$ cat a.rs  pub static A: fn() -> fn() = {  #[inline(never)]  fn f() {}  #[inline(always)]  || -> fn() { f } }; $ cat b.rs static A: fn() -> fn () = a::A; fn main() { A()() } $ rustc a.rs --crate-type=lib $ rustc b.rs --extern a -L. error: missing optimized MIR for an item in the crate `a`  | note: missing optimized MIR for this item (was the crate `a` compiled with `--emit=metadata`?)  --> /.../a.rs:3:5  | 3 | fn f() {}  | ^^^^^^ error: aborting due to 1 previous error