incorrect resolutions for type dependent paths in struct expression

[lcnr]

trait Foo: Sized {
    type Output;

    fn func() -> Self;
}

struct Type<T> { value: T }

impl<T: Default> Foo for Type<T> {
    type Output = Self;

    fn func() -> Self {
        Self::Output { value: Default::default() }
    }
}

stores the following resolution for Self::Output via fn write_resolution:

Ok((AssocTy, DefId(0:4 ~ test1[f74d]::Foo::Output)))

the node_substs for Self::Output are however empty. This makes the stored resolution completely useless as there isn't really a way to go from Foo::Output to Type<T>::Output which is what we actually need.

We should probably store <Foo as Type<T>>::Output instead. This happens here

rust/compiler/rustc_typeck/src/check/fn_ctxt/checks.rs

Lines 1592 to 1605 in 7425fb2

	QPath::TypeRelative(ref qself, ref segment) => {
	let ty = self.to_ty(qself);
	let result = <dyn AstConv<'_>>::associated_path_to_ty(
	self, hir_id, path_span, ty, qself, segment, true,
	);
	let ty = result.map(|(ty, _, _)| ty).unwrap_or_else(|_| self.tcx().ty_error());
	let result = result.map(|(_, kind, def_id)| (kind, def_id));
	// Write back the new resolution.
	self.write_resolution(hir_id, result);
	(result.map_or(Res::Err, |(kind, def_id)| Res::Def(kind, def_id)), ty)
	}

[lcnr]

this is needed to resolve the following fixme

rust/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

Lines 738 to 754 in 7e2733b

	// FIXME(#98711): Ideally we would also deal with type relative
	// paths here, even if that is quite rare.
	//
	// See the `need_type_info/expr-struct-type-relative-gat.rs` test
	// for an example where that would be needed.
	//
	// However, the `type_dependent_def_id` for `Self::Output` in an
	// impl is currently the `DefId` of `Output` in the trait definition
	// which makes this somewhat difficult and prevents us from just
	// using `self.path_inferred_subst_iter` here.
	hir::ExprKind::Struct(&hir::QPath::Resolved(_self_ty, path), _, _) => {
	if let Some(ty) = self.opt_node_type(expr.hir_id) {
	if let ty::Adt(_, substs) = ty.kind() {
	return Box::new(self.resolved_path_inferred_subst_iter(path, substs));
	}
	}
	}