Type Definition syntax::ext::base::BuiltinDeriveFn

type BuiltinDeriveFn = fn<'cx>(_: &'cx mut ExtCtxt, _: Span, _: &MetaItem, _: &Annotatable, _: &mut FnMut(Annotatable));

🔬 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?