Glad to see an explanation for why they bypassed cargo. I had wondered about that when the PR was posted as it didn't contain any documentation for why they were going off the beaten path. However, I'm a bit confused at the reasoning. Because a solution felt sub-optimal (vendoring an optional dependency), they went the route of invoking rustc directly? That seems a bit scorched earth especially when they later talk about needing another dependency offline and instead of vendoring both they instead worked around that in a different way.