Extremely slow startup performance on Windows 10 due to Command::output

[ZakisM]

rust-analyzer version: rust-analyzer 0.0.0 (c679648 2024-12-24)

rustc version:
rustc 1.83.0 (90b35a623 2024-11-26)
binary: rustc
commit-hash: 90b35a6239c3d8bdabc530a6a0816f7ff89a0aaf
commit-date: 2024-11-26
host: x86_64-pc-windows-msvc
release: 1.83.0
LLVM version: 19.1.1

editor or extension: N/A

relevant settings: Windows 10 Version 22H2 (OS Build 19045.5247)

repository link (if public, optional): (eg. rust-analyzer)

code snippet to reproduce:

rust-analyzer analysis-stats .

I noticed that rust-analyzer was extremely slow to start for a brand new project (cargo new empty_project) due to the Database loaded metadata step:

Database loaded: 9.57s, 14mb (metadata 9.29s, 380kb; build 64.65ms, 0b)

After some analysis I added some extra logging to this function:

fn utf8_stdout(mut cmd: Command) -> anyhow::Result<String> {
    let time = std::time::Instant::now();
    let output = cmd.output().with_context(|| format!("{cmd:?} failed"))?;
    eprintln!("[Duration {}ms]/[Current Dir {:?}] - {cmd:?}", time.elapsed().as_millis(), cmd.get_current_dir());
    if !output.status.success() {
        match String::from_utf8(output.stderr) {
            Ok(stderr) if !stderr.is_empty() => {
                bail!("{:?} failed, {}\nstderr:\n{}", cmd, output.status, stderr)
            }
            _ => bail!("{:?} failed, {}", cmd, output.status),
        }
    }
    let stdout = String::from_utf8(output.stdout)?;
    Ok(stdout.trim().to_owned())
}

Running analysis-stats with this extra logging enabled:

❯ rust-analyzer analysis-stats .
[Duration 2127ms]/[Current Dir Some("C:\\Users\\zakmi\\RustroverProjects\\empty_project")] - "C:\\Users\\zakmi\\.cargo\\bin\\rustc.exe" "--print" "sysroot"
[Duration 2210ms]/[Current Dir Some("C:\\Users\\zakmi\\.rustup\\toolchains\\stable-x86_64-pc-windows-msvc\\lib/rustlib/src/rust/library")] - "C:\\Users\\zakmi\\.cargo\\bin\\cargo.exe" "-Z" "unstable-options" "config" "get" "build.target"
[Duration 2231ms]/[Current Dir Some("C:\\Users\\zakmi\\.rustup\\toolchains\\stable-x86_64-pc-windows-msvc\\lib/rustlib/src/rust/library")] - "C:\\Users\\zakmi\\.cargo\\bin\\rustc.exe" "-vV"
[Duration 43ms]/[Current Dir Some("C:\\Users\\zakmi\\RustroverProjects\\empty_project")] - "C:\\Users\\zakmi\\.cargo\\bin\\cargo.exe" "--version"
[Duration 70ms]/[Current Dir Some("C:\\Users\\zakmi\\RustroverProjects\\empty_project")] - "C:\\Users\\zakmi\\.cargo\\bin\\cargo.exe" "rustc" "-Z" "unstable-options" "--print" "cfg"
[Duration 64ms]/[Current Dir Some("C:\\Users\\zakmi\\RustroverProjects\\empty_project")] - "C:\\Users\\zakmi\\.cargo\\bin\\cargo.exe" "rustc" "-Z" "unstable-options" "--print" "target-spec-json" "--" "-Z" "unstable-options"
[Duration 53ms]/[Current Dir Some("C:\\Users\\zakmi\\RustroverProjects\\empty_project")] - "C:\\Users\\zakmi\\.cargo\\bin\\cargo.exe" "-Z" "unstable-options" "config" "get" "build.target"
[Duration 14ms]/[Current Dir Some("C:\\Users\\zakmi\\RustroverProjects\\empty_project")] - "C:\\Users\\zakmi\\.rustup\\toolchains\\stable-x86_64-pc-windows-msvc\\bin\\rustc.exe" "-vV"
[Duration 52ms]/[Current Dir Some("C:\\Users\\zakmi\\RustroverProjects\\empty_project")] - "C:\\Users\\zakmi\\.cargo\\bin\\cargo.exe" "-Z" "unstable-options" "config" "get" "env"
Database loaded:     9.57s, 14mb (metadata 9.29s, 380kb; build 64.65ms, 0b)
  item trees: 1
Item Tree Collection: 240.40µs, 0b
  crates: 1, mods: 1, decls: 1, bodies: 1, adts: 0, consts: 0
Item Collection:     3.36s, 200mb
Body lowering:       363.42ms, 53mb
  exprs: 16, ??ty: 0 (0%), ?ty: 0 (0%), !ty: 0
  pats: 0, ??ty: 0 (100%), ?ty: 0 (100%), !ty: 0
Inference:           142.44ms, 19mb
MIR lowering:        514.80µs, 0b
Mir failed bodies: 0 (0%)
Data layouts:        100.00ns, 0b
Failed data layouts: 0 (100%)
Const evaluation:    100.00ns, 0b
Failed const evals: 0 (100%)
Total:               3.87s, 272mb

Commands like C:\Users\zakmi\.cargo\bin\rustc.exe --print sysroot take around 2 seconds, where as running them directly through the terminal take ~70ms:

❯ Measure-Command { C:\Users\zakmi\.cargo\bin\rustc.exe --print sysroot }

Days              : 0
Hours             : 0
Minutes           : 0
Seconds           : 0
Milliseconds      : 77
Ticks             : 779167
TotalDays         : 9.01813657407407E-07
TotalHours        : 2.16435277777778E-05
TotalMinutes      : 0.00129861166666667
TotalSeconds      : 0.0779167
TotalMilliseconds : 77.9167

This causes rust-analyzer performance to be very poor, especially on startup.

[Veykril]

That seems odd, I get

[Duration 60ms]/[Current Dir Some("C:\\workspace\\rust\\rust-analyzer")] - "C:\\Users\\lukas\\.cargo\\bin\\rustc.exe" "--print" "sysroot"
[Duration 17ms]/[Current Dir Some("C:\\Users\\lukas\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib/rustlib/src/rust/library")] - "\\\\?\\C:\\Users\\lukas\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\bin\\cargo.exe" "-Z" "unstable-opt
ions" "config" "get" "build.target"
[Duration 58ms]/[Current Dir Some("C:\\Users\\lukas\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib/rustlib/src/rust/library")] - "C:\\Users\\lukas\\.cargo\\bin\\rustc.exe" "-vV"
[Duration 24ms]/[Current Dir Some("C:\\workspace\\rust\\rust-analyzer")] - "C:\\Users\\lukas\\.cargo\\bin\\cargo.exe" "--version"
[Duration 105ms]/[Current Dir Some("C:\\workspace\\rust\\rust-analyzer")] - "C:\\Users\\lukas\\.cargo\\bin\\cargo.exe" "rustc" "-Z" "unstable-options" "--print" "cfg"
[Duration 66ms]/[Current Dir Some("C:\\workspace\\rust\\rust-analyzer")] - "C:\\Users\\lukas\\.cargo\\bin\\cargo.exe" "rustc" "-Z" "unstable-options" "--print" "target-spec-json" "--" "-Z" "unstable-options"
[Duration 25ms]/[Current Dir Some("C:\\workspace\\rust\\rust-analyzer")] - "C:\\Users\\lukas\\.cargo\\bin\\cargo.exe" "-Z" "unstable-options" "config" "get" "build.target"
[Duration 11ms]/[Current Dir Some("C:\\workspace\\rust\\rust-analyzer")] - "C:\\Users\\lukas\\.rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\bin\\rustc.exe" "-vV"
[Duration 26ms]/[Current Dir Some("C:\\workspace\\rust\\rust-analyzer")] - "C:\\Users\\lukas\\.cargo\\bin\\cargo.exe" "-Z" "unstable-options" "config" "get" "env"

There might be something fishy going on on your system?