eval: error messages mention definition with evalv3

[myitcv]

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

$ cue version
cue version v0.13.0-alpha.3

go version go1.24.0
      -buildmode exe
       -compiler gc
  DefaultGODEBUG gotestjsonbuildtext=1,multipathtcp=0,randseednop=0,rsa1024min=0,tlsmlkem=0,x509rsacrt=0,x509usepolicies=0
     CGO_ENABLED 1
          GOARCH arm64
            GOOS linux
         GOARM64 v8.0
             vcs git
    vcs.revision c565c1d31f2920ec79219ab04699e68fd32af93b
        vcs.time 2025-03-31T13:58:15Z
    vcs.modified false
cue.lang.version v0.13.0

Does this issue reproduce with the latest release?

Yes

What did you do?

# -- evalv2 --
env CUE_EXPERIMENT=evalv3=0
! exec cue export x.cue --out yaml
stderr 'config.serviceB.metadata.name: incomplete value string'

# -- evalv3 - CUE_DEBUG=sharing=0 --
env CUE_EXPERIMENT=evalv3=1
env CUE_DEBUG=sharing=0
! exec cue export x.cue --out yaml
stderr 'config.serviceB.metadata.name: incomplete value string'

# -- evalv3 - CUE_DEBUG=sharing=1 --
env CUE_EXPERIMENT=evalv3=1
env CUE_DEBUG=sharing=1
! exec cue export x.cue --out yaml
stderr 'config.serviceB.metadata.name: incomplete value string'

-- x.cue --
#Metadata: {
	name:      string
	namespace: string
}

#BaseConfig: {
	metadata: #Metadata
}

#Config: {
	metadata: #Metadata

	serviceA: #BaseConfig & {
		metadata: metadata
	}

	serviceB: #BaseConfig & {
		metadata: metadata
	}
}

config: #Config & {
	metadata: {
		name:      "test"
		namespace: "dev"
	}
}

What did you expect to see?

Passing test.

What did you see instead?

# -- evalv2 -- (0.010s)
# -- evalv3 - CUE_DEBUG=sharing=0 -- (0.037s)
# -- evalv3 - CUE_DEBUG=sharing=1 -- (0.030s)
> env CUE_EXPERIMENT=evalv3=1
> env CUE_DEBUG=sharing=1
> ! exec cue export x.cue --out yaml
[stderr]
#Metadata.name: incomplete value string:
    ./x.cue:2:13
#Metadata.namespace: incomplete value string:
    ./x.cue:3:13
[exit status 1]
> stderr 'config.serviceB.metadata.name: incomplete value string'
FAIL: repro.txtar:16: no match for `config.serviceB.metadata.name: incomplete value string` found in stderr
failed run

[mpvl]

This is probably a structure sharing issue. We are aware of this bug. You can verify this by turning sharing off.

[myitcv]

Updated withCUE_DEBUG=sharing to show that this appears to be a structure sharing issue.

[myitcv]

Now that this issue has fixed, my eyes have finally seen that the original CUE is really not as the author intended. It has a bug in it. So whilst the presence of the bug in the original repro served us well in terms of highlighting the structure sharing issue, I would like to note for completeness that the author's intent in the original CUE was almost certainly:

# -- evalv2 --
env CUE_EXPERIMENT=evalv3=0
exec cue export x.cue --out yaml
cmp stdout stdout.golden

# -- evalv3 - CUE_DEBUG=sharing=0 --
env CUE_EXPERIMENT=evalv3=1
env CUE_DEBUG=sharing=0
exec cue export x.cue --out yaml
cmp stdout stdout.golden

# -- evalv3 - CUE_DEBUG=sharing=1 --
env CUE_EXPERIMENT=evalv3=1
env CUE_DEBUG=sharing=1
exec cue export x.cue --out yaml
cmp stdout stdout.golden

-- x.cue --
#Metadata: {
	name:      string
	namespace: string
}

#BaseConfig: {
	metadata: #Metadata
}

#Config: {
	metadata: #Metadata

	serviceA: #BaseConfig & {
		"metadata": metadata
	}

	serviceB: #BaseConfig & {
		"metadata": metadata
	}
}

config: #Config & {
	metadata: {
		name:      "test"
		namespace: "dev"
	}
}
-- stdout.golden --
config:
  metadata:
    name: test
    namespace: dev
  serviceA:
    metadata:
      name: test
      namespace: dev
  serviceB:
    metadata:
      name: test
      namespace: dev

Which is confirmed as passing as of 7cfe774