Trait objects can be created with lifetime bounds that ignore input lifetimes

[lifthrasiir]

fn foo() -> Box<Reader + 'static> {
    let v = [1, 2, 3];
    box std::io::BufReader::new(v)
}

fn main() {
    let mut foo = foo();
    println!("{}", foo.read_to_end());
}

This should not compile, since v is &'a [u8] for some non-'static 'a and thus BufReader<'a> will contain &'a [u8] as well. It compiles fine however and results in the varying output depending on the optimization level (which shows that this is an UB out of the "safe" code).

Tested with rustc 0.13.0-nightly (1c3ddd297 2014-10-13 23:27:46 +0000) and playpen.

[zwarich]

A more self-contained example that shouldn't type-check:

fn f(v: &[u8]) -> Box<Clone + 'static> {
    box v
}

fn main() { }

[bkoropoff]

It seems that this has been possible since generalized lifetime bounds went in.

[nikomatsakis]

Huh. This was supposed to be fixed. I'll take a look.

[pnkfelix]

P-backcompat-lang, 1.0

[nikomatsakis]

OK, simple oversight. PR coming soon. Amazing we have no test for this. It occurs only with coercions. (In general, this code path could be cleaned up, and will be as part of implementing generalized where clauses, making these kinds of oversights harder to do.)