miri reports undefined behavior

[eric-seppanen]

$ cargo +nightly miri test
...
running 1 test
test src/lib.rs - (line 11) ... FAILED

failures:

---- src/lib.rs - (line 11) stdout ----
Test executable failed (exit status: 1).

stderr:
error: Undefined Behavior: trying to retag from <2453> for SharedReadWrite permission at alloc873[0x0], but that tag does not exist in the borrow stack for this location
   --> /home/eric/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ptr/non_null.rs:401:18
    |
401 |         unsafe { &*self.as_ptr().cast_const() }
    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |                  |
    |                  trying to retag from <2453> for SharedReadWrite permission at alloc873[0x0], but that tag does not exist in the borrow stack for this location
    |                  this error occurs as part of retag at alloc873[0x0..0x28]
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
    = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
help: <2453> was created by a SharedReadWrite retag at offsets [0x18..0x51]
   --> src/lib.rs:16:1
    |
8   | / executor::run(
9   | | async {
10  | |     let (s, mut r) = multishot::channel();
11  | |
...   |
33  | | }
34  | | );
    | |_^

$ cargo +nightly -V
cargo 1.78.0-nightly (f772ec022 2024-03-01)

[eric-seppanen]

Looks like this is due to the executor crate; I was able to reproduce it using async_channel also.
richardanaya/executor#13

[sbarral]

Thank you very much for the report and for pinning down the cause before I even woke up and started investigating :)
My bad for excluding doctests from the Miri CI checks, I will update the workflow.