`as_slice` will be stable in 1.7

[mcarton]

We need to decide what to do with the unstable_as_slice and unstable_as_mut_slice lints as these functions will be stable in 1.7 (ref. rust-lang/rust#30943). We could simply remove them or keep them and change their documentation to explain it’s better to use &v[..] (see rust-lang/rust#27729 for some arguments).
I think we can remove them as those functions are not inherently bad and can sometimes lead to slightly more readable code (.map(String::as_slice) vs. .map(|s| &*s) and y.happy().monkey().as_slice() vs. &(y.happy().monkey())[..]).

[fhartwig]

I agree that the lint should be removed. Warning because "using deref magic instead is nicer" is far too opinionated in my opinion.

[llogiq]

Hmmm...I think we need to have a story for deprecating lints. I think the lints could still be useful for people that intend (for whatever reason) to deploy on an older Rust version, so I think we shouldn't throw them away yet.

[mcarton]

In any case the documentation must be changed.

[oli-obk]

I think the lints could still be useful for people that intend (for whatever reason) to deploy on an older Rust version, so I think we shouldn't throw them away yet.

If they were using the old nightly, then it's very likely that clippy won't work with it anymore. Even if they use a new nightly for clippy and an old one for their normal compilation, there are probably breaking changes between those nightlies, so the new nightly won't compile the code meant for the old one. Thus they are locked-in to an old nightly and a clippy that ran on that nightly.

[mcarton]

By “older Rust version” he does not mean “older nightly version”, he means people compiling both without Clippy on Rust stable and with Clippy on the last nightly. For them keeping the lint might makes sense as a warning for when they use stable.
But the lint here warns about a feature that we now know will be stabilized (and is not any different in implementation in older version), so it does not make any harm to use it even on older Rust version. For me the lint was more a ”Hey, you’re using a feature which can trivially be replaced by something else and might disappear in 3 month” warning.

[oli-obk]

On stable they can't use the feature...

[mcarton]

Oh right, for some reason I thought that kind of feature could be explicitly allowed even on stable or beta 😳. You have a point then.

[llogiq]

Perhaps we could ask on rust-users and r/rust which Rust versions people are using? If most people are on current rust anyway, we may as well remove the lint.

[Manishearth]

I think to deprecate a lint, we should:

• Immediately move it to a clippy_deprecated group and make it Allow
• after time has passed, add a check_attribute pass that mentions that certain lints are unnecessary.
• after time has passed, keep the lint registered, but with a dummy lintpass (to avoid unknown_lints errors)
• remove it completely.

Perhaps we should first get the framework for more than 2 lint groups up? The idea is simple, have a custom macro instead of declare_lint, which can take the name of the lint group in as well. Make the python script work with both declare_lint and the new macro.

[mcarton]

Perhaps we should first get the framework for more than 2 lint groups up? The idea is simple, have a custom macro instead of declare_lint, which can take the name of the lint group in as well. Make the python script work with both declare_lint and the new macro.

👍 to that. Sometimes I’d also like an ”API breaking lints”-group that I could allow because I’m using clippy on a project that does not regularly use it and I don’t want to mess with their interface.