github.com/joomcode/cue@v0.4.4-0.20221111115225-539fe3512047/cue/testdata/builtins/list/issue332.txtar

-- in.cue --
import "list"

#d: {
	#x: string
	result: [#x]
}
#foo: {
	X=#x: _
	y:    list.FlattenN((#d & {#x: X}).result, 1)
}
r: #foo & {
	#x: "hello"
}
-- out/eval --
(struct){
  #d: (#struct){
    #x: (string){ string }
    result: (#list){
      0: (string){ string }
    }
  }
  #foo: (#struct){
    #x: (_){ _ }
    y: (#list){
      0: (string){ string }
    }
  }
  r: (#struct){
    #x: (string){ "hello" }
    y: (#list){
      0: (string){ "hello" }
    }
  }
}
-- out/compile --
--- in.cue
{
  #d: {
    #x: string
    result: [
      〈1;#x〉,
    ]
  }
  #foo: {
    #x: _
    y: 〈import;list〉.FlattenN((〈1;#d〉 & {
      #x: 〈1;#x〉
    }).result, 1)
  }
  r: (〈0;#foo〉 & {
    #x: "hello"
  })
}