Cloning &strs doesn't trigger borrow checker

[Manishearth]

MWE:

fn get() -> Option<String> {
 Some("hi".to_string())
}

fn main() {
 let y = match get() {
  Some(x) => x.as_slice().clone(),
  None => "hello"
 };
 let mut z = "something".to_string();
 for i in range(1,1000u) {
   z = format!("{}", i);
   println!("{}", z)
 }
 println!("{}", y)
}

The last thing it prints out should be "hi". Instead it prints out "99" -- it it looks like the String x is deallocated in the match, but the pointer to the freed memory lives on.

[Manishearth]

Changing "hi" to a longer string leads to varying results (I guess it's allocating different-sized Strings in different areas, which sounds logical)

[pcwalton]

cc @nikomatsakis

[Manishearth]

More minimal MWE:

fn main() {
 let y = {
  // "hello world" allocated
  "hello world".to_string().as_slice().clone()
  // "hello world" deallocated
 };
 // new string allocated in same spot
 let z = "something".to_string();
 println!("{}", y)
 // prints "somethingld"
}

I suspect results may vary depending on your system, but fiddling with the string length works.

[sfackler]

Looks like a dup of #19261

[Manishearth]

Seems correct.