From 9022a05ab2213e0d7b1abb34ee8d67eb439f8fbd Mon Sep 17 00:00:00 2001
From: Andrea Leopardi <an.leopardi@gmail.com>
Date: Wed, 12 Jul 2017 23:17:05 +0200
Subject: [PATCH] Force {Enum,Stream}.zip/1 to take a list of enumerabls as
 argument

Before this commit, there wasn't a clear check on these two functions accepting
only a list of enumerables as its argument. This lead to things like
https://github.com/elixir-lang/elixir/pull/6321.
---
 lib/elixir/lib/enum.ex                 | 6 +++---
 lib/elixir/lib/stream.ex               | 9 +++++----
 lib/elixir/test/elixir/enum_test.exs   | 6 +++++-
 lib/elixir/test/elixir/stream_test.exs | 5 +++++
 4 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/lib/elixir/lib/enum.ex b/lib/elixir/lib/enum.ex
index c0251d74bcf..855c418135a 100644
--- a/lib/elixir/lib/enum.ex
+++ b/lib/elixir/lib/enum.ex
@@ -2710,10 +2710,10 @@ defmodule Enum do
   end
 
   @doc """
-  Zips corresponding elements from a collection of enumerables
+  Zips corresponding elements from a list of enumerables
   into one list of tuples.
 
-  The zipping finishes as soon as any enumerable completes.
+  The zipping finishes as soon as any enumerable in the given list completes.
 
   ## Examples
 
@@ -2728,7 +2728,7 @@ defmodule Enum do
 
   def zip([]), do: []
 
-  def zip(enumerables) do
+  def zip(enumerables) when is_list(enumerables) do
     Stream.zip(enumerables).({:cont, []}, &{:cont, [&1 | &2]})
     |> elem(1)
     |> :lists.reverse
diff --git a/lib/elixir/lib/stream.ex b/lib/elixir/lib/stream.ex
index d58a34b4d48..d9eb8322f12 100644
--- a/lib/elixir/lib/stream.ex
+++ b/lib/elixir/lib/stream.ex
@@ -1033,10 +1033,10 @@ defmodule Stream do
   def zip(left, right), do: zip([left, right])
 
   @doc """
-  Zips corresponding elements from a collection of enumerables
+  Zips corresponding elements from a list of enumerables
   into one stream of tuples.
 
-  The zipping finishes as soon as any enumerable completes.
+  The zipping finishes as soon as any enumerable in the given list completes.
 
   ## Examples
 
@@ -1047,8 +1047,9 @@ defmodule Stream do
 
   """
   @spec zip([Enumerable.t]) :: Enumerable.t
-  def zip(enumerables) do
-    step      = &do_zip_step(&1, &2)
+  def zip(enumerables) when is_list(enumerables) do
+    step = &do_zip_step(&1, &2)
+
     enum_funs = Enum.map(enumerables, fn enum ->
       {&Enumerable.reduce(enum, &1, step), :cont}
     end)
diff --git a/lib/elixir/test/elixir/enum_test.exs b/lib/elixir/test/elixir/enum_test.exs
index 1b2ded61492..c3f4ebd707d 100644
--- a/lib/elixir/test/elixir/enum_test.exs
+++ b/lib/elixir/test/elixir/enum_test.exs
@@ -812,7 +812,11 @@ defmodule EnumTest do
     assert Enum.zip([[]]) == []
     assert Enum.zip([[1]]) == [{1}]
 
-    assert Enum.zip([[], [], [], []])  == []
+    assert Enum.zip([[], [], [], []]) == []
+
+    assert_raise FunctionClauseError, fn ->
+      Enum.zip(%{})
+    end
   end
 end
 
diff --git a/lib/elixir/test/elixir/stream_test.exs b/lib/elixir/test/elixir/stream_test.exs
index 74ca3777394..ae0f87b056a 100644
--- a/lib/elixir/test/elixir/stream_test.exs
+++ b/lib/elixir/test/elixir/stream_test.exs
@@ -1007,6 +1007,11 @@ test "transform/4 closes on nested errors" do
     cycle  = Stream.cycle([:a, :b, :c])
     assert Stream.zip([concat, cycle]) |> Enum.to_list ==
            [{1, :a}, {2, :b}, {3, :c}, {4, :a}, {5, :b}, {6, :c}]
+
+    assert_raise FunctionClauseError, fn ->
+      enum_of_enums = Stream.cycle([[1, 2], [:a, :b]])
+      Stream.zip(enum_of_enums)
+    end
   end
 
   test "zip/1 does not leave streams suspended" do