Num, NumCast, Unsigned, Float, Primitive and Int have been removed.

Throughout the docs, "failure" was replaced with "panics" if it means a
task panic. Otherwise, it remained as is, or changed to "errors" to
clearly differentiate it from a task panic.

In order to upgrade, simply rename the Extendable trait to Extend in
your code

Part of #18424

[breaking-change]

* Renames/deprecates the simplest and most obvious methods
* Adds FIXME(conventions)s for outstanding work
* Marks "handled" methods as unstable

NOTE: the semantics of reserve and reserve_exact have changed!
Other methods have had their semantics changed as well, but in a
way that should obviously not typecheck if used incorrectly.

Lots of work and breakage to come, but this handles most of the core
APIs and most eggregious breakage. Future changes should *mostly* focus on
niche collections, APIs, or simply back-compat additions.

[breaking-change]

This commit renames a number of extension traits for slices and string
slices, now that they have been refactored for DST. In many cases,
multiple extension traits could now be consolidated. Further
consolidation will be possible with generalized where clauses.

The renamings are consistent with the [new `-Prelude`
suffix](https://github.com/rust-lang/rfcs/pull/344). There are probably
a few more candidates for being renamed this way, but that is left for
API stabilization of the relevant modules.

Because this renames traits, it is a:

[breaking-change]

However, I do not expect any code that currently uses the standard
library to actually break.

Closes #17917

Add impls of the comparison operators for fixed-length arrays of lengths 0...32 and repair various cases where slices and fixed-length arrays were being compared.

upon (e.g., `&int` added to `int`).

This makes the low-level allocation API suitable for use cases where
out-of-memory conditions need to be handled.

Closes #18292

[breaking-change]

As part of the collections reform RFC, this commit removes all collections
traits in favor of inherent methods on collections themselves. All methods
should continue to be available on all collections.

This is a breaking change with all of the collections traits being removed and
no longer being in the prelude. In order to update old code you should move the
trait implementations to inherent implementations directly on the type itself.

Note that some traits had default methods which will also need to be implemented
to maintain backwards compatibility.

[breaking-change]
cc #18424

This commit enables implementations of IndexMut for a number of collections,
including Vec, RingBuf, SmallIntMap, TrieMap, TreeMap, and HashMap. At the same
time this deprecates the `get_mut` methods on vectors in favor of using the
indexing notation.

cc #18424

This commit adds the following impls:

    impl<T> Deref<[T]> for Vec<T>
    impl<T> DerefMut<[T]> for Vec<T>
    impl Deref<str> for String

This commit also removes all duplicated inherent methods from vectors and
strings as implementations will now silently call through to the slice
implementation. Some breakage occurred at std and beneath due to inherent
methods removed in favor of those in the slice traits and std doesn't use its
own prelude,

cc #18424

https://github.com/rust-lang/rfcs/pull/221

The current terminology of "task failure" often causes problems when
writing or speaking about code. You often want to talk about the
possibility of an operation that returns a Result "failing", but cannot
because of the ambiguity with task failure. Instead, you have to speak
of "the failing case" or "when the operation does not succeed" or other
circumlocutions.

Likewise, we use a "Failure" header in rustdoc to describe when
operations may fail the task, but it would often be helpful to separate
out a section describing the "Err-producing" case.

We have been steadily moving away from task failure and toward Result as
an error-handling mechanism, so we should optimize our terminology
accordingly: Result-producing functions should be easy to describe.

To update your code, rename any call to `fail!` to `panic!` instead.
Assuming you have not created your own macro named `panic!`, this
will work on UNIX based systems:

    grep -lZR 'fail!' . | xargs -0 -l sed -i -e 's/fail!/panic!/g'

You can of course also do this by hand.

[breaking-change]

Add @thestinger comment explaining that shrink_to_fit might drop down as close as possible but not to the minimun

Fixes #18302

r? @thestinger

- shrink_to_fit example is now more clear by asserting the capacity value

Spring cleaning is here! In the Fall! This commit removes quite a large amount
of deprecated functionality from the standard libraries. I tried to ensure that
only old deprecated functionality was removed.

This is removing lots and lots of deprecated features, so this is a breaking
change. Please consult the deprecation messages of the deleted code to see how
to migrate code forward if it still needs migration.

[breaking-change]

`IndexMut` on mutable vectors.

This fixes a bug whereby the mutability fixups for method behavior were
not kicking in after autoderef failed to happen at any level. It also
adds support for `Index` to the fixer-upper.

Closes #12825.

compiletest: compact "linux" "macos" etc.as "unix".
liballoc: remove a superfluous "use".
libcollections: remove invocations of deprecated methods in favor of
    their suggested replacements and use "_" for a loop counter.
libcoretest: remove invocations of deprecated methods;  also add
    "allow(deprecated)" for testing a deprecated method itself.
libglob: use "cfg_attr".
libgraphviz: add a test for one of data constructors.
libgreen: remove a superfluous "use".
libnum: "allow(type_overflow)" for type cast into u8 in a test code.
librustc: names of static variables should be in upper case.
libserialize: v[i] instead of get().
libstd/ascii: to_lowercase() instead of to_lower().
libstd/bitflags: modify AnotherSetOfFlags to use i8 as its backend.
    It will serve better for testing various aspects of bitflags!.
libstd/collections: "allow(deprecated)" for testing a deprecated
    method itself.
libstd/io: remove invocations of deprecated methods and superfluous "use".
    Also add #[test] where it was missing.
libstd/num: introduce a helper function to effectively remove
    invocations of a deprecated method.
libstd/path and rand: remove invocations of deprecated methods and
    superfluous "use".
libstd/task and libsync/comm: "allow(deprecated)" for testing
    a deprecated method itself.
libsync/deque: remove superfluous "unsafe".
libsync/mutex and once: names of static variables should be in upper case.
libterm: introduce a helper function to effectively remove
    invocations of a deprecated method.

We still see a few warnings about using obsoleted native::task::spawn()
in the test modules for libsync.  I'm not sure how I should replace them
with std::task::TaksBuilder and native::task::NativeTaskBuilder
(dependency to libstd?)
Signed-off-by: NNODA, Kai <nodakai@gmail.com>

[breaking-change]
Closes #17916

Also convert a number of `static mut` to just a plain old `static` and remove
some unsafe blocks.

Closes #17865

Using reallocate(old_ptr, old_size, new_size, align) makes a lot more
sense than reallocate(old_ptr, new_size, align, old_size) and matches up
with the order used by existing platform APIs like mremap.

Closes #17837

[breaking-change]

This provides a way to pass `&[T]` to functions taking `&U` where `U` is
a `Vec<T>`. This is useful in many cases not covered by the Equiv trait
or methods like `find_with` on TreeMap.

This reverts commit 40b9f5de.

This reverts commit df2f1fa7.

This reverts commit 6e0611a4.