Silent failure / partial output when json encoding a unresolved disjunction

[addreas]

My guess is that this has the same root cause as #1256.

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

$ cue version
cue version (devel) linux/amd64 

The master branch at commit 0f53054

Does this issue reproduce with the latest release?

Yes

What did you do?

exec cue eval

-- test.cue --
package test

import "encoding/json"

test: json.Marshal({test: (*1 | int) & (int | *2)})

What did you expect to see?

An error similar to the "encoding/yaml" equivalent:

error in call to encoding/yaml.Marshal: yaml: unsupported node 1|int|2 (*ast.BinaryExpr):
    ./test.cue:5:7

What did you see instead?

A single new line:

Partial output

Letting cue export do the json conversion silently fails differently:

exec cue export

-- test.cue --
package test

test: test: (*1 | int) & (int | *2)

Gets the partial output:

test: