rustc-ap-rustc_feature 677.0.0

Automatically published version of the package `rustc_feature` in the rust-lang/rust repository from commit d9cd4a33f53689bc0847775669a14f666a138fd7 The publishing script for this crate lives at: https://github.com/alexcrichton/rustc-auto-publish

# Feature gates This crate declares the set of past and present unstable features in the compiler. Feature gate checking itself is done in `librustc_ast_passes/feature_gate.rs` at the moment. Features are enabled in programs via the crate-level attributes of `#![feature(...)]` with a comma-separated list of features. For the purpose of future feature-tracking, once a feature gate is added, even if it is stabilized or removed, *do not remove it*. Instead, move the symbol to the `accepted` or `removed` modules respectively.