Tracking issue for warning for rust_2018_idioms by default

[shepmaster]

#[warn(rust_2018_idioms)] is not going to be enabled by default for Rust 2018 because we are taking a conservative stance and we aren't sure about how good the suggestions are yet.

The plan is to enable this lint by default some number of releases / months after Rust 2018 ships.

Progress

• bare_trait_objects is now set to warn (Warn on bare_trait_objects by default #61203)
• ellipsis_inclusive_range_patterns will soon be set to warn (Set ellipsis_inclusive_range_patterns lint to warn #61342)
• unused_extern_crates has open issues
• Tracking Issue for enabling elided_lifetimes_in_paths lints #91639
• elided_lifetimes_in_paths has open issues (Multiple anonymous lifetimes bounds upset compiler #60199, 2018 idioms: duplicate suggestion for anonymous lifetime #55768)
• Remove unused_extern_crates warning for crates used by nested code #44294
• strange rust_2018_idioms warning on code comment in clippy codebase #51881
• 2018 idioms: rustc-internal crates linted to be removed when they can't #56038
• edition idioms: Incorrect span in extern crate removal #56328
• 2018: fix lint on unused dependencies #57274
• New "warning incompatible with previous forbid in same scope" error #77713

This summary was last updated from this comment; check to see if there are new comments since then.

/cc @Centril @aturon @Mark-Simulacrum

[oberien]

Is there an update on this? I'd like to see at least some of the new currently allow-by-default lints to become warn-by-default. Personally I'm missing elided_lifetime_in_path the most, because these kinds of elided lifetimes regularly lead to hard to spot bugs.

[hellow554]

@oberien you could modify your environment variables and add

RUSTFLAGS="$RUSTFLAGS -W rust_2018_idioms"

and you have it enabled for all your projects on your local machine.

[memoryruins]

It would be great to have bare_trait_objects set to warn by default. I often see users in chats accidentally use trait objects when they did not intend to.

[Centril]

I have a few PRs:

• [WIP] BARE_TRAIT_OBJECTS -> Deny #59482
• [WIP] UNUSED_EXTERN_CRATES -> Deny #59483
• [WIP] ELLIPSIS_INCLUSIVE_RANGE_PATTERNS -> Deny #59484
• [WIP] ELIDED_LIFETIMES_IN_PATHS -> Deny #59485

which, unfortunately, I don't have time for at the moment.

Feel free to pick up any of them.

[memoryruins]

After setting bare_trait_objects to warn and running --bless on the tests, 300+ ui stderr files changed due to the warnings (expected after seeing the output from the previous PR ).

If there is still interest to see a crater run with deny set, I think it's possible to run crater without CI tests passing as long as if the build succeeds.

If we continued with warn, we could change many of the tests to use dyn, avoiding committing too much stderr noise. Some tests would be left bare to continue testing the ui of the lint. What do you think?

[Centril]

@memoryruins Feel free to send in a PR for warnings and I'll FCP that one. We can crank up to deny later.