-- in.cue --
b: { for k, v in a { "\(k)": v+1 } }
a: { b: 1, c: 2 }

x: { for k, v in y { "\(k)": v } }
y: {} // check that empty struct after reference works.

k: { for v in e { v } }
e: int
-- out/eval --
Errors:
k: invalid operand e (found int, want list or struct):
    ./in.cue:7:15

Result:
(_|_){
  // [eval]
  b: (struct){
    b: (int){ 2 }
    c: (int){ 3 }
  }
  a: (struct){
    b: (int){ 1 }
    c: (int){ 2 }
  }
  x: (struct){
  }
  y: (struct){
  }
  k: (_|_){
    // [eval] k: invalid operand e (found int, want list or struct):
    //     ./in.cue:7:15
  }
  e: (int){ int }
}
-- out/compile --
--- in.cue
{
  b: {
    for k, v in 〈1;a〉 {
      "\(〈1;k〉)": (〈1;v〉 + 1)
    }
  }
  a: {
    b: 1
    c: 2
  }
  x: {
    for k, v in 〈1;y〉 {
      "\(〈1;k〉)": 〈1;v〉
    }
  }
  y: {}
  k: {
    for _, v in 〈1;e〉 {
      〈1;v〉
    }
  }
  e: int
}