Question about Value.IsConcrete()?

[verdverm]

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

0.3.0

What did you do?

Called cue.Value.IsConcrete() via the Go API and got unexpected results. If this does indeed seem like a bug, then I can create a reproducer.

In the example below, calling IsConcrete() for ex.bar. reports true, is this expected?

#A: {
  a1: string
  a2: string | *""
}

#B: {
  foo: string
  bar: #A
}

ex: #B & {
  foo: "foo"
}

What did you expect to see?

ex.bar.IsConcrete() returning false

What did you see instead?

ex.bar.IsConcrete() returning true

[myitcv]

AFAIU, this is working "as expected" but is effectively the same problem of a list type defaulting to [], picked up in the required fields proposal. i.e. the default value of #A here is {}. What I think you are looking to distinguish is whether ex.bar is specified or not, and that is where the ! proposal comes in.

[mpvl]

It is working as expected because, as documented, a struct is always considered concrete.

As per the doc:

It does not verify that values of lists or structs are concrete themselves.