Static rustc_lint::builtin::UNSTABLE_FEATURES[]

static UNSTABLE_FEATURES: &Lint = &::lint::Lint{name: "UNSTABLE_FEATURES",
              default_level: ::lint::Allow,
              desc: "enabling unstable features (deprecated. do not use)",
              edition_deny: None,}
🔬 This is a nightly-only experimental API. (rustc_private)

this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml instead?