Investigate why Autoref doesn't work with Minicore/Tests

[davidbarsky]

• impl ForeignTrait for LocalStruct and impl ForeignTrait for &LocalStruct provide completions on let t = &TestStruct in both tests and a running binary.
• impl ForeignTrait for &LocalStruct only provides completions for provide completions on let t = TestStruct in a running binary.
  • This makes me think that there's a bug in minicore—or that I might not be understanding some important details—because this behavioral split reproduces with and without my filtering changes.

Originally posted by @davidbarsky in #16555 (comment)

[HKalbasi]

Doesn't adding more minicore flags help? Maybe minicore: deref is not enough? Supporting minicore: * could help in these situations.

[Veykril]

Hmm, actually that test can't work can it? Autoref only applies at most once, but for the call to be valid in that example we need to have a double reference, once for the receiver and once for the impl self type. So if we start from a TestStruct receiver we will only walk up to &TestStruct which is still not a valid callee for the impl

impl foo::TestTrait for &TestStruct {
    fn some_method(&self) {}
}

as that needs a receiver of &&TestStruct

[davidbarsky]

Oh, I think you're right: I think the lack of syntax highlighting in the fixture blinded me to the fact that even without my changes in #16555, the following does not get completions for some_method.

struct TestStruct;

impl crate_b::TestTrait for &TestStruct {
    fn some_method(&self) {}
}

#[test]
fn test() {
    let t = TestStruct;
    t.$0
}

There's no bug in minicore.