cmd/cue: incomplete value from default

[myitcv]

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

$ cue version
cue version +409dacf linux/amd64

Does this issue reproduce with the latest release?

Yes

What did you do?

package x

#Guide: {
	x: Steps.scenario_a.step1
	y: *Steps.scenario_a.step1 | #Step

	Steps: scenario_a: step1: *Steps.step1 | #Step

	Steps: step1: #Step
}

#Step: {
	Age: int
}

g: #Guide & {
	Steps: step1: #Step & {
		Age: 5
	}
	Steps: scenario_a: step1: #Step & {
		Age: 4
	}
}

Then:

$ cue eval --out json

What did you expect to see?

{
    "g": {
        "x": {
            "Age": 4
        },
        "y": {
            "Age": 4
        },
        "Steps": {
            "scenario_a": {
                "step1": {
                    "Age": 4
                }
            },
            "step1": {
                "Age": 5
            }
        }
    }
}

What did you see instead?

g.y: incomplete value {Age:4} | {Age:int}

Removing the Steps field (i.e. shifting everything "up" one level) does not cause the problem to manifest.

Marking as a "new evaluator" issue for now.

[mpvl]

This is correct behavior:

1. a reference does not itself resolve a disjunction (a reference may be a reference to a type, after all)
2. also from the M2 and D1 disjunction rules in the spec, you can see that both remaining values are tagged as default, so the remaining value is indeed ambiguous.

This is ultimately the result that there can be only one level of default. There may be useful to have a builtin that can at least pick a default during evaluation. Or maybe defaults should actually resolve upon reference. The idea of not doing so was that one can refer to a type that has a default as well. But maybe this is more confusing than not in practice and it seems bad practice anyway.

[myitcv]

Or maybe defaults should actually resolve upon reference.

Would this then mean that there can be multiple levels of defaults?

[mpvl]

Would this then mean that there can be multiple levels of defaults?

No that would still not mean that. It would even mean there is less possibility to propagate defaults than there is now.

[cueckoo]

This issue has been migrated to cue-lang/cue#577.

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