Make `#[derive(Copy)]` enough for both `Clone` and `Copy`

chrefr:

Your proposal won't be able to support this case anyway

You are right.

chrefr:

That does not matter, since the only edition still need to be supported, and the code for it must still be inside the compiler.

I didn't get it. What do you mean by "the only edition"? I think without that attribute, the only change needed in the compiler is that the Copy derive macro should resolve to edition2027::Copy builtin macro, which is almost nothing relative to other edition changes in terms of complexity. If we remove the Clone near Copy detection in the current compiler you mentioned, I guess the implementation actually become simpler.