Incorrect inference for default methods on generic traits

[brson]

trait A<T> {
    fn g(x: T) -> T { move x }
}

impl int: A<int> { }

fn main () {
    assert 0i.g(2i) == 2i;
}

/home/brian/dev/rust/src/test/run-pass/trait-default-method-bound-subst2.rs:8:16: 8:18 error: mismatched types: expected `'a` but found `int` (expected type parameter but found int)
/home/brian/dev/rust/src/test/run-pass/trait-default-method-bound-subst2.rs:8     assert 0i.g(2i) == 2i;
                                                                                              ^~
/home/brian/dev/rust/src/test/run-pass/trait-default-method-bound-subst2.rs:8:11: 8:25 error: binary operation == cannot be applied to type `'a`
/home/brian/dev/rust/src/test/run-pass/trait-default-method-bound-subst2.rs:8     assert 0i.g(2i) == 2i;
                                                                                         ^~~~~~~~~~~~~~
/home/brian/dev/rust/src/test/run-pass/trait-default-method-bound-subst2.rs:8:11: 8:25 error: mismatched types: expected `bool` but found `'a` (expected bool but found type parameter)
/home/brian/dev/rust/src/test/run-pass/trait-default-method-bound-subst2.rs:8     assert 0i.g(2i) == 2i;
                                                                                         ^~~~~~~~~~~~~~
error: aborting due to 3 previous errors

[catamorphism]

Reproduced as of eed2ca6

[catamorphism]

I noticed a comment in typeck::check::method::push_candidates_from_provided_methods that's just using an empty substitution all the time when checking default methods. This may be related; I annotated it with this issue number.

[msullivan]

Updated version

#[allow(default_methods)];

trait A<T> {
    fn g(&self, x: T) -> T { x }
}

impl A<int> for int { }

fn main () {
    assert!(0i.g(2i) == 2i);
}

fails with an ICE in trans. Probably is the same bug as #4102.

[msullivan]

push_candidates_from_provided_methods doesn't actually seem to get used... I am confused now.

[msullivan]

Bug was in trans. push_candidates_from_provided_methods is (it appears) dead code. The code path that calls it never gets exercised, it seems?

[msullivan]

Marking that this was part of #2794 for tracking purposes.