Inconsistent panic during `cargo vendor`

[obsgolem]

Problem

When running cargo vendor on stable or nightly, I inconsistently get a panic.

thread 'main' panicked at src\tools\cargo\src\cargo\ops\vendor.rs:412:45:
called `Result::unwrap()` on an `Err` value: StripPrefixError(())
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Steps

Minimal Cargo.toml

[package]
name = "tmp"
version = "0.1.0"
edition = "2024"

[dependencies]
regex = "1.11.1"

Run cargo vendor like 10 times and it should show up at least once.

Possible Solution(s)

No response

Notes

No response

Version

cargo 1.90.0-nightly (930b4f62c 2025-06-28)
release: 1.90.0-nightly
commit-hash: 930b4f62cfcd1f0eabdb30a56d91bf6844b739bf
commit-date: 2025-06-28
host: x86_64-pc-windows-msvc
libgit2: 1.9.0 (sys:0.20.2 vendored)
libcurl: 8.12.1-DEV (sys:0.4.80+curl-8.12.1 vendored ssl:Schannel)
os: Windows 10.0.26100 (Windows 11 Enterprise) [64-bit]

[epage]

The panic in question

cargo/src/cargo/ops/vendor.rs

Line 412 in 15165ca

let relative = p.strip_prefix(&src).unwrap();

which appears to be called by

cargo/src/cargo/ops/vendor.rs

Lines 294 to 301 in 15165ca

	if let Err(e) = fs::rename(&unpacked_src, &dst) {
	// This fallback is mainly for Windows 10 versions earlier than 1607.
	// The destination of `fs::rename` can't be a directory in older versions.
	// Can be removed once the minimal supported Windows version gets bumped.
	tracing::warn!("failed to `mv {unpacked_src:?} {dst:?}`: {e}");
	let paths: Vec<_> = walkdir(&unpacked_src).map(|e| e.into_path()).collect();
	cp_sources(pkg, src, &paths, &dst, &mut file_cksums, &mut tmp_buf, gctx)
	.with_context(|| format!("failed to copy vendored sources for {id}"))?;

[weihanglo]

The logic was added by this c2d3bc4 as a workaround if you are on Window older than Windows 10 1607.

I am not sure why it is inconsistent, perhaps file system issue not flushing?

[vksir]

For me, it's a inevitable panic. It really bothered me, which led me to try to fix it. Now I know why.

Env

OS: Windows 11 Version 24H2 
Cargo Version: 1.90
Cargo Command: D:/rust/cargo/bin/cargo.exe +1.90-x86_64-pc-windows-msvc vendor --respect-source-config C:\Users\vksir\AppData\Local\JetBrains\RustRover2025.2\intellij-rust\stdlib\1.90.0-9578ceb0ddc22376e03438e71197897420162751\vendor

Backtrace

thread 'main' panicked at src\cargo\ops\vendor.rs:412:45:
called `Result::unwrap()` on an `Err` value: StripPrefixError(())
stack backtrace:
   0:     0x7ff76c533052 - std::backtrace_rs::backtrace::win64::trace
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\..\..\backtrace\src\backtrace\win64.rs:85
   1:     0x7ff76c533052 - std::backtrace_rs::backtrace::trace_unsynchronized
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\..\..\backtrace\src\backtrace\mod.rs:66
   2:     0x7ff76c533052 - std::sys::backtrace::_print_fmt
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\sys\backtrace.rs:66
   3:     0x7ff76c533052 - std::sys::backtrace::impl$0::print::impl$0::fmt
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\sys\backtrace.rs:39
   4:     0x7ff76c55baeb - core::fmt::rt::Argument::fmt
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\core\src\fmt\rt.rs:173
   5:     0x7ff76c55baeb - core::fmt::write
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\core\src\fmt\mod.rs:1468
   6:     0x7ff76c52c357 - std::io::default_write_fmt
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\io\mod.rs:639
   7:     0x7ff76c52c357 - std::io::Write::write_fmt<std::sys::stdio::windows::Stderr>
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\io\mod.rs:1954
   8:     0x7ff76c532e95 - std::sys::backtrace::BacktraceLock::print
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\sys\backtrace.rs:42
   9:     0x7ff76c53860e - std::panicking::default_hook::closure$0
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\panicking.rs:300
  10:     0x7ff76c538384 - std::panicking::default_hook
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\panicking.rs:327
  11:     0x7ff76c5391ab - std::panicking::rust_panic_with_hook
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\panicking.rs:833
  12:     0x7ff76c538f59 - std::panicking::begin_panic_handler::closure$0
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\panicking.rs:706
  13:     0x7ff76c533e0f - std::sys::backtrace::__rust_end_short_backtrace<std::panicking::begin_panic_handler::closure_env$0,never$>
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\sys\backtrace.rs:174
  14:     0x7ff76c538b6e - std::panicking::begin_panic_handler
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\panicking.rs:697
  15:     0x7ff76c959751 - core::panicking::panic_fmt
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\core\src\panicking.rs:75
  16:     0x7ff76c959c20 - core::result::unwrap_failed
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\core\src\result.rs:1765
  17:     0x7ff76a54a0ed - enum2$<core::result::Result<ref$<std::path::Path>,std::path::StripPrefixError> >::unwrap
                               at D:\rust\rustup\toolchains\1.90-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\core\src\result.rs:1167
  18:     0x7ff76a54a0ed - cargo::ops::vendor::cp_sources
                               at E:\TmpCode\cargo\src\cargo\ops\vendor.rs:412
  19:     0x7ff76a5483e5 - cargo::ops::vendor::sync
                               at E:\TmpCode\cargo\src\cargo\ops\vendor.rs:300
  20:     0x7ff76a544cdb - cargo::ops::vendor::vendor
                               at E:\TmpCode\cargo\src\cargo\ops\vendor.rs:44
  21:     0x7ff769c495fa - cargo::commands::vendor::exec
                               at E:\TmpCode\cargo\src\bin\cargo\commands\vendor.rs:73
  22:     0x7ff769c22316 - enum2$<cargo::cli::Exec>::exec
                               at E:\TmpCode\cargo\src\bin\cargo\cli.rs:475
  23:     0x7ff769c1e540 - cargo::cli::main
                               at E:\TmpCode\cargo\src\bin\cargo\cli.rs:97
  24:     0x7ff769c30dfd - cargo::main
                               at E:\TmpCode\cargo\src\bin\cargo\main.rs:57
  25:     0x7ff769cb3c9b - core::ops::function::FnOnce::call_once<void (*)(),tuple$<> >
                               at D:\rust\rustup\toolchains\1.90-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\core\src\ops\function.rs:253
  26:     0x7ff769c61fce - core::hint::black_box
                               at D:\rust\rustup\toolchains\1.90-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\core\src\hint.rs:482
  27:     0x7ff769c61fce - std::sys::backtrace::__rust_begin_short_backtrace<void (*)(),tuple$<> >
                               at D:\rust\rustup\toolchains\1.90-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\std\src\sys\backtrace.rs:158
  28:     0x7ff769c15b81 - std::rt::lang_start::closure$0<tuple$<> >
                               at D:\rust\rustup\toolchains\1.90-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\std\src\rt.rs:206
  29:     0x7ff76c521c15 - std::rt::lang_start_internal::closure$0
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\rt.rs:175
  30:     0x7ff76c521c15 - std::panicking::catch_unwind::do_call
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\panicking.rs:589
  31:     0x7ff76c521c15 - std::panicking::catch_unwind
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\panicking.rs:552
  32:     0x7ff76c521c15 - std::panic::catch_unwind
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\panic.rs:359
  33:     0x7ff76c521c15 - std::rt::lang_start_internal
                               at /rustc/1159e78c4747b02ef996e55082b704c09b970588/library\std\src\rt.rs:171
  34:     0x7ff769c15b6a - std::rt::lang_start<tuple$<> >
                               at D:\rust\rustup\toolchains\1.90-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\std\src\rt.rs:205
  35:     0x7ff769c349e9 - main
  36:     0x7ff76c956d2c - invoke_main
                               at D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:78
  37:     0x7ff76c956d2c - __scrt_common_main_seh
                               at D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288
  38:     0x7ffa9ec5e8d7 - BaseThreadInitThunk
  39:     0x7ffa9fe1c34c - RtlUserThreadStart

Why Panic

cargo/src/cargo/ops/vendor.rs

Lines 294 to 301 in 15165ca

	if let Err(e) = fs::rename(&unpacked_src, &dst) {
	// This fallback is mainly for Windows 10 versions earlier than 1607.
	// The destination of `fs::rename` can't be a directory in older versions.
	// Can be removed once the minimal supported Windows version gets bumped.
	tracing::warn!("failed to `mv {unpacked_src:?} {dst:?}`: {e}");
	let paths: Vec<_> = walkdir(&unpacked_src).map(|e| e.into_path()).collect();
	cp_sources(pkg, src, &paths, &dst, &mut file_cksums, &mut tmp_buf, gctx)
	.with_context(|| format!("failed to copy vendored sources for {id}"))?;

At line 300, the src should be unpacked_src.

The src is the pkg root, and this function want to copy pkg file from tmp dir (tmp dir is unpacked_src) to dst dir.

cargo/src/cargo/ops/vendor.rs

Line 412 in 15165ca

let relative = p.strip_prefix(&src).unwrap();

So strip_prefix failed, the p is the file path from unpacked_src whose prefix is not same as src.

After I changed it, the problem is solved.

If this conclusion is correct, I would be happy to submit a PR to fix this problem. :)

[weihanglo]

@vksir nice catch! Feel free to submit a PR :)

Though I am more curious why you went through that code path, as it is tended for only Windows 10 earlier than 1607.

[vksir]

@vksir nice catch! Feel free to submit a PR :)

Though I am more curious why you went through that code path, as it is tended for only Windows 10 earlier than 1607.

More information:

1. I executed cargo vendor cmd as administartor. And I tried mv it manually, and it worked.
2. The packets that failed to move are not the same. It seems to lack regularity. It failed to move it the last time the command was executed, but it might succeed next time. But I never seen the utf8parse-0.2.2 movied scucceed.
3. Logs below,

   2.858528000s  WARN main:exec: cargo::ops::vendor: failed to `mv "\\\\?\\C:\\Users\\vksir\\AppData\\Local\\JetBrains\\RustRover2025.2\\intellij-rust\\stdlib\\1.90.0-9578ceb0ddc22376e03438e71197897420162751\\vendor\\.vendor-stagingERq1wq\\encoding_rs-0.8.35" "\\\\?\\C:\\Users\\vksir\\AppData\\Local\\JetBrains\\RustRover2025.2\\intellij-rust\\stdlib\\1.90.0-9578ceb0ddc22376e03438e71197897420162751\\vendor\\encoding_rs"`: 拒绝访问。 (os error 5)
   

[weihanglo]

@vksir

Would you mind running icacls to get the permissions for "C:\\Users\\vksir\\AppData\\Local\\JetBrains\\RustRover2025.2\\intellij-rust\\stdlib\\1.90.0-9578ceb0ddc22376e03438e71197897420162751\\vendor\\encoding_rs" and share with us?

Also, wonder if it was because JetBrains RustRover was holding the directory so that it cannot be renamed?

That said, your proposed fix is unrelated to these questions and should be fine go alone :)