error[E0015]: cannot call non-const fn `<() as Foo>::foo` in constant functions
  --> $DIR/non-const-op-const-closure-non-const-outer.rs:13:22
   |
LL |     (const || { (()).foo() })();
   |                      ^^^^^
   |
   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
help: add `#![feature(effects)]` to the crate attributes to enable
   |
LL + #![feature(effects)]
   |

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0015`.