evalv3: regression in API with disjunction containing closed struct

[rogpeppe]

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

v0.11.0-alpha.5

Does this issue reproduce with the latest stable release?

Yes (v0.10.0)

What did you do?

exec go mod tidy
! exec go run .

env CUE_EXPERIMENT=evalv3
! exec go run .

-- go.mod --
module test
require cuelang.org/go v0.11.0-alpha.5
-- main.go --
package main

import (
	"log"

	"cuelang.org/go/cue/cuecontext"
)

func main() {
	ctx := cuecontext.New()
        // Make sure script works with earlier CUE versions prior to https://review.gerrithub.io/c/cue-lang/cue/+/1202685
	if os.Getenv("CUE_EXPERIMENT") == "evalv3" {
		ctx = cuecontext.New(cuecontext.EvaluatorVersion(cuecontext.EvalV3))
	}
	a := ctx.CompileString(`null | close({a?: _})`)
	b := ctx.CompileString(`quux: "boom"`)
	err := a.Unify(b).Validate()
	if err != nil {
		log.Fatal(err)
	}
}

What did you expect to see?

Passing test. Both evalv2 and evalv3 should both fail to validate this example.

What did you see instead?

> exec go mod tidy
> ! exec go run .
[stderr]
main.go:15: 2 errors in empty disjunction: (and 2 more errors)
exit status 1
[exit status 1]
> env CUE_EXPERIMENT=evalv3
> ! exec go run .
FAIL: /tmp/x.txtar:5: unexpected command success

[rogpeppe]

Here's another failure, quite possibly related. Again I couldn't get this to fail in a single CUE file example:

exec go mod tidy
exec go run .

env CUE_EXPERIMENT=evalv3
exec go run .

-- go.mod --
module test
require cuelang.org/go v0.11.0-alpha.5

-- main.go --
package main

import (
	"log"
	"os"

	"cuelang.org/go/cue/cuecontext"
)

func main() {
	ctx := cuecontext.New()
	if os.Getenv("CUE_EXPERIMENT") == "evalv3" {
		ctx = cuecontext.New(cuecontext.EvaluatorVersion(cuecontext.EvalV3))
	}
	a := ctx.CompileString(`close({{[=~"a"]: _}})`)
	b := ctx.CompileString(`"a": 1`)
	err := a.Unify(b).Validate()
	if err != nil {
		log.Fatal(err)
	}
}

The failure I see is:

> exec go mod tidy
> exec go run .
> env CUE_EXPERIMENT=evalv3
> exec go run .
[stderr]
main.go:19: field not allowed: a
exit status 1
[exit status 1]
FAIL: /tmp/x.txtar:5: unexpected command failure

Note: if I remove the redundant braces inside the close call, I don't see the failure.