std: Deny most warnings in doctests

Allow a few specific ones but otherwise this helps ensure that our examples are
squeaky clean!

Closes #18199

18 files changed, 212 insertions, 225 deletions

diff --git a/src/libcore/macros.rs b/src/libcore/macros.rs
index c21898d088d..ece419af951 100644
--- a/src/libcore/macros.rs
+++ b/src/libcore/macros.rs
@@ -229,7 +229,6 @@ macro_rules! writeln {
 /// Iterators:
 ///
 /// ```
-/// # #![feature(core)]
 /// 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/libstd/collections/hash/set.rs b/src/libstd/collections/hash/set.rs
index 5fbc21797ab..f897d565321 100644
--- a/src/libstd/collections/hash/set.rs
+++ b/src/libstd/collections/hash/set.rs
@@ -304,7 +304,6 @@ impl<T, S> HashSet<T, S>
     /// # Examples
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::collections::HashSet;
     /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
     /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
@@ -335,7 +334,6 @@ impl<T, S> HashSet<T, S>
     /// # Examples
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::collections::HashSet;
     /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
     /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
@@ -362,7 +360,6 @@ impl<T, S> HashSet<T, S>
     /// # Examples
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::collections::HashSet;
     /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
     /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
@@ -388,7 +385,6 @@ impl<T, S> HashSet<T, S>
     /// # Examples
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::collections::HashSet;
     /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
     /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
@@ -471,7 +467,6 @@ impl<T, S> HashSet<T, S>
     /// # Examples
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::collections::HashSet;
     ///
     /// let set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
@@ -491,7 +486,6 @@ impl<T, S> HashSet<T, S>
     /// # Examples
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::collections::HashSet;
     ///
     /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
@@ -513,7 +507,6 @@ impl<T, S> HashSet<T, S>
     /// # Examples
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::collections::HashSet;
     ///
     /// let sup: HashSet<_> = [1, 2, 3].iter().cloned().collect();
@@ -535,7 +528,6 @@ impl<T, S> HashSet<T, S>
     /// # Examples
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::collections::HashSet;
     ///
     /// let sub: HashSet<_> = [1, 2].iter().cloned().collect();
diff --git a/src/libstd/collections/mod.rs b/src/libstd/collections/mod.rs
index 0ac97b71298..48b95ce6439 100644
--- a/src/libstd/collections/mod.rs
+++ b/src/libstd/collections/mod.rs
@@ -10,16 +10,18 @@
 
 //! Collection types.
 //!
-//! Rust's standard collection library provides efficient implementations of the most common
-//! general purpose programming data structures. By using the standard implementations,
-//! it should be possible for two libraries to communicate without significant data conversion.
-//!
-//! To get this out of the way: you should probably just use `Vec` or `HashMap`. These two
-//! collections cover most use cases for generic data storage and processing. They are
-//! exceptionally good at doing what they do. All the other collections in the standard
-//! library have specific use cases where they are the optimal choice, but these cases are
-//! borderline *niche* in comparison. Even when `Vec` and `HashMap` are technically suboptimal,
-//! they're probably a good enough choice to get started.
+//! Rust's standard collection library provides efficient implementations of the
+//! most common general purpose programming data structures. By using the
+//! standard implementations, it should be possible for two libraries to
+//! communicate without significant data conversion.
+//!
+//! To get this out of the way: you should probably just use `Vec` or `HashMap`.
+//! These two collections cover most use cases for generic data storage and
+//! processing. They are exceptionally good at doing what they do. All the other
+//! collections in the standard library have specific use cases where they are
+//! the optimal choice, but these cases are borderline *niche* in comparison.
+//! Even when `Vec` and `HashMap` are technically suboptimal, they're probably a
+//! good enough choice to get started.
 //!
 //! Rust's collections can be grouped into four major categories:
 //!
@@ -30,28 +32,31 @@
 //!
 //! # When Should You Use Which Collection?
 //!
-//! These are fairly high-level and quick break-downs of when each collection should be
-//! considered. Detailed discussions of strengths and weaknesses of individual collections
-//! can be found on their own documentation pages.
+//! These are fairly high-level and quick break-downs of when each collection
+//! should be considered. Detailed discussions of strengths and weaknesses of
+//! individual collections can be found on their own documentation pages.
 //!
 //! ### Use a `Vec` when:
-//! * You want to collect items up to be processed or sent elsewhere later, and don't care about
-//! any properties of the actual values being stored.
-//! * You want a sequence of elements in a particular order, and will only be appending to
-//! (or near) the end.
+//! * You want to collect items up to be processed or sent elsewhere later, and
+//!   don't care about any properties of the actual values being stored.
+//! * You want a sequence of elements in a particular order, and will only be
+//!   appending to (or near) the end.
 //! * You want a stack.
 //! * You want a resizable array.
 //! * You want a heap-allocated array.
 //!
 //! ### Use a `VecDeque` when:
-//! * You want a `Vec` that supports efficient insertion at both ends of the sequence.
+//! * You want a `Vec` that supports efficient insertion at both ends of the
+//!   sequence.
 //! * You want a queue.
 //! * You want a double-ended queue (deque).
 //!
 //! ### Use a `LinkedList` when:
-//! * You want a `Vec` or `VecDeque` of unknown size, and can't tolerate amortization.
+//! * You want a `Vec` or `VecDeque` of unknown size, and can't tolerate
+//!   amortization.
 //! * You want to efficiently split and append lists.
-//! * You are *absolutely* certain you *really*, *truly*, want a doubly linked list.
+//! * You are *absolutely* certain you *really*, *truly*, want a doubly linked
+//!   list.
 //!
 //! ### Use a `HashMap` when:
 //! * You want to associate arbitrary keys with an arbitrary value.
@@ -60,7 +65,8 @@
 //!
 //! ### Use a `BTreeMap` when:
 //! * You're interested in what the smallest or largest key-value pair is.
-//! * You want to find the largest or smallest key that is smaller or larger than something
+//! * You want to find the largest or smallest key that is smaller or larger
+//!   than something
 //! * You want to be able to get all of the entries in order on-demand.
 //! * You want a sorted map.
 //!
@@ -81,29 +87,34 @@
 //! * You want a `BitVec`, but want `Set` properties
 //!
 //! ### Use a `BinaryHeap` when:
-//! * You want to store a bunch of elements, but only ever want to process the "biggest"
-//! or "most important" one at any given time.
+//!
+//! * You want to store a bunch of elements, but only ever want to process the
+//!   "biggest" or "most important" one at any given time.
 //! * You want a priority queue.
 //!
 //! # Performance
 //!
-//! Choosing the right collection for the job requires an understanding of what each collection
-//! is good at. Here we briefly summarize the performance of different collections for certain
-//! important operations. For further details, see each type's documentation, and note that the
-//! names of actual methods may differ from the tables below on certain collections.
+//! Choosing the right collection for the job requires an understanding of what
+//! each collection is good at. Here we briefly summarize the performance of
+//! different collections for certain important operations. For further details,
+//! see each type's documentation, and note that the names of actual methods may
+//! differ from the tables below on certain collections.
 //!
-//! Throughout the documentation, we will follow a few conventions. For all operations,
-//! the collection's size is denoted by n. If another collection is involved in the operation, it
-//! contains m elements. Operations which have an *amortized* cost are suffixed with a `*`.
-//! Operations with an *expected* cost are suffixed with a `~`.
+//! Throughout the documentation, we will follow a few conventions. For all
+//! operations, the collection's size is denoted by n. If another collection is
+//! involved in the operation, it contains m elements. Operations which have an
+//! *amortized* cost are suffixed with a `*`.  Operations with an *expected*
+//! cost are suffixed with a `~`.
 //!
-//! All amortized costs are for the potential need to resize when capacity is exhausted.
-//! If a resize occurs it will take O(n) time. Our collections never automatically shrink,
-//! so removal operations aren't amortized. Over a sufficiently large series of
-//! operations, the average cost per operation will deterministically equal the given cost.
+//! All amortized costs are for the potential need to resize when capacity is
+//! exhausted.  If a resize occurs it will take O(n) time. Our collections never
+//! automatically shrink, so removal operations aren't amortized. Over a
+//! sufficiently large series of operations, the average cost per operation will
+//! deterministically equal the given cost.
 //!
-//! Only HashMap has expected costs, due to the probabilistic nature of hashing. It is
-//! theoretically possible, though very unlikely, for HashMap to experience worse performance.
+//! Only HashMap has expected costs, due to the probabilistic nature of hashing.
+//! It is theoretically possible, though very unlikely, for HashMap to
+//! experience worse performance.
 //!
 //! ## Sequences
 //!
@@ -120,7 +131,8 @@
 //!
 //! ## Maps
 //!
-//! For Sets, all operations have the cost of the equivalent Map operation. For BitSet,
+//! For Sets, all operations have the cost of the equivalent Map operation. For
+//! BitSet,
 //! refer to VecMap.
 //!
 //! |          | get       | insert   | remove   | predecessor |
@@ -129,85 +141,95 @@
 //! | BTreeMap | O(log n)  | O(log n) | O(log n) | O(log n)    |
 //! | VecMap   | O(1)      | O(1)?    | O(1)     | O(n)        |
 //!
-//! Note that VecMap is *incredibly* inefficient in terms of space. The O(1) insertion time
-//! assumes space for the element is already allocated. Otherwise, a large key may require a
-//! massive reallocation, with no direct relation to the number of elements in the collection.
-//! VecMap should only be seriously considered for small keys.
+//! Note that VecMap is *incredibly* inefficient in terms of space. The O(1)
+//! insertion time assumes space for the element is already allocated.
+//! Otherwise, a large key may require a massive reallocation, with no direct
+//! relation to the number of elements in the collection.  VecMap should only be
+//! seriously considered for small keys.
 //!
 //! Note also that BTreeMap's precise preformance depends on the value of B.
 //!
 //! # Correct and Efficient Usage of Collections
 //!
-//! Of course, knowing which collection is the right one for the job doesn't instantly
-//! permit you to use it correctly. Here are some quick tips for efficient and correct
-//! usage of the standard collections in general. If you're interested in how to use a
-//! specific collection in particular, consult its documentation for detailed discussion
-//! and code examples.
+//! Of course, knowing which collection is the right one for the job doesn't
+//! instantly permit you to use it correctly. Here are some quick tips for
+//! efficient and correct usage of the standard collections in general. If
+//! you're interested in how to use a specific collection in particular, consult
+//! its documentation for detailed discussion and code examples.
 //!
 //! ## Capacity Management
 //!
-//! Many collections provide several constructors and methods that refer to "capacity".
-//! These collections are generally built on top of an array. Optimally, this array would be
-//! exactly the right size to fit only the elements stored in the collection, but for the
-//! collection to do this would be very inefficient. If the backing array was exactly the
-//! right size at all times, then every time an element is inserted, the collection would
-//! have to grow the array to fit it. Due to the way memory is allocated and managed on most
-//! computers, this would almost surely require allocating an entirely new array and
-//! copying every single element from the old one into the new one. Hopefully you can
-//! see that this wouldn't be very efficient to do on every operation.
-//!
-//! Most collections therefore use an *amortized* allocation strategy. They generally let
-//! themselves have a fair amount of unoccupied space so that they only have to grow
-//! on occasion. When they do grow, they allocate a substantially larger array to move
-//! the elements into so that it will take a while for another grow to be required. While
-//! this strategy is great in general, it would be even better if the collection *never*
-//! had to resize its backing array. Unfortunately, the collection itself doesn't have
-//! enough information to do this itself. Therefore, it is up to us programmers to give it
-//! hints.
-//!
-//! Any `with_capacity` constructor will instruct the collection to allocate enough space
-//! for the specified number of elements. Ideally this will be for exactly that many
-//! elements, but some implementation details may prevent this. `Vec` and `VecDeque` can
-//! be relied on to allocate exactly the requested amount, though. Use `with_capacity`
-//! when you know exactly how many elements will be inserted, or at least have a
-//! reasonable upper-bound on that number.
-//!
-//! When anticipating a large influx of elements, the `reserve` family of methods can
-//! be used to hint to the collection how much room it should make for the coming items.
-//! As with `with_capacity`, the precise behavior of these methods will be specific to
-//! the collection of interest.
-//!
-//! For optimal performance, collections will generally avoid shrinking themselves.
-//! If you believe that a collection will not soon contain any more elements, or
-//! just really need the memory, the `shrink_to_fit` method prompts the collection
-//! to shrink the backing array to the minimum size capable of holding its elements.
-//!
-//! Finally, if ever you're interested in what the actual capacity of the collection is,
-//! most collections provide a `capacity` method to query this information on demand.
-//! This can be useful for debugging purposes, or for use with the `reserve` methods.
+//! Many collections provide several constructors and methods that refer to
+//! "capacity".  These collections are generally built on top of an array.
+//! Optimally, this array would be exactly the right size to fit only the
+//! elements stored in the collection, but for the collection to do this would
+//! be very inefficient. If the backing array was exactly the right size at all
+//! times, then every time an element is inserted, the collection would have to
+//! grow the array to fit it. Due to the way memory is allocated and managed on
+//! most computers, this would almost surely require allocating an entirely new
+//! array and copying every single element from the old one into the new one.
+//! Hopefully you can see that this wouldn't be very efficient to do on every
+//! operation.
+//!
+//! Most collections therefore use an *amortized* allocation strategy. They
+//! generally let themselves have a fair amount of unoccupied space so that they
+//! only have to grow on occasion. When they do grow, they allocate a
+//! substantially larger array to move the elements into so that it will take a
+//! while for another grow to be required. While this strategy is great in
+//! general, it would be even better if the collection *never* had to resize its
+//! backing array. Unfortunately, the collection itself doesn't have enough
+//! information to do this itself. Therefore, it is up to us programmers to give
+//! it hints.
+//!
+//! Any `with_capacity` constructor will instruct the collection to allocate
+//! enough space for the specified number of elements. Ideally this will be for
+//! exactly that many elements, but some implementation details may prevent
+//! this. `Vec` and `VecDeque` can be relied on to allocate exactly the
+//! requested amount, though. Use `with_capacity` when you know exactly how many
+//! elements will be inserted, or at least have a reasonable upper-bound on that
+//! number.
+//!
+//! When anticipating a large influx of elements, the `reserve` family of
+//! methods can be used to hint to the collection how much room it should make
+//! for the coming items.  As with `with_capacity`, the precise behavior of
+//! these methods will be specific to the collection of interest.
+//!
+//! For optimal performance, collections will generally avoid shrinking
+//! themselves.  If you believe that a collection will not soon contain any more
+//! elements, or just really need the memory, the `shrink_to_fit` method prompts
+//! the collection to shrink the backing array to the minimum size capable of
+//! holding its elements.
+//!
+//! Finally, if ever you're interested in what the actual capacity of the
+//! collection is, most collections provide a `capacity` method to query this
+//! information on demand.  This can be useful for debugging purposes, or for
+//! use with the `reserve` methods.
 //!
 //! ## Iterators
 //!
-//! Iterators are a powerful and robust mechanism used throughout Rust's standard
-//! libraries. Iterators provide a sequence of values in a generic, safe, efficient
-//! and convenient way. The contents of an iterator are usually *lazily* evaluated,
-//! so that only the values that are actually needed are ever actually produced, and
-//! no allocation need be done to temporarily store them. Iterators are primarily
-//! consumed using a `for` loop, although many functions also take iterators where
-//! a collection or sequence of values is desired.
-//!
-//! All of the standard collections provide several iterators for performing bulk
-//! manipulation of their contents. The three primary iterators almost every collection
-//! should provide are `iter`, `iter_mut`, and `into_iter`. Some of these are not
-//! provided on collections where it would be unsound or unreasonable to provide them.
+//! Iterators are a powerful and robust mechanism used throughout Rust's
+//! standard libraries. Iterators provide a sequence of values in a generic,
+//! safe, efficient and convenient way. The contents of an iterator are usually
+//! *lazily* evaluated, so that only the values that are actually needed are
+//! ever actually produced, and no allocation need be done to temporarily store
+//! them. Iterators are primarily consumed using a `for` loop, although many
+//! functions also take iterators where a collection or sequence of values is
+//! desired.
+//!
+//! All of the standard collections provide several iterators for performing
+//! bulk manipulation of their contents. The three primary iterators almost
+//! every collection should provide are `iter`, `iter_mut`, and `into_iter`.
+//! Some of these are not provided on collections where it would be unsound or
+//! unreasonable to provide them.
 //!
 //! `iter` provides an iterator of immutable references to all the contents of a
-//! collection in the most "natural" order. For sequence collections like `Vec`, this
-//! means the items will be yielded in increasing order of index starting at 0. For ordered
-//! collections like `BTreeMap`, this means that the items will be yielded in sorted order.
-//! For unordered collections like `HashMap`, the items will be yielded in whatever order
-//! the internal representation made most convenient. This is great for reading through
-//! all the contents of the collection.
+//! collection in the most "natural" order. For sequence collections like `Vec`,
+//! this means the items will be yielded in increasing order of index starting
+//! at 0. For ordered collections like `BTreeMap`, this means that the items
+//! will be yielded in sorted order.  For unordered collections like `HashMap`,
+//! the items will be yielded in whatever order the internal representation made
+//! most convenient. This is great for reading through all the contents of the
+//! collection.
 //!
 //! ```
 //! let vec = vec![1, 2, 3, 4];
@@ -216,8 +238,8 @@
 //! }
 //! ```
 //!
-//! `iter_mut` provides an iterator of *mutable* references in the same order as `iter`.
-//! This is great for mutating all the contents of the collection.
+//! `iter_mut` provides an iterator of *mutable* references in the same order as
+//! `iter`.  This is great for mutating all the contents of the collection.
 //!
 //! ```
 //! let mut vec = vec![1, 2, 3, 4];
@@ -226,13 +248,14 @@
 //! }
 //! ```
 //!
-//! `into_iter` transforms the actual collection into an iterator over its contents
-//! by-value. This is great when the collection itself is no longer needed, and the
-//! values are needed elsewhere. Using `extend` with `into_iter` is the main way that
-//! contents of one collection are moved into another. Calling `collect` on an iterator
-//! itself is also a great way to convert one collection into another. Both of these
-//! methods should internally use the capacity management tools discussed in the
-//! previous section to do this as efficiently as possible.
+//! `into_iter` transforms the actual collection into an iterator over its
+//! contents by-value. This is great when the collection itself is no longer
+//! needed, and the values are needed elsewhere. Using `extend` with `into_iter`
+//! is the main way that contents of one collection are moved into another.
+//! Calling `collect` on an iterator itself is also a great way to convert one
+//! collection into another. Both of these methods should internally use the
+//! capacity management tools discussed in the previous section to do this as
+//! efficiently as possible.
 //!
 //! ```
 //! let mut vec1 = vec![1, 2, 3, 4];
@@ -247,11 +270,12 @@
 //! let buf: VecDeque<_> = vec.into_iter().collect();
 //! ```
 //!
-//! Iterators also provide a series of *adapter* methods for performing common tasks to
-//! sequences. Among the adapters are functional favorites like `map`, `fold`, `skip`,
-//! and `take`. Of particular interest to collections is the `rev` adapter, that
-//! reverses any iterator that supports this operation. Most collections provide reversible
-//! iterators as the way to iterate over them in reverse order.
+//! Iterators also provide a series of *adapter* methods for performing common
+//! tasks to sequences. Among the adapters are functional favorites like `map`,
+//! `fold`, `skip`, and `take`. Of particular interest to collections is the
+//! `rev` adapter, that reverses any iterator that supports this operation. Most
+//! collections provide reversible iterators as the way to iterate over them in
+//! reverse order.
 //!
 //! ```
 //! let vec = vec![1, 2, 3, 4];
@@ -260,48 +284,50 @@
 //! }
 //! ```
 //!
-//! Several other collection methods also return iterators to yield a sequence of results
-//! but avoid allocating an entire collection to store the result in. This provides maximum
-//! flexibility as `collect` or `extend` can be called to "pipe" the sequence into any
-//! collection if desired. Otherwise, the sequence can be looped over with a `for` loop. The
-//! iterator can also be discarded after partial use, preventing the computation of the unused
-//! items.
+//! Several other collection methods also return iterators to yield a sequence
+//! of results but avoid allocating an entire collection to store the result in.
+//! This provides maximum flexibility as `collect` or `extend` can be called to
+//! "pipe" the sequence into any collection if desired. Otherwise, the sequence
+//! can be looped over with a `for` loop. The iterator can also be discarded
+//! after partial use, preventing the computation of the unused items.
 //!
 //! ## Entries
 //!
-//! The `entry` API is intended to provide an efficient mechanism for manipulating
-//! the contents of a map conditionally on the presence of a key or not. The primary
-//! motivating use case for this is to provide efficient accumulator maps. For instance,
-//! if one wishes to maintain a count of the number of times each key has been seen,
-//! they will have to perform some conditional logic on whether this is the first time
-//! the key has been seen or not. Normally, this would require a `find` followed by an
-//! `insert`, effectively duplicating the search effort on each insertion.
-//!
-//! When a user calls `map.entry(&key)`, the map will search for the key and then yield
-//! a variant of the `Entry` enum.
-//!
-//! If a `Vacant(entry)` is yielded, then the key *was not* found. In this case the
-//! only valid operation is to `insert` a value into the entry. When this is done,
-//! the vacant entry is consumed and converted into a mutable reference to the
-//! the value that was inserted. This allows for further manipulation of the value
-//! beyond the lifetime of the search itself. This is useful if complex logic needs to
-//! be performed on the value regardless of whether the value was just inserted.
-//!
-//! If an `Occupied(entry)` is yielded, then the key *was* found. In this case, the user
-//! has several options: they can `get`, `insert`, or `remove` the value of the occupied
-//! entry. Additionally, they can convert the occupied entry into a mutable reference
-//! to its value, providing symmetry to the vacant `insert` case.
+//! The `entry` API is intended to provide an efficient mechanism for
+//! manipulating the contents of a map conditionally on the presence of a key or
+//! not. The primary motivating use case for this is to provide efficient
+//! accumulator maps. For instance, if one wishes to maintain a count of the
+//! number of times each key has been seen, they will have to perform some
+//! conditional logic on whether this is the first time the key has been seen or
+//! not. Normally, this would require a `find` followed by an `insert`,
+//! effectively duplicating the search effort on each insertion.
+//!
+//! When a user calls `map.entry(&key)`, the map will search for the key and
+//! then yield a variant of the `Entry` enum.
+//!
+//! If a `Vacant(entry)` is yielded, then the key *was not* found. In this case
+//! the only valid operation is to `insert` a value into the entry. When this is
+//! done, the vacant entry is consumed and converted into a mutable reference to
+//! the the value that was inserted. This allows for further manipulation of the
+//! value beyond the lifetime of the search itself. This is useful if complex
+//! logic needs to be performed on the value regardless of whether the value was
+//! just inserted.
+//!
+//! If an `Occupied(entry)` is yielded, then the key *was* found. In this case,
+//! the user has several options: they can `get`, `insert`, or `remove` the
+//! value of the occupied entry. Additionally, they can convert the occupied
+//! entry into a mutable reference to its value, providing symmetry to the
+//! vacant `insert` case.
 //!
 //! ### Examples
 //!
-//! Here are the two primary ways in which `entry` is used. First, a simple example
-//! where the logic performed on the values is trivial.
+//! Here are the two primary ways in which `entry` is used. First, a simple
+//! example where the logic performed on the values is trivial.
 //!
 //! #### Counting the number of times each character in a string occurs
 //!
 //! ```
-//! # #![feature(collections)]
-//! use std::collections::btree_map::{BTreeMap, Entry};
+//! use std::collections::btree_map::BTreeMap;
 //!
 //! let mut count = BTreeMap::new();
 //! let message = "she sells sea shells by the sea shore";
@@ -318,15 +344,14 @@
 //! }
 //! ```
 //!
-//! When the logic to be performed on the value is more complex, we may simply use
-//! the `entry` API to ensure that the value is initialized, and perform the logic
-//! afterwards.
+//! When the logic to be performed on the value is more complex, we may simply
+//! use the `entry` API to ensure that the value is initialized, and perform the
+//! logic afterwards.
 //!
 //! #### Tracking the inebriation of customers at a bar
 //!
 //! ```
-//! # #![feature(collections)]
-//! use std::collections::btree_map::{BTreeMap, Entry};
+//! use std::collections::btree_map::BTreeMap;
 //!
 //! // A client of the bar. They have an id and a blood alcohol level.
 //! struct Person { id: u32, blood_alcohol: f32 }
diff --git a/src/libstd/fs.rs b/src/libstd/fs.rs
index 4e2dade9a3c..914830d9dcf 100644
--- a/src/libstd/fs.rs
+++ b/src/libstd/fs.rs
@@ -96,14 +96,16 @@ pub struct WalkDir {
 
 /// Options and flags which can be used to configure how a file is opened.
 ///
-/// This builder exposes the ability to configure how a `File` is opened and what operations are
-/// permitted on the open file. The `File::open` and `File::create` methods are aliases for
-/// commonly used options using this builder.
+/// This builder exposes the ability to configure how a `File` is opened and
+/// what operations are permitted on the open file. The `File::open` and
+/// `File::create` methods are aliases for commonly used options using this
+/// builder.
 ///
-/// Generally speaking, when using `OpenOptions`, you'll first call `new()`, then chain calls to
-/// methods to set each option, then call `open()`, passing the path of the file you're trying to
-/// open. This will give you a [`io::Result`][result] with a [`File`][file] inside that you can
-/// further operate on.
+/// Generally speaking, when using `OpenOptions`, you'll first call `new()`,
+/// then chain calls to methods to set each option, then call `open()`, passing
+/// the path of the file you're trying to open. This will give you a
+/// [`io::Result`][result] with a [`File`][file] inside that you can further
+/// operate on.
 ///
 /// [result]: ../io/type.Result.html
 /// [file]: struct.File.html
@@ -113,16 +115,15 @@ pub struct WalkDir {
 /// Opening a file to read:
 ///
 /// ```no_run
-/// use std::fs;
 /// use std::fs::OpenOptions;
 ///
 /// let file = OpenOptions::new().read(true).open("foo.txt");
 /// ```
 ///
-/// Opening a file for both reading and writing, as well as creating it if it doesn't exist:
+/// Opening a file for both reading and writing, as well as creating it if it
+/// doesn't exist:
 ///
 /// ```
-/// use std::fs;
 /// use std::fs::OpenOptions;
 ///
 /// let file = OpenOptions::new()
@@ -771,7 +772,9 @@ pub fn rename<P: AsRef<Path>, Q: AsRef<Path>>(from: P, to: Q) -> io::Result<()>
 /// ```no_run
 /// use std::fs;
 ///
-/// fs::copy("foo.txt", "bar.txt");
+/// # fn foo() -> std::io::Result<()> {
+/// try!(fs::copy("foo.txt", "bar.txt"));
+/// # Ok(()) }
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn copy<P: AsRef<Path>, Q: AsRef<Path>>(from: P, to: Q) -> io::Result<u64> {
diff --git a/src/libstd/io/prelude.rs b/src/libstd/io/prelude.rs
index 333ae8f26a0..880770eb414 100644
--- a/src/libstd/io/prelude.rs
+++ b/src/libstd/io/prelude.rs
@@ -14,6 +14,7 @@
 //! by adding a glob import to the top of I/O heavy modules:
 //!
 //! ```
+//! # #![allow(unused_imports)]
 //! use std::io::prelude::*;
 //! ```
 //!
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index df81981c3f4..b329494a052 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -103,7 +103,8 @@
        html_favicon_url = "http://www.rust-lang.org/favicon.ico",
        html_root_url = "http://doc.rust-lang.org/nightly/",
        html_playground_url = "http://play.rust-lang.org/")]
-#![doc(test(no_crate_inject))]
+#![doc(test(no_crate_inject, attr(deny(warnings))))]
+#![doc(test(attr(allow(dead_code, deprecated, unused_variables, unused_mut))))]
 
 #![feature(alloc)]
 #![feature(box_syntax)]
diff --git a/src/libstd/net/addr.rs b/src/libstd/net/addr.rs
index 886f252fb19..3abf805c7f6 100644
--- a/src/libstd/net/addr.rs
+++ b/src/libstd/net/addr.rs
@@ -281,7 +281,6 @@ impl hash::Hash for SocketAddrV6 {
 /// Some examples:
 ///
 /// ```no_run
-/// # #![feature(net)]
 /// use std::net::{SocketAddrV4, TcpStream, UdpSocket, TcpListener, Ipv4Addr};
 ///
 /// fn main() {
@@ -302,7 +301,7 @@ impl hash::Hash for SocketAddrV6 {
 ///     let tcp_l = TcpListener::bind("localhost:12345");
 ///
 ///     let mut udp_s = UdpSocket::bind(("127.0.0.1", port)).unwrap();
-///     udp_s.send_to(&[7], (ip, 23451));
+///     udp_s.send_to(&[7], (ip, 23451)).unwrap();
 /// }
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/libstd/net/tcp.rs b/src/libstd/net/tcp.rs
index 04d1013af1f..2da6f7420ac 100644
--- a/src/libstd/net/tcp.rs
+++ b/src/libstd/net/tcp.rs
@@ -27,7 +27,6 @@ use sys_common::{AsInner, FromInner};
 /// # Examples
 ///
 /// ```no_run
-/// # #![feature(net)]
 /// use std::io::prelude::*;
 /// use std::net::TcpStream;
 ///
@@ -47,7 +46,6 @@ pub struct TcpStream(net_imp::TcpStream);
 /// # Examples
 ///
 /// ```no_run
-/// # #![feature(net)]
 /// use std::net::{TcpListener, TcpStream};
 /// use std::thread;
 ///
diff --git a/src/libstd/net/udp.rs b/src/libstd/net/udp.rs
index 7b14e4dbea6..bec9c09bc31 100644
--- a/src/libstd/net/udp.rs
+++ b/src/libstd/net/udp.rs
@@ -27,7 +27,6 @@ use sys_common::{AsInner, FromInner};
 /// # Examples
 ///
 /// ```no_run
-/// # #![feature(net)]
 /// use std::net::UdpSocket;
 ///
 /// # fn foo() -> std::io::Result<()> {
diff --git a/src/libstd/num/f32.rs b/src/libstd/num/f32.rs
index 0ae4d3c5bd6..6128469c60e 100644
--- a/src/libstd/num/f32.rs
+++ b/src/libstd/num/f32.rs
@@ -422,7 +422,6 @@ impl f32 {
     /// [subnormal][subnormal], or `NaN`.
     ///
     /// ```
-    /// # #![feature(std_misc)]
     /// use std::f32;
     ///
     /// let min = f32::MIN_POSITIVE; // 1.17549435e-38f32
@@ -856,7 +855,7 @@ impl f32 {
     /// Convert radians to degrees.
     ///
     /// ```
-    /// # #![feature(std_misc, core)]
+    /// # #![feature(std_misc)]
     /// use std::f32::{self, consts};
     ///
     /// let angle = consts::PI;
@@ -987,7 +986,6 @@ impl f32 {
     /// * Else: `self - other`
     ///
     /// ```
-    /// # #![feature(std_misc)]
     /// use std::f32;
     ///
     /// let x = 3.0f32;
@@ -1008,7 +1006,6 @@ impl f32 {
     /// Take the cubic root of a number.
     ///
     /// ```
-    /// # #![feature(std_misc)]
     /// use std::f32;
     ///
     /// let x = 8.0f32;
@@ -1210,8 +1207,6 @@ impl f32 {
     /// number is close to zero.
     ///
     /// ```
-    /// use std::f64;
-    ///
     /// let x = 7.0f64;
     ///
     /// // e^(ln(7)) - 1
diff --git a/src/libstd/num/mod.rs b/src/libstd/num/mod.rs
index 2de03e2e72d..ea516e5b20b 100644
--- a/src/libstd/num/mod.rs
+++ b/src/libstd/num/mod.rs
@@ -280,7 +280,6 @@ pub trait Float
     /// [subnormal][subnormal], or `NaN`.
     ///
     /// ```
-    /// # #![feature(std_misc)]
     /// use std::num::Float;
     /// use std::f32;
     ///
@@ -307,7 +306,6 @@ pub trait Float
     /// predicate instead.
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::num::{Float, FpCategory};
     /// use std::f32;
     ///
@@ -417,7 +415,6 @@ pub trait Float
     /// number is `Float::nan()`.
     ///
     /// ```
-    /// # #![feature(std_misc)]
     /// use std::num::Float;
     /// use std::f64;
     ///
@@ -441,7 +438,6 @@ pub trait Float
     /// - `Float::nan()` if the number is `Float::nan()`
     ///
     /// ```
-    /// # #![feature(std_misc)]
     /// use std::num::Float;
     /// use std::f64;
     ///
@@ -686,7 +682,6 @@ pub trait Float
     /// Convert radians to degrees.
     ///
     /// ```
-    /// # #![feature(std_misc, core)]
     /// use std::num::Float;
     /// use std::f64::consts;
     ///
@@ -701,7 +696,7 @@ pub trait Float
     /// Convert degrees to radians.
     ///
     /// ```
-    /// # #![feature(std_misc, core)]
+    /// # #![feature(std_misc)]
     /// use std::num::Float;
     /// use std::f64::consts;
     ///
@@ -849,7 +844,6 @@ pub trait Float
     /// Computes the sine of a number (in radians).
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::num::Float;
     /// use std::f64;
     ///
@@ -864,7 +858,6 @@ pub trait Float
     /// Computes the cosine of a number (in radians).
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::num::Float;
     /// use std::f64;
     ///
@@ -879,7 +872,6 @@ pub trait Float
     /// Computes the tangent of a number (in radians).
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::num::Float;
     /// use std::f64;
     ///
@@ -895,7 +887,6 @@ pub trait Float
     /// [-1, 1].
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::num::Float;
     /// use std::f64;
     ///
@@ -913,7 +904,6 @@ pub trait Float
     /// [-1, 1].
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::num::Float;
     /// use std::f64;
     ///
@@ -949,7 +939,6 @@ pub trait Float
     /// * `y < 0`: `arctan(y/x) - pi` -> `(-pi, -pi/2)`
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::num::Float;
     /// use std::f64;
     ///
@@ -975,7 +964,6 @@ pub trait Float
     /// `(sin(x), cos(x))`.
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::num::Float;
     /// use std::f64;
     ///
@@ -1011,7 +999,6 @@ pub trait Float
     /// the operations were performed separately.
     ///
     /// ```
-    /// # #![feature(std_misc, core)]
     /// use std::num::Float;
     /// use std::f64;
     ///
@@ -1028,7 +1015,6 @@ pub trait Float
     /// Hyperbolic sine function.
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::num::Float;
     /// use std::f64;
     ///
@@ -1047,7 +1033,6 @@ pub trait Float
     /// Hyperbolic cosine function.
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::num::Float;
     /// use std::f64;
     ///
@@ -1066,7 +1051,6 @@ pub trait Float
     /// Hyperbolic tangent function.
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::num::Float;
     /// use std::f64;
     ///
@@ -1113,7 +1097,6 @@ pub trait Float
     /// Inverse hyperbolic tangent function.
     ///
     /// ```
-    /// # #![feature(core)]
     /// use std::num::Float;
     /// use std::f64;
     ///
diff --git a/src/libstd/old_io/mod.rs b/src/libstd/old_io/mod.rs
index 5e93757668c..f62b1a836fd 100644
--- a/src/libstd/old_io/mod.rs
+++ b/src/libstd/old_io/mod.rs
@@ -48,7 +48,7 @@
 //! * Read lines from stdin
 //!
 //!     ```rust
-//!     # #![feature(old_io, old_path)]
+//!     # #![feature(old_io)]
 //!     use std::old_io as io;
 //!     use std::old_io::*;
 //!
diff --git a/src/libstd/old_io/net/ip.rs b/src/libstd/old_io/net/ip.rs
index 099fe657f26..f5310292b91 100644
--- a/src/libstd/old_io/net/ip.rs
+++ b/src/libstd/old_io/net/ip.rs
@@ -414,7 +414,7 @@ pub struct ParseError;
 /// Some examples:
 ///
 /// ```rust,no_run
-/// # #![feature(old_io, core, convert)]
+/// # #![feature(old_io)]
 /// # #![allow(unused_must_use)]
 ///
 /// use std::old_io::{TcpStream, TcpListener};
diff --git a/src/libstd/old_io/net/pipe.rs b/src/libstd/old_io/net/pipe.rs
index 3a071e832af..7b23c3e1d03 100644
--- a/src/libstd/old_io/net/pipe.rs
+++ b/src/libstd/old_io/net/pipe.rs
@@ -191,7 +191,7 @@ impl UnixListener {
     /// let server = Path::new("/path/to/my/socket");
     /// let stream = UnixListener::bind(&server);
     /// for mut client in stream.listen().incoming() {
-    ///     client.write(&[1, 2, 3, 4]);
+    ///     let _ = client.write(&[1, 2, 3, 4]);
     /// }
     /// # }
     /// ```
diff --git a/src/libstd/old_io/process.rs b/src/libstd/old_io/process.rs
index ad2d5b46819..b55d1f4db07 100644
--- a/src/libstd/old_io/process.rs
+++ b/src/libstd/old_io/process.rs
@@ -367,7 +367,7 @@ impl Command {
     /// # Examples
     ///
     /// ```
-    /// # #![feature(old_io, core, convert)]
+    /// # #![feature(old_io)]
     /// use std::old_io::Command;
     ///
     /// let output = match Command::new("cat").arg("foot.txt").output() {
diff --git a/src/libstd/old_path/mod.rs b/src/libstd/old_path/mod.rs
index 9c88533d3ba..22561c96f63 100644
--- a/src/libstd/old_path/mod.rs
+++ b/src/libstd/old_path/mod.rs
@@ -144,12 +144,10 @@ pub trait GenericPath: Clone + GenericPathUnsafe {
     ///
     /// # Examples
     ///
-    /// ```
+    /// ```no_run
     /// # #![feature(old_path)]
-    /// use std::old_path::{Path, GenericPath};
-    /// # foo();
-    /// # #[cfg(windows)] fn foo() {}
-    /// # #[cfg(unix)] fn foo() {
+    /// # fn main() {
+    /// use std::old_path::Path;
     /// let path = Path::new("foo/bar");
     /// # }
     /// ```
@@ -170,12 +168,10 @@ pub trait GenericPath: Clone + GenericPathUnsafe {
     ///
     /// # Examples
     ///
-    /// ```
+    /// ```no_run
     /// # #![feature(old_path)]
-    /// use std::old_path::{Path, GenericPath};
-    /// # foo();
-    /// # #[cfg(windows)] fn foo() {}
-    /// # #[cfg(unix)] fn foo() {
+    /// # fn main() {
+    /// use std::old_path::Path;
     /// let x: &[u8] = b"foo\0";
     /// assert!(Path::new_opt(x).is_none());
     /// # }
diff --git a/src/libstd/process.rs b/src/libstd/process.rs
index 52f5965db80..36c0b3e466f 100644
--- a/src/libstd/process.rs
+++ b/src/libstd/process.rs
@@ -38,8 +38,6 @@ use thread;
 /// # Examples
 ///
 /// ```should_panic
-/// # #![feature(process)]
-///
 /// use std::process::Command;
 ///
 /// let output = Command::new("/bin/cat").arg("file.txt").output().unwrap_or_else(|e| {
@@ -267,10 +265,8 @@ impl Command {
     /// # Examples
     ///
     /// ```
-    /// # #![feature(process)]
     /// use std::process::Command;
-    ///
-    /// let output = Command::new("cat").arg("foot.txt").output().unwrap_or_else(|e| {
+    /// let output = Command::new("cat").arg("foo.txt").output().unwrap_or_else(|e| {
     ///     panic!("failed to execute process: {}", e)
     /// });
     ///
@@ -291,7 +287,6 @@ impl Command {
     /// # Examples
     ///
     /// ```
-    /// # #![feature(process)]
     /// use std::process::Command;
     ///
     /// let status = Command::new("ls").status().unwrap_or_else(|e| {
diff --git a/src/libstd/thread/mod.rs b/src/libstd/thread/mod.rs
index 5fe6e80d6e9..cd480f8c29e 100644
--- a/src/libstd/thread/mod.rs
+++ b/src/libstd/thread/mod.rs
@@ -99,6 +99,7 @@
 //! `println!` and `panic!` for the child thread:
 //!
 //! ```rust
+//! # #![allow(unused_must_use)]
 //! use std::thread;
 //!
 //! thread::Builder::new().name("child1".to_string()).spawn(move || {