This commit is an implementation of [RFC 1066][rfc] where the conclusion was
that leaking a value is a safe operation in Rust code, so updating the signature
of this function follows suit.

[rfc]: https://github.com/rust-lang/rfcs/blob/master/text/1066-safe-mem-forget.md

Closes #25186

Perform unsafe initialization up front and then only afterward the mutex is in
place do we initialize it.

Now that `std::old_io` has been removed for quite some time the naming real
estate here has opened up to allow these modules to move back to their proper
names.

These all had a typo where they were accessing the seconds field, not the
nanoseconds field.

Apparently implementations are allowed to return EDEADLK instead of blocking
forever, in which case this can lead to unsafety in the `RwLock` primitive
exposed by the standard library. A debug-build of the standard library would
have caught this error (due to the debug assert), but we don't ship debug
builds right now.

This commit adds explicit checks for the EDEADLK error code and triggers a panic
to ensure the call does not succeed.

Closes #25012

This is the last remaining portion of #24796

This commit is an implementation of [RFC 1044][rfc] which adds additional
surface area to the `std::fs` module. All new APIs are `#[unstable]` behind
assorted feature names for each one.

[rfc]: https://github.com/rust-lang/rfcs/pull/1044

The new APIs added are:

* `fs::canonicalize` - bindings to `realpath` on unix and
  `GetFinalPathNameByHandle` on windows.
* `fs::symlink_metadata` - similar to `lstat` on unix
* `fs::FileType` and accessor methods as `is_{file,dir,symlink}`
* `fs::Metadata::file_type` - accessor for the raw file type
* `fs::DirEntry::metadata` - acquisition of metadata which is free on Windows
  but requires a syscall on unix.
* `fs::DirEntry::file_type` - access the file type which may not require a
  syscall on most platforms.
* `fs::DirEntry::file_name` - access just the file name without leading
  components.
* `fs::PathExt::symlink_metadata` - convenience method for the top-level
  function.
* `fs::PathExt::canonicalize` - convenience method for the top-level
  function.
* `fs::PathExt::read_link` - convenience method for the top-level
  function.
* `fs::PathExt::read_dir` - convenience method for the top-level
  function.
* `std::os::raw` - type definitions for raw OS/C types available on all
  platforms.
* `std::os::$platform` - new modules have been added for all currently supported
  platforms (e.g. those more specific than just `unix`).
* `std::os::$platform::raw` - platform-specific type definitions. These modules
  are populated with the bare essentials necessary for lowing I/O types into
  their raw representations, and currently largely consist of the `stat`
  definition for unix platforms.

This commit also deprecates `Metadata::{modified, accessed}` in favor of
inspecting the raw representations via the lowering methods of `Metadata`.

Inspecting the current thread's info may not always work due to the TLS value
having been destroyed (or is actively being destroyed). The code for printing
a panic message assumed, however, that it could acquire the thread's name
through this method.

Instead this commit propagates the `Option` outwards to allow the
`std::panicking` module to handle the case where the current thread isn't
present.

While it solves the immediate issue of #24313, there is still another underlying
issue of panicking destructors in thread locals will abort the process.

Closes #24313

Statically linked executables do not succeed (aka MUSL-based executables).

This commit modifies the standard library and its dependencies to link correctly
when built against MUSL. This primarily ensures that the right libraries are
linked against and when they're linked against they're linked against
statically.

These functions were intended to be introduced as `#[stable]` as a stable API
was deprecated in favor of them, but they just erroneously forgot the stability
attributes.

Much of this code hasn't been updated in quite some time and this commit does a
small audit of the functionality:

* Implementation functions now centralize all functionality on a locally defined
  `Thread` type.
* The `detach` method has been removed in favor of a `Drop` implementation. This
  notably fixes leaking thread handles on Windows.
* The `Thread` structure is now appropriately annotated with `Send` and `Sync`
  automatically on Windows and in a custom fashion on Unix.
* The unsafety of creating a thread has been pushed out to the right boundaries
  now.

Closes #24442

This commit removes all the old casting/generic traits from `std::num` that are
no longer in use by the standard library. This additionally removes the old
`strconv` module which has not seen much use in quite a long time. All generic
functionality has been supplanted with traits in the `num` crate and the
`strconv` module is supplanted with the [rust-strconv crate][rust-strconv].

[rust-strconv]: https://github.com/lifthrasiir/rust-strconv

This is a breaking change due to the removal of these deprecated crates, and the
alternative crates are listed above.

[breaking-change]

On Windows, when you create a symbolic link you must specify whether it
points to a directory or a file, even if it is created dangling, while
on Unix, the same symbolic link could point to a directory, a file, or
nothing at all.  Furthermore, on Windows special privilege is necessary
to use a symbolic link, while on Unix, you can generally create a
symbolic link in any directory you have write privileges to.

This means that it is unlikely to be able to use symbolic links purely
portably; anyone who uses them will need to think about the cross
platform implications.  This means that using platform-specific APIs
will make it easier to see where code will need to differ between the
platforms, rather than trying to provide some kind of compatibility
wrapper.

Furthermore, `soft_link` has no precedence in any other API, so to avoid
confusion, move back to the more standard `symlink` terminology.

Create a `std::os::unix::symlink` for the Unix version that is
destination type agnostic, as well as `std::os::windows::{symlink_file,
symlink_dir}` for Windows.

Because this is a stable API, leave a compatibility wrapper in
`std::fs::soft_link`, which calls `symlink` on Unix and `symlink_file`
on Windows, preserving the existing behavior of `soft_link`.

Looks like these were missed in bf4e77d4.

This patch adds a `Debug` impl for `std::fs::File`.

On all platforms (Unix and Windows) it shows the file descriptor.

On Linux, it displays the path and access mode as well.

Ideally we should show the path/mode for all platforms, not just Linux,
but this will do for now.

cc #24570

This commit entirely removes the old I/O, path, and rand modules. All
functionality has been deprecated and unstable for quite some time now!

The logic for only closing file descriptors >= 3 was inherited from quite some
time ago and ends up meaning that some internal APIs are less consistent than
they should be. By unconditionally closing everything entering a `FileDesc` we
ensure that we're consistent in our behavior as well as robustly handling the
stdio case.

* De-indent quite a bit by removing usage of FnOnce closures
* Clearly separate code for the parent/child after the fork
* Use `fs2::{File, OpenOptions}` instead of calling `open` manually
* Use RAII to close I/O objects wherever possible
* Remove loop for closing all file descriptors, all our own ones are now
  `CLOEXEC` by default so they cannot be inherited

This commit starts to set the CLOEXEC flag for all files and sockets opened by
the standard library by default on all unix platforms. There are a few points of
note in this commit:

* The implementation is not 100% satisfactory in the face of threads. File
  descriptors only have the `F_CLOEXEC` flag set *after* they are opened,
  allowing for a fork/exec to happen in the middle and leak the descriptor.
  Some platforms do support atomically opening a descriptor while setting the
  `CLOEXEC` flag, and it is left as a future extension to bind these apis as it
  is unclear how to do so nicely at this time.

* The implementation does not offer a method of opting into the old behavior of
  not setting `CLOEXEC`. This will possibly be added in the future through
  extensions on `OpenOptions`, for example.

* This change does not yet audit any Windows APIs to see if the handles are
  inherited by default by accident.

This is a breaking change for users who call `fork` or `exec` outside of the
standard library itself and expect file descriptors to be inherted. All file
descriptors created by the standard library will no longer be inherited.

[breaking-change]

As pointed out in [RFC issue 1043][rfc] it is quite useful to have the standard
I/O types to provide the contract that they are the sole owner of the underlying
object they represent. This guarantee enables writing safe interfaces like the
`MemoryMap` API sketched out in that issue.

[rfc]: https://github.com/rust-lang/rfcs/issues/1043

As constructing objects from these raw handles may end up violating these
ownership gurantees, the functions for construction are now marked unsafe.

[breaking-change]
Closes rust-lang/rfcs#1043

This commit stabilizes the old `io::Error::from_os_error` after being renamed to
use the `raw_os_error` terminology instead. This function is often useful when
writing bindings to OS functions but only actually converting to an I/O error at
a later point.

write_fmt calls write for each formatted field. The default implementation of write_fmt is used,
which will call write on not-yet-locked stdout (and write locking after), therefore making print!
in multithreaded environment still interleave contents of two separate prints.

This patch implements reentrant mutexes, changes stdio handles to use these mutexes and overrides
write_fmt to lock the stdio handle for the whole duration of the call.

This commit is an implementation of [RFC 979][rfc] which changes the meaning of
the count parameter to the `splitn` function on strings and slices. The
parameter now means the number of items that are returned from the iterator, not
the number of splits that are made.

[rfc]: https://github.com/rust-lang/rfcs/pull/979

Closes #23911
[breaking-change]

This commit stabilizes a few remaining bits of the `io::Error` type:

* The `Error::new` method is now stable. The last `detail` parameter was removed
  and the second `desc` parameter was generalized to `E: Into<Box<Error>>` to
  allow creating an I/O error from any form of error. Currently there is no form
  of downcasting, but this will be added in time.

* An implementation of `From<&str> for Box<Error>` was added to liballoc to
  allow construction of errors from raw strings.

* The `Error::raw_os_error` method was stabilized as-is.

* Trait impls for `Clone`, `Eq`, and `PartialEq` were removed from `Error` as it
  is not possible to use them with trait objects.

This is a breaking change due to the modification of the `new` method as well as
the removal of the trait implementations for the `Error` type.

[breaking-change]

This commit cleans out a large amount of deprecated APIs from the standard
library and some of the facade crates as well, updating all users in the
compiler and in tests as it goes along.

This commit is an implementation of [RFC #1011][rfc] which adds an `exit`
function to the standard library for immediately terminating the current process
with a specified exit code.

[rfc]: https://github.com/rust-lang/rfcs/pull/1011

* Marks `#[stable]` the contents of the `std::convert` module.

* Added methods `PathBuf::as_path`, `OsString::as_os_str`,
  `String::as_str`, `Vec::{as_slice, as_mut_slice}`.

* Deprecates `OsStr::from_str` in favor of a new, stable, and more
  general `OsStr::new`.

* Adds unstable methods `OsString::from_bytes` and `OsStr::{to_bytes,
  to_cstring}` for ergonomic FFI usage.

[breaking-change]

This commit stabilizes the `std::num` module:

* The `Int` and `Float` traits are deprecated in favor of (1) the
  newly-added inherent methods and (2) the generic traits available in
  rust-lang/num.

* The `Zero` and `One` traits are reintroduced in `std::num`, which
  together with various other traits allow you to recover the most
  common forms of generic programming.

* The `FromStrRadix` trait, and associated free function, is deprecated
  in favor of inherent implementations.

* A wide range of methods and constants for both integers and floating
  point numbers are now `#[stable]`, having been adjusted for integer
  guidelines.

* `is_positive` and `is_negative` are renamed to `is_sign_positive` and
  `is_sign_negative`, in order to address #22985

* The `Wrapping` type is moved to `std::num` and stabilized;
  `WrappingOps` is deprecated in favor of inherent methods on the
  integer types, and direct implementation of operations on
  `Wrapping<X>` for each concrete integer type `X`.

Closes #22985
Closes #21069

[breaking-change]

This commit stabilizes the platform-specific `io` modules, specifically around
the traits having to do with the raw representation of each object on each
platform.

Specifically, the following material was stabilized:

* `AsRaw{Fd,Socket,Handle}`
* `RawFd` (renamed from `Fd`)
* `RawHandle` (renamed from `Handle`)
* `RawSocket` (renamed from `Socket`)
* `AsRaw{Fd,Socket,Handle}` implementations
* `std::os::{unix, windows}::io`

The following material was added as `#[unstable]`:

* `FromRaw{Fd,Socket,Handle}`
* Implementations for various primitives

There are a number of future improvements that are possible to make to this
module, but this should cover a good bit of functionality desired from these
modules for now. Some specific future additions may include:

* `IntoRawXXX` traits to consume the raw representation and cancel the
  auto-destructor.
* `Fd`, `Socket`, and `Handle` abstractions that behave like Rust objects and
  have nice methods for various syscalls.

At this time though, these are considered backwards-compatible extensions and
will not be stabilized at this time.

This commit is a breaking change due to the addition of `Raw` in from of the
type aliases in each of the platform-specific modules.

[breaking-change]

This commit revises `path` and `os_str` to use blanket impls for `From`
on reference types. This both cuts down on the number of required impls,
and means that you can pass through e.g. `T: AsRef<OsStr>` to
`PathBuf::from` without an intermediate call to `as_ref`.

It also makes a FIXME note for later generalizing the blanket impls for
`AsRef` and `AsMut` to use `Deref`/`DerefMut`, once it is possible to do
so.

Now that support has been removed, all lingering use cases are renamed.