Writing harnesses under e.g. rust-analyzer gives a poor experience

[tedinski]

Writing a harness, either under cfg(kani) or not, should leave people with a natural experience in their editors, including autocomplete, red-squigglies for errors, documentation, not being greyed-out, etc.

There are multiple issues to think about here, including:

• Having the kani crate (etc) available
• Dealing with cfg(kani) and cfg(test)

But there are likely further issues, because we've observed a customer not seeing errors at all (i.e. not even reporting kani as an unknown symbol.) We should investigate whether there are further issues on our side here...

[celinval]

@tedinski / @adpaco-aws can you please try the following instructions for vscode? https://users.rust-lang.org/t/passing-feature-flags-to-rust-analyzer/45918/3

Note that rust-analyzer does have a --all-targets option. So I don't think that's a rust-analyzer limitation.

[celinval]

For CLion, the option looks like:

[adpaco-aws]

I've that option on and it doesn't work for me (in VSCode).