In reviewing Peter's patch to auto-generate the backend/nodes support files, I compared what the patch's script produces to what is in the code now. I found several discrepancies in the recently-added parse node types for JSON functions, and as far as I can see every one of those discrepancies is an error in the existing code. Some of them are relatively harmless (e.g. COPY_LOCATION_FIELD isn't really different from COPY_SCALAR_FIELD), but some of them definitely are live bugs. I propose the attached patch.
