error[E0308]: mismatched types
  --> $DIR/fn-ptr.rs:11:21
   |
LL | #[target_feature(enable = "sse2")]
   | ---------------------------------- `#[target_feature]` added here
...
LL |     let foo: fn() = foo;
   |              ----   ^^^
   |              |      |
   |              |      cannot coerce functions with `#[target_feature]` to safe function pointers
   |              |      help: consider casting to a fn pointer: `foo as fn()`
   |              expected due to this
   |
   = note: expected fn pointer `fn()`
                 found fn item `fn() {foo}`
   = note: fn items are distinct from fn pointers
   = note: functions with `#[target_feature]` can only be coerced to `unsafe` function pointers

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.