error[E0308]: mismatched types
  --> $DIR/fn-ptr.rs:9:21
   |
LL | #[target_feature(enable = "sse2")]
   | ---------------------------------- `#[target_feature]` added here
...
LL |     let foo: fn() = foo;
   |              ----   ^^^ cannot coerce functions with `#[target_feature]` to safe function pointers
   |              |
   |              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
   = note: when the arguments and return types match, functions can be coerced to function pointers
help: consider casting to a fn pointer
   |
LL |     let foo: fn() = foo as fn();
   |                     ~~~~~~~~~~~

error: aborting due to previous error

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