Demonstrate surprising Dialyzer warning for list comprehension

demo.ex

defmodule Demo do
  def test1a, do: [1]

  def test1b(x) do
    # demo.ex:6: The created fun has no local return
    for e <- test1a, do: x
  end

  def test2a, do: 1
  
  def test2b(x) do
    for e <- [test2a], do: x
  end

  def test3a, do: [1]

  def test3b(x) do
    for e <- test3a, do: 1
  end

  def test4a, do: [1]

  def test4b do
    for e <- test4a, do: e
  end
end