Variable capture in closures is too restrictive

[dovreshef]

This program

fn main() {
    let mut x: int;
    let closure = || { x = 42; };
    closure();
}

Output error: capture of possibly uninitialized variable: 'x', even though as an lvalue there is no danger of uninitialized usage. Could the compiler be made smarter about this? Maybe add a rule that if the variable first appearance in the closure is as an lvalue it's ok.

[alexcrichton]

cc #2202 and @nikomatsakis

[huonw]

Triage; no change; I imagine this could be a bit harder with unboxed closures (since closures then have a more transparent representation, with less magic).

[nikomatsakis]

I think this will never be fixed. In general, we model closures in the compiler and in the language as a kind of advanced sugar for things you could type yourself, and the fact is that the captured variable is being bundled up into the environment when it is not initialized. Nominating for closure.

[nikomatsakis]

Decided to just close.