Stream.zip/1 with empty list induces memory spike

[alecostard]

Elixir and Erlang/OTP versions

Erlang/OTP 25 [erts-13.1.5] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit:ns]

Elixir 1.14.3 (compiled with Erlang/OTP 25)

Operating system

x86_64 GNU/Linux

Current behavior

When executed, the line below consumes all memory:

 [] |> Stream.zip() |> Enum.to_list()

A less nasty way to check is to run the following while monitoring ram/cpu:

spawn(fn ->
  :timer.kill_after(3000)
  [] |> Stream.zip() |> Enum.to_list()
  IO.puts("done")
end)

Expected behavior

When "materialized", Stream.zip([]) should not cause a memory spike and just be the empty list.

[] == [] |> Stream.zip() |> Enum.to_list() 

[alecostard]

Tested on the main branch and the problem is there too. Looking at the stream.ex, I believe this happens due to an infinite recursion with zip_list/4, since zip_list([], {:cont, _something}, fun, zip_fun) calls zip_list_heads_tails([], [], []), which returns {[], []}, making zip_list/4 recurse with zip_list([], {:cont, _something2}, acc), fun, zip_fun).

A new clause

defp zip_list([], {:cont, acc}, _fun, _zip_fun), do: {:done, acc}

seems to solve this problem, but I may be missing something.

Since this comes from zip_list/4, it also affects Stream.zip_with/2

[whatyouhide]

@alecostard yep, a PR is welcome!