Compilation error with Rust 1.89.0 - `raw_os_error() method not found` on TryLockError

[rjan90]

A user in Lotus reported getting build errors coming from bellperson when using rust version 1.89.0:

Environment:

• OS: Ubuntu 22.04
• Rust version: 1.89.0 (29483883e 2025-08-04)
• bellperson version: 0.26.0
• Context: Building Lotus v1.34.0-rc2 with FFI_BUILD_FROM_SOURCE=1

Error:

error[E0599]: no method named `raw_os_error` found for enum `std::fs::TryLockError` in the current scope
   --> /root/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/bellperson-0.26.0/src/gpu/locks.rs:176:20
    |
176 |             if err.raw_os_error() == fs2::lock_contended_error().raw_os_error() {
    |                    ^^^^^^^^^^^^ method not found in `std::fs::TryLockError`
    |
note: the method `raw_os_error` exists on the type `std::io::Error`

Root Cause:

Rust 1.89.0 appears to have removed or changed the raw_os_error() method on std::fs::TryLockError, causing a compilation failure in src/gpu/locks.rs:176.

Workaround:

Downgrading to Rust 1.87.0 resolved the issue.