This also ensure that dropping a generator won't leak upvars if dropping
one of them panics

There are two moments when a BufRead object needs to empty it's internal
buffer:

- In a seek call;
- In a read call when all data in the internal buffer had been already
  consumed and the output buffer has a greater or equal size than the
  internal buffer.

In both cases, the buffer was not being properly emptied, but only
marked as consumed (self.pos = self.cap). That should be no problem if
the inner reader is only Read, but if it is Seek as well, then it's
possible to access the data in the buffer by using the seek_relative
method. In order to prevent this from happening, both self.pos and
self.cap should be set to 0.

Two test cases were added to detect that failure:

- test_buffered_reader_invalidated_after_read
- test_buffered_reader_invalidated_after_seek

Both tests are very similar to each other. The inner reader contains the
following data: [5, 6, 7, 0, 1, 2, 3, 4]. The buffer capacity is 3
bytes.

- First, we call fill_buffer, which loads [5, 6, 7] into the internal
  buffer, and then consume those 3 bytes.
- Then we either read the 5 remaining bytes in a single read call or we
  move to the end of the stream by calling seek. In both cases the
  buffer should be emptied to prevent the previous data [5, 6, 7] from
  being read.
- We now call seek_relative(-2) and read two bytes, which should give us
  the last 2 bytes of the stream: [3, 4].

Before this commit, the the seek_relative method would consider that
we're still in the range of the internal buffer, so instead of fetching
data from the inner reader, it would return the two last bytes that were
incorrectly still in the buffer: [6, 7]. Therefore, the test would fail.

Now, when seek_relative is called the buffer is empty. So the expected
data [3, 4] is fetched from the inner reader and the test passes.

The pause instruction requires SSE2 but was being unconditionally used
on targets without it, resulting in undefined behavior.

This PR fixes that by only using the pause intrinsic if SSE2 is available.

It also removes the inline assembly which was not required since these
instructions are available in core::arch, and extends support of
the spin_loop hint to arm targets with the v6 feature which also
support the yield instruction.

Closes rust-lang#59237 .

…ss fix

When failing to parse struct-like enum variants, the ADT gets recorded
as having no fields. Record that we have actually recovered during
parsing of this variant to avoid complaing about non-existing fields
when actually using it.

…cks, r=davidtwco

Fixes for the generator transform

* Moves cleanup annotations in pretty printed MIR so that they can be tested
* Correctly determines which drops are in cleanup blocks when elaborating generator drops
* Use the correct state for poisoning a generator

Closes rust-lang#58892

…iplett

Add new test case for possible bug in BufReader

When reading a large chunk from a BufReader, if all the bytes from the buffer have been already consumed, the internal buffer is bypassed entirely. However, it is not invalidated, and it's possible to access its contents using the `seek_relative` method, because it tries to reuse the existing buffer.

…uietMisdreavus

Add default keyword handling in rustdoc

Fixes rust-lang#58898.

r? @QuietMisdreavus

…alexcrichton

Refactor tools/build-mainfest

I saw some duplication in rust-lang#58990 and got an itch... Will likely need to be rebased when that lands. Hopefully the PR should have zero semantic changes...

r? @alexcrichton

…r=steveklabnik

Update and clean up several parts of CONTRIBUTING.md

Remove inline assembly from hint::spin_loop

This PR removes the inline assembly which was not required since these
instructions are available in core::arch, and extends support of
the spin_loop hint to arm targets with the v6 feature which also
support the yield instruction.

…chenkov

Use a valid name for graphviz graphs

Hiridification has broken graphviz output because `HirId` has a more complex display implemetation than `NodeId`. Since the id was just used to generate a distinct identifier, we just pull out the various constituent indexed.

Make meta-item API compatible with `LocalInternedString::get` soundness fix

r? @Zoxc

…etrochenkov

Do not complain about non-existing fields after parse recovery

When failing to parse struct-like enum variants, the ADT gets recorded
as having no fields. Record that we have actually recovered during
parsing of this variant to avoid complaing about non-existing fields
when actually using it.

Fix rust-lang#57361.

Do not encode gensymed imports in metadata

(Unless they are underscore `_` imports which are re-gensymed on crate loading, see rust-lang#56392.)

We cannot encode gensymed imports properly in metadata and if we encode them improperly, we can get erroneous name conflicts downstream.
Gensymed imports are produced by the compiler, so we control their set, and can be sure that none of them needs being encoded for use from other crates.

A workaround that fixes rust-lang#59243.