Kani doesn't work with Rust versions below 1.77

[clubby789]

cargo +1.76 new demo
cd demo
cargo +1.76 kani

This results in the error

error: expected a version like "1.32"
error: Failed to execute cargo (exit status: 101). Found 0 compilation errors.

#3593 uses the package ID from cargo metadata as the argument to -p, but before the package ID spec was stabilized in 1.77, the package ID couldn't be used in this way.

Feel free to close if supporting older Rust versions is not desired

[tautschnig]

We'd very much welcome patches to support both old and new versions. Else we'd have to ask you to use an older version of Kani, which should still be available from our releases page.

[clubby789]

@carolynzech To elaborate on the issue above: While Kani mostly uses the linked nightly Rust toolchain, when gathering metadata we run cargo metadata which uses the system's rustup cargo shim. This respects any +version overrides, rust-toolchain.toml in the project directory etc. If rustup resolves to a pre-1.77 version of Cargo, this means we get a package identifier that has an invalid format for the -p argument leading to the above error.

[carolynzech]

This respects any +version overrides, rust-toolchain.toml in the project directory etc. If rustup resolves to a pre-1.77 version of Cargo, this means we get a package identifier that has an invalid format for the -p argument leading to the above error.

Right, that makes sense to me. My point in #3972 is that users shouldn't invoke Kani with +version overrides anyway, so rather than quietly fix it in the background by using our rust-toolchain.toml file, it's better to error so they get a hint that they're doing something wrong. If we just fix it in the background, they'll think that we're using their +version when we're not, which may lead to more confusion down the line.