Missing in_band_lifetimes suggestion

[leonardo-m]

//#![feature(in_band_lifetimes)]
fn foo(data: &'a mut [u32]) -> &'a [u32] {
    data
}
fn main() {}

Gives (rustc 1.46.0-nightly 50fc24d 2020-06-25):

error[E0261]: use of undeclared lifetime name `'a`
 --> ...\test.rs:2:15
  |
2 | fn foo(data: &'a mut [u32]) -> &'a [u32] {
  |       -       ^^ undeclared lifetime
  |       |
  |       help: consider introducing lifetime `'a` here: `<'a>`

error[E0261]: use of undeclared lifetime name `'a`
 --> ...\test.rs:2:33
  |
2 | fn foo(data: &'a mut [u32]) -> &'a [u32] {
  |       -                         ^^ undeclared lifetime
  |       |
  |       help: consider introducing lifetime `'a` here: `<'a>`

Like most other features I'd like rustc to suggest using in_band_lifetimes if it's a Nightly compiler.