Latest kani version breaks CI job

[tcharding]

Thanks for your tool!

We run kani daily in CI and also on each PR we run it with cargo kani --codegen-only.

Today the --codegen-only job broke. It looks like its something to do with the latest release of kani but I'm not sure why its turned up today when the release came out 10 days ago.

The build warning we are seeing is:

error[E0658]: use of unstable library feature 'proc_macro_byte_character'
   --> /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/proc-macro2-1.0.80/src/wrapper.rs:871:21
    |
871 |                     proc_macro::Literal::byte_character(byte)
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |

I tried using kani v0.48.0 and the job succeeds.

Example of job failing: https://github.com/rust-bitcoin/rust-bitcoin/actions/runs/8682612259/job/23807404841#step:3:288
CI passing after version pinned: rust-bitcoin/rust-bitcoin#2686

And this is how we are running the job:

  Kani:
    runs-on: ubuntu-20.04
    steps:
      - name: 'Checkout your code.'
        uses: actions/checkout@v4

      - name: 'Kani build proofs'
        uses: model-checking/kani-github-action@v1.1
        with:
          args: '--only-codegen'

[tautschnig]

Please see #3138 for some initial discussion (including pointers to non-Kani projects that seem to be affected). #3144 will fix this problem via toolchain upgrade.

[tcharding]

Legend, thank you.

[celinval]

@tcharding were you able to verify that kani-0.50.0 fixes your issue? Thanks!

[tcharding]

Yep fixed! Thanks a bunch.

[tcharding]

Verified with rust-bitcoin/rust-bitcoin#2709