⚙️ This is an internal compiler API. (rustc_private)
This crate is being loaded from the sysroot, a permanently unstable location for private compiler dependencies. It is not intended for general use. Prefer using a public version of this crate from crates.io via Cargo.toml.
A vector type optimized for cases where this size is usually 0 (cf. SmallVector).
The Option<Box<..>> wrapping allows us to represent a zero sized vector with None,
which uses only a single (null) pointer.