Use after free in safe code. Trait bound with +'static is ignored when implementing some trait

[vacavaca]

This code compiles on stable and it supposed to be safe:

use std::fmt::Display;

trait Printer {
    fn print<P: Display>(&self, printable: P);
}

struct TestObj;

impl Printer for TestObj {
    fn print<P: Display + 'static>(&self, printable: P) {}
}

fn main() {}

Rust Playground: https://play.rust-lang.org/?gist=4831916a69026aa1eb6ebca8719fddcd&version=stable&backtrace=2

But I expected to see an error like "P: 'static appears on the impl method but not on the corresponding trait method".
Furthermore only bounds defined on the function in Trait definition are checked when I use methods on the TestObj struct
so I can pass a non 'static reference to the struct method print and it assumed to be 'static.

With that I can write something like this:

use std::fmt::Display;

trait Printer {
    fn set_string<S: Display>(&mut self, S);

    fn print(&self);
}

#[derive(Default)]
struct ConcretePrinter {
    string: Option<Box<Display>>,
}

impl Printer for ConcretePrinter {
    fn set_string<S: Display + 'static>(&mut self, string: S) {
        self.string = Some(Box::new(string));  // save string for the later use
    }

    fn print(&self) {
        self.string
            .as_ref()
            .map(|some_string| println!("{}", some_string));
    }
}

fn main() {
    let mut a = ConcretePrinter::default();

    {
        let heap_string = "hello".to_string();
        let reference = &heap_string;   // displayable but not static

        a.set_string(reference);        // only Printer bounds checked here
    }                                   // 'hello' string dropped

    a.print();                          // use after free
}

rustc 1.9.0 (e4e8b66 2016-05-18)
binary: rustc
commit-hash: e4e8b66
commit-date: 2016-05-18
host: x86_64-unknown-linux-gnu
release: 1.9.0

Rust Playground: https://play.rust-lang.org/?gist=e95ac4f83f16b062ee8b7c53ed52d5e2&version=stable&backtrace=0

[petrochenkov]

Duplicate of #18937