Improve help for recursion limit errors

- Tweak help message and suggested limit (handle `0` case).
- Add test for #75602 (it was already fixed, maybe can be resolved too).

Fixes #76424

Fix generics where bounds order

Fixes #88809.

Like said on the above issue, the issue is that we were expecting `Symbol` comparisons to be string-based but they are integer-based (because `Symbol` is an integer), messing up the bounds order. To fix it, I simply stored into a `FxIndexMap` instead.

r? ``@jyn514``

Remove ignore-tidy-undocumented-unsafe from core::slice::sort

Write down the missing safety arguments to be able to remove `ignore-tidy-undocumented-unsafe` from `core::slice::sort`.

Helps with #66219

``@rustbot`` label C-cleanup T-libs

Fix union keyword highlighting in rustdoc HTML sources

I followed this logic: if I find an ident "union", I check if it followed by another ident or not. If it's the case, then I consider this is a keyword because it's declaring a union type.

To do so I created a new Iterator which allows to peek the next items without moving the current iterator position.

This is part of https://github.com/rust-lang/rust/issues/85016. If the fix makes sense, I'll extend it to other weak keywords (the issue only mentions they exist but https://doc.rust-lang.org/nightly/reference/keywords.html#weak-keywords only talks about `dyn` and `'static` so not sure if there is anything else to be done?).

cc `@notriddle` (you're one of the last ones who worked on this part of rustdoc so here you go 😉 )
r? `@jyn514`

Fix Windows LLVM issue.

GitHub image 20210928.2 added LLVM 12.0.1 to the stock image.  However, the `lldb` executable doesn't work, it fails with:

> C:/Program Files/LLVM/bin/lldb.exe: error while loading shared libraries: ?: cannot open shared object file: No such file or directory

We probably don't want to start testing LLDB on windows anyways (at least not without intent).

The hacky solution for now is to just delete the system LLVM.

Restructure std::rt

These changes should reduce binary size slightly while at the same slightly improving performance of startup, thread spawning and `std::thread::current()`. I haven't verified if the compiler is able to optimize some of these cases already, but at least for some others the compiler is unable to do these optimizations as they slightly change behavior in cases where program startup would crash anyway by omitting a backtrace and panic location.

I can remove 6f6bb167 if preferred.

Rollup of 8 pull requests

Successful merges:

 - #87260 (Libgccjit codegen)
 - #89212 (x.py: run `rustup toolchain link` in setup)
 - #89233 (Hide `<...> defined here` note if the source is not available)
 - #89235 (make junit output more consistent with default format)
 - #89255 (Fix incorrect disambiguation suggestion for associated items)
 - #89276 (Fix the population of the `union.impls` field)
 - #89283 (Add regression test for issue #83564)
 - #89318 (rustc_session: Remove lint store from `Session`)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Update Clippy

Delayed Clippy sync

r? `@Manishearth`

Add an intermediate representation to exhaustiveness checking

The exhaustiveness checking algorithm keeps deconstructing patterns into a `Constructor` and some `Fields`, but does so a bit all over the place. This PR introduces a new representation for patterns that already has that information, so we only compute it once at the start.
I find this makes code easier to follow. In particular `DeconstructedPat::specialize` is a lot simpler than what happened before, and more closely matches the description of the algorithm. I'm also hoping this could help for the project of librarifying exhaustiveness for rust_analyzer since it decouples the algorithm from `rustc_middle::Pat`.

rustc_session: Remove lint store from `Session`

It was added in https://github.com/rust-lang/rust/pull/75534, but after the cleanup in https://github.com/rust-lang/rust/pull/87070 it's no longer necessary.

Add regression test for issue #83564

cc #83564

r? ``@davidtwco``

Fix the population of the `union.impls` field

This pull-request fix the population of the `union.impls` field that was forgot when the `Union` type was introduce as a split from the `Struct` type https://github.com/rust-lang/rust/pull/81500.

``@rustbot`` label +T-rustdoc +A-rustdoc-json

Fix incorrect disambiguation suggestion for associated items

Fixes #88806. I have not added a new test case, because the erroneous behavior is already present in existing test cases.

make junit output more consistent with default format

The default format of libtest includes new-lines between each section to ensure the label output from cargo is on it's own line

<pre><font color="#A1B56C"><b>❯</b></font> <font color="#A1B56C">cargo</font><font color="#D8D8D8"> </font><font color="#A1B56C">test</font>
<font color="#A1B56C"><b>   Compiling</b></font> test-test v0.1.0 (/home/jlusby/tmp/test-test)
<font color="#A1B56C"><b>    Finished</b></font> test [unoptimized + debuginfo] target(s) in 0.59s
<font color="#A1B56C"><b>     Running</b></font> unittests (target/debug/deps/test_test-639f369234319c09)

running 1 test
test tests::it_works ... <font color="#A1B56C">ok</font>

test result: <font color="#A1B56C">ok</font>. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

<font color="#A1B56C"><b>   Doc-tests</b></font> test-test

running 0 tests

test result: <font color="#A1B56C">ok</font>. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

</pre>

But when the junit outputter was added to libtest these newlines were omitted, resulting in some "fun" output when run via cargo.

Note the `Doc-tests` text at the end of the first line of xml.

<pre><font color="#A1B56C"><b>❯</b></font> <font color="#A1B56C">cargo</font><font color="#D8D8D8"> </font><font color="#A1B56C">test</font><font color="#D8D8D8"> </font><font color="#A1B56C">--</font><font color="#D8D8D8"> </font><font color="#A1B56C">-Zunstable-options</font><font color="#D8D8D8"> </font><font color="#A1B56C">--format</font><font color="#D8D8D8"> </font><font color="#A1B56C">junit</font>
<font color="#A1B56C"><b>    Finished</b></font> test [unoptimized + debuginfo] target(s) in 0.00s
<font color="#A1B56C"><b>     Running</b></font> unittests (target/debug/deps/test_test-639f369234319c09)
&lt;?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot;?&gt;&lt;testsuites&gt;&lt;testsuite name=&quot;test&quot; package=&quot;test&quot; id=&quot;0&quot; errors=&quot;0&quot; failures=&quot;0&quot; tests=&quot;1&quot; skipped=&quot;0&quot; &gt;&lt;testcase classname=&quot;tests&quot; name=&quot;it_works&quot; time=&quot;0&quot;/&gt;&lt;system-out/&gt;&lt;system-err/&gt;&lt;/testsuite&gt;&lt;/testsuites&gt;<font color="#A1B56C"><b>   Doc-tests</b></font> test-test
&lt;?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot;?&gt;&lt;testsuites&gt;&lt;testsuite name=&quot;test&quot; package=&quot;test&quot; id=&quot;0&quot; errors=&quot;0&quot; failures=&quot;0&quot; tests=&quot;0&quot; skipped=&quot;0&quot; &gt;&lt;system-out/&gt;&lt;system-err/&gt;&lt;/testsuite&gt;&lt;/testsuites&gt;

</pre>

After this PR the junit output includes the same style of newlines as the pretty format

<pre><font color="#A1B56C"><b>❯</b></font> <font color="#A1B56C">cargo</font><font color="#D8D8D8"> </font><font color="#A1B56C">test</font><font color="#D8D8D8"> </font><font color="#A1B56C">--</font><font color="#D8D8D8"> </font><font color="#A1B56C">-Zunstable-options</font><font color="#D8D8D8"> </font><font color="#A1B56C">--format</font><font color="#D8D8D8"> </font><font color="#A1B56C">junit</font>
<font color="#A1B56C"><b>   Compiling</b></font> test-test v0.1.0 (/home/jlusby/tmp/test-test)
<font color="#A1B56C"><b>    Finished</b></font> test [unoptimized + debuginfo] target(s) in 0.39s
<font color="#A1B56C"><b>     Running</b></font> unittests (target/debug/deps/test_test-42c2320bb9450c69)

&lt;?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot;?&gt;&lt;testsuites&gt;&lt;testsuite name=&quot;test&quot; package=&quot;test&quot; id=&quot;0&quot; errors=&quot;0&quot; failures=&quot;0&quot; tests=&quot;1&quot; skipped=&quot;0&quot; &gt;&lt;testcase classname=&quot;tests&quot; name=&quot;it_works&quot; time=&quot;0&quot;/&gt;&lt;system-out/&gt;&lt;system-err/&gt;&lt;/testsuite&gt;&lt;/testsuites&gt;

<font color="#A1B56C"><b>   Doc-tests</b></font> test-test

&lt;?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot;?&gt;&lt;testsuites&gt;&lt;testsuite name=&quot;test&quot; package=&quot;test&quot; id=&quot;0&quot; errors=&quot;0&quot; failures=&quot;0&quot; tests=&quot;0&quot; skipped=&quot;0&quot; &gt;&lt;system-out/&gt;&lt;system-err/&gt;&lt;/testsuite&gt;&lt;/testsuites&gt;

</pre>

Hide `<...> defined here` note if the source is not available

Fixes #89159. Similar to #87088.

r? ``@estebank``

x.py: run `rustup toolchain link` in setup

Addresses #89206

r? ``@jyn514``

Libgccjit codegen

This PR introduces a subtree for a gcc-based codegen backend to the repository, per decision in https://github.com/rust-lang/compiler-team/issues/442. We do not yet expect to ship this backend on nightly or run tests in CI, but we do verify that the backend checks (i.e., `cargo check`) successfully.

Work is expected to progress primarily in https://github.com/rust-lang/rustc_codegen_gcc, with semi-regular upstreaming, like with other subtrees.

Rustup

This needs a review this time. Especially https://github.com/rust-lang/rust-clippy/commit/521bf8f0fa18c7f130505f0a902ab0e65a76cec2 cc `@camsteffen` I think this is necessary now, because `itertools` is no longer a dependency of `clippy_utils` and therefore this path can't be found 🤔

( I forgot about the sync last week. I should get to document this process better, so other people can do it when I'm not around )

changelog: none

Since clippy_utils doesn't depend on the itertools crate anymore, the
lint can't find the path.

Add more tracing instrumentation

I changed or added all this while working on a branch and pulled it out so we can merge it on its own.

Add SOLID targets

This PR introduces new tier 3 targets for [SOLID](https://www.kmckk.co.jp/eng/SOLID/) embedded development platform by Kyoto Microcomputer Co., Ltd.

|          Target name           | `target_arch` | `target_vendor` | `target_os`  |
|--------------------------------|---------------|-----------------|--------------|
| `aarch64-kmc-solid_asp3`       | `aarch64`     | `kmc`           | `solid_asp3` |
| `armv7a-kmc-solid_asp3-eabi`   | `arm`         | `kmc`           | `solid_asp3` |
| `armv7a-kmc-solid_asp3-eabihf` | `arm`         | `kmc`           | `solid_asp3` |

## Related PRs

- [ ] `libc`: https://github.com/rust-lang/libc/pull/2227
- [ ] `cc`: https://github.com/alexcrichton/cc-rs/pull/609

## Non-blocking Issues

- [ ] The target kernel can support `Thread::unpark` directly, but this property is not utilized because the underlying kernel feature is used to implement `Condvar` and it's unclear whether `std` should guarantee that parking tokens are not clobbered by other synchronization primitives.
- [ ] The rustc book: The page title "\*-kmc-solid-\*" shows up as "-kmc-solid-" in TOC

## Tier 3 Target Policy

As tier 3 targets, the new targets are required to adhere to [the tier 3 target policy](https://doc.rust-lang.org/nightly/rustc/target-tier-policy.html#tier-3-target-policy) requirements. This section quotes each requirement in entirety and describes how they are met.

> - A tier 3 target must have a designated developer or developers (the "target maintainers") on record to be CCed when issues arise regarding the target. (The mechanism to track and CC such developers may evolve over time.)

See [`src/doc/rustc/src/platform-support/kmc-solid.md`](https://github.com/kawadakk/rust/blob/release-add-solid-support/src/doc/rustc/src/platform-support/kmc-solid.md).

> - Targets must use naming consistent with any existing targets; for instance, a target for the same CPU or OS as an existing Rust target should use the same name for that CPU or OS. Targets should normally use the same names and naming conventions as used elsewhere in the broader ecosystem beyond Rust (such as in other toolchains), unless they have a very good reason to diverge. Changing the name of a target can be highly disruptive, especially once the target reaches a higher tier, so getting the name right is important even for a tier 3 target.
>     - Target names should not introduce undue confusion or ambiguity unless absolutely necessary to maintain ecosystem compatibility. For example, if the name of the target makes people extremely likely to form incorrect beliefs about what it targets, the name should be changed or augmented to disambiguate it.

The new target names follow this format: `$ARCH-$VENDOR-$OS-$ABI`, which is already adopted by most existing targets. `$ARCH` and `$ABI` follow the convention: `aarch64-*` for AArch64, `armv7a-*-eabi` for Armv7-A with EABI. `$OS` is used to distinguish multiple variations of the platform in a somewhat similar way to the Apple targets, though we are only adding one variation in this PR. `$VENDOR` denotes the platform vendor name similarly to the Apple, Solaris, SGX, and VxWorks targets.

`$OS` corresponds to the value of `target_os` and takes the format `solid-$KERNEL`. The inclusion of a hyphen prevents unique decomposition of target names, though the mapping between target names and target attributes isn't trivial in the first place, e.g., because of the Android targets.

More targets may be added later, as we support other base kernels (there are at least three at the point of writing) and are interested in supporting other processor architectures in the future.

> - Tier 3 targets may have unusual requirements to build or use, but must not create legal issues or impose onerous legal terms for the Rust project or for Rust developers or users.
>     - The target must not introduce license incompatibilities.
>     - Anything added to the Rust repository must be under the standard Rust license (`MIT OR Apache-2.0`).
>     - The target must not cause the Rust tools or libraries built for any other host (even when supporting cross-compilation to the target) to depend on any new dependency less permissive than the Rust licensing policy. This applies whether the dependency is a Rust crate that would require adding new license exceptions (as specified by the `tidy` tool in the rust-lang/rust repository), or whether the dependency is a native library or binary. In other words, the introduction of the target must not cause a user installing or running a version of Rust or the Rust tools to be subject to any new license requirements.
>     - If the target supports building host tools (such as `rustc` or `cargo`), those host tools must not depend on proprietary (non-FOSS) libraries, other than ordinary runtime libraries supplied by the platform and commonly used by other binaries built for the target. For instance, `rustc` built for the target may depend on a common proprietary C runtime library or console output library, but must not depend on a proprietary code generation library or code optimization library. Rust's license permits such combinations, but the Rust project has no interest in maintaining such combinations within the scope of Rust itself, even at tier 3.
>     - Targets should not require proprietary (non-FOSS) components to link a functional binary or library.
>     - "onerous" here is an intentionally subjective term. At a minimum, "onerous" legal/licensing terms include but are *not* limited to: non-disclosure requirements, non-compete requirements, contributor license agreements (CLAs) or equivalent, "non-commercial"/"research-only"/etc terms, requirements conditional on the employer or employment of any particular Rust developers, revocable terms, any requirements that create liability for the Rust project or its developers or users, or any requirements that adversely affect the livelihood or prospects of the Rust project or its developers or users.

We intend to make the contribution fully available under the standard Rust license with no additional legal restrictions whatsoever. This PR does not introduce any new dependency less permissive than the Rust license policy, and we are willing to ensure this doesn't happen for future contributions regarding the new targets.

The new targets don't support building host tools.

Although the new targets use a platform-provided C compiler toolchain, it can be substituted by [GNU Arm Embedded Toolchain](https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-rm) for testing purposes.

> - Tier 3 targets should attempt to implement as much of the standard libraries as possible and appropriate (`core` for most targets, `alloc` for targets that can support dynamic memory allocation, `std` for targets with an operating system or equivalent layer of system-provided functionality), but may leave some code unimplemented (either unavailable or stubbed out as appropriate), whether because the target makes it impossible to implement or challenging to implement. The authors of pull requests are not obligated to avoid calling any portions of the standard library on the basis of a tier 3 target not implementing those portions.

Most features are implemented. The following features are not implemented due to the lack of native support:

- `fs::File::{file_attr, truncate, duplicate, set_permissions}`
- `fs::{symlink, link, canonicalize}`
- Process creation
- Command-line arguments

~~Networking is not implemented yet, and we intend to add it as soon as it's ready.~~
Edit (2021-07-07): Networking is now implemented.

Backtrace generation is not really a good fit for embedded targets, so it's intentionally left unimplemented. Unwinding is functional, however.

> - The target must provide documentation for the Rust community explaining how to build for the target, using cross-compilation if possible. If the target supports running tests (even if they do not pass), the documentation must explain how to run tests for the target, using emulation if possible or dedicated hardware if necessary.

See [`src/doc/rustc/src/platform-support/kmc-solid.md`](https://github.com/kawadakk/rust/blob/release-add-solid-support/src/doc/rustc/src/platform-support/kmc-solid.md). Running tests is not supported.

> - Neither this policy nor any decisions made regarding targets shall create any binding agreement or estoppel by any party. If any member of an approving Rust team serves as one of the maintainers of a target, or has any legal or employment requirement (explicit or implicit) that might affect their decisions regarding a target, they must recuse themselves from any approval decisions regarding the target's tier status, though they may otherwise participate in discussions.
>     - This requirement does not prevent part or all of this policy from being cited in an explicit contract or work agreement (e.g. to implement or maintain support for a target). This requirement exists to ensure that a developer or team responsible for reviewing and approving a target does not face any legal threats or obligations that would prevent them from freely exercising their judgment in such approval, even if such judgment involves subjective matters or goes beyond the letter of these requirements.
> - Tier 3 targets must not impose burden on the authors of pull requests, or other developers in the community, to maintain the target. In particular, do not post comments (automated or manual) on a PR that derail or suggest a block on the PR based on a tier 3 target. Do not send automated messages or notifications (via any medium, including via ``@`)` to a PR author or others involved with a PR regarding a tier 3 target, unless they have opted into such messages.
>     - Backlinks such as those generated by the issue/PR tracker when linking to an issue or PR are not considered a violation of this policy, within reason. However, such messages (even on a separate repository) must not generate notifications to anyone involved with a PR who has not requested such notifications.
> - Patches adding or updating tier 3 targets must not break any existing tier 2 or tier 1 target, and must not knowingly break another tier 3 target without approval of either the compiler team or the maintainers of the other tier 3 target.
>     - In particular, this may come up when working on closely related targets, such as variations of the same architecture with different features. Avoid introducing unconditional uses of features that another variation of the target may not have; use conditional compilation or runtime detection, as appropriate, to let each target run code supported by that target.

We acknowledge these requirements and intend to ensure they are met.

There are no closely related targets at the moment.

Update changelog to 1.56

As expected a pretty short changelog, because of the missed sync last release cycle.

[Rendered](https://github.com/flip1995/rust-clippy/blob/changelog/CHANGELOG.md)

changelog: none

Auto merge of #89293 - TaKO8Ki:fix-confusing-error-for-path-separator-to-refer-to-an-struct-item, r=estebank

Suggest using the path separator for tuple struct

Fix confusing error message `constructor is not visible here due to private fields` for tuple struct

closes #83450

Use the correct edition for syntax highlighting doctests

Previously it would unconditionally use edition 2015, which was incorrect.

Helps with https://github.com/rust-lang/rust/issues/89135 in that you can now override the doctest to be 2018 edition instead of being forced to fix the error. This doesn't resolve any of the deeper problems that rustdoc disagrees with most rust users on what a code block is.

cc `@Mark-Simulacrum`

#7594: Adding new 'while_let_some_result' linting

Excited for the opportunity to contribute to Clippy! Since the latest Bay Area Rust Meetup, I've been looking for an opportunity and found it 😄

Please let me know how I can improve this PR! Much of it is similar to ``[`if_let_some_result`]``, but I followed the description in the issue to create its own linting rules. Looking forward to feedback, and continuing to work on Clippy in the future!

changelog: Renamed Lint: `if_let_some_result` is now called [`match_result_ok`]. Now also handles `while let` case.