Deny warnings on CI

[ouuan]

This mainly captures unused variables/imports related to ghost codes / no_std. Examples are #1121 and #1126.

Now the CI will fail, waiting for those two PRs.

[ouuan]

There are some concerns at rust-lang/cargo#8424 regarding setting RUSTFLAGS. The main concern is that it may override rustflags in .cargo/config.toml. Now only the line_count tool uses a local .cargo/config.toml, and vargo is overriding the RUSTFLAGS env.

I'm not sure what's the best way to deny warnings on CI for Verus:

• Setting RUSTFLAGS may break if we add a .cargo/config.toml in the future, and we might waste time finding out why it breaks.
• Should we add -Dwarnings in vargo on CI?
• Can we apply cargo clippy? It has a -D warnings command-line option.

[utaal]

Hi @ouuan, thanks for the PR, but I don't have the bandwidth at the moment to look into this. One of the other maintainers may be able to have a look later.

At the current stage of development, I think warnings in CI are acceptable.

[ouuan]

At the current stage of development, I think warnings in CI are acceptable.

Now we only have warnings with special compilation flags. It might be too strict if clippy is used, but the default warnings are easy to avoid.

[utaal]

We may be making some significant changes to the CI process soon, so I don't think this is the time to make this change (and I don't have time to look into the RUSTFLAGS issue) so I'll close this for now. If one of the other contributors @verus-lang/verus-devs wants to pick this up, please do.