Jack Huey [Sun, 22 Aug 2021 00:56:29 +0000 (20:56 -0400)]
Rollup merge of #88072 - kit-981:feature/build-ios-toolchain-on-linux, r=Mark-Simulacrum
Allow the iOS toolchain to be built on Linux
The iOS toolchain can be built on Linux with minor changes. The compilation will invoke `xcrun` to find the path to the iPhone SDK but a fake `xcrun` executable can be used.
```
#!/bin/sh
echo "/path/to/sdk"
```
The iOS toolchain can then be built and linked with rustup.
It's possible to take this toolchain and compile an iOS executable with it. This requires the ld64 linker and an iOS SDK. The ld64 linker can be taken from [cctools](https://github.com/tpoechtrager/cctools-port). A project's .cargo/config can then be edited to use the linker for this target.
Jack Huey [Sun, 22 Aug 2021 00:56:28 +0000 (20:56 -0400)]
Rollup merge of #88057 - ehuss:releases-doc-macros, r=Mark-Simulacrum
Update RELEASES to clarify attribute macro values.
As noted in #87681, macros do not work with the `#[path]` attribute. Since the places where macros *can* be used is very limited, I have changed this to just focus on `#[doc]` which is the only attribute where this is really useful.
bors [Sat, 21 Aug 2021 18:32:37 +0000 (18:32 +0000)]
Auto merge of #82776 - jyn514:extern-url-fallback, r=GuillaumeGomez
Give precedence to `html_root_url` over `--extern-html-root-url` by default, but add a way to opt-in to the previous behavior
## What is an HTML root url?
It tells rustdoc where it should link when documentation for a crate is
not available locally; for example, when a crate is a dependency of a
crate documented with `cargo doc --no-deps`.
## What is the difference between `html_root_url` and `--extern-html-root-url`?
Both of these tell rustdoc what the HTML root should be set to.
`doc(html_root_url)` is set by the crate author, while
`--extern-html-root-url` is set by the person documenting the crate.
These are often different. For example, docs.rs uses
`--extern-html-root-url https://docs.rs/crate-name/version` to ensure
all crates have documentation, even if `html_root_url` is not set.
Conversely, crates such as Rocket set `doc(html_root_url =
"https://api.rocket.rs")`, because they prefer users to view the
documentation on their own site.
Crates also set `html_root_url` to ensure they have
documentation when building locally when offline. This is unfortunate to
require, because it's more work from the library author. It also makes
it impossible to distinguish between crates that want to be viewed on a
different site (e.g. Rocket) and crates that just want documentation to
be visible offline at all (e.g. Tokio). I have authored a separate
change to the API guidelines to no longer recommend doing this:
rust-lang/api-guidelines#230.
## Why change the default?
In the past, docs.rs has been the main user of `--extern-html-root-url`.
However, it's useful for other projects as well. In particular, Cargo
wants to pass it by default when running `--no-deps`
(rust-lang/cargo#8296).
Unfortunately, for these other use cases, the priority order is
inverted. They want to give *precedence* to the URL the crate picks, and
only fall back to the `--extern-html-root` if no `html_root_url` is
present. That allows passing `--extern-html-root` unconditionally,
without having to parse the source code to see what attributes are
present.
For docs.rs, however, we still want to keep the old behavior, so that
all links on docs.rs stay on the site.
bors [Sat, 21 Aug 2021 15:51:50 +0000 (15:51 +0000)]
Auto merge of #88134 - rylev:force-warn-improvements, r=nikomatsakis
Force warn improvements
As part of stablization of the `--force-warn` option (#86516) I've made the following changes:
* Error when the `warnings` lint group is based to the `--force-warn` option
* Tests have been updated to make it easier to understand the semantics of `--force-warn`
bors [Sat, 21 Aug 2021 09:25:28 +0000 (09:25 +0000)]
Auto merge of #87570 - nikic:llvm-13, r=nagisa
Upgrade to LLVM 13
Work in progress update to LLVM 13. Main changes:
* InlineAsm diagnostics reported using SrcMgr diagnostic kind are now handled. Previously these used a separate diag handler.
* Codegen tests are updated for additional attributes.
* Some data layouts have changed.
* Switch `#[used]` attribute from `llvm.used` to `llvm.compiler.used` to avoid SHF_GNU_RETAIN flag introduced in https://reviews.llvm.org/D97448, which appears to trigger a bug in older versions of gold.
* Set `LLVM_INCLUDE_TESTS=OFF` to avoid Python 3.6 requirement.
Upstream issues:
* ~~https://bugs.llvm.org/show_bug.cgi?id=51210 (InlineAsm diagnostic reporting for module asm)~~ Fixed by https://github.com/llvm/llvm-project/commit/1558bb80c01b695ce12642527cbfccf16cf54ece.
* ~~https://bugs.llvm.org/show_bug.cgi?id=51476 (Miscompile on AArch64 due to incorrect comparison elimination)~~ Fixed by https://github.com/llvm/llvm-project/commit/81b106584f2baf33e09be2362c35c1bf2f6bfe94.
* https://bugs.llvm.org/show_bug.cgi?id=51207 (Can't set custom section flags anymore). Problematic change reverted in our fork, https://reviews.llvm.org/D107216 posted for upstream revert.
* https://bugs.llvm.org/show_bug.cgi?id=51211 (Regression in codegen for #83623). This is an optimization regression that we may likely have to eat for this release. The fix for #83623 was based on an incorrect premise, and this needs to be properly addressed in the MergeICmps pass.
bors [Sat, 21 Aug 2021 01:29:12 +0000 (01:29 +0000)]
Auto merge of #88149 - Mark-Simulacrum:prep-never-type, r=jackh726
Refactor fallback code to prepare for never type
This PR contains cherry-picks of some of `@nikomatsakis's` work from #79366, and shouldn't (AFAICT) represent any change in behavior. However, the refactoring is good regardless of the never type work being landed, and will reduce the size of those eventual PR(s) (and rebase pain).
I am not personally an expert on this code, and the commits are essentially 100% `@nikomatsakis's,` but they do seem reasonable to me by my understanding. Happy to edit with review, of course. Commits are best reviewed in sequence rather than all together.
bors [Fri, 20 Aug 2021 23:04:57 +0000 (23:04 +0000)]
Auto merge of #88087 - jesyspa:issue-87935-box, r=jackh726
Check that a box expression's type is Sized
This resolves [issue 87935](https://github.com/rust-lang/rust/issues/87935).
This makes E0161 (move from an unsized rvalue) much less common. I've replaced the test to use [this case](https://github.com/rust-lang/rust/blob/master/src/test/ui/object-safety/object-safety-by-value-self-use.rs), when a boxed `dyn` trait is passed by value, but that isn't an error when `unsized_locals` is enabled. I think it may be possible to get rid of E0161 entirely by checking that case earlier, but I'm not sure if that's desirable?
Niko Matsakis [Sat, 21 Nov 2020 20:47:14 +0000 (15:47 -0500)]
create `Coercion` obligations given 2 unbound type variables
Motivation: in upcoming commits, we are going to create a graph of the
coercion relationships between variables. We want to
distinguish *coercion* specifically from other sorts of subtyping, as
it indicates values flowing from one place to another via assignment.
Niko Matsakis [Sat, 21 Nov 2020 20:33:36 +0000 (15:33 -0500)]
move the `sub-unify` check and extend the documentation a bit
I didn't like the sub-unify code executing when a predicate was
ENQUEUED, that felt fragile. I would have preferred to move the
sub-unify code so that it only occurred during generalization, but
that impacted diagnostics, so having it also occur when we process
subtype predicates felt pretty reasonable. (I guess we only need one
or the other, but I kind of prefer both, since the generalizer
ultimately feels like the *right* place to guarantee the properties we
want.)
bors [Fri, 20 Aug 2021 19:06:46 +0000 (19:06 +0000)]
Auto merge of #83093 - the8472:smaller-instant-hammer, r=Amanieu
where available use AtomicU{64,128} instead of mutex for Instant backsliding protection
This decreases the overhead of backsliding protection on x86 systems with unreliable TSC, e.g. windows. And on aarch64 systems where 128bit atomics are available.
The following benchmarks were taken on x86_64 linux though by overriding `actually_monotonic()`, the numbers may look different on other platforms
```
# actually_monotonic() == true
test time::tests::instant_contention_01_threads ... bench: 44 ns/iter (+/- 0)
test time::tests::instant_contention_02_threads ... bench: 44 ns/iter (+/- 0)
test time::tests::instant_contention_04_threads ... bench: 44 ns/iter (+/- 0)
test time::tests::instant_contention_08_threads ... bench: 44 ns/iter (+/- 0)
test time::tests::instant_contention_16_threads ... bench: 44 ns/iter (+/- 0)
# 1x AtomicU64
test time::tests::instant_contention_01_threads ... bench: 65 ns/iter (+/- 0)
test time::tests::instant_contention_02_threads ... bench: 157 ns/iter (+/- 20)
test time::tests::instant_contention_04_threads ... bench: 281 ns/iter (+/- 53)
test time::tests::instant_contention_08_threads ... bench: 555 ns/iter (+/- 77)
test time::tests::instant_contention_16_threads ... bench: 883 ns/iter (+/- 107)
# mutex
test time::tests::instant_contention_01_threads ... bench: 60 ns/iter (+/- 2)
test time::tests::instant_contention_02_threads ... bench: 770 ns/iter (+/- 231)
test time::tests::instant_contention_04_threads ... bench: 1,347 ns/iter (+/- 45)
test time::tests::instant_contention_08_threads ... bench: 2,693 ns/iter (+/- 114)
test time::tests::instant_contention_16_threads ... bench: 5,244 ns/iter (+/- 487)
```
Since I don't have an arm machine with 128bit atomics I wasn't able to benchmark the AtomicU128 implementation.
bors [Fri, 20 Aug 2021 11:00:55 +0000 (11:00 +0000)]
Auto merge of #87329 - sunfishcode:sunfishcode/io-safety, r=joshtriplett
I/O safety.
Introduce `OwnedFd` and `BorrowedFd`, and the `AsFd` trait, and
implementations of `AsFd`, `From<OwnedFd>` and `From<T> for OwnedFd`
for relevant types, along with Windows counterparts for handles and
sockets.
Highlights:
- The doc comments at the top of library/std/src/os/unix/io/mod.rs and library/std/src/os/windows/io/mod.rs
- The new types and traits in library/std/src/os/unix/io/fd.rs and library/std/src/os/windows/io/handle.rs
- The removal of the `RawHandle` struct the Windows impl, which had the same name as the `RawHandle` type alias, and its functionality is now folded into `Handle`.
Managing five levels of wrapping (File wraps sys::fs::File wraps sys::fs::FileDesc wraps OwnedFd wraps RawFd, etc.) made for a fair amount of churn and verbose as/into/from sequences in some places. I've managed to simplify some of them, but I'm open to ideas here.
bors [Fri, 20 Aug 2021 07:30:28 +0000 (07:30 +0000)]
Auto merge of #88000 - bjorn3:fix_cg_llvm_clif_compile, r=Mark-Simulacrum
Fix compiling other codegen backends when llvm is enabled
Extracted from #81746
Without this change rustbuild will not pass the required linker argument to find libllvm. While other backends likely don't use libllvm, it is necessary to be able to link against rustc_driver as the llvm backend is linked into it.
This PR fixes an ICE when trying to unwrap an Err. This error appears when trying to convert a PlaceBuilder into Place when upvars can't yet be resolved. We should only try to convert a PlaceBuilder into Place if upvars can be resolved.
This PR fixes an ICE where a match discriminant is not being read when expected. This ICE was the result of a missing edge case which assumed that if a pattern is of type `PatKind::TupleStruct(..) | PatKind::Path(..) | PatKind::Struct(..) | PatKind::Tuple(..)` then a place could only be a multi variant if the place is of type kind Adt.
Niko Matsakis [Fri, 20 Nov 2020 10:52:27 +0000 (05:52 -0500)]
shallow resolve target type in coercion
We used to avoid doing this because we didn't want to make coercion depend on
the state of inference. For better or worse, we have moved away from this
position over time. Therefore, I am going to go ahead and resolve the `b`
target type early on so that it is done uniformly.
(The older technique for managing this was always something of a hack
regardless; if we really wanted to avoid integrating coercion and inference we
needed to be more disciplined about it.)
bors [Thu, 19 Aug 2021 20:31:05 +0000 (20:31 +0000)]
Auto merge of #88165 - GuillaumeGomez:rollup-4o0v2ps, r=GuillaumeGomez
Rollup of 8 pull requests
Successful merges:
- #86123 (Preserve more spans in internal `rustc_queries!` macro)
- #87874 (Add TcpStream type to TcpListener::incoming docs)
- #88034 (rustc_privacy: Replace `HirId`s and `DefId`s with `LocalDefId`s where possible)
- #88050 (Remove `HashStable` impls for `FileName` and `RealFileName`)
- #88093 ([rustdoc] Wrap code blocks in `<code>` tag)
- #88146 (Add tests for some `feature(const_evaluatable_checked)` incr comp issues)
- #88153 (Update .mailmap)
- #88159 (Use a trait instead of the now disallowed missing trait there)
Dan Gohman [Thu, 29 Jul 2021 20:36:44 +0000 (13:36 -0700)]
Rename OptionFileHandle to HandleOrInvalid and make it just wrap an Option<OwnedHandle>
The name (and updated documentation) make the FFI-only usage clearer, and wrapping Option<OwnedHandle> avoids the need to write a separate Drop or Debug impl.
Dan Gohman [Thu, 1 Jul 2021 04:44:30 +0000 (21:44 -0700)]
I/O safety.
Introduce `OwnedFd` and `BorrowedFd`, and the `AsFd` trait, and
implementations of `AsFd`, `From<OwnedFd>` and `From<T> for OwnedFd`
for relevant types, along with Windows counterparts for handles and
sockets.
Guillaume Gomez [Thu, 19 Aug 2021 17:30:12 +0000 (19:30 +0200)]
Rollup merge of #88159 - spastorino:fix-unused-generic-param-test, r=oli-obk
Use a trait instead of the now disallowed missing trait there
To properly test the unused generic parameter and just that we need to use a trait in the tait. Missing the trait there is already tested and is not what we meant to test here.
Guillaume Gomez [Thu, 19 Aug 2021 17:30:09 +0000 (19:30 +0200)]
Rollup merge of #88093 - Kobzol:rustdoc-wrap-code-in-code-tag, r=GuillaumeGomez
[rustdoc] Wrap code blocks in <code> tag
This PR modifies Rustdoc output so that fenced code snippets, items and whole file source codes are wrapped in `<pre><code>` instead of just `<pre>`. This should improve the semantic meaning of the generated content.
I'm not sure what to do about `render_attributes_in_pre` and `render_attributes_in_code`. These functions were clearly expected to be used for things inside `<pre>` or `<code>`, and since I added `<code>` in this PR, some of them will be used in a different context than before. However, it seems to me that even before they were not consistent. For example, `item_constant` used `render_attributes_in_code` for its attributes, however there was no `<code>` used for constants before this PR...
Should I create some `rustdoc-gui` tests? For example to check that all `<pre>` tags have a `<code>` child?
Guillaume Gomez [Thu, 19 Aug 2021 17:30:07 +0000 (19:30 +0200)]
Rollup merge of #88050 - Aaron1011:filename-hash-stable, r=michaelwoerister
Remove `HashStable` impls for `FileName` and `RealFileName`
These impls were unused, and incorrectly hashed the local
(non-remapped) path for `RealFileName::Remapped` (which would
break reproducible builds if these impls were used).
Guillaume Gomez [Thu, 19 Aug 2021 17:30:05 +0000 (19:30 +0200)]
Rollup merge of #87874 - schneems:schneems/tcpstream-iterator-type, r=Mark-Simulacrum
Add TcpStream type to TcpListener::incoming docs
## Context
While going through the "The Rust Programming Language" book (Klabnik & Nichols), the TCP server example directs us to use TcpListener::incoming. I was curious how I could pass this value to a function (before reading ahead in the book), so I looked up the docs to determine the signature.
When I opened the docs, I found https://doc.rust-lang.org/std/net/struct.TcpListener.html#method.incoming, which didn't mention TcpStream anywhere in the example.
Eventually, I clicked on https://doc.rust-lang.org/std/net/struct.TcpListener.html#method.accept in the docs (after clicking a few other locations first), and was able to surmise that the value contained TcpStream.
## Opportunity
While this type is mentioned several times in this doc, I feel that someone should be able to fully use the results of the TcpListner::incoming iterator based solely on the docs of just this method.
## Implementation
I took the code from the top-level TcpListener https://doc.rust-lang.org/std/net/struct.TcpListener.html#method.incoming and blended it with the existing docs for TcpListener::incoming https://doc.rust-lang.org/std/net/struct.TcpListener.html#method.incoming.
It does make the example a little longer, and it also introduces a little duplication. It also gives the reader the type signatures they need to move on to the next step.
## Additional considerations
I noticed that in this doc, `handle_connection` and `handle_client` are both used to accept a TcpStream in the docs on this page. I want to standardize on one function name convention, so readers don't accidentally think two different concepts are being referenced. I didn't want to cram do too much in one PR, I can update this PR to make that change, or I could send another PR (if you would like).
First attempted contribution to Rust (and I'm also still very new, hence reading through the rust book for the first time)! Would you please let me know what you think?
Guillaume Gomez [Thu, 19 Aug 2021 17:30:04 +0000 (19:30 +0200)]
Rollup merge of #86123 - Aaron1011:query-span, r=cjgillot
Preserve more spans in internal `rustc_queries!` macro
We now preserve the span of the various query modifiers, and
use the span of the query's name for the commas that we
generate to separate the modifiers. This makes debugging issues with the
internal query macro infrastructure much nicer - previously, we
would get errors messages pointing at the entire call site
(the `rustc_queries!` invocation), which isn't very useful.
This should have no effect when compilation succeeds.
A concrete example of an error message produced after this changed:
bors [Thu, 19 Aug 2021 17:20:59 +0000 (17:20 +0000)]
Auto merge of #88151 - alexcrichton:update-backtrace, r=Mark-Simulacrum
Update the backtrace crate in libstd
This commit updates the backtrace crate in libstd now that dependencies
have been updated to use `memchr` from the standard library as well.
This is mostly just making sure deps are up-to-date and have all the
latest-and-greatest fixes and such.
Alex Crichton [Thu, 19 Aug 2021 02:44:24 +0000 (19:44 -0700)]
Update the backtrace crate in libstd
This commit updates the backtrace crate in libstd now that dependencies
have been updated to use `memchr` from the standard library as well.
This is mostly just making sure deps are up-to-date and have all the
latest-and-greatest fixes and such.
bors [Thu, 19 Aug 2021 09:08:11 +0000 (09:08 +0000)]
Auto merge of #88002 - hermitcore:unbox-mutex, r=dtolnay
Unbox mutexes, condvars and rwlocks on hermit
[RustyHermit](https://github.com/hermitcore/rusty-hermit) provides now movable synchronization primitives and we are able to unbox mutexes and condvars.
bors [Thu, 19 Aug 2021 06:27:17 +0000 (06:27 +0000)]
Auto merge of #87986 - Aaron1011:incr-double-panic, r=estebank
Prevent double panic when handling incremental fingerprint mismatch
When an incremental fingerprint mismatch occurs, we debug-print
our `DepNode` and query result. Unfortunately, the debug printing
process may cause us to run additional queries, which can result
in a re-entrant fingerprint mismatch error.
To avoid a double panic, this commit adds a thread-local variable
to detect re-entrant calls.
Joshua Nelson [Thu, 4 Mar 2021 20:03:22 +0000 (15:03 -0500)]
Give precedence to `html_root_url` over `--extern-html-root-url` by default, but add a way to opt-in to the previous behavior
## What is an HTML root url?
It tells rustdoc where it should link when documentation for a crate is
not available locally; for example, when a crate is a dependency of a
crate documented with `cargo doc --no-deps`.
## What is the difference between `html_root_url` and `--extern-html-root-url`?
Both of these tell rustdoc what the HTML root should be set to.
`doc(html_root_url)` is set by the crate author, while
`--extern-html-root-url` is set by the person documenting the crate.
These are often different. For example, docs.rs uses
`--extern-html-root-url https://docs.rs/crate-name/version` to ensure
all crates have documentation, even if `html_root_url` is not set.
Conversely, crates such as Rocket set `doc(html_root_url =
"https://api.rocket.rs")`, because they prefer users to view the
documentation on their own site.
Crates also set `html_root_url` to ensure they have
documentation when building locally when offline. This is unfortunate to
require, because it's more work from the library author. It also makes
it impossible to distinguish between crates that want to be viewed on a
different site (e.g. Rocket) and crates that just want documentation to
be visible offline at all (e.g. Tokio). I have authored a separate
change to the API guidelines to no longer recommend doing this:
https://github.com/rust-lang/api-guidelines/pull/230.
## Why change the default?
In the past, docs.rs has been the main user of `--extern-html-root-url`.
However, it's useful for other projects as well. In particular, Cargo
wants to pass it by default when running `--no-deps`
(https://github.com/rust-lang/cargo/issues/8296).
Unfortunately, for these other use cases, the priority order is
inverted. They want to give *precedence* to the URL the crate picks, and
only fall back to the `--extern-html-root` if no `html_root_url` is
present. That allows passing `--extern-html-root` unconditionally,
without having to parse the source code to see what attributes are
present.
For docs.rs, however, we still want to keep the old behavior, so that
all links on docs.rs stay on the site.
bors [Thu, 19 Aug 2021 03:45:50 +0000 (03:45 +0000)]
Auto merge of #88143 - GuillaumeGomez:rollup-sgh318f, r=GuillaumeGomez
Rollup of 10 pull requests
Successful merges:
- #87818 (Fix anchors display in rustdoc)
- #87983 (Use more accurate spans when proposing adding lifetime to item)
- #88012 (Change WASI's `RawFd` from `u32` to `c_int` (`i32`).)
- #88031 (Make `BuildHasher` object safe)
- #88036 (Fix dead code warning when inline const is used in pattern)
- #88082 (Take into account jobs number for rustdoc GUI tests)
- #88109 (Fix environment variable getter docs)
- #88111 (Add background-color on clickable definitions in source code)
- #88129 (Fix dataflow graphviz bug, make dataflow graphviz modules public)
- #88136 (Move private_unused.rs test to impl-trait)
Guillaume Gomez [Wed, 18 Aug 2021 17:55:04 +0000 (19:55 +0200)]
Rollup merge of #88129 - willcrichton:expose-graphviz-modules, r=ecstatic-morse
Fix dataflow graphviz bug, make dataflow graphviz modules public
I'm working on a rustc plugin that uses the dataflow framework for MIR analysis. I've found the graphviz utilities extremely helpful for debugging. However, I had to fork the compiler to expose them since they're currently private. I would appreciate if they could be made public so I can build against a nightly instead of a custom fork. Specifically, this PR:
* Makes public the `rustc_mir::dataflow::framework::graphviz` module.
* Makes public the `rustc_mir::util::pretty::write_mir_fn` function.
Here's a concrete example of how I'm using the graphviz module: https://github.com/willcrichton/flowistry/blob/97b843b8b06b4004fbb79b5fcfca3e33c7143bc0/src/slicing/mod.rs#L186-L203
Additionally, this PR fixes a small bug in the diff code that incorrectly shows the updated object as the old object.
Guillaume Gomez [Wed, 18 Aug 2021 17:55:02 +0000 (19:55 +0200)]
Rollup merge of #88109 - inquisitivecrystal:env-docs, r=m-ou-se
Fix environment variable getter docs
`@RalfJung` pointed out a number of errors and suboptimal choices I made in my documentation for #86183. This PR should (hopefully) fix the problems they've identified.
Guillaume Gomez [Wed, 18 Aug 2021 17:54:56 +0000 (19:54 +0200)]
Rollup merge of #88012 - sunfishcode:sunfishcode/wasi-raw-fd-c-int, r=alexcrichton
Change WASI's `RawFd` from `u32` to `c_int` (`i32`).
WASI previously used `u32` as its `RawFd` type, since its "file descriptors"
are unsigned table indices, and there's no fundamental reason why WASI can't
have more than 2^31 handles.
However, this creates myriad little incompability problems with code
that also supports Unix platforms, where `RawFd` is `c_int`. While WASI
isn't a Unix, it often shares code with Unix, and this difference made
such shared code inconvenient. #87329 is the most recent example of such
code.
So, switch WASI to use `c_int`, which is `i32`. This will mean that code
intending to support WASI should ideally avoid assuming that negative file
descriptors are invalid, even though POSIX itself says that file descriptors
are never negative.
This is a breaking change, but `RawFd` is considerd an experimental
feature in [the documentation].
bors [Wed, 18 Aug 2021 15:54:59 +0000 (15:54 +0000)]
Auto merge of #86700 - lqd:matthews-nll-hrtb-errors, r=nikomatsakis
Matthew's work on improving NLL's "higher-ranked subtype error"s
This PR rebases `@matthewjasper's` [branch](https://github.com/matthewjasper/rust/tree/nll-hrtb-errors) which has great work to fix the obscure higher-ranked subtype errors that are tracked in #57374.
These are a blocker to turning full NLLs on, and doing some internal cleanups to remove some of the old region code.
The goal is so `@nikomatsakis` can take a look at this early, and I'll then do my best to help do the changes and followup work to land this work, and move closer to turning off the migration mode.
I've only updated the branch and made it compile, removed a warning or two.
r? `@nikomatsakis`
(Here's the [zulip topic to discuss this](https://rust-lang.zulipchat.com/#narrow/stream/122657-t-compiler.2Fwg-nll/topic/.2357374.3A.20improving.20higher-ranked.20subtype.20errors.20via.20.2386700) that Niko wanted)