Strange test runner issue in mentoring request

Programming Rust
1

I was browsing through mentoring requests and noticed this one: Exercism

It seems to be a report an unsupported nightly features in the test file. I cannot reproduce it, the Cargo.toml file looks perfectly fine, the request is from only 13 days ago.

It’s possible that the error could be from a long time ago and a long forgotten bug which I don’t know about. I was going to accept the mentoring request and tell the student to try to submit again, but thought I should mention this, just in case.

For future reference, here is the error received in the test run:

We received the following error when we ran your code:

WARNING: student did not upload Cargo.lock. This may cause build errors.
   Compiling paasio v0.0.0 (/mnt/exercism-iteration)
error[E0658]: use of unstable library feature 'io_error_other'
   --> tests/paasio.rs:397:13
    |
397 |         Err(Error::other(Self::MESSAGE))
    |             ^^^^^^^^^^^^
    |
    = note: see issue #91946 <https://github.com/rust-lang/rust/issues/91946> for more information
    = help: add `#![feature(io_error_other)]` to the crate attributes to enable

error[E0658]: use of unstable library feature 'io_error_other'
   --> tests/paasio.rs:410:13
    |
410 |         Err(Error::other(Self::MESSAGE))
    |             ^^^^^^^^^^^^
    |
    = note: see issue #91946 <https://github.com/rust-lang/rust/issues/91946> for more information
    = help: add `#![feature(io_error_other)]` to the crate attributes to enable

error[E0658]: use of unstable library feature 'io_error_other'
   --> tests/paasio.rs:414:13
    |
414 |         Err(Error::other(Self::MESSAGE))
    |             ^^^^^^^^^^^^
    |
    = note: see issue #91946 <https://github.com/rust-lang/rust/issues/91946> for more information
    = help: add `#![feature(io_error_other)]` to the crate attributes to enable

For more information about this error, try `rustc --explain E0658`.
error: could not compile `paasio` due to 3 previous errors
warning: build failed, waiting for other jobs to finish...
2

That is very strange. The feature was stabilized in Rust 1.74 and I updated the test runner to that in December 2023. The tests using the feature were added in July 2024.

I’m also noticing this part of the error message:

student did not upload Cargo.lock

This is coming from our own tooling. But I changed the message from Cargo.lock to Cargo.toml a looong time ago. (We don’t want students to upload the lock file, that will make dependency issues more likely.)

It looks to me like an extremely outdated version of the test runner was responsible for this.