Resolve types properly in const eval

[oli-obk]

r? @eddyb

cc @arielb1

[eddyb]

Can you add a test, with an associated const forwarding to another, generically?
That sort of thing wouldn't work without this change.

[oli-obk]

Can you add a test, with an associated const forwarding to another, generically?
That sort of thing wouldn't work without this change.

I tried. But it was a silent error before, and it works now, so there's no difference. Using the assoc constant won't work generically out of other reasons: https://play.rust-lang.org/?gist=54e162b150e745236878f2f0eca06de3&version=stable

[eddyb]

@oli-obk There's no forwarding going on there between two impls' associated consts - and you can't have array lengths that depend on type parameters yet.

Closer to what I meant: https://play.rust-lang.org/?gist=e0ec487c9566ea8f8187eb14d82e62ac&version=nightly

[arielb1]

Isn't this normalization also needed in the Def::Method(id) | Def::Fn(id) arm, and also for types fetched from expr_ty?

[oli-obk]

technically we only need it for Def::AssociatedConst, but it's a nop for Def::Const

[arielb1]

Another test for broken subst logic (this shouldn't ICE):

#![allow(unused)]

trait Foo {
    const BAR: Self;
}

impl Foo for i32 {
    const BAR: Self = 4;
}
impl Foo for i64 {
    const BAR: Self = 3;
}

struct Bar<T: ?Sized>(usize, std::marker::PhantomData<T>);

impl<T: ?Sized> Foo for Bar<T> {
    const BAR: Self = Bar(4, std::marker::PhantomData);
}

impl<T: ?Sized> Bar<T> {
    fn foo() {
        let x = Self::BAR.0;
        let x: &'static usize = &Self::BAR.0;
        let x: [i32; Self::BAR.0] = [1, 2];
    }
}

fn main() {
    let x: [i32; i32::BAR as usize] = [1, 2, 3, 4];
    let x: [i32; i64::BAR as usize] = [1, 2, 3];
}

r+ with proper tests

[oli-obk]

@arielb1 That subst doesn't come from const eval, it comes from https://github.com/rust-lang/rust/blob/master/src/librustc/traits/project.rs#L357

[eddyb]

You should remove this.

[eddyb]

Wait, this too, I think? Since the example doesn't use size_of anymore.

[oli-obk]

done

[oli-obk]

travis likes it + comments addressed

[eddyb]

@bors r+

[bors]

📌 Commit 1ee0ff3 has been approved by eddyb

[bors]

⌛ Testing commit 1ee0ff3 with merge e0febe7...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: eddyb
Pushing e0febe7 to master...