Regression: "error finalizing incremental compilation session directory. Access is denied. (os error 5)" when building on Windows

[ssg]

This is a reincarnation of #86929 but possibly for a different root cause. This one seems to only happen on ReFS (Dev Drive) volumes on Windows regardless if Windows Defender is enabled or not.

The issue reproduces on rust 1.90.0 and onward (the latest I tried is 1.92.0), but it does not reproduce on rust 1.89.0

Failing build output (tried on xxhash-rust repository at 7026cd705195f502283f97aafc9ea41930099c68):

PS S:\github\xxhash-rust>rustup default 1.90.0
info: using existing install for '1.90.0-x86_64-pc-windows-msvc'
info: default toolchain set to '1.90.0-x86_64-pc-windows-msvc'

  1.90.0-x86_64-pc-windows-msvc unchanged - rustc 1.90.0 (1159e78c4 2025-09-14)

PS S:\github\xxhash-rust>rustc --version --verbose
rustc 1.90.0 (1159e78c4 2025-09-14)
binary: rustc
commit-hash: 1159e78c4747b02ef996e55082b704c09b970588
commit-date: 2025-09-14
host: x86_64-pc-windows-msvc
release: 1.90.0
LLVM version: 20.1.8

PS S:\github\xxhash-rust>cargo build
warning: error finalizing incremental compilation session directory `\\?\S:\github\xxhash-rust\target\debug\incremental\xxhash_rust-3cf7c3qx5vrse\s-hevy05ia4q-02o7lki-working`: Access is denied. (os error 5)

warning: `xxhash-rust` (lib) generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.08s

succeeding build:

PS S:\github\xxhash-rust>rustup default 1.89.0
info: using existing install for '1.89.0-x86_64-pc-windows-msvc'
info: default toolchain set to '1.89.0-x86_64-pc-windows-msvc'

  1.89.0-x86_64-pc-windows-msvc unchanged - rustc 1.89.0 (29483883e 2025-08-04)

PS S:\github\xxhash-rust>rustc --version --verbose
rustc 1.89.0 (29483883e 2025-08-04)
binary: rustc
commit-hash: 29483883eed69d5fb4db01964cdf2af4d86e9cb2
commit-date: 2025-08-04
host: x86_64-pc-windows-msvc
release: 1.89.0
LLVM version: 20.1.7

PS S:\github\xxhash-rust>cargo build
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.08s
PS S:\github\xxhash-rust>

Meta

rustc --version --verbose:

rustc 1.92.0 (ded5c06cf 2025-12-08)
binary: rustc
commit-hash: ded5c06cf21d2b93bffd5d884aa6e96934ee4234
commit-date: 2025-12-08
host: x86_64-pc-windows-msvc
release: 1.92.0
LLVM version: 21.1.3```

No backtrace available.

[ssg]

I can reproduce the issue on an NTFS volume only if I copy the folder on ReFS volume to the NTFS volume (see how the error message still refers to the incremental working file in the ReFS volume):

PS D:\github\xxhash-rust>cargo build
warning: error finalizing incremental compilation session directory `\\?\S:\github\xxhash-rust\target\debug\incremental\xxhash_rust-3cf7c3qx5vrse\s-hevy05ia4q-02o7lki-working`: Access is denied. (os error 5)

warning: `xxhash-rust` (lib) generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.02s

cargo clean + cargo build fixes this issue on the NTFS volume and I'm able to build the project without issues on NTFS.

[ssg]

The directory s-hevy05ia4q-02o7lki-working exists in the target.

I renamed s-hevy05ia4q-02o7lki-working to s-hevy05ia4q-02o7lki manually. The issue keeps happening. There is no -working directory created anymore, but I still get the same rename error.

The relevant source that's giving this warning:

rust/compiler/rustc_incremental/src/persist/fs.rs

Line 369 in 22c74ba

sess.dcx().emit_warn(errors::Finalize { path: &incr_comp_session_dir, err: e });

[psandana]

Discussing with a colleague, one nit thing is to change the text from error to warning. Having a "warning" that emits an "error" is confusing.

[ssg]

Discussing with a colleague, one nit thing is to change the text from error to warning. Having a "warning" that emits an "error" is confusing.

I agree. "couldn't finalize" or "failed to finalize" instead of "error finalizing" would sound better and be much less panic inducing. :)

[ChrisDenton]

I would like to solve the underlying issue but if someone wants to PR a change in wording I for one would accept it.

Btw, I can't reproduce this on my machine (where I use a dev drive) so I'm wondering what's different about my set up. Do you have developer mode enabled?

[ssg]

Do you have developer mode enabled?

Yes.

[psandana]

BTW, I also struggled to reproduce it in new projects. Even copy/pasting the same faulty code. In the project that I see this more often, we are running several cargo calls concurrently from MsBuild.

Most probably you need the IDE open, so rust-analyzer is running and at the same time you are compiling from console.

[ssg]

I also lost the repro, but I could reproduce it again after several retries. And, once it starts reproducing, it doesn't go away. IDE was never open.

PS S:\>cd github\xxhash-rust
PS S:\github\xxhash-rust>cargo build
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.16s
PS S:\github\xxhash-rust>cargo build
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.02s
PS S:\github\xxhash-rust>cargo clean
     Removed 18 files, 34.4KiB total
PS S:\github\xxhash-rust>cargo build
   Compiling xxhash-rust v0.8.15 (S:\github\xxhash-rust)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.74s
PS S:\github\xxhash-rust>cargo build
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.02s
PS S:\github\xxhash-rust>cargo clean
     Removed 18 files, 34.4KiB total
PS S:\github\xxhash-rust>cargo build
   Compiling xxhash-rust v0.8.15 (S:\github\xxhash-rust)
warning: error finalizing incremental compilation session directory `\\?\S:\github\xxhash-rust\target\debug\incremental\xxhash_rust-0qefvuzynp6yt\s-hey5oaztmu-04xn8u6-working`: Access is denied. (os error 5)

warning: `xxhash-rust` (lib) generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.28s
PS S:\github\xxhash-rust>cargo build
warning: error finalizing incremental compilation session directory `\\?\S:\github\xxhash-rust\target\debug\incremental\xxhash_rust-0qefvuzynp6yt\s-hey5oaztmu-04xn8u6-working`: Access is denied. (os error 5)

warning: `xxhash-rust` (lib) generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.02s
PS S:\github\xxhash-rust>cargo build
warning: error finalizing incremental compilation session directory `\\?\S:\github\xxhash-rust\target\debug\incremental\xxhash_rust-0qefvuzynp6yt\s-hey5oaztmu-04xn8u6-working`: Access is denied. (os error 5)

warning: `xxhash-rust` (lib) generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.02s
PS S:\github\xxhash-rust>cargo build
warning: error finalizing incremental compilation session directory `\\?\S:\github\xxhash-rust\target\debug\incremental\xxhash_rust-0qefvuzynp6yt\s-hey5oaztmu-04xn8u6-working`: Access is denied. (os error 5)

warning: `xxhash-rust` (lib) generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.02s

[ssg]

Basically on Windows, cargo clean; cargo build shows the warning on ReFS 50% of the time while that never happens on NTFS. It doesn't seem to matter if IDE is open or not.

[mmgeorge]

Running into this as well -- Dev Drive (ReFS). Only seeing this with rust analyzer also running.