Parse multiple consts from a single keyword

[bstrie]

This feels like it should work:

const bar: int = 1,  // This should mirror the `let` syntax
      foo: int = 4;

fn main() {
    let baz: int = 0,
        qux: int = 1;
}

But instead you get:

const.rs:1:18: 1:19 error: expected `;` but found `,`
const.rs:1 const bar: int = 1,
                             ^

[sanxiyn]

Nominating for backwards compatible milestone.

[pcwalton]

We're considering removing the multiple-let assignment syntax.

[graydon]

team has some dissent about the desirability of the form altogether, accepting for backwards compatibility since one possible outcome involves removing the let x = 0, y = 1; form entirely.

[nikomatsakis]

One point: I am unhappy with how mut extends to all variables in a single let. Removing multiple variables would address this question as well.

[catamorphism]

I agree with @nikomatsakis 's point about mut. I don't care one way or the other in general, but I think the mut extending-to-all-variables thing is an accident waiting to happen. Removing multiple variables is the simplest solution to that.

[graydon]

accepted for backwards-compatible milestone

[pcwalton]

Multiple lets are gone so I assume we don't want to do this for static either.