Auto merge of #50345 - kennytm:rollup, r=kennytm

Rollup of 7 pull requests

Successful merges:

 - #50233 (Make `Vec::new` a `const fn`)
 - #50312 (Add more links in panic docs)
 - #50316 (Fix some broken links in docs.)
 - #50325 (Add a few more tests for proc macro feature gating)
 - #50327 (Display correct unused field suggestion for nested struct patterns)
 - #50330 (check that #[used] is used only on statics)
 - #50344 (Update Cargo to 2018-04-28 122fd5be5201913d42e219e132d6569493583bca)

Failed merges:

src/liballoc/lib.rs

@@ -124,6 +124,7 @@
 #![feature(pointer_methods)]
 #![feature(inclusive_range_fields)]
 #![cfg_attr(stage0, feature(generic_param_attrs))]
+#![feature(rustc_const_unstable)]
 
 #![cfg_attr(not(test), feature(fn_traits, i128))]
 #![cfg_attr(test, feature(test))]

src/liballoc/raw_vec.rs

@@ -56,14 +56,16 @@ pub struct RawVec<T, A: Alloc = Global> {
 impl<T, A: Alloc> RawVec<T, A> {
     /// Like `new` but parameterized over the choice of allocator for
     /// the returned RawVec.
-    pub fn new_in(a: A) -> Self {
+    pub const fn new_in(a: A) -> Self {
         // !0 is usize::MAX. This branch should be stripped at compile time.
-        let cap = if mem::size_of::<T>() == 0 { !0 } else { 0 };
+        // FIXME(mark-i-m): use this line when `if`s are allowed in `const`
+        //let cap = if mem::size_of::<T>() == 0 { !0 } else { 0 };
 
         // Unique::empty() doubles as "unallocated" and "zero-sized allocation"
         RawVec {
             ptr: Unique::empty(),
-            cap,
+            // FIXME(mark-i-m): use `cap` when ifs are allowed in const
+            cap: [0, !0][(mem::size_of::<T>() == 0) as usize],
             a,
         }
     }
@@ -120,7 +122,7 @@ impl<T> RawVec<T, Global> {
     /// RawVec with capacity 0. If T has 0 size, then it makes a
     /// RawVec with capacity `usize::MAX`. Useful for implementing
     /// delayed allocation.
-    pub fn new() -> Self {
+    pub const fn new() -> Self {
         Self::new_in(Global)
     }
 

src/liballoc/vec.rs

@@ -322,7 +322,8 @@ impl<T> Vec<T> {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn new() -> Vec<T> {
+    #[rustc_const_unstable(feature = "const_vec_new")]
+    pub const fn new() -> Vec<T> {
         Vec {
             buf: RawVec::new(),
             len: 0,

src/libcore/iter/iterator.rs

@@ -1094,6 +1094,8 @@ pub trait Iterator {
     /// `flatten()` a three-dimensional array the result will be
     /// two-dimensional and not one-dimensional. To get a one-dimensional
     /// structure, you have to `flatten()` again.
+    ///
+    /// [`flat_map()`]: #method.flat_map
     #[inline]
     #[unstable(feature = "iterator_flatten", issue = "48213")]
     fn flatten(self) -> Flatten<Self>

src/libcore/marker.rs

@@ -602,6 +602,8 @@ unsafe impl<'a, T: ?Sized> Freeze for &'a mut T {}
 /// `Pin` pointer.
 ///
 /// This trait is automatically implemented for almost every type.
+///
+/// [`Pin`]: ../mem/struct.Pin.html
 #[unstable(feature = "pin", issue = "49150")]
 pub unsafe auto trait Unpin {}
 

src/libcore/ptr.rs

@@ -2552,10 +2552,9 @@ impl<T: Sized> Unique<T> {
     /// This is useful for initializing types which lazily allocate, like
     /// `Vec::new` does.
     // FIXME: rename to dangling() to match NonNull?
-    pub fn empty() -> Self {
+    pub const fn empty() -> Self {
         unsafe {
-            let ptr = mem::align_of::<T>() as *mut T;
-            Unique::new_unchecked(ptr)
+            Unique::new_unchecked(mem::align_of::<T>() as *mut T)
         }
     }
 }

src/librustc/hir/check_attr.rs

@@ -31,6 +31,7 @@ enum Target {
     Expression,
     Statement,
     Closure,
+    Static,
     Other,
 }
 
@@ -43,6 +44,7 @@ impl Target {
             hir::ItemEnum(..) => Target::Enum,
             hir::ItemConst(..) => Target::Const,
             hir::ItemForeignMod(..) => Target::ForeignMod,
+            hir::ItemStatic(..) => Target::Static,
             _ => Target::Other,
         }
     }
@@ -102,6 +104,7 @@ impl<'a, 'tcx> CheckAttrVisitor<'a, 'tcx> {
         }
 
         self.check_repr(item, target);
+        self.check_used(item, target);
     }
 
     /// Check if an `#[inline]` is applied to a function or a closure.
@@ -305,6 +308,15 @@ impl<'a, 'tcx> CheckAttrVisitor<'a, 'tcx> {
             }
         }
     }
+
+    fn check_used(&self, item: &hir::Item, target: Target) {
+        for attr in &item.attrs {
+            if attr.name().map(|name| name == "used").unwrap_or(false) && target != Target::Static {
+                self.tcx.sess
+                    .span_err(attr.span, "attribute must be applied to a `static` variable");
+            }
+        }
+    }
 }
 
 impl<'a, 'tcx> Visitor<'tcx> for CheckAttrVisitor<'a, 'tcx> {

src/librustc/middle/liveness.rs

@@ -111,6 +111,7 @@ use ty::{self, TyCtxt};
 use lint;
 use util::nodemap::{NodeMap, NodeSet};
 
+use std::collections::VecDeque;
 use std::{fmt, usize};
 use std::io::prelude::*;
 use std::io;
@@ -412,18 +413,43 @@ fn visit_local<'a, 'tcx>(ir: &mut IrMaps<'a, 'tcx>, local: &'tcx hir::Local) {
 }
 
 fn visit_arm<'a, 'tcx>(ir: &mut IrMaps<'a, 'tcx>, arm: &'tcx hir::Arm) {
-    for pat in &arm.pats {
-        // for struct patterns, take note of which fields used shorthand (`x` rather than `x: x`)
+    for mut pat in &arm.pats {
+        // For struct patterns, take note of which fields used shorthand
+        // (`x` rather than `x: x`).
         //
-        // FIXME: according to the rust-lang-nursery/rustc-guide book, `NodeId`s are to be phased
-        // out in favor of `HirId`s; however, we need to match the signature of `each_binding`,
-        // which uses `NodeIds`.
+        // FIXME: according to the rust-lang-nursery/rustc-guide book, `NodeId`s are to be
+        // phased out in favor of `HirId`s; however, we need to match the signature of
+        // `each_binding`, which uses `NodeIds`.
         let mut shorthand_field_ids = NodeSet();
-        if let hir::PatKind::Struct(_, ref fields, _) = pat.node {
-            for field in fields {
-                if field.node.is_shorthand {
-                    shorthand_field_ids.insert(field.node.pat.id);
+        let mut pats = VecDeque::new();
+        pats.push_back(pat);
+        while let Some(pat) = pats.pop_front() {
+            use hir::PatKind::*;
+            match pat.node {
+                Binding(_, _, _, ref inner_pat) => {
+                    pats.extend(inner_pat.iter());
                 }
+                Struct(_, ref fields, _) => {
+                    for field in fields {
+                        if field.node.is_shorthand {
+                            shorthand_field_ids.insert(field.node.pat.id);
+                        }
+                    }
+                }
+                Ref(ref inner_pat, _) |
+                Box(ref inner_pat) => {
+                    pats.push_back(inner_pat);
+                }
+                TupleStruct(_, ref inner_pats, _) |
+                Tuple(ref inner_pats, _) => {
+                    pats.extend(inner_pats.iter());
+                }
+                Slice(ref pre_pats, ref inner_pat, ref post_pats) => {
+                    pats.extend(pre_pats.iter());
+                    pats.extend(inner_pat.iter());
+                    pats.extend(post_pats.iter());
+                }
+                _ => {}
             }
         }
 

src/libstd/collections/hash/table.rs

@@ -79,7 +79,7 @@ impl TaggedHashUintPtr {
 ///
 /// Essential invariants of this structure:
 ///
-///   - if t.hashes[i] == EMPTY_BUCKET, then `Bucket::at_index(&t, i).raw`
+///   - if `t.hashes[i] == EMPTY_BUCKET`, then `Bucket::at_index(&t, i).raw`
 ///     points to 'undefined' contents. Don't read from it. This invariant is
 ///     enforced outside this module with the `EmptyBucket`, `FullBucket`,
 ///     and `SafeHash` types.

src/libstd/ffi/c_str.rs

@@ -1118,6 +1118,7 @@ impl CStr {
     ///
     /// [`Cow`]: ../borrow/enum.Cow.html
     /// [`Borrowed`]: ../borrow/enum.Cow.html#variant.Borrowed
+    /// [`Owned`]: ../borrow/enum.Cow.html#variant.Owned
     /// [`str`]: ../primitive.str.html
     /// [`String`]: ../string/struct.String.html
     ///

src/libstd/panic.rs

@@ -31,10 +31,14 @@ pub use core::panic::{PanicInfo, Location};
 /// A marker trait which represents "panic safe" types in Rust.
 ///
 /// This trait is implemented by default for many types and behaves similarly in
-/// terms of inference of implementation to the `Send` and `Sync` traits. The
-/// purpose of this trait is to encode what types are safe to cross a `catch_unwind`
+/// terms of inference of implementation to the [`Send`] and [`Sync`] traits. The
+/// purpose of this trait is to encode what types are safe to cross a [`catch_unwind`]
 /// boundary with no fear of unwind safety.
 ///
+/// [`Send`]: ../marker/trait.Send.html
+/// [`Sync`]: ../marker/trait.Sync.html
+/// [`catch_unwind`]: ./fn.catch_unwind.html
+///
 /// ## What is unwind safety?
 ///
 /// In Rust a function can "return" early if it either panics or calls a
@@ -95,12 +99,13 @@ pub use core::panic::{PanicInfo, Location};
 ///
 /// ## When should `UnwindSafe` be used?
 ///
-/// Is not intended that most types or functions need to worry about this trait.
-/// It is only used as a bound on the `catch_unwind` function and as mentioned above,
-/// the lack of `unsafe` means it is mostly an advisory. The `AssertUnwindSafe`
-/// wrapper struct in this module can be used to force this trait to be
-/// implemented for any closed over variables passed to the `catch_unwind` function
-/// (more on this below).
+/// It is not intended that most types or functions need to worry about this trait.
+/// It is only used as a bound on the `catch_unwind` function and as mentioned
+/// above, the lack of `unsafe` means it is mostly an advisory. The
+/// [`AssertUnwindSafe`] wrapper struct can be used to force this trait to be
+/// implemented for any closed over variables passed to `catch_unwind`.
+///
+/// [`AssertUnwindSafe`]: ./struct.AssertUnwindSafe.html
 #[stable(feature = "catch_unwind", since = "1.9.0")]
 #[rustc_on_unimplemented = "the type {Self} may not be safely transferred \
                             across an unwind boundary"]
@@ -109,11 +114,14 @@ pub auto trait UnwindSafe {}
 /// A marker trait representing types where a shared reference is considered
 /// unwind safe.
 ///
-/// This trait is namely not implemented by `UnsafeCell`, the root of all
+/// This trait is namely not implemented by [`UnsafeCell`], the root of all
 /// interior mutability.
 ///
 /// This is a "helper marker trait" used to provide impl blocks for the
-/// `UnwindSafe` trait, for more information see that documentation.
+/// [`UnwindSafe`] trait, for more information see that documentation.
+///
+/// [`UnsafeCell`]: ../cell/struct.UnsafeCell.html
+/// [`UnwindSafe`]: ./trait.UnwindSafe.html
 #[stable(feature = "catch_unwind", since = "1.9.0")]
 #[rustc_on_unimplemented = "the type {Self} may contain interior mutability \
                             and a reference may not be safely transferrable \
@@ -122,14 +130,15 @@ pub auto trait RefUnwindSafe {}
 
 /// A simple wrapper around a type to assert that it is unwind safe.
 ///
-/// When using `catch_unwind` it may be the case that some of the closed over
+/// When using [`catch_unwind`] it may be the case that some of the closed over
 /// variables are not unwind safe. For example if `&mut T` is captured the
 /// compiler will generate a warning indicating that it is not unwind safe. It
 /// may not be the case, however, that this is actually a problem due to the
-/// specific usage of `catch_unwind` if unwind safety is specifically taken into
+/// specific usage of [`catch_unwind`] if unwind safety is specifically taken into
 /// account. This wrapper struct is useful for a quick and lightweight
 /// annotation that a variable is indeed unwind safe.
 ///
+/// [`catch_unwind`]: ./fn.catch_unwind.html
 /// # Examples
 ///
 /// One way to use `AssertUnwindSafe` is to assert that the entire closure
@@ -318,18 +327,22 @@ impl<T: fmt::Debug> fmt::Debug for AssertUnwindSafe<T> {
 /// panic and allowing a graceful handling of the error.
 ///
 /// It is **not** recommended to use this function for a general try/catch
-/// mechanism. The `Result` type is more appropriate to use for functions that
+/// mechanism. The [`Result`] type is more appropriate to use for functions that
 /// can fail on a regular basis. Additionally, this function is not guaranteed
 /// to catch all panics, see the "Notes" section below.
 ///
-/// The closure provided is required to adhere to the `UnwindSafe` trait to ensure
+/// [`Result`]: ../result/enum.Result.html
+///
+/// The closure provided is required to adhere to the [`UnwindSafe`] trait to ensure
 /// that all captured variables are safe to cross this boundary. The purpose of
 /// this bound is to encode the concept of [exception safety][rfc] in the type
 /// system. Most usage of this function should not need to worry about this
 /// bound as programs are naturally unwind safe without `unsafe` code. If it
-/// becomes a problem the associated `AssertUnwindSafe` wrapper type in this
-/// module can be used to quickly assert that the usage here is indeed unwind
-/// safe.
+/// becomes a problem the [`AssertUnwindSafe`] wrapper struct can be used to quickly
+/// assert that the usage here is indeed unwind safe.
+///
+/// [`AssertUnwindSafe`]: ./struct.AssertUnwindSafe.html
+/// [`UnwindSafe`]: ./trait.UnwindSafe.html
 ///
 /// [rfc]: https://github.com/rust-lang/rfcs/blob/master/text/1236-stabilize-catch-panic.md
 ///
@@ -364,9 +377,11 @@ pub fn catch_unwind<F: FnOnce() -> R + UnwindSafe, R>(f: F) -> Result<R> {
 
 /// Triggers a panic without invoking the panic hook.
 ///
-/// This is designed to be used in conjunction with `catch_unwind` to, for
+/// This is designed to be used in conjunction with [`catch_unwind`] to, for
 /// example, carry a panic across a layer of C code.
 ///
+/// [`catch_unwind`]: ./fn.catch_unwind.html
+///
 /// # Notes
 ///
 /// Note that panics in Rust are not always implemented via unwinding, but they

src/libstd/panicking.rs

@@ -76,7 +76,9 @@ static mut HOOK: Hook = Hook::Default;
 /// is invoked. As such, the hook will run with both the aborting and unwinding
 /// runtimes. The default hook prints a message to standard error and generates
 /// a backtrace if requested, but this behavior can be customized with the
-/// `set_hook` and `take_hook` functions.
+/// `set_hook` and [`take_hook`] functions.
+///
+/// [`take_hook`]: ./fn.take_hook.html
 ///
 /// The hook is provided with a `PanicInfo` struct which contains information
 /// about the origin of the panic, including the payload passed to `panic!` and
@@ -121,6 +123,10 @@ pub fn set_hook(hook: Box<Fn(&PanicInfo) + 'static + Sync + Send>) {
 
 /// Unregisters the current panic hook, returning it.
 ///
+/// *See also the function [`set_hook`].*
+///
+/// [`set_hook`]: ./fn.set_hook.html
+///
 /// If no custom hook is registered, the default hook will be returned.
 ///
 /// # Panics