evaluator: cue.SelectorOp found where none expected; cue.Dereference required

[myitcv]

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

$ cue version
cue version v0.0.0-20231124103318-47d6dcedde5c

go version go1.21.3
      -buildmode exe
       -compiler gc
  DefaultGODEBUG panicnil=1
     CGO_ENABLED 1
          GOARCH arm64
            GOOS linux
             vcs git
    vcs.revision 47d6dcedde5c8c8623758044eb247c172ba4e4bf
        vcs.time 2023-11-24T10:33:18Z
    vcs.modified false

Does this issue reproduce with the latest release?

Yes

What did you do?

go mod tidy
go run .
cmp stdout stdout.golden

-- go.mod --
module example

go 1.21.3

require cuelang.org/go v0.6.0

-- main.go --
package main

import (
	"fmt"
	"log"

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

func main() {

	ctx := cuecontext.New()

	cueString := `
	#def:{ foobar:[ ... #FOO | #BAR] }
	#FOO: "foo" | "FOO"
	#BAR: "bar" | "BAR"
	`
	v := ctx.CompileString(cueString)

	// The use of cue.AnyIndex "selects" the constraint
	field := v.LookupPath(cue.MakePath(cue.Def("def"), cue.Str("foobar"), cue.AnyIndex))

	var disjunctionElements []cue.Value
	var work cue.Value
	todo := []cue.Value{field}
	for len(todo) > 0 {
		work, todo = todo[0], todo[1:]
		op, values := work.Expr()
		switch op {
		case cue.NoOp:
			// We have an element in the disjunction
			disjunctionElements = append(disjunctionElements, values...)
		case cue.OrOp:
			// We need to break down the "element" more
			todo = append(todo, values...)
		default:
			log.Fatalf("unexpected op: %#v, %v", op, values)
		}
	}
	fmt.Printf("%#v", disjunctionElements)
}
-- stdout.golden --
[]cue.Value{"foo", "FOO", "bar", "BAR"}

What did you expect to see?

Passing test.

What did you see instead?

$ ts repro.txtar
> go mod tidy
> go run .
[stderr]
main.go:39: unexpected op: 3, [%!v(PANIC=Format method: unsupported type *adt.NodeLink) "#FOO"]
exit status 1

[exit status 1]
FAIL: /tmp/testscript2935393692/repro.txtar/script.txtar:2: unexpected go command failure

[rogpeppe]

I just came across this issue in a slightly different form, with a somewhat simpler reproducer:

exec go mod tidy
exec go run main.go
! stderr PANIC

-- go.mod --
module test

require cuelang.org/go v0.12.1
-- main.go --
package main

import (
	"log"

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

func main() {
	ctx := cuecontext.New()
	v := ctx.CompileString(`
x: false
y: x
`)
	d := v.LookupPath(cue.MakePath(cue.Str("y")))
	op, args := d.Expr()
	log.Printf("op %v; %d args", op, len(args))
	for i, arg := range args {
		log.Printf("%d. %v", i, arg)
	}
}

This prints the following:

> exec go mod tidy
> exec go run main.go
[stderr]
op .; 2 args
0. %!v(PANIC=Format method: unsupported type *adt.NodeLink)
1. "x"
> ! stderr PANIC
FAIL: /tmp/x.txtar:3: unexpected match for `PANIC` found in stderr: PANIC

[adb-sh]

same issue here :/ any news on this?