overflow evaluating the requirement <[Test<'a>] as std::borrow::ToOwned>::Owned

[steveklabnik]

This code does not compile:

use std::borrow::Cow;

enum Test <'a> {
    Int(u8),
    Bytes(Cow<'a, [u8]>),
    Array(Cow<'a, [Test<'a>]>),
}

I would expect it to be the same as this code, which does compile:

use std::borrow::Cow;

enum Test <'a> {
    Int(u8),
    Bytes(Cow<'a, [u8]>),
    Array(VecOrSlice<'a>),
}

enum VecOrSlice<'a> {
    Vec(Vec<Test<'a>>),
    Slice(&'a [Test<'a>]),
}

I am not sure if this is a reasonable expectation or not, though.

[jonas-schievink]

Duplicate of #23714

[Arnavion]

This is more closely related to #38962 and #47032 than #23714 , since #23714 is doing shenanigans with a custom ToOwned impl that breaks for a different reason.