XO0152: rune literal that is empty, unterminated, or holds more than one character

A rune literal is exactly one character (or one escape) between single quotes: 'a', '\n', '\u{1F600}'. '', 'ab', and an unclosed 'a are rejected. Text of several characters is a Str and uses double quotes. See core 1.6.

Example

fn f() -> Str {
  let s = 'ab'
  "${s}"
}

Fix

fn f() -> Str {
  let s = "ab"
  s
}

Run xo explain XO0152 for this text in a terminal, or see section 10.6 of the specification.