I see, it's clause 6 in the OSI definition:

  6. No discrimination against fields of endeavor: The license must not restrict anyone from making use of the program in a specific field of endeavor. For example, it may not restrict the program from being used in a business, or from being used for genetic research.

So it's one or the other. Basically, Copilot makes all open source software (according to the OSI definition) necessarily use-without-attribution. Your code is my code. Your work is instantly my work, and no credit will be given.

I think this is a special case, illustrating that these new language models require us to reformulate our conception of what "open source" and "fair use" entails.

The laws and definitions need to adapt to a changing world.