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
resolve: Make sure indeterminate and inconsistent macro resolutions always generate errors
Addresses the issue described in https://github.com/rust-lang/rust/pull/50911#issuecomment-392560525
I haven't come up with a minimized reproduction yet, but confirmed that `npbot` now generates the correct error with `![feature(use_extern_macros)]`.
reset anonymous-lifetime-mode as we enter `()` scopes
Background:
The anonymous lifetime mode is used to prohibit elided lifetimes where
they didn't used to be permitted, and instead require that `'_` be
used. For example:
```rust
impl Trait for Ref<T> { .. }
// ^^^^^^ ERROR: should be `Ref<'_, T>`
```
When we are parsing the parts of the impl header, we enter into an alternate mode called `CreateParameter`. In this mode, we give an error for things like `Ref<T>`, but for elided lifetimes in a reference type like `&T` we make the elided lifetime into an in-band lifetime:
4f99f37b7e/src/librustc/hir/lowering.rs (L4017-L4035)
This was not intended to change behavior because we only enter into that mode in contexts where elision was not historically permitted. However, the problem is that we fail to reset the mode when we enter into bounds like `Fn(&u32)`, where elision *was* allowed -- the same occurs for fn types like `fn(&u32`). This PR restores the original mode in those contexts.
Fixes#51008
r? @cramertj
rustc: don't visit lifetime parameters through visit_lifetime.
Ideally we'd also not use the `Lifetime` struct for parameters, but I'll leave that to @varkor (#48149).
Fixes#51185 (discovered while auditing all the `visit_lifetime` implementations).
r? @nikomatsakis
Background:
The anonymous lifetime mode is used to prohibit elided lifetimes where
they didn't used to be permitted, and instead require that `'_` be
used. For example:
```rust
impl Trait for Ref<T> { .. }
// ^^^^^^ ERROR: should be `Ref<'_, T>`
```
When we are parsing the parts of the impl header, we enter into an
alternate mode called `CreateParameter`. In this mode, we give an
error for things like `Ref<T>`, but for elided lifetimes in a
reference type like `&T` we make the elided lifetime into an in-band
lifetime:
4f99f37b7e/src/librustc/hir/lowering.rs (L4017-L4035)
This was not intended to change behavior because we only enter into
that mode in contexts where elision was not historically
permitted. However, the problem is that we fail to reset the mode when
we enter into bounds like `Fn(&u32)`, where elision *was* allowed --
the same occurs for fn types like `fn(&u32`). This PR restores the
original mode in those contexts.
