evaluator: eval3 produces errors, the old one doesn't

[loisch]

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

$ cue version
cue version v0.12.0

go version go1.23.5
      -buildmode exe
       -compiler gc
       -trimpath true
  DefaultGODEBUG asynctimerchan=1,gotypesalias=0,httpservecontentkeepheaders=1,tls3des=1,tlskyber=0,x509keypairleaf=0,x509negativeserial=1
     CGO_ENABLED 1
          GOARCH arm64
            GOOS darwin
         GOARM64 v8.0
cue.lang.version v0.12.0

Does this issue reproduce with the latest stable release?

Yes, and also with a build of current commit 5d2da07.

What did you do?

The following reproducer shows different results with old and new evaluator:

env CUE_EXPERIMENT=evalv3=0
exec cue vet test.cue
env CUE_EXPERIMENT=evalv3=1
! exec cue vet test.cue

-- test.cue --
#PatientViewSections: {
	[string]: #PatientViewSection
}

#PatientViewSection: #PvSection

#PvSection: {
	Section: {
		display?: string
		entries:  #PatientViewEntries
	}
	_json: [for k, v in Section.entries {(k): v._json}]
}

#PatientViewEntries: [string]: #PatientViewEntry

#PatientViewEntry: {
	#PvSingleForm | #PvLink
}

#PvSingleForm: {
	SingleForm: {
		formId:                 string
		showNumberOfInstances?: bool
	}
	_json: [{
		"iDoc":     "singleFormIDoc"
		"X-FormId": SingleForm.formId
	},
		//if SingleForm.showNumberOfInstances != _|_ {
		//	"X-ShowNumberOfInstances": "\(SingleForm.showNumberOfInstances)"
		//}
	]
}

#PvLink: {
	Link: {
		icon?:    string
		sections: #PatientViewSections
	}
	_json: [for k, v in Link.sections {(k): v._json}]
}

#TabcatsJson: {
	config: {
		tabcats: #PatientViewSections
		...
	}
	json: {
		//tabcats: #OrgContents
		tabcats: [for k, v in config.tabcats {(k): v._json}]
	}
}

tabcatsExample: #TabcatsJson
tabcatsExample: {
	_e1: #PatientViewEntry
	_e1: {
		Link: {
			sections: "Formulare": {
				Section: entries: "Fotodokumentation": _e2
			}
		}
	}
	_e2: #PatientViewEntry
	_e2: {
		SingleForm: {
			formId: "fotodokumentation"
		}
	}
	_s: #PvSection
	_s: Section: entries: "Dokumentation": _e1
	config: {
		tabcats: "02": _s
	}
}

What did you expect to see?

A failing test. If the old evaluator is wrong and the new evaluator is right rejecting the file, I'd furthermore expect a better error message, because I don't understand what's wrong. I think the reason might be that #PvSection is used twice in the example and that these two instances are somehow unified. But that's just guessing.

What did you see instead?

A passing test.

[loisch]

Works with current master at 04fa872

[myitcv]

Thanks for testing, @loisch. I'm adding a regression test here to lock in the behaviour: https://review.gerrithub.io/c/cue-lang/cue/+/1211873