This change makes it possible to make changes to the module.cue schema while still using a closed schema for earlier versions. We refuse module.cue files that declare a version newer than the current CUE version. The language.version field is now mandatory in modules mode because otherwise we cannot tell which schema we should be using. Also remove the unimplemented features from the schema for now: they're always there in the history and the proposal when we come to implement them, but they complicate the schema for no good reason. One unfortunate thing is that the error message when a field is defined that's explicitly unimplemented is not good. In the absence of an `error` CUE builtin, we should be able to fix that in a subsequent CL by inspecting the error to see whether any of the lines include the `unimplemented` identifier. Signed-off-by: Roger Peppe <rogpeppe@gmail.com> Change-Id: I7bfef3b37e5b66bdbd8fe0614c1b815c7d9f1285 Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1193275 TryBot-Result: CUEcueckoo <cueckoo@cuelang.org> Reviewed-by: Daniel Martí <mvdan@mvdan.cc> Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>