Unnecessarily order dependent type inference

[crlf0710]

fn main1() {
    let vec1 = [1,2,3,4,5].into_iter().collect();
    let _vec2 : &Vec<usize> = &vec1;
    // this compiles
    println!("{}", vec1[0]);
}

fn main2() {
    let vec1 = [1,2,3,4,5].into_iter().collect();
    // this doesn't compile
    println!("{}", vec1[0]);
    let _vec2 : &Vec<usize> = &vec1;
}

I wonder if it is possible to make the two code snippets act the same?

[crlf0710]

Interestingly, this compiles fine:

fn main3() {
    let vec1 = [1,2,3,4,5].into_iter().collect();
    let x = <_ as core::ops::Index<usize>>::index(&vec1, 0);
    let _vec2 : &Vec<usize> = &vec1;
}

What's the lowering difference here?

[ireina7]

And this compiles fine too:

fn main() {
    let vec1 = [1, 2, 3].into_iter().collect();
    let x = Index::index(&vec1, 0);
    let _vec2: &Vec<usize> = &vec1;
}