Reference `clippy_utils` docs on nightly-rustc and some other documentation updates
The `clippy_utils` crate is now part of the nightly-rustc documentation. See [**very beautiful documentation**](https://doc.rust-lang.org/nightly/nightly-rustc/clippy_utils/). This PR references them in our documentation and updates some other documentation.
changelog: none
`cmp_s_u` is a tiny helper function only used by `cmp` and isn't useful on
it's own. Making it a nested function of `cmp` makes that clear and as a
bonus it's easier to call and doesn't require a `#[must_use]` attribute.
Update `str` utils to prevent ICEs and FNs
This PR reworks some string handling for lints regarding enum naming. I hope the refactoring will prevent future ICEs and help with new bug free implementations.
It might be better to review this PR by going through the commits, as `clippy_utils::camel_case` was renamed to `clippy_utils::str_utils` and then changed further. GH sadly doesn't really make the changes that obvious 🙃
Not too much more to say. Have a nice day 🌞
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Fixes: rust-lang/rust-clippy#7869
changelog: ICE Fix: [`enum_variant_names`] #7869
make test module detection more strict
I started with some small improvements to clippy_utils/src/lib.rs, but then found that our "test" module detection would also catch words containing "test" like e.g. "attestation". So I made this a bit more strict (splitting by `'_'` and checking for `test` or `tests`), adding a test case as I went.
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*Please write a short comment explaining your change (or "none" for internal only changes)*
changelog: none
Coerce const FnDefs to implement const Fn traits
You can now pass a FnDef to a function expecting `F` where `F: ~const FnTrait`.
r? ``@oli-obk``
``@rustbot`` label T-compiler F-const_trait_impl
