Member function call breaks type inference

[stepancheg]

Code:

#[derive(Default)]
struct Foo;

impl Foo {
    fn set_quux(&mut self, v: u32) {
    }
}

fn main() {
    let mut v: Vec<Foo> = Vec::new();

    // this works perfectly: type of msg1 is inferred
    let mut msg1 = Default::default();
    v.push(msg1);

    // type of msg2 is explicitly specified
    let mut msg2: Foo = Default::default();
    msg2.set_quux(17);
    v.push(msg2);

    // type of msg3 could be inferred from parameter type of v.push(...)
    // although compiler reports:
    // error: the type of this value must be known in this context
    let mut msg3 = Default::default();
    msg3.set_quux(19); // <-- on this line
    v.push(msg3);
}

[pythonesque]

I think this might be the same as (or at least related to) #25165, which is also an instance of type inference breaking when you use a member function.

[steveklabnik]

Triage: no change

[Mark-Simulacrum]

Yeah, I'm going to close in favor of #25165 because it represents the underlying problem here.