Clean generics in `fixture::default()`

[la10736]

Clean generics in `fixture::default()`

[la10736]

Maybe the problem in the general case is really hard to resolve. Take follow example:

use rstest::*;

#[fixture]
pub fn i() -> u32 {
    42
}

#[fixture]
pub fn fx<I>(i: I) -> impl Iterator<Item=I> {
    std::iter::once(i)
}

#[test]
fn resolve() {
    assert_eq!(42, fx::default().next().unwrap())
}

In this case default() should have an explicit return type impl Iterator<Item=u32>. We should try to understand

1. what i() return type is
2. what i fixture is in this context take care of renaming too (module resolution job become after procedural macro resolution)

So: try to investigate a default_fixture!() macro implementation or something else.

[la10736]

As workaround to solve all general case we introduce follow syntax in fixture macro:

#[fixture(default<impl Iterator<Item=u32>>)]

[la10736]

Done