... maybe vet should only warn if the array size exceeds some number of bytes?

Just out of curiosity, how can vet statically determine the size of an array? Never mind. Just saw that the arrays in question have fixed length.

It is correct to do so, and can even be the right thing to do in many cases. It's therefore not something that vet can complain about. (See the src/cmd/vet/README for details.)

Perhaps golint is a better choice. Feel free to suggest that.

It's not obvious to me that this is a style issue. Even if it were, for k, v := range array (the "wrong" one) certainly looks nicer and less surprising than for k, v := range array[:] (the "right" one).

However, I can see why this doesn't quite fit vet either, since use of it still produces a correct program. I'm starting to see a significant number of issues that don't quite fit vet (focus on correctness), and doesn't fit lint (focus on style)... there seems to be a number of checks proposed that catch problems that aren't strictly wrong, but heavily suspicious, this being an example of one. Maybe these checks should go into a third-party tool like go-staticcheck?

I don't think it's a fit for any of my tools, either, for essentially the same reason as for why it shouldn't go into vet.