Missed cycle detection

[verdverm]

What version of CUE are you using (cue version)?

beta.5

Does this issue reproduce with the latest release?

have tried other versions

What did you do?

exec cue eval cycle.cue
-- cycle.cue --
#A: {
        env: [string]: string
        env: FOO: "bar"

        #foo: {
                env: env
                env: OPTION: "true"
        }
}

What did you expect to see?

Error about cyclical value for env: env

What did you see instead?

#A: {
    env: {
        FOO: "bar"
    }
    #foo: {
        env: {
            OPTION: "true"
        }
    }
}

There is also this curious output:

#A: {
        #foo: {
                env: env
        }
}

cue eval results in

#A: {
    #foo: {
        env: _
    }
}

[mpvl]

It is technically correct cue: env: env logically means env == env, so it's a tautology, but valid. The evaluation indeed is env: _. This is all correct.
The eval correct you show is incorrect (the env field itself is missing), but I'm getting the correct output on my machine.

That said, in reality this is almost never intended, and it should at least be a vet check.
This is a duplicate of #466, btw.

[cueckoo]

This issue has been migrated to cue-lang/cue#787.

For more details about CUE's migration to a new home, please see cue-lang/cue#1078.