Functional struct update allows copy of noncopyable values

[bblum]

This program segfaults when trying to run the destructor for "a". "b"'s destructor runs first and prints 2, then "a"'s destructor tries to access a zeroed-out ARC.

use extra::arc::*;
struct A { y: ARC<int>, x: ARC<int> }
impl Drop for A {
    fn finalize(&self) { println(fmt!("x=%?", self.x.get())); }
}
fn main() {
    let a = A { y: ARC(1), x: ARC(2) }; 
    let _b = A { y: ARC(3), ..a };
}

[bblum]

where did the A-kindchk and A-linearity tags go?

nominating well-covered

[bblum]

It should really just desugar into

{ let mut old_thing = ...;
  old_thing.updated_field1 = expr1;
  ...;
  old_thing.updated_fieldN = exprN;
  old_thing }

[huonw]

Triage: appears to be fixed, test landing in #8932.