Constant syntax::feature_gate::EXPLAIN_DEPR_CUSTOM_DERIVE

pub const EXPLAIN_DEPR_CUSTOM_DERIVE: &'static str = "`#[derive]` for custom traits is deprecated and will be removed in the future. Prefer using procedural macro custom derive."

🔬 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?