Spitting out lines or paragraphs from a repo is most likely fair use.
Unless you can reproduce a substantial portion of a repo, I think it’s going to be an uphill battle to argue it isn’t fair use. Though I suspect Copilot’s suppression feature will make doing so impossible.
Assuming the reports of it producing the fast inverse square root function, comments included, from the Quake 3 engine were true; spitting out the whole function, comments included, doesn't look OK to me.
Either way, the whole copilot thing smells of 'the issue of copyright infringement is more copyright infringement' to me.
Unless you can reproduce a substantial portion of a repo, I think it’s going to be an uphill battle to argue it isn’t fair use. Though I suspect Copilot’s suppression feature will make doing so impossible.