Trait Nightly 

pub trait Nightly {
    // Required methods
    fn emit_unstable_feature(
        &self,
        feature: UnstableFeature,
        allowed_features: &AllowedFeatures,
    ) -> bool;
    fn emit_unstable_feature_bundle<F: IntoIterator<Item = UnstableFeature>>(
        &self,
        features: F,
        allowed_features: &AllowedFeatures,
        bundle_name: &str,
    ) -> bool;
}

Adds AutoCfg::emit_unstable_feature

Required Methods

fn emit_unstable_feature( &self, feature: UnstableFeature, allowed_features: &AllowedFeatures, ) -> bool

Offers at least 2 cfg flags for all known features

Feature enablement: cfg(unstable_...)

• To be used at top-level crate via #![cfg_attr(unstable_foo, feature(foo))]

Cfg-gating: cfg(has_...)

• Do not rely on #[cfg(not(unstable_foo))] to suggest that feature(foo) is stable!
• There are 3 reasons that #[cfg(unstable_foo)] could be false:
  1. The build is using stable/beta or the feature is not on the allow-features whitelist
  2. The feature has been stabilised
  3. The compiler is from before the feature was implemented
• All known features have a #[cfg(has_...)] for this purpose.

Note

• You must pass a set of AllowedFeatures, created by calling cargo_allowed_features
• If you need to test that a feature is available in order to cfg-gate your code and it is not on the list of known features, please raise a PR with a suggested probe.
• Returns true if has_... has been set. This means OtherFeature will always return false

fn emit_unstable_feature_bundle<F: IntoIterator<Item = UnstableFeature>>( &self, features: F, allowed_features: &AllowedFeatures, bundle_name: &str, ) -> bool

Calls emit_unstable_feature for all given features, additionally setting has_{bundlename} & returning true if all features are available.

Note

• This will always return false if any of the features are OtherFeature

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors

impl Nightly for AutoCfg