impl Clone for ::std_unicode::char::{ToLowercase, ToUppercase}

Improve --help performance for x.py

Since compiling the bootstrap command doesn't require any submodules,
we can skip updating submodules when a --help command is passed in.
On my machine, this saves 1 minute if the submodules are already
downloaded, and 10 minutes if run on a clean repo.

This commit also adds a message before compiling/downloading anything
when a --help command is passed in, to tell the user WHY --help
takes so long to complete. It also points the user to the bootstrap
README.md for faster help.

Finally, this fixes one warning message that still referenced using
make instead of x.py, even though x.py is now the standard way of
building rust.

Closes #37305

Disable NEON on musl ARMv7

`armv7-unknown-linux-musleabihf` target diverged a bit from `armv7-unknown-linux-gnueabihf` target. This PR re-syncs them.

Fix #47765.

add readme for librustdoc

In the same vein as the other compiler-library readmes, here's one for rustdoc! It's mainly a "how does rustdoc even" blog-post-style writeup, but i wanted to have something in-repo so people could get a sense of what bits did what.

Rollup (unsupervised)

less risky PRs, to run overnight

Fixes #47311.
r? @nrc

Fixes #47311.
r? @nrc

Fixes #47311.
r? @nrc

Fixes #47311.
r? @nrc

Fixes #47311.
r? @nrc

Fixes #47311.
r? @nrc

Fixes #47311.
r? @nrc

Revert "correct subtle bug in the type variable code"

This reverts commit ccd92c2a.

This commit is the source of a major perf regression, and was not
intended to be included in #47861. At some point I must have
accidentally re-added the commit.

Fixes #48660.

r? @nikomatsakis

Replace Rc with Lrc for shared data

This replaces `Rc`s reachable from `TyCtxt` with `Lrc`. This has no effect unless `cfg(parallel_queries)` is set. It also contains a fix for the `Decodable` impl for `Arc`.

r? @nikomatsakis

also minor doc fixes.

Closes #43941

This reverts commit ccd92c2a.

This commit is the source of a major perf regression, and was not
intended to be included in #47861. At some point I must have
accidentally re-added the commit.

It was an existing solution to tell the user why a --help command
takes a long time to process. However, it would only print if the
stage0 rust compiler needed to be downloaded, it came after
update_submodules (which took a long time), and it was immediately
followed by download messages and loading bars, meaning users could
easily gloss over the message.

This commit also moves the help message out of main(), and instead
puts it at the top of bootstrap(). main() is intended to be minimal,
only handling error messages.

Another rollup

None

Rebased refactorings for Chalk

The code is Niko's, I just handled the rebase.

r? @nikomatsakis

Currently rustc isn't always the best at producing deterministic builds of a
crate when the source directory of a crate is changed. This is happening due to
what appears two different sources:

* First the `-L` paths passed to rustc are hashed into the crate hash. These
  paths through Cargo are typically absolute paths that can vary if the build
  directory changes.

* Next the paths passed to `--extern` are also hashed which like `-L` can change
  if the build directory changes.

This commit fixes these two sources of nondeterminism by ensuring that avoiding
tracking the hashes of these arguments on the command line. For `-L` paths
they're either related to loading crates (whose hashes are tracked elsewhere) or
native librarise used in the linking phase (which isn't incremental). The
`--extern` paths are similar in that they're related to crate resolution which
is already tracked independently of the command line arguments.

Closes #48019

Add AArch64 features to whitelist

Fix link to rustc guide in README.md

This is a follow-up to #48479 and fixes a minor bug with the link to the rustc guide in the README.

r? @nikomatsakis

cc @mark-i-m

Add regression test for #48551

[Issue link](https://github.com/rust-lang/rust/issues/48551)

Stabilize LocalKey::try_with

The `LocalKey::try_with` method is now stabilized.

`LocalKey::state` and `LocalKeyState` marked as deprecated. Although, is there any reason to keep them - should we perhaps remove them completely?

Closes #27716

r? @alexcrichton

rustc: Tweak funclet cleanups of ffi functions

This commit is targeted at addressing #48251 by specifically fixing a case where
a longjmp over Rust frames on MSVC runs cleanups, accidentally running the
"abort the program" cleanup as well. Added in #46833 `extern` ABI functions in
Rust will abort the process if Rust panics, and currently this is modeled as a
normal cleanup like all other destructors.

Unfortunately it turns out that `longjmp` on MSVC is implemented with SEH, the
same mechanism used to implement panics in Rust. This means that `longjmp` over
Rust frames will run Rust cleanups (even though we don't necessarily want it
to). Notably this means that if you `longjmp` over a Rust stack frame then that
probably means you'll abort the program because one of the cleanups will abort
the process.

After some discussion on IRC it turns out that `longjmp` doesn't run cleanups
for *caught* exceptions, it only runs cleanups for cleanup pads. Using this
information this commit tweaks the codegen for an `extern` function to
a catch-all clause for exceptions instead of a cleanup block. This catch-all is
equivalent to the C++ code:

    try {
        foo();
    } catch (...) {
        bar();
    }

and in fact our codegen here is designed to match exactly what clang emits for
that C++ code!

With this tweak a longjmp over Rust code will no longer abort the process. A
longjmp will continue to "accidentally" run Rust cleanups (destructors) on MSVC.
Other non-MSVC platforms will not rust destructors with a longjmp, so we'll
probably still recommend "don't have destructors on the stack", but in any case
this is a more surgical fix than #48567 and should help us stick to standard
personality functions a bit longer.

Fix find_width_of_character_at_span bounds check

Commit 0bd96671 added bounds checking of our current target byte position to prevent infinite loops. Unfortunately it was comparing the file-relative `target` versus the global `file_start_pos` and `file_end_pos`.

The result is failing to detect multibyte characters unless their file-relative offset fit within their global offset. This causes other parts of the compiler to generate spans pointing to the middle of a
multibyte character which will ultimately panic in `bytepos_to_file_charpos`.

Fix by comparing the `target` to the total file size when moving forward and doing checked subtraction when moving backwards. This should preserve the intent of the bounds check while removing the offset confusion.

cc @davidtwco

Fixes #48508

Support parentheses in patterns under feature gate

This is a prerequisite for any other extensions to pattern syntax - `|` with multiple patterns, type ascription, `..PAT` in slice patterns.

Closes https://github.com/rust-lang/rfcs/issues/554

Remove E0245; improve E0404

Fix #36337

Somehow this is currently breaking --explain, but I don't understand how.

r? @estebank

Auto-toolstate management follow-up.

Tracking comment: https://github.com/rust-lang/rust/issues/45861#issuecomment-367302777

* Fixed rust-lang-nursery/rust-toolstate#1, a proper link to the PR will be included.
* Fixed rust-lang-nursery/rust-toolstate#2, a comment will be posted to the PR if the toolstate changed
* Toolstate regression will be rejected at the last week of the 6-week cycle (currently entirely date-based).
* Implemented https://internals.rust-lang.org/t/the-current-submodule-setup-is-not-tenable/6593, moved doc tests of Nomicon, Reference, Rust-by-Example and The Book to the "tools" job and thus allowed to fail like other external tools.