Auto merge of #29544 - Ryman:reduce_doc_warnings, r=steveklabnik

Did this alphabetically, so I didn't see [how `std` was doing things](https://dxr.mozilla.org/rust/source/src/libstd/lib.rs#215) till I was nearly finished. If you prefer to add crate-level-whitelists like std instead of test-level, I can rebase with that strategy.

A number of these commits can probably be dropped as the crates don't have much to test, and are deprecated. Let me know which if any to drop! (can also squash after review if desired)

r? @steveklabnik

47 files changed, 168 insertions, 69 deletions

diff --git a/mk/tests.mk b/mk/tests.mk
index 052d0c18ed4..73aec5de8da 100644
--- a/mk/tests.mk
+++ b/mk/tests.mk
@@ -25,7 +25,8 @@ $(eval $(call RUST_CRATE,collectionstest))
 TEST_TARGET_CRATES = $(filter-out core rustc_unicode alloc_system libc \
 		     		  alloc_jemalloc,$(TARGET_CRATES)) \
 			collectionstest coretest
-TEST_DOC_CRATES = $(DOC_CRATES)
+TEST_DOC_CRATES = $(DOC_CRATES) arena flate fmt_macros getopts graphviz \
+                log rand rbml serialize syntax term test
 TEST_HOST_CRATES = $(filter-out rustc_typeck rustc_borrowck rustc_resolve \
 		   		rustc_trans rustc_lint,\
                      $(HOST_CRATES))
diff --git a/src/doc/trpl/documentation.md b/src/doc/trpl/documentation.md
index dc91c90b0fd..80aed0d1ca7 100644
--- a/src/doc/trpl/documentation.md
+++ b/src/doc/trpl/documentation.md
@@ -620,6 +620,18 @@ You can control a few aspects of the HTML that `rustdoc` generates through the
 
 This sets a few different options, with a logo, favicon, and a root URL.
 
+### Configuring documentation tests
+
+You can also configure the way that `rustdoc` tests your documentation examples
+through the `#![doc(test(..))]` attribute.
+
+```rust
+#![doc(test(attr(allow(unused_variables), deny(warnings))))]
+```
+
+This allows unused variables within the examples, but will fail the test for any
+other lint warning thrown.
+
 ## Generation options
 
 `rustdoc` also contains a few other options on the command line, for further customization:
diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index 899e7de4ed5..4113f67e617 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -70,7 +70,7 @@
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/",
        issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
-       test(no_crate_inject))]
+       test(no_crate_inject, attr(allow(unused_variables), deny(warnings))))]
 #![no_std]
 #![cfg_attr(not(stage0), needs_allocator)]
 
diff --git a/src/libarena/lib.rs b/src/libarena/lib.rs
index 5bc1c44e1b1..2234d3608f3 100644
--- a/src/libarena/lib.rs
+++ b/src/libarena/lib.rs
@@ -28,7 +28,8 @@
 #![crate_type = "dylib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
-       html_root_url = "https://doc.rust-lang.org/nightly/")]
+       html_root_url = "https://doc.rust-lang.org/nightly/",
+       test(no_crate_inject, attr(deny(warnings))))]
 
 #![feature(alloc)]
 #![feature(box_syntax)]
diff --git a/src/libcollections/binary_heap.rs b/src/libcollections/binary_heap.rs
index 30fc22e400a..72547a9a5d2 100644
--- a/src/libcollections/binary_heap.rs
+++ b/src/libcollections/binary_heap.rs
@@ -233,6 +233,7 @@ impl<T: Ord> BinaryHeap<T> {
     ///
     /// ```
     /// #![feature(binary_heap_extras)]
+    /// # #![allow(deprecated)]
     ///
     /// use std::collections::BinaryHeap;
     /// let heap = BinaryHeap::from_vec(vec![9, 1, 2, 7, 3, 2]);
diff --git a/src/libcollections/borrow.rs b/src/libcollections/borrow.rs
index bd1864b28cd..9b8f8c8f5bb 100644
--- a/src/libcollections/borrow.rs
+++ b/src/libcollections/borrow.rs
@@ -72,6 +72,7 @@ impl<T> ToOwned for T where T: Clone {
 /// ```
 /// use std::borrow::Cow;
 ///
+/// # #[allow(dead_code)]
 /// fn abs_all(input: &mut Cow<[i32]>) {
 ///     for i in 0..input.len() {
 ///         let v = input[i];
diff --git a/src/libcollections/btree/set.rs b/src/libcollections/btree/set.rs
index 121668fbb9d..0c70a1544ef 100644
--- a/src/libcollections/btree/set.rs
+++ b/src/libcollections/btree/set.rs
@@ -89,6 +89,7 @@ impl<T: Ord> BTreeSet<T> {
     /// # Examples
     ///
     /// ```
+    /// # #![allow(unused_mut)]
     /// use std::collections::BTreeSet;
     ///
     /// let mut set: BTreeSet<i32> = BTreeSet::new();
diff --git a/src/libcollections/fmt.rs b/src/libcollections/fmt.rs
index a31ad6c1093..990575ebbb3 100644
--- a/src/libcollections/fmt.rs
+++ b/src/libcollections/fmt.rs
@@ -150,6 +150,7 @@
 //! implement a method of the signature:
 //!
 //! ```
+//! # #![allow(dead_code)]
 //! # use std::fmt;
 //! # struct Foo; // our custom type
 //! # impl fmt::Display for Foo {
@@ -174,7 +175,6 @@
 //! like:
 //!
 //! ```
-//! #![feature(fmt_flags)]
 //! use std::fmt;
 //!
 //! #[derive(Debug)]
@@ -288,6 +288,7 @@
 //! off, some example usage is:
 //!
 //! ```
+//! # #![allow(unused_must_use)]
 //! use std::fmt;
 //! use std::io::{self, Write};
 //!
diff --git a/src/libcollections/lib.rs b/src/libcollections/lib.rs
index 670c32776df..54b98c6e179 100644
--- a/src/libcollections/lib.rs
+++ b/src/libcollections/lib.rs
@@ -27,7 +27,7 @@
        html_root_url = "https://doc.rust-lang.org/nightly/",
        html_playground_url = "https://play.rust-lang.org/",
        issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
-       test(no_crate_inject))]
+       test(no_crate_inject, attr(allow(unused_variables), deny(warnings))))]
 
 #![allow(trivial_casts)]
 #![cfg_attr(test, allow(deprecated))] // rand
diff --git a/src/libcollections/slice.rs b/src/libcollections/slice.rs
index e6391f5c988..85aefbfffb1 100644
--- a/src/libcollections/slice.rs
+++ b/src/libcollections/slice.rs
@@ -852,6 +852,7 @@ pub trait SliceConcatExt<T: ?Sized> {
     /// # Examples
     ///
     /// ```
+    /// # #![allow(deprecated)]
     /// assert_eq!(["hello", "world"].connect(" "), "hello world");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/libcollections/str.rs b/src/libcollections/str.rs
index 104fbe699e0..a5013f4e75b 100644
--- a/src/libcollections/str.rs
+++ b/src/libcollections/str.rs
@@ -298,7 +298,7 @@ impl str {
     /// done by `.chars()` or `.char_indices()`.
     ///
     /// ```
-    /// #![feature(str_char, core)]
+    /// #![feature(str_char)]
     ///
     /// use std::str::CharRange;
     ///
@@ -358,7 +358,7 @@ impl str {
     /// done by `.chars().rev()` or `.char_indices()`.
     ///
     /// ```
-    /// #![feature(str_char, core)]
+    /// #![feature(str_char)]
     ///
     /// use std::str::CharRange;
     ///
@@ -634,6 +634,7 @@ impl str {
     /// # Examples
     ///
     /// ```
+    /// # #![allow(deprecated)]
     /// let four_lines = "foo\r\nbar\n\r\nbaz";
     /// let v: Vec<&str> = four_lines.lines_any().collect();
     ///
@@ -643,6 +644,7 @@ impl str {
     /// Leaving off the trailing character:
     ///
     /// ```
+    /// # #![allow(deprecated)]
     /// let four_lines = "foo\r\nbar\n\r\nbaz\n";
     /// let v: Vec<&str> = four_lines.lines_any().collect();
     ///
@@ -1179,8 +1181,6 @@ impl str {
     /// # Examples
     ///
     /// ```
-    /// #![feature(str_match_indices)]
-    ///
     /// let v: Vec<_> = "abcXXXabcYYYabc".match_indices("abc").collect();
     /// assert_eq!(v, [(0, "abc"), (6, "abc"), (12, "abc")]);
     ///
@@ -1216,8 +1216,6 @@ impl str {
     /// # Examples
     ///
     /// ```
-    /// #![feature(str_match_indices)]
-    ///
     /// let v: Vec<_> = "abcXXXabcYYYabc".rmatch_indices("abc").collect();
     /// assert_eq!(v, [(12, "abc"), (6, "abc"), (0, "abc")]);
     ///
diff --git a/src/libcollections/string.rs b/src/libcollections/string.rs
index 4255665681c..804e798c600 100644
--- a/src/libcollections/string.rs
+++ b/src/libcollections/string.rs
@@ -55,6 +55,7 @@ impl String {
     /// # Examples
     ///
     /// ```
+    /// # #![allow(unused_mut)]
     /// let mut s = String::new();
     /// ```
     #[inline]
@@ -73,6 +74,20 @@ impl String {
     ///
     /// ```
     /// let mut s = String::with_capacity(10);
+    ///
+    /// // The String contains no chars, even though it has capacity for more
+    /// assert_eq!(s.len(), 0);
+    ///
+    /// // These are all done without reallocating...
+    /// let cap = s.capacity();
+    /// for i in 0..10 {
+    ///     s.push('a');
+    /// }
+    ///
+    /// assert_eq!(s.capacity(), cap);
+    ///
+    /// // ...but this may make the vector reallocate
+    /// s.push('a');
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/libcollections/vec.rs b/src/libcollections/vec.rs
index c4e4059429f..9153d624268 100644
--- a/src/libcollections/vec.rs
+++ b/src/libcollections/vec.rs
@@ -242,6 +242,7 @@ impl<T> Vec<T> {
     /// # Examples
     ///
     /// ```
+    /// # #![allow(unused_mut)]
     /// let mut vec: Vec<i32> = Vec::new();
     /// ```
     #[inline]
diff --git a/src/libcore/cell.rs b/src/libcore/cell.rs
index 9fcc2b3412a..59b05c21d80 100644
--- a/src/libcore/cell.rs
+++ b/src/libcore/cell.rs
@@ -76,6 +76,7 @@
 //! a trait method that was originally defined to take `&self`.
 //!
 //! ```
+//! # #![allow(dead_code)]
 //! use std::cell::RefCell;
 //!
 //! struct Graph {
@@ -125,6 +126,7 @@
 //! }
 //!
 //! struct RcBox<T> {
+//! # #[allow(dead_code)]
 //!     value: T,
 //!     refcount: Cell<usize>
 //! }
@@ -776,6 +778,7 @@ impl<'b, T: ?Sized> DerefMut for RefMut<'b, T> {
 /// use std::cell::UnsafeCell;
 /// use std::marker::Sync;
 ///
+/// # #[allow(dead_code)]
 /// struct NotThreadSafe<T> {
 ///     value: UnsafeCell<T>,
 /// }
diff --git a/src/libcore/cmp.rs b/src/libcore/cmp.rs
index 302c9d0c369..5458a7b9c38 100644
--- a/src/libcore/cmp.rs
+++ b/src/libcore/cmp.rs
@@ -140,8 +140,6 @@ impl Ordering {
     /// This method can be used to reverse a comparison:
     ///
     /// ```
-    /// use std::cmp::Ordering;
-    ///
     /// let mut data: &mut [_] = &mut [2, 10, 5, 8];
     ///
     /// // sort the array from largest to smallest.
@@ -263,8 +261,6 @@ pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     /// # Examples
     ///
     /// ```
-    /// use std::cmp::Ordering;
-    ///
     /// let result = 1.0 < 2.0;
     /// assert_eq!(result, true);
     ///
diff --git a/src/libcore/default.rs b/src/libcore/default.rs
index cbad72eae3d..12c4a5ca200 100644
--- a/src/libcore/default.rs
+++ b/src/libcore/default.rs
@@ -15,6 +15,7 @@
 //! that define a set of options:
 //!
 //! ```
+//! # #[allow(dead_code)]
 //! struct SomeOptions {
 //!     foo: i32,
 //!     bar: f32,
@@ -24,6 +25,7 @@
 //! How can we define some default values? You can use `Default`:
 //!
 //! ```
+//! # #[allow(dead_code)]
 //! #[derive(Default)]
 //! struct SomeOptions {
 //!     foo: i32,
@@ -40,6 +42,7 @@
 //! If you have your own type, you need to implement `Default` yourself:
 //!
 //! ```
+//! # #![allow(dead_code)]
 //! enum Kind {
 //!     A,
 //!     B,
@@ -66,6 +69,7 @@
 //! If you want to override a particular option, but still retain the other defaults:
 //!
 //! ```
+//! # #[allow(dead_code)]
 //! # #[derive(Default)]
 //! # struct SomeOptions {
 //! #     foo: i32,
@@ -88,6 +92,7 @@ use marker::Sized;
 /// # Examples
 ///
 /// ```
+/// # #[allow(dead_code)]
 /// #[derive(Default)]
 /// struct SomeOptions {
 ///     foo: i32,
@@ -114,6 +119,7 @@ pub trait Default: Sized {
     /// Making your own:
     ///
     /// ```
+    /// # #[allow(dead_code)]
     /// enum Kind {
     ///     A,
     ///     B,
diff --git a/src/libcore/hash/mod.rs b/src/libcore/hash/mod.rs
index 4e038f455e1..0899dc28848 100644
--- a/src/libcore/hash/mod.rs
+++ b/src/libcore/hash/mod.rs
@@ -45,6 +45,7 @@
 //!
 //! struct Person {
 //!     id: u32,
+//! # #[allow(dead_code)]
 //!     name: String,
 //!     phone: u64,
 //! }
diff --git a/src/libcore/intrinsics.rs b/src/libcore/intrinsics.rs
index ea4792bb495..a094bcd0192 100644
--- a/src/libcore/intrinsics.rs
+++ b/src/libcore/intrinsics.rs
@@ -334,6 +334,7 @@ extern "rust-intrinsic" {
     /// use std::mem;
     /// use std::ptr;
     ///
+    /// # #[allow(dead_code)]
     /// fn swap<T>(x: &mut T, y: &mut T) {
     ///     unsafe {
     ///         // Give ourselves some scratch space to work with
@@ -372,6 +373,7 @@ extern "rust-intrinsic" {
     /// ```
     /// use std::ptr;
     ///
+    /// # #[allow(dead_code)]
     /// unsafe fn from_buf_raw<T>(ptr: *const T, elts: usize) -> Vec<T> {
     ///     let mut dst = Vec::with_capacity(elts);
     ///     dst.set_len(elts);
diff --git a/src/libcore/iter.rs b/src/libcore/iter.rs
index f8c6e3cfdd7..8558927e4ac 100644
--- a/src/libcore/iter.rs
+++ b/src/libcore/iter.rs
@@ -241,6 +241,7 @@
 //! method calls a closure on each element it iterates over:
 //!
 //! ```
+//! # #![allow(unused_must_use)]
 //! let v = vec![1, 2, 3, 4, 5];
 //! v.iter().map(|x| println!("{}", x));
 //! ```
@@ -419,7 +420,7 @@ pub trait Iterator {
     ///
     /// ```
     /// // an infinite iterator has no upper bound
-    /// let iter = (0..);
+    /// let iter = 0..;
     ///
     /// assert_eq!((0, None), iter.size_hint());
     /// ```
@@ -709,6 +710,7 @@ pub trait Iterator {
     /// If you're doing some sort of side effect, prefer [`for`] to `map()`:
     ///
     /// ```
+    /// # #![allow(unused_must_use)]
     /// // don't do this:
     /// (0..5).map(|x| println!("{}", x));
     ///
@@ -2695,7 +2697,7 @@ impl<'a, I: DoubleEndedIterator + ?Sized> DoubleEndedIterator for &'a mut I {
 ///
 /// ```
 /// // a finite range knows exactly how many times it will iterate
-/// let five = (0..5);
+/// let five = 0..5;
 ///
 /// assert_eq!(5, five.len());
 /// ```
@@ -2761,7 +2763,7 @@ pub trait ExactSizeIterator: Iterator {
     ///
     /// ```
     /// // a finite range knows exactly how many times it will iterate
-    /// let five = (0..5);
+    /// let five = 0..5;
     ///
     /// assert_eq!(5, five.len());
     /// ```
diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index 94408072932..df7b7c437c3 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -60,7 +60,7 @@
        html_root_url = "https://doc.rust-lang.org/nightly/",
        html_playground_url = "https://play.rust-lang.org/",
        issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/")]
-#![doc(test(no_crate_inject))]
+#![doc(test(no_crate_inject, attr(allow(unused_variables), deny(warnings))))]
 
 #![no_core]
 #![allow(raw_pointer_derive)]
diff --git a/src/libcore/macros.rs b/src/libcore/macros.rs
index a4a2552025b..bc8656b32b8 100644
--- a/src/libcore/macros.rs
+++ b/src/libcore/macros.rs
@@ -247,6 +247,7 @@ macro_rules! writeln {
 /// Match arms:
 ///
 /// ```
+/// # #[allow(dead_code)]
 /// fn foo(x: Option<i32>) {
 ///     match x {
 ///         Some(n) if n >= 0 => println!("Some(Non-negative)"),
@@ -260,6 +261,7 @@ macro_rules! writeln {
 /// Iterators:
 ///
 /// ```
+/// # #[allow(dead_code)]
 /// fn divide_by_three(x: u32) -> u32 { // one of the poorest implementations of x/3
 ///     for i in 0.. {
 ///         if 3*i < i { panic!("u32 overflow"); }
diff --git a/src/libcore/marker.rs b/src/libcore/marker.rs
index 2f2dcc41a1c..6e6ae618527 100644
--- a/src/libcore/marker.rs
+++ b/src/libcore/marker.rs
@@ -42,6 +42,7 @@ impl<T> !Send for *mut T { }
 /// `?Sized` can be used to remove this bound if it is not appropriate.
 ///
 /// ```
+/// # #![allow(dead_code)]
 /// struct Foo<T>(T);
 /// struct Bar<T: ?Sized>(T);
 ///
@@ -106,6 +107,7 @@ pub trait Unsize<T: ?Sized> {
 /// `struct` can be `Copy`:
 ///
 /// ```
+/// # #[allow(dead_code)]
 /// struct Point {
 ///    x: i32,
 ///    y: i32,
@@ -115,6 +117,7 @@ pub trait Unsize<T: ?Sized> {
 /// A `struct` can be `Copy`, and `i32` is `Copy`, so therefore, `Point` is eligible to be `Copy`.
 ///
 /// ```
+/// # #![allow(dead_code)]
 /// # struct Point;
 /// struct PointList {
 ///     points: Vec<Point>,
@@ -303,6 +306,7 @@ macro_rules! impls{
 /// ```
 /// use std::marker::PhantomData;
 ///
+/// # #[allow(dead_code)]
 /// struct Slice<'a, T:'a> {
 ///     start: *const T,
 ///     end: *const T,
@@ -323,6 +327,7 @@ macro_rules! impls{
 /// mismatches by enforcing types in the method implementations:
 ///
 /// ```
+/// # #![allow(dead_code)]
 /// # trait ResType { fn foo(&self); }
 /// # struct ParamType;
 /// # mod foreign_lib {
@@ -393,6 +398,8 @@ mod impls {
 /// #![feature(reflect_marker)]
 /// use std::marker::Reflect;
 /// use std::any::Any;
+///
+/// # #[allow(dead_code)]
 /// fn foo<T:Reflect+'static>(x: &T) {
 ///     let any: &Any = x;
 ///     if any.is::<u32>() { println!("u32"); }
diff --git a/src/libcore/mem.rs b/src/libcore/mem.rs
index a87d135e425..2f01ea38340 100644
--- a/src/libcore/mem.rs
+++ b/src/libcore/mem.rs
@@ -92,6 +92,7 @@ pub use intrinsics::transmute;
 /// use std::mem;
 /// use std::ptr;
 ///
+/// # #[allow(dead_code)]
 /// fn swap<T>(x: &mut T, y: &mut T) {
 ///     unsafe {
 ///         // Give ourselves some scratch space to work with
@@ -151,6 +152,7 @@ pub fn size_of_val<T: ?Sized>(val: &T) -> usize {
 /// # Examples
 ///
 /// ```
+/// # #![allow(deprecated)]
 /// use std::mem;
 ///
 /// assert_eq!(4, mem::min_align_of::<i32>());
@@ -167,6 +169,7 @@ pub fn min_align_of<T>() -> usize {
 /// # Examples
 ///
 /// ```
+/// # #![allow(deprecated)]
 /// use std::mem;
 ///
 /// assert_eq!(4, mem::min_align_of_val(&5i32));
@@ -414,6 +417,7 @@ pub fn swap<T>(x: &mut T, y: &mut T) {
 /// `self`, allowing it to be returned:
 ///
 /// ```
+/// # #![allow(dead_code)]
 /// use std::mem;
 /// # struct Buffer<T> { buf: Vec<T> }
 /// impl<T> Buffer<T> {
diff --git a/src/libcore/ops.rs b/src/libcore/ops.rs
index 1bfdafa7133..7ad49eef8f7 100644
--- a/src/libcore/ops.rs
+++ b/src/libcore/ops.rs
@@ -947,6 +947,7 @@ shr_impl_all! { u8 u16 u32 u64 usize i8 i16 i32 i64 isize }
 ///     }
 /// }
 ///
+/// # #[allow(unused_assignments)]
 /// fn main() {
 ///     let mut foo = Foo;
 ///     foo += Foo;
@@ -996,6 +997,7 @@ add_assign_impl! { usize u8 u16 u32 u64 isize i8 i16 i32 i64 f32 f64 }
 ///     }
 /// }
 ///
+/// # #[allow(unused_assignments)]
 /// fn main() {
 ///     let mut foo = Foo;
 ///     foo -= Foo;
@@ -1045,6 +1047,7 @@ sub_assign_impl! { usize u8 u16 u32 u64 isize i8 i16 i32 i64 f32 f64 }
 ///     }
 /// }
 ///
+/// # #[allow(unused_assignments)]
 /// fn main() {
 ///     let mut foo = Foo;
 ///     foo *= Foo;
@@ -1094,6 +1097,7 @@ mul_assign_impl! { usize u8 u16 u32 u64 isize i8 i16 i32 i64 f32 f64 }
 ///     }
 /// }
 ///
+/// # #[allow(unused_assignments)]
 /// fn main() {
 ///     let mut foo = Foo;
 ///     foo /= Foo;
@@ -1143,6 +1147,7 @@ div_assign_impl! { usize u8 u16 u32 u64 isize i8 i16 i32 i64 f32 f64 }
 ///     }
 /// }
 ///
+/// # #[allow(unused_assignments)]
 /// fn main() {
 ///     let mut foo = Foo;
 ///     foo %= Foo;
@@ -1192,6 +1197,7 @@ rem_assign_impl! { usize u8 u16 u32 u64 isize i8 i16 i32 i64 f32 f64 }
 ///     }
 /// }
 ///
+/// # #[allow(unused_assignments)]
 /// fn main() {
 ///     let mut foo = Foo;
 ///     foo &= Foo;
@@ -1241,6 +1247,7 @@ bitand_assign_impl! { bool usize u8 u16 u32 u64 isize i8 i16 i32 i64 }
 ///     }
 /// }
 ///
+/// # #[allow(unused_assignments)]
 /// fn main() {
 ///     let mut foo = Foo;
 ///     foo |= Foo;
@@ -1290,6 +1297,7 @@ bitor_assign_impl! { bool usize u8 u16 u32 u64 isize i8 i16 i32 i64 }
 ///     }
 /// }
 ///
+/// # #[allow(unused_assignments)]
 /// fn main() {
 ///     let mut foo = Foo;
 ///     foo ^= Foo;
@@ -1339,6 +1347,7 @@ bitxor_assign_impl! { bool usize u8 u16 u32 u64 isize i8 i16 i32 i64 }
 ///     }
 /// }
 ///
+/// # #[allow(unused_assignments)]
 /// fn main() {
 ///     let mut foo = Foo;
 ///     foo <<= Foo;
@@ -1407,6 +1416,7 @@ shl_assign_impl_all! { u8 u16 u32 u64 usize i8 i16 i32 i64 isize }
 ///     }
 /// }
 ///
+/// # #[allow(unused_assignments)]
 /// fn main() {
 ///     let mut foo = Foo;
 ///     foo >>= Foo;
diff --git a/src/libcore/option.rs b/src/libcore/option.rs
index 26e00867d84..7a3b83f68d0 100644
--- a/src/libcore/option.rs
+++ b/src/libcore/option.rs
@@ -275,6 +275,7 @@ impl<T> Option<T> {
     ///
     /// ```
     /// #![feature(as_slice)]
+    /// # #![allow(deprecated)]
     ///
     /// let mut x = Some("Diamonds");
     /// {
diff --git a/src/libcore/result.rs b/src/libcore/result.rs
index 71219155cc3..6e1f120a1db 100644
--- a/src/libcore/result.rs
+++ b/src/libcore/result.rs
@@ -16,6 +16,7 @@
 //! and containing an error value.
 //!
 //! ```
+//! # #[allow(dead_code)]
 //! enum Result<T, E> {
 //!    Ok(T),
 //!    Err(E)
@@ -104,6 +105,7 @@
 //! something like this:
 //!
 //! ```no_run
+//! # #![allow(unused_must_use)] // \o/
 //! use std::fs::File;
 //! use std::io::prelude::*;
 //!
@@ -143,6 +145,7 @@
 //! # use std::fs::File;
 //! # use std::io::prelude::*;
 //! # use std::io;
+//! # #[allow(dead_code)]
 //! fn write_message() -> io::Result<()> {
 //!     let mut file = try!(File::create("valuable_data.txt"));
 //!     try!(file.write_all(b"important message"));
@@ -160,6 +163,7 @@
 //! It replaces this:
 //!
 //! ```
+//! # #![allow(dead_code)]
 //! use std::fs::File;
 //! use std::io::prelude::*;
 //! use std::io;
@@ -189,6 +193,7 @@
 //! With this:
 //!
 //! ```
+//! # #![allow(dead_code)]
 //! use std::fs::File;
 //! use std::io::prelude::*;
 //! use std::io;
@@ -422,6 +427,7 @@ impl<T, E> Result<T, E> {
     ///
     /// ```
     /// #![feature(as_slice)]
+    /// # #![allow(deprecated)]
     ///
     /// let mut x: Result<&str, u32> = Ok("Gold");
     /// {
diff --git a/src/libcore/str/mod.rs b/src/libcore/str/mod.rs
index 18334ba91c6..7954bc3a0bf 100644
--- a/src/libcore/str/mod.rs
+++ b/src/libcore/str/mod.rs
@@ -142,8 +142,6 @@ impl Utf8Error {
     /// Basic usage:
     ///
     /// ```
-    /// #![feature(utf8_error)]
-    ///
     /// use std::str;
     ///
     /// // some invalid bytes, in a vector
diff --git a/src/libflate/lib.rs b/src/libflate/lib.rs
index 51f38752329..513379b6558 100644
--- a/src/libflate/lib.rs
+++ b/src/libflate/lib.rs
@@ -23,7 +23,8 @@
 #![crate_type = "dylib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
-       html_root_url = "https://doc.rust-lang.org/nightly/")]
+       html_root_url = "https://doc.rust-lang.org/nightly/",
+       test(attr(deny(warnings))))]
 
 #![feature(libc)]
 #![feature(staged_api)]
diff --git a/src/libfmt_macros/lib.rs b/src/libfmt_macros/lib.rs
index ed767ab1e5c..dc69f38e4e7 100644
--- a/src/libfmt_macros/lib.rs
+++ b/src/libfmt_macros/lib.rs
@@ -24,7 +24,8 @@
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/",
-       html_playground_url = "https://play.rust-lang.org/")]
+       html_playground_url = "https://play.rust-lang.org/",
+       test(attr(deny(warnings))))]
 
 #![feature(staged_api)]
 #![feature(unicode)]
diff --git a/src/libgetopts/lib.rs b/src/libgetopts/lib.rs
index ab34f2e48ca..f49451f827d 100644
--- a/src/libgetopts/lib.rs
+++ b/src/libgetopts/lib.rs
@@ -30,9 +30,11 @@
 //! file name following `-o`, and accepts both `-h` and `--help` as optional flags.
 //!
 //! ```{.rust}
+//! #![feature(rustc_private)]
+//!
 //! extern crate getopts;
 //! use getopts::{optopt,optflag,getopts,OptGroup,usage};
-//! use std::os;
+//! use std::env;
 //!
 //! fn do_work(inp: &str, out: Option<String>) {
 //!     println!("{}", inp);
@@ -44,11 +46,11 @@
 //!
 //! fn print_usage(program: &str, opts: &[OptGroup]) {
 //!     let brief = format!("Usage: {} [options]", program);
-//!     print!("{}", usage(brief, opts));
+//!     print!("{}", usage(&brief, opts));
 //! }
 //!
 //! fn main() {
-//!     let args: Vec<String> = os::args();
+//!     let args: Vec<String> = env::args().collect();
 //!
 //!     let program = args[0].clone();
 //!
@@ -56,22 +58,22 @@
 //!         optopt("o", "", "set output file name", "NAME"),
 //!         optflag("h", "help", "print this help menu")
 //!     ];
-//!     let matches = match getopts(args[1..], opts) {
+//!     let matches = match getopts(&args[1..], opts) {
 //!         Ok(m) => { m }
 //!         Err(f) => { panic!(f.to_string()) }
 //!     };
 //!     if matches.opt_present("h") {
-//!         print_usage(program, opts);
+//!         print_usage(&program, opts);
 //!         return;
 //!     }
 //!     let output = matches.opt_str("o");
 //!     let input = if !matches.free.is_empty() {
 //!         matches.free[0].clone()
 //!     } else {
-//!         print_usage(program, opts);
+//!         print_usage(&program, opts);
 //!         return;
 //!     };
-//!     do_work(input, output);
+//!     do_work(&input, output);
 //! }
 //! ```
 
@@ -88,7 +90,8 @@
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/",
-       html_playground_url = "https://play.rust-lang.org/")]
+       html_playground_url = "https://play.rust-lang.org/",
+       test(attr(deny(warnings))))]
 
 #![deny(missing_docs)]
 #![feature(staged_api)]
diff --git a/src/libgraphviz/lib.rs b/src/libgraphviz/lib.rs
index b82b7d122b3..1fb54ed9071 100644
--- a/src/libgraphviz/lib.rs
+++ b/src/libgraphviz/lib.rs
@@ -47,7 +47,7 @@
 //! which is cyclic.
 //!
 //! ```rust
-//! #![feature(rustc_private, core, into_cow)]
+//! #![feature(rustc_private, into_cow)]
 //!
 //! use std::borrow::IntoCow;
 //! use std::io::Write;
@@ -150,9 +150,8 @@
 //! entity `&sube`).
 //!
 //! ```rust
-//! #![feature(rustc_private, core, into_cow)]
+//! #![feature(rustc_private)]
 //!
-//! use std::borrow::IntoCow;
 //! use std::io::Write;
 //! use graphviz as dot;
 //!
@@ -174,10 +173,10 @@
 //!         dot::Id::new(format!("N{}", n)).unwrap()
 //!     }
 //!     fn node_label<'b>(&'b self, n: &Nd) -> dot::LabelText<'b> {
-//!         dot::LabelText::LabelStr(self.nodes[*n].as_slice().into_cow())
+//!         dot::LabelText::LabelStr(self.nodes[*n].into())
 //!     }
 //!     fn edge_label<'b>(&'b self, _: &Ed) -> dot::LabelText<'b> {
-//!         dot::LabelText::LabelStr("&sube;".into_cow())
+//!         dot::LabelText::LabelStr("&sube;".into())
 //!     }
 //! }
 //!
@@ -209,9 +208,8 @@
 //! Hasse-diagram for the subsets of the set `{x, y}`.
 //!
 //! ```rust
-//! #![feature(rustc_private, core, into_cow)]
+//! #![feature(rustc_private)]
 //!
-//! use std::borrow::IntoCow;
 //! use std::io::Write;
 //! use graphviz as dot;
 //!
@@ -234,10 +232,10 @@
 //!     }
 //!     fn node_label<'b>(&'b self, n: &Nd<'b>) -> dot::LabelText<'b> {
 //!         let &(i, _) = n;
-//!         dot::LabelText::LabelStr(self.nodes[i].into_cow())
+//!         dot::LabelText::LabelStr(self.nodes[i].into())
 //!     }
 //!     fn edge_label<'b>(&'b self, _: &Ed<'b>) -> dot::LabelText<'b> {
-//!         dot::LabelText::LabelStr("&sube;".into_cow())
+//!         dot::LabelText::LabelStr("&sube;".into())
 //!     }
 //! }
 //!
@@ -283,7 +281,8 @@
 #![crate_type = "dylib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
-       html_root_url = "https://doc.rust-lang.org/nightly/")]
+       html_root_url = "https://doc.rust-lang.org/nightly/",
+       test(attr(allow(unused_variables), deny(warnings))))]
 
 #![feature(into_cow)]
 #![feature(str_escape)]
diff --git a/src/liblog/lib.rs b/src/liblog/lib.rs
index 9cb835bd852..1de7ebfffde 100644
--- a/src/liblog/lib.rs
+++ b/src/liblog/lib.rs
@@ -13,6 +13,7 @@
 //! # Examples
 //!
 //! ```
+//! # #![feature(rustc_private)]
 //! #[macro_use] extern crate log;
 //!
 //! fn main() {
@@ -167,7 +168,8 @@
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/",
-       html_playground_url = "https://play.rust-lang.org/")]
+       html_playground_url = "https://play.rust-lang.org/",
+       test(attr(deny(warnings))))]
 #![deny(missing_docs)]
 
 #![feature(box_syntax)]
diff --git a/src/liblog/macros.rs b/src/liblog/macros.rs
index 46b51f50c85..803a2df9ccc 100644
--- a/src/liblog/macros.rs
+++ b/src/liblog/macros.rs
@@ -19,6 +19,7 @@
 /// # Examples
 ///
 /// ```
+/// # #![feature(rustc_private)]
 /// #[macro_use] extern crate log;
 ///
 /// fn main() {
@@ -67,6 +68,7 @@ macro_rules! log {
 /// # Examples
 ///
 /// ```
+/// # #![feature(rustc_private)]
 /// #[macro_use] extern crate log;
 ///
 /// fn main() {
@@ -92,6 +94,7 @@ macro_rules! error {
 /// # Examples
 ///
 /// ```
+/// # #![feature(rustc_private)]
 /// #[macro_use] extern crate log;
 ///
 /// fn main() {
@@ -116,6 +119,7 @@ macro_rules! warn {
 /// # Examples
 ///
 /// ```
+/// # #![feature(rustc_private)]
 /// #[macro_use] extern crate log;
 ///
 /// fn main() {
@@ -142,6 +146,7 @@ macro_rules! info {
 /// # Examples
 ///
 /// ```
+/// # #![feature(rustc_private)]
 /// #[macro_use] extern crate log;
 ///
 /// fn main() {
@@ -165,9 +170,10 @@ macro_rules! debug {
 /// # Examples
 ///
 /// ```
+/// # #![feature(rustc_private)]
 /// #[macro_use] extern crate log;
 ///
-/// struct Point { x: int, y: int }
+/// struct Point { x: i32, y: i32 }
 /// fn some_expensive_computation() -> Point { Point { x: 1, y: 2 } }
 ///
 /// fn main() {
diff --git a/src/librand/lib.rs b/src/librand/lib.rs
index b5a1eb9520c..cf2118b45a4 100644
--- a/src/librand/lib.rs
+++ b/src/librand/lib.rs
@@ -23,7 +23,8 @@
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/",
-       html_playground_url = "https://play.rust-lang.org/")]
+       html_playground_url = "https://play.rust-lang.org/",
+       test(attr(deny(warnings))))]
 #![no_std]
 #![staged_api]
 #![unstable(feature = "rand",
diff --git a/src/librbml/lib.rs b/src/librbml/lib.rs
index 1c6cb06d54a..a1b15cd9e6f 100644
--- a/src/librbml/lib.rs
+++ b/src/librbml/lib.rs
@@ -121,7 +121,8 @@
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/",
-       html_playground_url = "https://play.rust-lang.org/")]
+       html_playground_url = "https://play.rust-lang.org/",
+       test(attr(deny(warnings))))]
 
 #![feature(rustc_private)]
 #![feature(staged_api)]
diff --git a/src/librustc_unicode/lib.rs b/src/librustc_unicode/lib.rs
index 467c9746900..79ce8aacae8 100644
--- a/src/librustc_unicode/lib.rs
+++ b/src/librustc_unicode/lib.rs
@@ -31,7 +31,7 @@
        html_root_url = "https://doc.rust-lang.org/nightly/",
        html_playground_url = "https://play.rust-lang.org/",
        issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
-       test(no_crate_inject))]
+       test(no_crate_inject, attr(allow(unused_variables), deny(warnings))))]
 #![no_std]
 
 #![feature(core_char_ext)]
diff --git a/src/librustc_unicode/u_str.rs b/src/librustc_unicode/u_str.rs
index 2347cdebf22..57d96bf4371 100644
--- a/src/librustc_unicode/u_str.rs
+++ b/src/librustc_unicode/u_str.rs
@@ -190,6 +190,7 @@ impl<'a> Iterator for Utf16Items<'a> {
 ///
 /// ```
 /// #![feature(unicode, decode_utf16)]
+/// # #![allow(deprecated)]
 ///
 /// extern crate rustc_unicode;
 ///
diff --git a/src/libserialize/json.rs b/src/libserialize/json.rs
index 452feed3cdb..9e1e3c6a558 100644
--- a/src/libserialize/json.rs
+++ b/src/libserialize/json.rs
@@ -77,8 +77,9 @@
 //! serialization API, using the derived serialization code.
 //!
 //! ```rust
-//! extern crate serialize;
-//! use serialize::json;
+//! # #![feature(rustc_private)]
+//! extern crate serialize as rustc_serialize; // for the deriving below
+//! use rustc_serialize::json;
 //!
 //! // Automatically generate `Decodable` and `Encodable` trait implementations
 //! #[derive(RustcDecodable, RustcEncodable)]
@@ -111,6 +112,7 @@
 //! ### Simple example of `ToJson` usage
 //!
 //! ```rust
+//! # #![feature(rustc_private)]
 //! extern crate serialize;
 //! use serialize::json::{self, ToJson, Json};
 //!
@@ -150,6 +152,7 @@
 //! ### Verbose example of `ToJson` usage
 //!
 //! ```rust
+//! # #![feature(rustc_private)]
 //! extern crate serialize;
 //! use std::collections::BTreeMap;
 //! use serialize::json::{self, Json, ToJson};
@@ -185,7 +188,7 @@
 //!     let json_str: String = json_obj.to_string();
 //!
 //!     // Deserialize like before
-//!     let decoded: TestStruct = json::decode(json_str)).unwrap();
+//!     let decoded: TestStruct = json::decode(&json_str).unwrap();
 //! }
 //! ```
 
diff --git a/src/libserialize/lib.rs b/src/libserialize/lib.rs
index 5b7bec41723..4a766f14531 100644
--- a/src/libserialize/lib.rs
+++ b/src/libserialize/lib.rs
@@ -26,7 +26,8 @@ Core encoding and decoding interfaces.
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/",
-       html_playground_url = "https://play.rust-lang.org/")]
+       html_playground_url = "https://play.rust-lang.org/",
+       test(attr(allow(unused_variables), deny(warnings))))]
 
 #![feature(box_syntax)]
 #![feature(collections)]
diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 8c9c8835087..1f34af617d5 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -908,13 +908,15 @@ pub enum Expr_ {
 /// separately. `position` represents the index of the associated
 /// item qualified with this Self type.
 ///
-///     <Vec<T> as a::b::Trait>::AssociatedItem
-///      ^~~~~     ~~~~~~~~~~~~~~^
-///      ty        position = 3
+/// ```ignore
+/// <Vec<T> as a::b::Trait>::AssociatedItem
+///  ^~~~~     ~~~~~~~~~~~~~~^
+///  ty        position = 3
 ///
-///     <Vec<T>>::AssociatedItem
-///      ^~~~~    ^
-///      ty       position = 0
+/// <Vec<T>>::AssociatedItem
+///  ^~~~~    ^
+///  ty       position = 0
+/// ```
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub struct QSelf {
     pub ty: P<Ty>,
diff --git a/src/libsyntax/ext/deriving/generic/mod.rs b/src/libsyntax/ext/deriving/generic/mod.rs
index 5c6e2fce8ad..5a0fc4fda0c 100644
--- a/src/libsyntax/ext/deriving/generic/mod.rs
+++ b/src/libsyntax/ext/deriving/generic/mod.rs
@@ -54,6 +54,7 @@
 //! following snippet
 //!
 //! ```rust
+//! # #![allow(dead_code)]
 //! struct A { x : i32 }
 //!
 //! struct B(i32);
@@ -88,7 +89,7 @@
 //!
 //! ```rust
 //! trait PartialEq {
-//!     fn eq(&self, other: &Self);
+//!     fn eq(&self, other: &Self) -> bool;
 //! }
 //! impl PartialEq for i32 {
 //!     fn eq(&self, other: &i32) -> bool {
@@ -905,7 +906,7 @@ impl<'a> MethodDef<'a> {
         })
     }
 
-    /// ```
+    /// ```ignore
     /// #[derive(PartialEq)]
     /// struct A { x: i32, y: i32 }
     ///
@@ -1010,7 +1011,7 @@ impl<'a> MethodDef<'a> {
                                       &StaticStruct(struct_def, summary))
     }
 
-    /// ```
+    /// ```ignore
     /// #[derive(PartialEq)]
     /// enum A {
     ///     A1,
@@ -1596,7 +1597,7 @@ pub fn cs_fold<F>(use_foldl: bool,
 /// Call the method that is being derived on all the fields, and then
 /// process the collected results. i.e.
 ///
-/// ```
+/// ```ignore
 /// f(cx, span, vec![self_1.method(__arg_1_1, __arg_2_1),
 ///                  self_2.method(__arg_1_2, __arg_2_2)])
 /// ```
diff --git a/src/libsyntax/ext/format.rs b/src/libsyntax/ext/format.rs
index c56342371c8..af0e7ce5c8d 100644
--- a/src/libsyntax/ext/format.rs
+++ b/src/libsyntax/ext/format.rs
@@ -77,9 +77,10 @@ struct Context<'a, 'b:'a> {
 /// expressions.
 ///
 /// If parsing succeeds, the return value is:
-///
-///     Some((fmtstr, unnamed arguments, ordering of named arguments,
-///           named arguments))
+/// ```ignore
+/// Some((fmtstr, unnamed arguments, ordering of named arguments,
+///       named arguments))
+/// ```
 fn parse_args(ecx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
               -> Option<(P<ast::Expr>, Vec<P<ast::Expr>>, Vec<String>,
                          HashMap<String, P<ast::Expr>>)> {
diff --git a/src/libsyntax/lib.rs b/src/libsyntax/lib.rs
index 524ac655d88..0cd27d1b0cc 100644
--- a/src/libsyntax/lib.rs
+++ b/src/libsyntax/lib.rs
@@ -23,7 +23,8 @@
 #![crate_type = "rlib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
-       html_root_url = "https://doc.rust-lang.org/nightly/")]
+       html_root_url = "https://doc.rust-lang.org/nightly/",
+       test(attr(deny(warnings))))]
 
 #![feature(associated_consts)]
 #![feature(drain)]
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index fde1058a785..1e38eebec5d 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -3965,7 +3965,7 @@ impl<'a> Parser<'a> {
 
     /// Parses an optional `where` clause and places it in `generics`.
     ///
-    /// ```
+    /// ```ignore
     /// where T : Trait<U, V> + 'b, 'a : 'b
     /// ```
     pub fn parse_where_clause(&mut self) -> PResult<ast::WhereClause> {
diff --git a/src/libsyntax/print/pp.rs b/src/libsyntax/print/pp.rs
index 7c5a46465f5..cbbd5289a5a 100644
--- a/src/libsyntax/print/pp.rs
+++ b/src/libsyntax/print/pp.rs
@@ -11,8 +11,10 @@
 //! This pretty-printer is a direct reimplementation of Philip Karlton's
 //! Mesa pretty-printer, as described in appendix A of
 //!
-//!     STAN-CS-79-770: "Pretty Printing", by Derek C. Oppen.
-//!     Stanford Department of Computer Science, 1979.
+//! ````ignore
+//! STAN-CS-79-770: "Pretty Printing", by Derek C. Oppen.
+//! Stanford Department of Computer Science, 1979.
+//! ````
 //!
 //! The algorithm's aim is to break a stream into as few lines as possible
 //! while respecting the indentation-consistency requirements of the enclosing
diff --git a/src/libterm/lib.rs b/src/libterm/lib.rs
index ced3a7d47d7..99bbd951766 100644
--- a/src/libterm/lib.rs
+++ b/src/libterm/lib.rs
@@ -53,7 +53,8 @@
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/",
-       html_playground_url = "https://play.rust-lang.org/")]
+       html_playground_url = "https://play.rust-lang.org/",
+       test(attr(deny(warnings))))]
 #![deny(missing_docs)]
 
 #![feature(box_syntax)]
diff --git a/src/libtest/lib.rs b/src/libtest/lib.rs
index 69b1d37bfc4..89442fe1096 100644
--- a/src/libtest/lib.rs
+++ b/src/libtest/lib.rs
@@ -32,7 +32,8 @@
 #![crate_type = "dylib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
-       html_root_url = "https://doc.rust-lang.org/nightly/")]
+       html_root_url = "https://doc.rust-lang.org/nightly/",
+       test(attr(deny(warnings))))]
 
 #![feature(asm)]
 #![feature(box_syntax)]