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Use fstatat() in DirEntry::metadata on Apple platforms #147986

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@jesseschalken jesseschalken commented Oct 22, 2025 •
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Apple supports fstatat on macOS >=10.10 (source), and according to Platform Support the oldest supported version is 10.12.

Google says iOS >=10 supports fstatat but doesn't provide a source. *-apple-ios says the minimum supported iOS version is 10.0.

Unsure about tvOS, watchOS and visionOS, hoping CI can confirm this.

I am testing with fastdu which is effectively a stress test for DirEntry::metadata. In one test this provides a 1.13x speedup.

$ hyperfine --warmup 1 'target/release/fastdu testdir' 'fastdu testdir'
Benchmark 1: target/release/fastdu testdir
  Time (mean ± σ):     154.6 ms ±  17.4 ms    [User: 31.7 ms, System: 187.6 ms]
  Range (min … max):   148.4 ms … 225.5 ms    19 runs
 
Benchmark 2: fastdu testdir
  Time (mean ± σ):     175.3 ms ±  15.8 ms    [User: 50.0 ms, System: 196.2 ms]
  Range (min … max):   165.4 ms … 211.7 ms    17 runs
 
Summary
  target/release/fastdu testdir ran
    1.13 ± 0.16 times faster than fastdu testdir

You can also reproduce a speedup with a program like this (providing a directory with many entries):

fn main() {
    let args: Vec<_> = std::env::args_os().collect();
    let dir: PathBuf = args[1].clone().into();

    for entry in dir.read_dir().as_mut().unwrap() {
        let entry = entry.as_ref().unwrap();
        let metadata = entry.metadata();
        let metadata = metadata.as_ref().unwrap();
        println!("{} {}", metadata.len(), entry.file_name().display());
    }
}
$ hyperfine './target/release/main testdir' './main testdir'
Benchmark 1: ./target/release/main testdir
  Time (mean ± σ):     148.3 ms ±   5.2 ms    [User: 23.1 ms, System: 122.9 ms]
  Range (min … max):   145.2 ms … 167.2 ms    19 runs
 
Benchmark 2: ./main testdir
  Time (mean ± σ):     164.4 ms ±   9.5 ms    [User: 32.6 ms, System: 128.8 ms]
  Range (min … max):   158.5 ms … 199.5 ms    17 runs
 
Summary
  ./target/release/main testdir ran
    1.11 ± 0.07 times faster than ./main testdir

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Oct 22, 2025
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BlackHoleFox
BlackHoleFox approved these changes Oct 24, 2025
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Looks good to me. fstatat is in all of the various SDK's public headers and its more darwin functionality then anything platform specific. And yeah available before Rust's current minimum Apple OS versions.

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