rust-lang / rust

add error_occured field to ConstQualifs,

fix #76064

I wasn't sure what `in_return_place` actually did and not sure why it returns `ConstQualifs` while it's sibling functions return `bool`. So I tried to make as minimal changes to the structure as possible. Please point out whether I have to refactor it or not.

r? `@oli-obk`
cc `@RalfJung`

specialize io::copy to use copy_file_range, splice or sendfile

Fixes #74426.
Also covers #60689 but only as an optimization instead of an official API.

The specialization only covers std-owned structs so it should avoid the problems with #71091

Currently linux-only but it should be generalizable to other unix systems that have sendfile/sosplice and similar.

There is a bit of optimization potential around the syscall count. Right now it may end up doing more syscalls than the naive copy loop when doing short (<8KiB) copies between file descriptors.

The test case executes the following:

```
[pid 103776] statx(3, "", AT_STATX_SYNC_AS_STAT|AT_EMPTY_PATH, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0644, stx_size=17, ...}) = 0
[pid 103776] write(4, "wxyz", 4)        = 4
[pid 103776] write(4, "iklmn", 5)       = 5
[pid 103776] copy_file_range(3, NULL, 4, NULL, 5, 0) = 5

```

0-1 `stat` calls to identify the source file type. 0 if the type can be inferred from the struct from which the FD was extracted
𝖬 `write` to drain the `BufReader`/`BufWriter` wrappers. only happen when buffers are present. 𝖬 ≾ number of wrappers present. If there is a write buffer it may absorb the read buffer contents first so only result in a single write. Vectored writes would also be an option but that would require more invasive changes to `BufWriter`.
𝖭 `copy_file_range`/`splice`/`sendfile` until file size, EOF or the byte limit from `Take` is reached. This should generally be *much* more efficient than the read-write loop and also have other benefits such as DMA offload or extent sharing.

## Benchmarks

```

OLD

test io::tests::bench_file_to_file_copy         ... bench:      21,002 ns/iter (+/- 750) = 6240 MB/s    [ext4]
test io::tests::bench_file_to_file_copy         ... bench:      35,704 ns/iter (+/- 1,108) = 3671 MB/s  [btrfs]
test io::tests::bench_file_to_socket_copy       ... bench:      57,002 ns/iter (+/- 4,205) = 2299 MB/s
test io::tests::bench_socket_pipe_socket_copy   ... bench:     142,640 ns/iter (+/- 77,851) = 918 MB/s

NEW

test io::tests::bench_file_to_file_copy         ... bench:      14,745 ns/iter (+/- 519) = 8889 MB/s    [ext4]
test io::tests::bench_file_to_file_copy         ... bench:       6,128 ns/iter (+/- 227) = 21389 MB/s   [btrfs]
test io::tests::bench_file_to_socket_copy       ... bench:      13,767 ns/iter (+/- 3,767) = 9520 MB/s
test io::tests::bench_socket_pipe_socket_copy   ... bench:      26,471 ns/iter (+/- 6,412) = 4951 MB/s
```

rustc_target: Mark UEFI targets as `is_like_windows`/`is_like_msvc`

And document what `is_like_windows` and `is_like_msvc` actually mean in more detail.

Addresses FIXMEs left from #71030.
r? `@nagisa`

rustc_target: Change os and vendor values to "none" and "unknown" for some targets

Closes #77730
r? `@ehuss`

rustc_parse: Remove optimization for 0-length streams in `collect_tokens`

The optimization conflates empty token streams with unknown token stream, which is at least suspicious, and doesn't affect performance because 0-length token streams are very rare.

r? `@Aaron1011`

Check predicates from blanket trait impls while testing if they apply

fixes #78673

Previously EOVERFLOW handling was only applied for io::copy specialization
but not for fs::copy sharing the same code.

Additionally we lower the chunk size to 1GB since we have a user report
that older kernels may return EINVAL when passing 0x8000_0000
but smaller values succeed.

… to work

Android builds use feature level 14, the libc wrapper for splice is gated
on feature level 21+ so we have to invoke the syscall directly.
Additionally the emulator doesn't seem to support it so we also have to
add ENOSYS checks.

Fix and re-enable two coverage tests on MacOS

Note, in the coverage-reports test, the comment about MacOS was wrong.
The setting is based on config.toml llvm `optimize` setting. There
doesn't appear to be any environment variable I can check, and I
don't think we should add one. Testing the binary itself is a more
reliable way to check anyway.

For the coverage-spanview test, I removed the dependency on sed
altogether, which is much less ugly than trying to work around the
MacOS sed differences.

I tested these changes on Linux, Windows, and Mac.

r? `@tmandry`
FYI `@wesleywiser`

…of calling stat()

also adds handling for edge-cases involving large sparse files where sendfile could fail with EOVERFLOW

`impl Write for &mut T where T: Write`, thus the same should
apply to the specialization traits

…tches when sending to pipes

splice returns to userspace when the pipe is full, sendfile
just blocks until it's done, this can achieve much higher throughput

Currently it only applies to linux systems. It can be extended to make use
of similar syscalls on other unix systems.

Update cargo

Fixing an important publish bug.

2 commits in 8662ab427a8d6ad8047811cc4d78dbd20dd07699..2af662e22177a839763ac8fb70d245a680b15214
2020-11-12 03:47:53 +0000 to 2020-11-12 19:04:56 +0000
- Fix publishing with optional dependencies. (rust-lang/cargo#8853)
- Minor typo in features.md (rust-lang/cargo#8851)

Rollup of 6 pull requests

Successful merges:

 - #77151 (Add regression test for issue #76042)
 - #77996 (Doc change: Remove mention of `fnv` in HashMap)
 - #78463 (Add type to `ConstKind::Placeholder`)
 - #78984 (Rustdoc check option)
 - #78985 (add dropck test for const params)
 - #78996 (add explicit test for const param promotion)

Failed merges:

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

add explicit test for const param promotion

r? `@RalfJung`

add dropck test for const params

r? `@nikomatsakis` or `@varkor`

Rustdoc check option

The ultimate goal behind this option would be to have `rustdoc --check` being run when you use `cargo check` as a second step.

r? `@jyn514`

Add type to `ConstKind::Placeholder`

I simply threaded `<'tcx>` through everything that required it. I'm not sure whether this is the correct thing to do, but it seems to work.

r? `@nikomatsakis`

Doc change: Remove mention of `fnv` in HashMap

Disclaimer: I am the author of [aHash](https://github.com/tkaitchuck/aHash).

This changes the Rustdoc in `HashMap` from mentioning the `fnv` crate to mentioning the `aHash` crate, as an alternative `Hasher` implementation.

### Why

Fnv [has poor hash quality](https://github.com/rurban/smhasher), is [slow for larger keys](https://github.com/tkaitchuck/aHash/blob/master/compare/readme.md#speed), and does not provide dos resistance, because it is unkeyed (this can also cause [other problems](https://accidentallyquadratic.tumblr.com/post/153545455987/rust-hash-iteration-reinsertion)).

Fnv has acceptable performance for integers and has very poor performance with keys >32 bytes. This is the reason it was removed from the standard library in #37229 .

Because regardless of which dimension you value, there are better alternatives, it does not make sense for anyone to consider using `fnv`.

The text mentioning `fnv` in the standard library continues to create confusion: rust-lang/hashbrown#153  rust-lang/hashbrown#9 . There are also a number of [crates using it](https://crates.io/crates/fnv/reverse_dependencies) a great many of which are hashing strings (Which is when Fnv is the [worst](https://github.com/cbreeden/fxhash#benchmarks), [possible](https://github.com/tkaitchuck/aHash#speed), [choice](http://cglab.ca/~abeinges/blah/hash-rs/).)

I think aHash makes the most sense to mention as an alternative because it is the most credible option (in my obviously biased opinion). It offers [good performance on numbers and strings](https://github.com/tkaitchuck/aHash/blob/master/compare/readme.md#speed), is [of high quality](https://github.com/tkaitchuck/aHash#hash-quality), and [provides dos resistance](https://github.com/tkaitchuck/aHash/wiki/How-aHash-is-resists-DOS-attacks). It is popular (see [stats](https://crates.io/crates/ahash)) and is the default hasher for [hashbrown](https://crates.io/crates/hashbrown) and [dashmap](https://crates.io/crates/dashmap) which are the most popular alternative hashmaps. Finally it does not have any of the [`gotcha` cases](https://github.com/tkaitchuck/aHash#fxhash) that `FxHash` suffers from. (Which is the other popular hashing option when DOS attacks are not a concern)

Signed-off-by: Tom Kaitchuck <tom.kaitchuck@emc.com>

Add regression test for issue #76042

Originally posted in #76042 (comment).
r? `@pnkfelix`

Eliminate some temporary vectors

This PR changes `get_item_attrs` and `get_item_variances` to return iterator impls instead of vectors. On top of that, this PR replaces some seemingly unnecessary vectors with iterators or SmallVec, and also reserves space where we know (the minimum) number of elements that will be inserted. This change hopes to remove a few heap allocations and unnecessary copies.

Co-authored-by: lcnr <bastian_kauschke@hotmail.de>