Fix edge case for String.contains?

Author: alco

lib/elixir/lib/string.ex

@@ -886,11 +886,23 @@ defmodule String do
   """
   @spec contains?(t, t | [t]) :: boolean
 
-  def contains?(_, "") do
+  def contains?(string, matches) when is_list(matches) do
+    Enum.any?(matches, do_contains(string, &1))
+  end
+
+  def contains?(string, match) do
+    do_contains(string, match)
+  end
+
+  defp do_contains(_, "") do
     true
   end
 
-  def contains?(string, matches) do
-    :nomatch != :binary.match(string, matches)
+  defp do_contains(string, match) when is_binary(match) do
+    :nomatch != :binary.match(string, match)
+  end
+
+  defp do_contains(_, _) do
+    raise ArgumentError
   end
 end

lib/elixir/test/elixir/string_test.exs

@@ -332,20 +332,25 @@ defmodule StringTest do
   end
 
   test :contains? do
-    assert String.contains? "", ""
-    assert String.contains? "abc", ""
-    assert String.contains? "abc", ["", "x"]
-
-    refute String.contains? "", " "
-    refute String.contains? "", "a"
-
+    ## Normal cases ##
     assert String.contains? "elixir of life", "of"
     assert String.contains? "エリクシア", "シ"
     assert String.contains? "elixir of life", ["mercury", "life"]
     refute String.contains? "exlixir of life", "death"
     refute String.contains? "エリクシア", "仙"
     refute String.contains? "elixir of life", ["death", "mercury", "eternal life"]
 
+    ## Edge cases ##
+    assert String.contains? "", ""
+    assert String.contains? "abc", ""
+    assert String.contains? "abc", ["", "x"]
+
+    refute String.contains? "", " "
+    refute String.contains? "", "a"
+
+    ## Sanity checks ##
+    assert String.contains? "", ["", ""]
+    assert String.contains? "abc", ["", ""]
     assert_raise ArgumentError, fn ->
       String.contains? "abc", [["b"], "b"]
     end