Make some std::intrinsics `const fn`s
Making some rustc intrinsics (`ctpop`, `cttz`, `ctlz` and `bswap`) `const fn`s.
This is a pre-step to being able to make `swap_bytes`, `to_be` and `from_be` constant functions. That in itself could be ergonomic and useful. But even better is that it would allow `Ipv4Addr::new` etc becoming `const fn`s as well. Which might be really useful since I find it quite common to want to define them as constants.
r? @oli-obk
The old text was: "The precise definition is: a type T is Sync if &T is Send."
Since we've also got
```
impl<'a, T> Send for &'a T
where
T: Sync + ?Sized,
```
I purpose we can change the `if` to `if and only if` to make it more precise.
Arc downcast
Implement `downcast` for `Arc<Any + Send + Sync>` as part of #44608, and gated by the same `rc_downcast` feature.
This PR is mostly lightly-edited cut'n'paste.
This has two additional changes:
- The `downcast` implementation needs `Any + Send + Sync` implementations for `is` and `Debug`, and I added `downcast_ref` and `downcast_mut` for completeness/consistency. (Can these be insta-stabilized?)
- At @SimonSapin's suggestion, I converted `Arc` and `Rc` to use `NonNull::cast` to avoid an `unsafe` block in each which tidied things up nicely.
Per discussion in https://github.com/rust-lang/rust/issues/51245#issuecomment-393651083
This allows more flexibility in what can be done with the API. This also
splits `rtabort!` into `dumb_print` happening in the default hook and
`abort_internal`, happening in the actual oom handler after calling the
hook. Registering an empty function thus makes the oom handler not print
anything but still abort.
Cc: @alexcrichton
Register outlives predicates from queries the right way around.
Closes#49354
The region constraints from queries need to be reversed from sub to outlives.
Note: wf checking reports these errors before NLL, so I'm not sure if there's any case when these predicates need to be created at all.
cc @nikomatsakis
Rollup of 7 pull requests
Successful merges:
- #49546 (Stabilize short error format)
- #51123 (Update build instructions)
- #51146 (typeck: Do not pass the field check on field error)
- #51193 (Fixes some style issues in rustdoc "implementations on Foreign types")
- #51213 (fs: copy: Use File::set_permissions instead of fs::set_permissions)
- #51227 (mod.rs isn't beautiful)
- #51240 (Two minor parsing tweaks)
Failed merges:
We only need to implement it for `Any + Send + Sync` because in practice
that's the only useful combination for `Arc` and `Any`.
Implementation for #44608 under the `rc_downcast` feature.
fs: copy: Use File::set_permissions instead of fs::set_permissions
We already got the open file descriptor at this point.
Don't make the kernel resolve the path again.
Update build instructions
It get stuck at the cloning step.
`./x.py build `
Updating only changed submodules
Updating submodule src/llvm
Submodule 'src/llvm' (https://github.com/rust-lang/llvm.git) registered for path 'src/llvm'
Cloning into '/home/username/rust/src/llvm'...
When subtracting an Instant from another, the function will panick when `RHS > self`, but the error message confusingly displays a different error:
```rust
let i = Instant::now();
let other = Instant::now();
if other > i {
println!("{:?}", i - other);
}
```
This results in a panic:
```
thread 'test_instant' panicked at 'other was less than the current instant', libstd/sys/unix/time.rs:292:17
```
std::fs::DirEntry.metadata(): use fstatat instead of lstat when possible
When reading a directory with `read_dir`, querying metadata for a resulting `DirEntry` is done by building the whole path and then `lstat`ing it, which requires the kernel to resolve the whole path. Instead, one
can use the file descriptor to the enumerated directory and use `fstatat`. This make the resolving step
unnecessary.
This PR implements using `fstatat` on linux, android and emscripten.
## Compatibility across targets
`fstatat` is POSIX.
* Linux >= 2.6.19 according to https://linux.die.net/man/2/fstatat
* android according to https://android.googlesource.com/platform/bionic/+/master/libc/libc.map.txt#392
* emscripten according to 7f89560101/system/include/libc/sys/stat.h (L76)
The man page says "A similar system call exists on Solaris." but I haven't found it.
## Compatibility with old platforms
This was introduced with glibc 2.4 according to the man page. The only information I could find about the minimal version of glibc rust must support is this discussion https://internals.rust-lang.org/t/bumping-glibc-requirements-for-the-rust-toolchain/5111/10
The conclusion, if I understand correctly, is that currently rust supports glibc >= 2.3.4 but the "real" requirement is Centos 5 with glibc 2.5. This PR would make the minimal version 2.4, so this should be fine.
## Benefit
I did the following silly benchmark:
```rust
use std::io;
use std::fs;
use std::os::linux::fs::MetadataExt;
use std::time::Instant;
fn main() -> Result<(), io::Error> {
let mut n = 0;
let mut size = 0;
let start = Instant::now();
for entry in fs::read_dir("/nix/store/.links")? {
let entry = entry?;
let stat = entry.metadata()?;
size += stat.st_size();
n+=1;
}
println!("{} files, size {}, time {:?}", n, size, Instant::now().duration_since(start));
Ok(())
}
```
On warm cache, with current rust nightly:
```
1014099 files, size 76895290022, time Duration { secs: 2, nanos: 65832118 }
```
(between 2.1 and 2.9 seconds usually)
With this PR:
```
1014099 files, size 76895290022, time Duration { secs: 1, nanos: 581662953 }
```
(1.5 to 1.6 seconds usually).
approximately 40% faster :)
On cold cache there is not much to gain because path lookup (which we spare) would have been a cache hit:
Before
```
1014099 files, size 76895290022, time Duration { secs: 391, nanos: 739874992 }
```
After
```
1014099 files, size 76895290022, time Duration { secs: 388, nanos: 431567396 }
```
## Testing
The tests were run on linux `x86_64`
```
python x.py test src/tools/tidy
./x.py test src/libstd
```
and the above benchmark.
I did not test any other target.
remove notion of Implicit derefs from mem-cat
`PointerKind` is included in `LoanPath` and hence forms part of the equality check; this led to having two unequal paths that both represent `*x`, depending on whether the `*` was inserted automatically or explicitly. Bad mojo.
Fixes#51117
r? @eddyb
`PointerKind` is included in `LoanPath` and hence forms part of the
equality check; this led to having two unequal paths that both
represent `*x`, depending on whether the `*` was inserted
automatically or explicitly. Bad mojo. The `note` field, in contrast,
is intended more-or-less primarily for this purpose of adding extra
data.
[MIR] Change "scopes" from "visibility scopes" to "source scopes".
These scopes are already used for source-oriented diagnostics, lint levels and unsafety checks.
This PR generalizes the naming around scopes, making the type `SourceScope`, and flips (across several commits) the relationship/priority between `LocalDecl`'s "visibility" and "syntactic" scopes.
r? @nikomatsakis
