rustc-ap-rustc_feature 638.0.0

Automatically published version of the package `rustc_feature` in the rust-lang/rust repository from commit 30ca215b4e38b32aa7abdd635c5e2d56f5724494 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.