librustc: Check structure constructors against their types.

[pcwalton]

This breaks code like:

struct Point<T> {
    x: T,
    y: T,
}

let pt = Point::<bool> {
    x: 1,
    y: 2,
};

Change this code to not contain a type error. For example:

let pt = Point::<int> {
    x: 1,
    y: 2,
};

Closes #15875.

[breaking-change]

r? @huonw

[lilyball]

First sentence here, I assume you mean "and the corresponding type has no type parameters".

[pcwalton]

@kballard Fixed.

[lilyball]

Do we use the full word "structure" in other errors, instead of "struct"? Similarly, do we have precedent for the phrase "structure constructor"? My inclination is to call it a "struct literal".

[pcwalton]

Yes, we use "structure" in other errors.

[pcwalton]

I realized this doesn't handle some edge cases. Going to rework a bit.

[lilyball]

Just yesterday I was wondering if Point::<int> { ... } actually worked. So I'm happy to see you fixing this :) But I'll let someone else review for correctness, I don't know this section of the code.

[huonw]

I assume this closes #9620 too.

[pcwalton]

re-r? @huonw

[huonw]

Travis says this line has trailing whitespace.

[pcwalton]

@huonw Fixed.