/dataflow/impls/borrows.rs
+++ b/src/librustc_mir/dataflow/impls/borrows.rs
@@ -246,7 +246,7 @@ impl<'a, 'gcx, 'tcx> BitDenotation for Borrows<'a, 'gcx, 'tcx> {
                 // re-consider the current implementations of the
                 // propagate_call_return method.
 
-                if let mir::Rvalue::Ref(region, _, ref place) = **rhs {
+                if let mir::Rvalue::Ref(_, _, ref place) = **rhs {
                     if place.ignore_borrow(
                         self.tcx,
                         self.mir,
@@ -258,13 +258,6 @@ impl<'a, 'gcx, 'tcx> BitDenotation for Borrows<'a, 'gcx, 'tcx> {
                         panic!("could not find BorrowIndex for location {:?}", location);
                     });
 
-                    assert!(self.borrow_set.region_map
-                        .get(&region.to_region_vid())
-                        .unwrap_or_else(|| {
-                            panic!("could not find BorrowIndexs for RegionVid {:?}", region);
-                        })
-                        .contains(&index)
-                    );
                     sets.gen(*index);
 
                     // Issue #46746: Two-phase borrows handles
diff --git a/src/librustc_mir/monomorphize/partitioning.rs b/src/librustc_mir/monomorphize/partitioning.rs
index 3a6ee6da422..528942df29f 100644
--- a/src/librustc_mir/monomorphize/partitioning.rs
+++ b/src/librustc_mir/monomorphize/partitioning.rs
@@ -585,7 +585,7 @@ fn merge_codegen_units<'tcx>(tcx: TyCtxt<'_, 'tcx, 'tcx>,
     // smallest into each other) we're sure to start off with a deterministic
     // order (sorted by name). This'll mean that if two cgus have the same size
     // the stable sort below will keep everything nice and deterministic.
-    codegen_units.sort_by_key(|cgu| cgu.name().clone());
+    codegen_units.sort_by_key(|cgu| *cgu.name());
 
     // Merge the two smallest codegen units until the target size is reached.
     while codegen_units.len() > target_cgu_count {
@@ -985,7 +985,7 @@ fn collect_and_partition_mono_items<'a, 'tcx>(
                 output.push_str(" @@");
                 let mut empty = Vec::new();
                 let cgus = item_to_cgus.get_mut(i).unwrap_or(&mut empty);
-                cgus.as_mut_slice().sort_by_cached_key(|&(ref name, _)| name.clone());
+                cgus.sort_by_key(|(name, _)| *name);
                 cgus.dedup();
                 for &(ref cgu_name, (linkage, _)) in cgus.iter() {
                     output.push_str(" ");
diff --git a/src/librustc_mir/transform/cleanup_post_borrowck.rs b/src/librustc_mir/transform/cleanup_post_borrowck.rs
index c0edd3926d3..6d7fc404edb 100644
--- a/src/librustc_mir/transform/cleanup_post_borrowck.rs
+++ b/src/librustc_mir/transform/cleanup_post_borrowck.rs
@@ -10,17 +10,25 @@
 
 //! This module provides two passes:
 //!
-//!   - [CleanAscribeUserType], that replaces all
-//!     [StatementKind::AscribeUserType] statements with [StatementKind::Nop].
-//!   - [CleanFakeReadsAndBorrows], that replaces all [FakeRead] statements and
-//!     borrows that are read by [FakeReadCause::ForMatchGuard] fake reads with
-//!     [StatementKind::Nop].
+//!   - [`CleanAscribeUserType`], that replaces all [`AscribeUserType`]
+//!     statements with [`Nop`].
+//!   - [`CleanFakeReadsAndBorrows`], that replaces all [`FakeRead`] statements
+//!     and borrows that are read by [`ForMatchGuard`] fake reads with [`Nop`].
 //!
-//! The [CleanFakeReadsAndBorrows] "pass" is actually implemented as two
+//! The `CleanFakeReadsAndBorrows` "pass" is actually implemented as two
 //! traversals (aka visits) of the input MIR. The first traversal,
-//! [DeleteAndRecordFakeReads], deletes the fake reads and finds the temporaries
-//! read by [ForMatchGuard] reads, and [DeleteFakeBorrows] deletes the
-//! initialization of those temporaries.
+//! [`DeleteAndRecordFakeReads`], deletes the fake reads and finds the
+//! temporaries read by [`ForMatchGuard`] reads, and [`DeleteFakeBorrows`]
+//! deletes the initialization of those temporaries.
+//!
+//! [`CleanAscribeUserType`]: cleanup_post_borrowck::CleanAscribeUserType
+//! [`CleanFakeReadsAndBorrows`]: cleanup_post_borrowck::CleanFakeReadsAndBorrows
+//! [`DeleteAndRecordFakeReads`]: cleanup_post_borrowck::DeleteAndRecordFakeReads
+//! [`DeleteFakeBorrows`]: cleanup_post_borrowck::DeleteFakeBorrows
+//! [`AscribeUserType`]: rustc::mir::StatementKind::AscribeUserType
+//! [`Nop`]: rustc::mir::StatementKind::Nop
+//! [`FakeRead`]: rustc::mir::StatementKind::FakeRead
+//! [`ForMatchGuard`]: rustc::mir::FakeReadCause::ForMatchGuard
 
 use rustc_data_structures::fx::FxHashSet;
 
diff --git a/src/librustc_mir/util/borrowck_errors.rs b/src/librustc_mir/util/borrowck_errors.rs
index ae0483e3c14..8566f845f23 100644
--- a/src/librustc_mir/util/borrowck_errors.rs
+++ b/src/librustc_mir/util/borrowck_errors.rs
@@ -261,6 +261,7 @@ pub trait BorrowckErrors<'cx>: Sized + Copy {
         old_loan_span: Span,
         old_opt_via: &str,
         previous_end_span: Option<Span>,
+        second_borrow_desc: &str,
         o: Origin,
     ) -> DiagnosticBuilder<'cx> {
         let mut err = struct_span_err!(
@@ -274,7 +275,10 @@ pub trait BorrowckErrors<'cx>: Sized + Copy {
             kind_new,
             OGN = o
         );
-        err.span_label(new_loan_span, format!("borrow occurs here{}", opt_via));
+        err.span_label(
+            new_loan_span,
+            format!("{}borrow occurs here{}", second_borrow_desc, opt_via),
+        );
         err.span_label(
             old_loan_span,
             format!("{} construction occurs here{}", container_name, old_opt_via),
diff --git a/src/librustc_resolve/build_reduced_graph.rs b/src/librustc_resolve/build_reduced_graph.rs
index 0fa41cb484f..da4cd73923e 100644
--- a/src/librustc_resolve/build_reduced_graph.rs
+++ b/src/librustc_resolve/build_reduced_graph.rs
@@ -318,7 +318,7 @@ impl<'a, 'cl> Resolver<'a, 'cl> {
                         // This particular use tree
                         &tree, id, &prefix, true,
                         // The whole `use` item
-                        parent_scope.clone(), item, ty::Visibility::Invisible, root_span,
+                        parent_scope, item, ty::Visibility::Invisible, root_span,
                     );
                 }
             }
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index fd8f70b19e7..1d903476f16 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -3948,10 +3948,7 @@ pub fn path_to_def_local(tcx: &TyCtxt, path: &[&str]) -> Option<DefId> {
     let mut path_it = path.iter().peekable();
 
     loop {
-        let segment = match path_it.next() {
-            Some(segment) => segment,
-            None => return None,
-        };
+        let segment = path_it.next()?;
 
         for item_id in mem::replace(&mut items, HirVec::new()).iter() {
             let item = tcx.hir.expect_item(item_id.id);
@@ -3986,10 +3983,7 @@ pub fn path_to_def(tcx: &TyCtxt, path: &[&str]) -> Option<DefId> {
         let mut path_it = path.iter().skip(1).peekable();
 
         loop {
-            let segment = match path_it.next() {
-                Some(segment) => segment,
-                None => return None,
-            };
+            let segment = path_it.next()?;
 
             for item in mem::replace(&mut items, Lrc::new(vec![])).iter() {
                 if item.ident.name == *segment {
diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index 3365eb6d780..1194df20ad6 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -2220,13 +2220,13 @@ impl<'a> Item<'a> {
                 return None;
             }
         } else {
-            let (krate, src_root) = match cache.extern_locations.get(&self.item.def_id.krate) {
-                Some(&(ref name, ref src, Local)) => (name, src),
-                Some(&(ref name, ref src, Remote(ref s))) => {
+            let (krate, src_root) = match *cache.extern_locations.get(&self.item.def_id.krate)? {
+                (ref name, ref src, Local) => (name, src),
+                (ref name, ref src, Remote(ref s)) => {
                     root = s.to_string();
                     (name, src)
                 }
-                Some(&(_, _, Unknown)) | None => return None,
+                (_, _, Unknown) => return None,
             };
 
             clean_srcpath(&src_root, file, false, |component| {
diff --git a/src/librustdoc/html/static/.eslintrc.js b/src/librustdoc/html/static/.eslintrc.js
new file mode 100644
index 00000000000..c7af41ac969
--- /dev/null
+++ b/src/librustdoc/html/static/.eslintrc.js
@@ -0,0 +1,21 @@
+module.exports = {
+    "env": {
+        "browser": true,
+        "es6": true
+    },
+    "extends": "eslint:recommended",
+    "parserOptions": {
+        "ecmaVersion": 2015,
+        "sourceType": "module"
+    },
+    "rules": {
+        "linebreak-style": [
+            "error",
+            "unix"
+        ],
+        "semi": [
+            "error",
+            "always"
+        ]
+    }
+};
diff --git a/src/librustdoc/html/static/main.js b/src/librustdoc/html/static/main.js
index 781f99cd693..125277fc5d3 100644
--- a/src/librustdoc/html/static/main.js
+++ b/src/librustdoc/html/static/main.js
@@ -10,8 +10,12 @@
  * except according to those terms.
  */
 
-/*jslint browser: true, es5: true */
-/*globals $: true, rootPath: true */
+// From rust:
+/* global ALIASES, currentCrate, rootPath */
+
+// Local js definitions:
+/* global addClass, getCurrentValue, hasClass */
+/* global isHidden onEach, removeClass, updateLocalStorage */
 
 if (!String.prototype.startsWith) {
     String.prototype.startsWith = function(searchString, position) {
@@ -1300,7 +1304,16 @@ if (!String.prototype.endsWith) {
                 output = '<div class="search-failed"' + extraStyle + '>No results :(<br/>' +
                     'Try on <a href="https://duckduckgo.com/?q=' +
                     encodeURIComponent('rust ' + query.query) +
-                    '">DuckDuckGo</a>?</div>';
+                    '">DuckDuckGo</a>?<br/><br/>' +
+                    'Or try looking in one of these:<ul><li>The <a ' +
+                    'href="https://doc.rust-lang.org/reference/index.html">Rust Reference</a> for' +
+                    ' technical details about the language.</li><li><a ' +
+                    'href="https://doc.rust-lang.org/rust-by-example/index.html">Rust By Example' +
+                    '</a> for expository code examples.</a></li><li>The <a ' +
+                    'href="https://doc.rust-lang.org/book/index.html">Rust Book</a> for ' +
+                    'introductions to language features and the language itself.</li><li><a ' +
+                    'href="https://docs.rs">Docs.rs</a> for documentation of crates released on ' +
+                    '<a href="https://crates.io/">crates.io</a>.</li></ul></div>';
             }
             return [output, length];
         }
diff --git a/src/librustdoc/html/static/rustdoc.css b/src/librustdoc/html/static/rustdoc.css
index b6242457ae2..83129d93a68 100644
--- a/src/librustdoc/html/static/rustdoc.css
+++ b/src/librustdoc/html/static/rustdoc.css
@@ -135,7 +135,6 @@ summary {
 
 code, pre {
 	font-family: "Source Code Pro", monospace;
-	white-space: pre-wrap;
 }
 .docblock code, .docblock-short code {
 	border-radius: 3px;
@@ -283,7 +282,7 @@ nav.sub {
 	padding-left: 0;
 }
 
-:not(.source) .example-wrap {
+.rustdoc:not(.source) .example-wrap {
 	display: inline-flex;
 	margin-bottom: 10px;
 }
@@ -301,8 +300,9 @@ nav.sub {
 	text-align: right;
 }
 
-:not(.source) .example-wrap > pre.rust {
+.rustdoc:not(.source) .example-wrap > pre.rust {
 	width: 100%;
+	overflow-x: auto;
 }
 
 body:not(.source) .example-wrap > pre {
@@ -1132,6 +1132,13 @@ pre.rust {
 	margin-top: 20px;
 }
 
+.search-failed > ul {
+	text-align: left;
+	max-width: 570px;
+	margin-left: auto;
+	margin-right: auto;
+}
+
 #titles {
 	height: 35px;
 }
diff --git a/src/librustdoc/html/static/source-script.js b/src/librustdoc/html/static/source-script.js
index 1db8218dae6..03b0955a34c 100644
--- a/src/librustdoc/html/static/source-script.js
+++ b/src/librustdoc/html/static/source-script.js
@@ -10,6 +10,12 @@
  * except according to those terms.
  */
 
+// From rust:
+/* global sourcesIndex */
+
+// Local js definitions:
+/* global addClass, getCurrentValue, hasClass, removeClass, updateLocalStorage */
+
 function getCurrentFilePath() {
     var parts = window.location.pathname.split("/");
     var rootPathParts = window.rootPath.split("/");
diff --git a/src/librustdoc/html/static/storage.js b/src/librustdoc/html/static/storage.js
index 150001a7514..e8f0c03d91a 100644
--- a/src/librustdoc/html/static/storage.js
+++ b/src/librustdoc/html/static/storage.js
@@ -10,6 +10,9 @@
  * except according to those terms.
  */
 
+// From rust:
+/* global resourcesSuffix */
+
 var currentTheme = document.getElementById("themeStyle");
 var mainTheme = document.getElementById("mainThemeStyle");
 
diff --git a/src/librustdoc/html/static/themes/dark.css b/src/librustdoc/html/static/themes/dark.css
index acf9a8cca64..29388f096ee 100644
--- a/src/librustdoc/html/static/themes/dark.css
+++ b/src/librustdoc/html/static/themes/dark.css
@@ -285,7 +285,7 @@ pre.ignore:hover, .information:hover + pre.ignore {
 	color: rgba(255,142,0,1);
 }
 
-.search-failed > a {
+.search-failed a {
 	color: #0089ff;
 }
 
diff --git a/src/librustdoc/html/static/themes/light.css b/src/librustdoc/html/static/themes/light.css
index d98f1718a6a..d37cfa4142f 100644
--- a/src/librustdoc/html/static/themes/light.css
+++ b/src/librustdoc/html/static/themes/light.css
@@ -279,7 +279,7 @@ pre.ignore:hover, .information:hover + pre.ignore {
 	color: rgba(255,142,0,1);
 }
 
-.search-failed > a {
+.search-failed a {
 	color: #0089ff;
 }
 
diff --git a/src/libstd/env.rs b/src/libstd/env.rs
index 9066c0b7694..d14efa2e3c7 100644
--- a/src/libstd/env.rs
+++ b/src/libstd/env.rs
@@ -828,7 +828,7 @@ pub mod consts {
     /// - s390x
     /// - sparc64
     #[stable(feature = "env", since = "1.0.0")]
-    pub const ARCH: &'static str = super::arch::ARCH;
+    pub const ARCH: &str = super::arch::ARCH;
 
     /// The family of the operating system. Example value is `unix`.
     ///
@@ -837,7 +837,7 @@ pub mod consts {
     /// - unix
     /// - windows
     #[stable(feature = "env", since = "1.0.0")]
-    pub const FAMILY: &'static str = os::FAMILY;
+    pub const FAMILY: &str = os::FAMILY;
 
     /// A string describing the specific operating system in use.
     /// Example value is `linux`.
@@ -856,7 +856,7 @@ pub mod consts {
     /// - android
     /// - windows
     #[stable(feature = "env", since = "1.0.0")]
-    pub const OS: &'static str = os::OS;
+    pub const OS: &str = os::OS;
 
     /// Specifies the filename prefix used for shared libraries on this
     /// platform. Example value is `lib`.
@@ -866,7 +866,7 @@ pub mod consts {
     /// - lib
     /// - `""` (an empty string)
     #[stable(feature = "env", since = "1.0.0")]
-    pub const DLL_PREFIX: &'static str = os::DLL_PREFIX;
+    pub const DLL_PREFIX: &str = os::DLL_PREFIX;
 
     /// Specifies the filename suffix used for shared libraries on this
     /// platform. Example value is `.so`.
@@ -877,7 +877,7 @@ pub mod consts {
     /// - .dylib
     /// - .dll
     #[stable(feature = "env", since = "1.0.0")]
-    pub const DLL_SUFFIX: &'static str = os::DLL_SUFFIX;
+    pub const DLL_SUFFIX: &str = os::DLL_SUFFIX;
 
     /// Specifies the file extension used for shared libraries on this
     /// platform that goes after the dot. Example value is `so`.
@@ -888,7 +888,7 @@ pub mod consts {
     /// - dylib
     /// - dll
     #[stable(feature = "env", since = "1.0.0")]
-    pub const DLL_EXTENSION: &'static str = os::DLL_EXTENSION;
+    pub const DLL_EXTENSION: &str = os::DLL_EXTENSION;
 
     /// Specifies the filename suffix used for executable binaries on this
     /// platform. Example value is `.exe`.
@@ -900,7 +900,7 @@ pub mod consts {
     /// - .pexe
     /// - `""` (an empty string)
     #[stable(feature = "env", since = "1.0.0")]
-    pub const EXE_SUFFIX: &'static str = os::EXE_SUFFIX;
+    pub const EXE_SUFFIX: &str = os::EXE_SUFFIX;
 
     /// Specifies the file extension, if any, used for executable binaries
     /// on this platform. Example value is `exe`.
@@ -910,72 +910,72 @@ pub mod consts {
     /// - exe
     /// - `""` (an empty string)
     #[stable(feature = "env", since = "1.0.0")]
-    pub const EXE_EXTENSION: &'static str = os::EXE_EXTENSION;
+    pub const EXE_EXTENSION: &str = os::EXE_EXTENSION;
 }
 
 #[cfg(target_arch = "x86")]
 mod arch {
-    pub const ARCH: &'static str = "x86";
+    pub const ARCH: &str = "x86";
 }
 
 #[cfg(target_arch = "x86_64")]
 mod arch {
-    pub const ARCH: &'static str = "x86_64";
+    pub const ARCH: &str = "x86_64";
 }
 
 #[cfg(target_arch = "arm")]
 mod arch {
-    pub const ARCH: &'static str = "arm";
+    pub const ARCH: &str = "arm";
 }
 
 #[cfg(target_arch = "aarch64")]
 mod arch {
-    pub const ARCH: &'static str = "aarch64";
+    pub const ARCH: &str = "aarch64";
 }
 
 #[cfg(target_arch = "mips")]
 mod arch {
-    pub const ARCH: &'static str = "mips";
+    pub const ARCH: &str = "mips";
 }
 
 #[cfg(target_arch = "mips64")]
 mod arch {
-    pub const ARCH: &'static str = "mips64";
+    pub const ARCH: &str = "mips64";
 }
 
 #[cfg(target_arch = "powerpc")]
 mod arch {
-    pub const ARCH: &'static str = "powerpc";
+    pub const ARCH: &str = "powerpc";
 }
 
 #[cfg(target_arch = "powerpc64")]
 mod arch {
-    pub const ARCH: &'static str = "powerpc64";
+    pub const ARCH: &str = "powerpc64";
 }
 
 #[cfg(target_arch = "s390x")]
 mod arch {
-    pub const ARCH: &'static str = "s390x";
+    pub const ARCH: &str = "s390x";
 }
 
 #[cfg(target_arch = "sparc64")]
 mod arch {
-    pub const ARCH: &'static str = "sparc64";
+    pub const ARCH: &str = "sparc64";
 }
 
 #[cfg(target_arch = "le32")]
 mod arch {
-    pub const ARCH: &'static str = "le32";
+    pub const ARCH: &str = "le32";
 }
 
 #[cfg(target_arch = "asmjs")]
 mod arch {
-    pub const ARCH: &'static str = "asmjs";
+    pub const ARCH: &str = "asmjs";
 }
 
 #[cfg(target_arch = "wasm32")]
 mod arch {
-    pub const ARCH: &'static str = "wasm32";
+    pub const ARCH: &str = "wasm32";
 }
 
 #[cfg(test)]
diff --git a/src/libstd/ffi/c_str.rs b/src/libstd/ffi/c_str.rs
index 66718b95408..7c7f83967e0 100644
--- a/src/libstd/ffi/c_str.rs
+++ b/src/libstd/ffi/c_str.rs
@@ -671,7 +671,7 @@ impl fmt::Debug for CStr {
 #[stable(feature = "cstr_default", since = "1.10.0")]
 impl<'a> Default for &'a CStr {
     fn default() -> &'a CStr {
-        const SLICE: &'static [c_char] = &[0];
+        const SLICE: &[c_char] = &[0];
         unsafe { CStr::from_ptr(SLICE.as_ptr()) }
     }
 }
@@ -1475,7 +1475,7 @@ mod tests {
 
     #[test]
     fn cstr_const_constructor() {
-        const CSTR: &'static CStr = unsafe {
+        const CSTR: &CStr = unsafe {
             CStr::from_bytes_with_nul_unchecked(b"Hello, world!\0")
         };
 
diff --git a/src/libstd/keyword_docs.rs b/src/libstd/keyword_docs.rs
index 13cf3133dcd..c1eaf29bb44 100644
--- a/src/libstd/keyword_docs.rs
+++ b/src/libstd/keyword_docs.rs
@@ -65,7 +65,7 @@ mod as_keyword { }
 /// look like this:
 ///
 /// ```rust
-/// const WORDS: &'static str = "hello rust!";
+/// const WORDS: &str = "hello rust!";
 /// ```
 ///
 /// Thanks to static lifetime elision, you usually don't have to explicitly use 'static:
diff --git a/src/libstd/path.rs b/src/libstd/path.rs
index a153456370c..9fad40c5649 100644
--- a/src/libstd/path.rs
+++ b/src/libstd/path.rs
@@ -1397,6 +1397,9 @@ impl<'a> From<&'a Path> for Box<Path> {
 
 #[stable(feature = "path_buf_from_box", since = "1.18.0")]
 impl From<Box<Path>> for PathBuf {
+    /// Converts a `Box<Path>` into a `PathBuf`
+    ///
+    /// This conversion does not allocate or copy memory.
     fn from(boxed: Box<Path>) -> PathBuf {
         boxed.into_path_buf()
     }
@@ -1404,6 +1407,10 @@ impl From<Box<Path>> for PathBuf {
 
 #[stable(feature = "box_from_path_buf", since = "1.20.0")]
 impl From<PathBuf> for Box<Path> {
+    /// Converts a `PathBuf` into a `Box<Path>`
+    ///
+    /// This conversion currently should not allocate memory,
+    /// but this behavior is not guaranteed on all platforms or in all future versions.
     fn from(p: PathBuf) -> Box<Path> {
         p.into_boxed_path()
     }
@@ -1426,6 +1433,9 @@ impl<'a, T: ?Sized + AsRef<OsStr>> From<&'a T> for PathBuf {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl From<OsString> for PathBuf {
+    /// Converts a `OsString` into a `PathBuf`
+    ///
+    /// This conversion does not allocate or copy memory.
     fn from(s: OsString) -> PathBuf {
         PathBuf { inner: s }
     }
@@ -1433,6 +1443,9 @@ impl From<OsString> for PathBuf {
 
 #[stable(feature = "from_path_buf_for_os_string", since = "1.14.0")]
 impl From<PathBuf> for OsString {
+    /// Converts a `PathBuf` into a `OsString`
+    ///
+    /// This conversion does not allocate or copy memory.
     fn from(path_buf : PathBuf) -> OsString {
         path_buf.inner
     }
@@ -1440,6 +1453,9 @@ impl From<PathBuf> for OsString {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl From<String> for PathBuf {
+    /// Converts a `String` into a `PathBuf`
+    ///
+    /// This conversion does not allocate or copy memory.
     fn from(s: String) -> PathBuf {
         PathBuf::from(OsString::from(s))
     }
@@ -1536,6 +1552,7 @@ impl<'a> From<Cow<'a, Path>> for PathBuf {
 
 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 impl From<PathBuf> for Arc<Path> {
+    /// Converts a Path into a Rc by copying the Path data into a new Rc buffer.
     #[inline]
     fn from(s: PathBuf) -> Arc<Path> {
         let arc: Arc<OsStr> = Arc::from(s.into_os_string());
@@ -1545,6 +1562,7 @@ impl From<PathBuf> for Arc<Path> {
 
 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 impl<'a> From<&'a Path> for Arc<Path> {
+    /// Converts a Path into a Rc by copying the Path data into a new Rc buffer.
     #[inline]
     fn from(s: &Path) -> Arc<Path> {
         let arc: Arc<OsStr> = Arc::from(s.as_os_str());
@@ -1554,6 +1572,7 @@ impl<'a> From<&'a Path> for Arc<Path> {
 
 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 impl From<PathBuf> for Rc<Path> {
+    /// Converts a Path into a Rc by copying the Path data into a new Rc buffer.
     #[inline]
     fn from(s: PathBuf) -> Rc<Path> {
         let rc: Rc<OsStr> = Rc::from(s.into_os_string());
@@ -1563,6 +1582,7 @@ impl From<PathBuf> for Rc<Path> {
 
 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 impl<'a> From<&'a Path> for Rc<Path> {
+    /// Converts a Path into a Rc by copying the Path data into a new Rc buffer.
     #[inline]
     fn from(s: &Path) -> Rc<Path> {
         let rc: Rc<OsStr> = Rc::from(s.as_os_str());
diff --git a/src/libstd/sys/cloudabi/shims/env.rs b/src/libstd/sys/cloudabi/shims/env.rs
index 31777aa94bc..c7691e3b2df 100644
--- a/src/libstd/sys/cloudabi/shims/env.rs
+++ b/src/libstd/sys/cloudabi/shims/env.rs
@@ -9,11 +9,11 @@
 // except according to those terms.
 
 pub mod os {
-    pub const FAMILY: &'static str = "cloudabi";
-    pub const OS: &'static str = "cloudabi";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "cloudabi";
+    pub const OS: &str = "cloudabi";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
diff --git a/src/libstd/sys/redox/env.rs b/src/libstd/sys/redox/env.rs
index 669b7520df8..75e35046fb7 100644
--- a/src/libstd/sys/redox/env.rs
+++ b/src/libstd/sys/redox/env.rs
@@ -9,11 +9,11 @@
 // except according to those terms.
 
 pub mod os {
-    pub const FAMILY: &'static str = "redox";
-    pub const OS: &'static str = "redox";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "redox";
+    pub const OS: &str = "redox";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
diff --git a/src/libstd/sys/redox/path.rs b/src/libstd/sys/redox/path.rs
index e6a267dd5d9..b1a4ed30404 100644
--- a/src/libstd/sys/redox/path.rs
+++ b/src/libstd/sys/redox/path.rs
@@ -35,5 +35,5 @@ pub fn parse_prefix(path: &OsStr) -> Option<Prefix> {
     }
 }
 
-pub const MAIN_SEP_STR: &'static str = "/";
+pub const MAIN_SEP_STR: &str = "/";
 pub const MAIN_SEP: char = '/';
diff --git a/src/libstd/sys/redox/process.rs b/src/libstd/sys/redox/process.rs
index 4370c1e0502..8f6d83c544a 100644
--- a/src/libstd/sys/redox/process.rs
+++ b/src/libstd/sys/redox/process.rs
@@ -143,7 +143,7 @@ impl Command {
 
     pub fn spawn(&mut self, default: Stdio, needs_stdin: bool)
                  -> io::Result<(Process, StdioPipes)> {
-         const CLOEXEC_MSG_FOOTER: &'static [u8] = b"NOEX";
+         const CLOEXEC_MSG_FOOTER: &[u8] = b"NOEX";
 
          if self.saw_nul {
              return Err(io::Error::new(ErrorKind::InvalidInput,
diff --git a/src/libstd/sys/unix/env.rs b/src/libstd/sys/unix/env.rs
index ad116c57f55..1b6838f0295 100644
--- a/src/libstd/sys/unix/env.rs
+++ b/src/libstd/sys/unix/env.rs
@@ -10,176 +10,176 @@
 
 #[cfg(target_os = "linux")]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "linux";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "linux";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
 
 #[cfg(target_os = "macos")]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "macos";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".dylib";
-    pub const DLL_EXTENSION: &'static str = "dylib";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "macos";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".dylib";
+    pub const DLL_EXTENSION: &str = "dylib";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
 
 #[cfg(target_os = "ios")]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "ios";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".dylib";
-    pub const DLL_EXTENSION: &'static str = "dylib";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "ios";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".dylib";
+    pub const DLL_EXTENSION: &str = "dylib";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
 
 #[cfg(target_os = "freebsd")]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "freebsd";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "freebsd";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
 
 #[cfg(target_os = "dragonfly")]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "dragonfly";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "dragonfly";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
 
 #[cfg(target_os = "bitrig")]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "bitrig";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "bitrig";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
 
 #[cfg(target_os = "netbsd")]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "netbsd";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "netbsd";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
 
 #[cfg(target_os = "openbsd")]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "openbsd";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "openbsd";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
 
 #[cfg(target_os = "android")]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "android";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "android";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
 
 #[cfg(target_os = "solaris")]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "solaris";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "solaris";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
 
 #[cfg(target_os = "haiku")]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "haiku";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "haiku";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
 
 #[cfg(all(target_os = "emscripten", target_arch = "asmjs"))]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "emscripten";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = ".js";
-    pub const EXE_EXTENSION: &'static str = "js";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "emscripten";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = ".js";
+    pub const EXE_EXTENSION: &str = "js";
 }
 
 #[cfg(all(target_os = "emscripten", target_arch = "wasm32"))]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "emscripten";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = ".js";
-    pub const EXE_EXTENSION: &'static str = "js";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "emscripten";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = ".js";
+    pub const EXE_EXTENSION: &str = "js";
 }
 
 #[cfg(target_os = "fuchsia")]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "fuchsia";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "fuchsia";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
 
 #[cfg(target_os = "l4re")]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "l4re";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "l4re";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
 
 #[cfg(target_os = "hermit")]
 pub mod os {
-    pub const FAMILY: &'static str = "unix";
-    pub const OS: &'static str = "hermit";
-    pub const DLL_PREFIX: &'static str = "lib";
-    pub const DLL_SUFFIX: &'static str = ".so";
-    pub const DLL_EXTENSION: &'static str = "so";
-    pub const EXE_SUFFIX: &'static str = "";
-    pub const EXE_EXTENSION: &'static str = "";
+    pub const FAMILY: &str = "unix";
+    pub const OS: &str = "hermit";
+    pub const DLL_PREFIX: &str = "lib";
+    pub const DLL_SUFFIX: &str = ".so";
+    pub const DLL_EXTENSION: &str = "so";
+    pub const EXE_SUFFIX: &str = "";
+    pub const EXE_EXTENSION: &str = "";
 }
diff --git a/src/libstd/sys/unix/path.rs b/src/libstd/sys/unix/path.rs
index bf9af7a4353..834b4b448dc 100644
--- a/src/libstd/sys/unix/path.rs
+++ b/src/libstd/sys/unix/path.rs
@@ -25,5 +25,5 @@ pub fn parse_prefix(_: &OsStr) -> Option<Prefix> {
     None
 }
 
-pub const MAIN_SEP_STR: &'static str = "/";
+pub const MAIN_SEP_STR: &str = "/";
 pub const MAIN_SEP: char = '/';
diff --git a/src/libstd/sys/unix/process/process_unix.rs b/src/libstd/sys/unix/process/process_unix.rs
index bfbf12f34ee..3248f424460 100644
--- a/src/libstd/sys/unix/process/process_unix.rs
+++ b/src/libstd/sys/unix/process/process_unix.rs
@@ -22,7 +22,7 @@ use sys;
 impl Command {
     pub fn spawn(&mut self, default: Stdio, needs_stdin: bool)
                  -> io::Result<(Process, StdioPipes)> {
-        const CLOEXEC_MSG_FOOTER: &'static [u8] = b"NOEX";
+        const CLOEXEC_MSG_FOOTER: &[u8] = b"NOEX";
 
         let envp = self.capture_env();
 
diff --git a/src/libstd/sys/wasm/env.rs b/src/libstd/sys/wasm/env.rs
index 1422042bd02..09235a944ee 100644
--- a/src/libstd/sys/wasm/env.rs
+++ b/src/libstd/sys/wasm/env.rs
@@ -9,11 +9,11 @@
 // except according to those terms.
 
 pub mod os {
-    pub const FAMILY: &'static str = "";
-    pub const OS: &'static str = "";
-    pub const DLL_PREFIX: &'static str = "";
-    pub const DLL_SUFFIX: &'static str = ".wasm";
-    pub const DLL_EXTENSION: &'static str = "wasm";
-    pub const EXE_SUFFIX: &'static str = ".wasm";
-    pub const EXE_EXTENSION: &'static str = "wasm";
+    pub const FAMILY: &str = "";
+    pub const OS: &str = "";
+    pub const DLL_PREFIX: &str = "";
+    pub const DLL_SUFFIX: &str = ".wasm";
+    pub const DLL_EXTENSION: &str = "wasm";
+    pub const EXE_SUFFIX: &str = ".wasm";
+    pub const EXE_EXTENSION: &str = "wasm";
 }
diff --git a/src/libstd/sys/wasm/path.rs b/src/libstd/sys/wasm/path.rs
index 395b8c1e40e..fcc9d617a87 100644
--- a/src/libstd/sys/wasm/path.rs
+++ b/src/libstd/sys/wasm/path.rs
@@ -25,5 +25,5 @@ pub fn parse_prefix(_: &OsStr) -> Option<Prefix> {
     None
 }
 
-pub const MAIN_SEP_STR: &'static str = "/";
+pub const MAIN_SEP_STR: &str = "/";
 pub const MAIN_SEP: char = '/';
diff --git a/src/libstd/sys/windows/env.rs b/src/libstd/sys/windows/env.rs
index e6d74895774..4523df04f24 100644
--- a/src/libstd/sys/windows/env.rs
+++ b/src/libstd/sys/windows/env.rs
@@ -9,11 +9,11 @@
 // except according to those terms.
 
 pub mod os {
-    pub const FAMILY: &'static str = "windows";
-    pub const OS: &'static str = "windows";
-    pub const DLL_PREFIX: &'static str = "";
-    pub const DLL_SUFFIX: &'static str = ".dll";
-    pub const DLL_EXTENSION: &'static str = "dll";
-    pub const EXE_SUFFIX: &'static str = ".exe";
-    pub const EXE_EXTENSION: &'static str = "exe";
+    pub const FAMILY: &str = "windows";
+    pub const OS: &str = "windows";
+    pub const DLL_PREFIX: &str = "";
+    pub const DLL_SUFFIX: &str = ".dll";
+    pub const DLL_EXTENSION: &str = "dll";
+    pub const EXE_SUFFIX: &str = ".exe";
+    pub const EXE_EXTENSION: &str = "exe";
 }
diff --git a/src/libstd/sys/windows/os.rs b/src/libstd/sys/windows/os.rs
index 29ea82c2053..4d7b7236c59 100644
--- a/src/libstd/sys/windows/os.rs
+++ b/src/libstd/sys/windows/os.rs
@@ -48,8 +48,8 @@ pub fn error_string(mut errnum: i32) -> String {
         // `[MS-ERREF]`: https://msdn.microsoft.com/en-us/library/cc231198.aspx
         if (errnum & c::FACILITY_NT_BIT as i32) != 0 {
             // format according to https://support.microsoft.com/en-us/help/259693
-            const NTDLL_DLL: &'static [u16] = &['N' as _, 'T' as _, 'D' as _, 'L' as _, 'L' as _,
-                                                '.' as _, 'D' as _, 'L' as _, 'L' as _, 0];
+            const NTDLL_DLL: &[u16] = &['N' as _, 'T' as _, 'D' as _, 'L' as _, 'L' as _,
+                                        '.' as _, 'D' as _, 'L' as _, 'L' as _, 0];
             module = c::GetModuleHandleW(NTDLL_DLL.as_ptr());
 
             if module != ptr::null_mut() {
diff --git a/src/libstd/sys/windows/path.rs b/src/libstd/sys/windows/path.rs
index 98d62a0c953..385ea8e0531 100644
--- a/src/libstd/sys/windows/path.rs
+++ b/src/libstd/sys/windows/path.rs
@@ -91,10 +91,7 @@ pub fn parse_prefix<'a>(path: &'a OsStr) -> Option<Prefix> {
     }
 
     fn parse_two_comps(mut path: &[u8], f: fn(u8) -> bool) -> Option<(&[u8], &[u8])> {
-        let first = match path.iter().position(|x| f(*x)) {
-            None => return None,
-            Some(x) => &path[..x],
-        };
+        let first = &path[..path.iter().position(|x| f(*x))?];
         path = &path[(first.len() + 1)..];
         let idx = path.iter().position(|x| f(*x));
         let second = &path[..idx.unwrap_or(path.len())];
@@ -102,5 +99,5 @@ pub fn parse_prefix<'a>(path: &'a OsStr) -> Option<Prefix> {
     }
 }
 
-pub const MAIN_SEP_STR: &'static str = "\\";
+pub const MAIN_SEP_STR: &str = "\\";
 pub const MAIN_SEP: char = '\\';
diff --git a/src/libstd/sys_common/wtf8.rs b/src/libstd/sys_common/wtf8.rs
index 19ce932aa12..3530b7af9ad 100644
--- a/src/libstd/sys_common/wtf8.rs
+++ b/src/libstd/sys_common/wtf8.rs
@@ -40,7 +40,7 @@ use str;
 use sync::Arc;
 use sys_common::AsInner;
 
-const UTF8_REPLACEMENT_CHARACTER: &'static str = "\u{FFFD}";
+const UTF8_REPLACEMENT_CHARACTER: &str = "\u{FFFD}";
 
 /// A Unicode code point: from U+0000 to U+10FFFF.
 ///
diff --git a/src/libsyntax/ext/tt/macro_parser.rs b/src/libsyntax/ext/tt/macro_parser.rs
index 8fd9590a664..68d94b43dba 100644
--- a/src/libsyntax/ext/tt/macro_parser.rs
+++ b/src/libsyntax/ext/tt/macro_parser.rs
@@ -309,7 +309,7 @@ fn create_matches(len: usize) -> Box<[Rc<NamedMatchVec>]> {
         vec![]
     } else {
         let empty_matches = Rc::new(SmallVec::new());
-        vec![empty_matches.clone(); len]
+        vec![empty_matches; len]
     }.into_boxed_slice()
 }
 
diff --git a/src/test/run-pass/impl-trait/example-calendar.rs b/src/test/run-pass/impl-trait/example-calendar.rs
index e6dd421f48f..7373828427e 100644
--- a/src/test/run-pass/impl-trait/example-calendar.rs
+++ b/src/test/run-pass/impl-trait/example-calendar.rs
@@ -753,10 +753,7 @@ where It: Iterator {
     type Item = Vec<It::Item>;
 
     fn next(&mut self) -> Option<Vec<It::Item>> {
-        let first = match self.it.next() {
-            Some(e) => e,
-            None => return None
-        };
+        let first = self.it.next()?;
 
         let mut result = Vec::with_capacity(self.n);
         result.push(first);
diff --git a/src/test/ui/E0501.ast.nll.stderr b/src/test/ui/E0501.ast.nll.stderr
index 72fda9079d6..8a3fce3a554 100644
--- a/src/test/ui/E0501.ast.nll.stderr
+++ b/src/test/ui/E0501.ast.nll.stderr
@@ -7,7 +7,7 @@ LL |         inside_closure(a)
    |                        - first borrow occurs due to use of `a` in closure
 LL |     };
 LL |     outside_closure_1(a); //[ast]~ ERROR cannot borrow `*a` as mutable because previous closure requires unique access
-   |                       ^ borrow occurs here
+   |                       ^ second borrow occurs here
 ...
 LL |     drop(bar);
    |          --- first borrow later used here
@@ -21,7 +21,7 @@ LL |         inside_closure(a)
    |                        - first borrow occurs due to use of `a` in closure
 ...
 LL |     outside_closure_2(a); //[ast]~ ERROR cannot borrow `*a` as immutable because previous closure requires unique access
-   |                       ^ borrow occurs here
+   |                       ^ second borrow occurs here
 ...
 LL |     drop(bar);
    |          --- first borrow later used here
diff --git a/src/test/ui/E0501.mir.stderr b/src/test/ui/E0501.mir.stderr
index 72fda9079d6..8a3fce3a554 100644
--- a/src/test/ui/E0501.mir.stderr
+++ b/src/test/ui/E0501.mir.stderr
@@ -7,7 +7,7 @@ LL |         inside_closure(a)
    |                        - first borrow occurs due to use of `a` in closure
 LL |     };
 LL |     outside_closure_1(a); //[ast]~ ERROR cannot borrow `*a` as mutable because previous closure requires unique access
-   |                       ^ borrow occurs here
+   |                       ^ second borrow occurs here
 ...
 LL |     drop(bar);
    |          --- first borrow later used here
@@ -21,7 +21,7 @@ LL |         inside_closure(a)
    |                        - first borrow occurs due to use of `a` in closure
 ...
 LL |     outside_closure_2(a); //[ast]~ ERROR cannot borrow `*a` as immutable because previous closure requires unique access
-   |                       ^ borrow occurs here
+   |                       ^ second borrow occurs here
 ...
 LL |     drop(bar);
    |          --- first borrow later used here
diff --git a/src/test/ui/borrowck/borrowck-insert-during-each.nll.stderr b/src/test/ui/borrowck/borrowck-insert-during-each.nll.stderr
index 123d475f1c0..84fc69465cb 100644
--- a/src/test/ui/borrowck/borrowck-insert-during-each.nll.stderr
+++ b/src/test/ui/borrowck/borrowck-insert-during-each.nll.stderr
@@ -10,7 +10,7 @@ LL | |         |a| { //~ ERROR closure requires unique access to `f`
 LL | |             f.n.insert(*a);
    | |             - first borrow occurs due to use of `f` in closure
 LL | |         })
-   | |__________^ borrow occurs here
+   | |__________^ second borrow occurs here
 
 error[E0500]: closure requires unique access to `f` but it is already borrowed
   --> $DIR/borrowck-insert-during-each.rs:27:9
diff --git a/src/test/ui/existential_types/private_unused.rs b/src/test/ui/existential_types/private_unused.rs
new file mode 100644
index 00000000000..736d812bc0a
--- /dev/null
+++ b/src/test/ui/existential_types/private_unused.rs
@@ -0,0 +1,13 @@
+// compile-pass
+
+#[deny(warnings)]
+
+enum Empty { }
+trait Bar<T> {}
+impl Bar<Empty> for () {}
+
+fn boo() -> impl Bar<Empty> {}
+
+fn main() {
+    boo();
+}
diff --git a/src/test/ui/generator/yield-while-ref-reborrowed.nll.stderr b/src/test/ui/generator/yield-while-ref-reborrowed.nll.stderr
index 8dabb3c2505..60163d78e78 100644
--- a/src/test/ui/generator/yield-while-ref-reborrowed.nll.stderr
+++ b/src/test/ui/generator/yield-while-ref-reborrowed.nll.stderr
@@ -7,7 +7,7 @@ LL |         let a = &mut *x;
    |                       - first borrow occurs due to use of `x` in generator
 ...
 LL |     println!("{}", x); //~ ERROR
-   |                    ^ borrow occurs here
+   |                    ^ second borrow occurs here
 LL |     b.resume();
    |     - first borrow later used here
 
diff --git a/src/test/ui/nll/closure-borrow-spans.stderr b/src/test/ui/nll/closure-borrow-spans.stderr
index 3e423dadd19..98a261657b1 100644
--- a/src/test/ui/nll/closure-borrow-spans.stderr
+++ b/src/test/ui/nll/closure-borrow-spans.stderr
@@ -126,7 +126,7 @@ LL |     let f = || *x = 0;
    |             |
    |             closure construction occurs here
 LL |     let y = &x; //~ ERROR
-   |             ^^ borrow occurs here
+   |             ^^ second borrow occurs here
 LL |     f.use_ref();
    |     - first borrow later used here
 
@@ -138,7 +138,7 @@ LL |     let f = || *x = 0;
    |             |
    |             closure construction occurs here
 LL |     let y = &mut x; //~ ERROR
-   |             ^^^^^^ borrow occurs here
+   |             ^^^^^^ second borrow occurs here
 LL |     f.use_ref();
    |     - first borrow later used here
 
diff --git a/src/tools/compiletest/src/errors.rs b/src/tools/compiletest/src/errors.rs
index dd2e5557c16..8d20a9e2717 100644
--- a/src/tools/compiletest/src/errors.rs
+++ b/src/tools/compiletest/src/errors.rs
@@ -119,10 +119,7 @@ fn parse_expected(
     line: &str,
     tag: &str,
 ) -> Option<(WhichLine, Error)> {
-    let start = match line.find(tag) {
-        Some(i) => i,
-        None => return None,
-    };
+    let start = line.find(tag)?;
     let (follow, adjusts) = if line[start + tag.len()..].chars().next().unwrap() == '|' {
         (true, 0)
     } else {
diff --git a/src/tools/compiletest/src/header.rs b/src/tools/compiletest/src/header.rs
index ed2114b6530..f4a82aeb307 100644
--- a/src/tools/compiletest/src/header.rs
+++ b/src/tools/compiletest/src/header.rs
@@ -707,14 +707,8 @@ impl Config {
 
     fn parse_custom_normalization(&self, mut line: &str, prefix: &str) -> Option<(String, String)> {
         if self.parse_cfg_name_directive(line, prefix) == ParsedNameDirective::Match {
-            let from = match parse_normalization_string(&mut line) {
-                Some(s) => s,
-                None => return None,
-            };
-            let to = match parse_normalization_string(&mut line) {
-                Some(s) => s,
-                None => return None,
-            };
+            let from = parse_normalization_string(&mut line)?;
+            let to = parse_normalization_string(&mut line)?;
             Some((from, to))
         } else {
             None
@@ -873,14 +867,8 @@ fn expand_variables(mut value: String, config: &Config) -> String {
 /// ```
 fn parse_normalization_string(line: &mut &str) -> Option<String> {
     // FIXME support escapes in strings.
-    let begin = match line.find('"') {
-        Some(i) => i + 1,
-        None => return None,
-    };
-    let end = match line[begin..].find('"') {
-        Some(i) => i + begin,
-        None => return None,
-    };
+    let begin = line.find('"')? + 1;
+    let end = line[begin..].find('"')? + begin;
     let result = line[begin..end].to_owned();
     *line = &line[end + 1..];
     Some(result)
diff --git a/src/tools/linkchecker/main.rs b/src/tools/linkchecker/main.rs
index 11c83819eaa..e6bf9a28572 100644
--- a/src/tools/linkchecker/main.rs
+++ b/src/tools/linkchecker/main.rs
@@ -332,10 +332,7 @@ fn maybe_redirect(source: &str) -> Option<String> {
     const REDIRECT: &'static str = "<p>Redirecting to <a href=";
 
     let mut lines = source.lines();
-    let redirect_line = match lines.nth(6) {
-        Some(l) => l,
-        None => return None,
-    };
+    let redirect_line = lines.nth(6)?;
 
     redirect_line.find(REDIRECT).map(|i| {
         let rest = &redirect_line[(i + REDIRECT.len() + 1)..];