This was fixed with the upgrade to LLVM 11 in #73526.
It seems extremely unlikey that this exact issue will ever reoccur,
since slight modifications to the code caused the crash to stop
happening. However, it can't hurt to have a test for it.

Implement Make `handle_alloc_error` default to panic (for no_std + liballoc)

Related: https://github.com/rust-lang/rust/issues/66741

Guarded with `#![feature(default_alloc_error_handler)]` a default
`alloc_error_handler` is called, if a custom allocator is used and no
other custom `#[alloc_error_handler]` is defined.

Unbox mutexes and condvars on some platforms

Both mutexes and condition variables contained a Box containing the actual os-specific object. This was done because moving these objects may cause undefined behaviour on some platforms.

However, this is not needed on Windows[1], Wasm[2], cloudabi[2], and 'unsupported'[3], were the box was only needlessly making them less efficient.

This change gets rid of the box on those platforms.

On those platforms, `Condvar` can no longer verify it is only used with one `Mutex`, as mutexes no longer have a stable address. This was addressed and considered acceptable in #76932.

[1]\: https://docs.microsoft.com/en-us/windows/win32/api/synchapi/nf-synchapi-initializesrwlock
[2]\: These are just a single atomic integer together with futex wait/wake calls/instructions.
[3]\: The `unsupported` platform doesn't support multiple threads at all.

Rollup of 11 pull requests

Successful merges:

 - #75143 (Use `tracing` spans to trace the entire MIR interp stack)
 - #75699 (Uplift drop-bounds lint from clippy)
 - #76768 (Test and reject out-of-bounds shuffle vectors)
 - #77190 (updated p! macro to accept literals)
 - #77388 (Add some regression tests)
 - #77419 (Create E0777 error code for invalid argument in derive)
 - #77447 (BTreeMap: document DrainFilterInner better)
 - #77468 (Fix test name)
 - #77469 (Improve rustdoc error for failed intra-doc link resolution)
 - #77473 (Make --all-targets in x.py check opt-in)
 - #77508 (Fix capitalization in blog post name)

Failed merges:

r? `@ghost`

Fix capitalization in blog post name

Make --all-targets in x.py check opt-in

In particular due to #76822, making this the default is currently suboptimal.

r? @ecstatic-morse

Improve rustdoc error for failed intra-doc link resolution

The previous error was confusing since it made it sound like you can't
link to items that are defined outside the current module.

Also suggested importing the item.

r? @jyn514

Fix test name

Remove trailing `-`.

BTreeMap: document DrainFilterInner better

r? @Mark-Simulacrum

Create E0777 error code for invalid argument in derive

The second commit is to fix a nit reported by @jyn514 [here](https://github.com/rust-lang/rust/pull/76406/files#r485186592).

Add some regression tests

Closes #66501
Closes #68951
Closes #72565
Closes #74244
Closes #75299

The first issue is fixed in 1.43.0, other issues are fixed in the recent nightly.

updated p! macro to accept literals

Closes #70948

Huge thanks @EddyB for helping me out!

Test and reject out-of-bounds shuffle vectors

Fixes #73542.

Uplift drop-bounds lint from clippy

Bounds on `T: Drop` do nothing, so they should warn.

Use `tracing` spans to trace the entire MIR interp stack

r? @RalfJung

While being very verbose, this allows really good tracking of what's going on. While I considered schemes like the previous indenter that we had (which we could get by using the `tracing-tree` crate), this will break down horribly with things like multithreaded rustc. Instead, we can now use `RUSTC_LOG` to restrict the things being traced. You could specify a filter in a way that only shows the logging of a specific frame.

![screenshot of command line output of the new formatting](https://user-images.githubusercontent.com/332036/89291343-aa40de00-d65a-11ea-9f6c-ea06c1806327.png)

If we lower the span's level to `debug`, then in `info` level logging we'd not see the frames, but in `debug` level we would see them. The filtering rules in `tracing` are super powerful, but  I'm not sure if we can specify a filter so we do see `debug` level events, but *not* the `frame` spans. The documentation at https://docs.rs/tracing-subscriber/0.2.10/tracing_subscriber/struct.EnvFilter.html makes me think that we can only turn on things, not turn off things at a more precise level.

cc @hawkw

Use less divisions in display u128/i128

This PR is an absolute mess, and I need to test if it improves the speed of fmt::Display for u128/i128, but I think it's correct.
It hopefully is more efficient by cutting u128 into at most 2 u64s, and also chunks by 1e16 instead of just 1e4.

Also I specialized the implementations for uints to always be non-false because it bothered me that it was checked at all

Do not merge until I benchmark it and also clean up the god awful mess of spaghetti.
Based on prior work in #44583

cc: `@Dylan-DPC`

Due to work on `itoa` and suggestion in original issue:
r? `@dtolnay`

Returns values up to 2*usize by value

Addresses https://github.com/rust-lang/rust/pull/76986#discussion_r498306837 and https://github.com/rust-lang/rust/pull/76986#issuecomment-696415287 by doing the optimization on all targets.

This matches what we do for functions returning `&[T]` and other fat pointers, so it should be Harmless™

update Miri

Fixes https://github.com/rust-lang/rust/issues/77406
r? `@ghost` Cc `@rust-lang/miri`

Allow Weak::as_ptr and friends for unsized T

Relaxes `impl<T> Weak<T>` to `impl<T: ?Sized> Weak<T>` for the methods `rc::Weak::as_ptr`, `into_raw`, and `from_raw`.

Follow-up to #73845, which did most of the impl work to make these functions work for `T: ?Sized`.

We still have to adjust the implementation of `Weak::from_raw` here, however, because I missed a use of `ptr.is_null()` previously. This check was necessary when `into`/`from_raw` were first implemented, as `into_raw` returned `ptr::null()` for dangling weak. However, we now just (wrapping) offset dangling weaks' pointers the same as nondangling weak, so the null check is no longer necessary (or even hit). (I can submit just 17a928f as a separate PR if desired.)

As a nice side effect, moves the `fn is_dangling` definition closer to `Weak::new`, which creates the dangling weak.

This technically stabilizes that "something like `align_of_val_raw`" is possible to do. However, I believe the part of the functionality required by these methods here -- specifically, getting the alignment of a pointee from a pointer where it may be dangling iff the pointee is `Sized` -- is uncontroversial enough to stabilize these methods without a way to implement them on stable Rust.

r? `@RalfJung,` who reviewed #73845.

ATTN: This changes (relaxes) the (input) generic bounds on stable fn!

This matches Cargo behavior and avoids the (somewhat expensive) double checking,
as well as the unfortunate duplicate error messages (#76822,
rust-lang/cargo#5128).

Remove --cfg dox from rustdoc.rs

This was added in https://github.com/rust-lang/rust/pull/53076 because
several dependencies were using `cfg(dox)` instead of `cfg(rustdoc)` (now `cfg(doc)`).
I ran `rg 'cfg\(dox\)'` on the source tree with no matches, so I think
this is now safe to remove.

r? `@Mark-Simulacrum`
cc `@QuietMisdreavus` :)

Bump version to 1.49.0

r? `@pietroalbini`

The new error was confusing when there was partial resolution (something
like `std::io::nonexistent`); the old one is better for those cases.

Rollup of 8 pull requests

Successful merges:

 - #75377 (Fix Debug implementations of some of the HashMap and BTreeMap iterator types)
 - #76107 (Write manifest for MAJOR.MINOR channel to enable rustup convenience)
 - #76745 (Move Wrapping<T> ui tests into library)
 - #77182 (Add missing examples for Fd traits)
 - #77251 (Bypass const_item_mutation if const's type has Drop impl)
 - #77264 (Only use LOCAL_{STDOUT,STDERR} when set_{print/panic} is used. )
 - #77421 (Revert "resolve: Avoid "self-confirming" import resolutions in one more case")
 - #77452 (Permit ty::Bool in const generics for v0 mangling)

Failed merges:

r? `@ghost`