Static lifetimes checking regression in rustc 1.41.0

[ilyavennik]

I tried this code:

static FOO: u8 = 42;
static mut BAR: &'static u8 = &FOO;

fn main() {
    unsafe {
        println!("{}", BAR);
        foo();
        println!("{}", BAR);
    }
}

fn foo() {
    let n = 42;
    unsafe {
        BAR = &n;
    }
}

I expected to see this:

error[E0597]: `n` does not live long enough
  --> src/main.rs:15:15
   |
15 |         BAR = &n;
   |         ------^^
   |         |     |
   |         |     borrowed value does not live long enough
   |         assignment requires that `n` is borrowed for `'static`
16 |     }
17 | }
   | - `n` dropped here while still borrowed

error: aborting due to previous error

For more information about this error, try `rustc --explain E0597`.

Instead, happens undefined behavior. Program successfully compiles in the Rust stable 1.41.0 but fails to compile in stable 1.40.0 (thats what I want).

[ecstatic-morse]

Regressed in a449535, likely #66587 cc @matthewjasper.

[nikomatsakis]

Visited in the compiler team triage meeting. It would be good to look into closing this ASAP. @matthewjasper do you think you'll have time to investigate? If not, I'd want to find someone else.

[nikomatsakis]

We've assigned this speculatively to @matthewjasper -- if you think you won't be able to investigate promptly, though, feel free to unassign and ping t-compiler for reassignment, @matthewjasper.

[eddyb]

I expected the behavior to match that of this example (which still errors):

fn foo(p: *mut &'static u8) {
    let n = 42;
    unsafe {
        *p = &n;
    }
}

I wonder if the 'static gets erased somehow. Maybe an "user type annotation" is required on the *mut T from a static mut FOO: T, to give it a lifetime'd type?