Accept the trim option when splitting strings

By default `trim` will be set to true. Because `:binary.strip` only
removes empty strings from the end of the result, we have to apply a
filter to remove empty strings from the beginning before returning.

Author: vanstee

lib/elixir/lib/string.ex

@@ -163,12 +163,17 @@ defmodule String do
   The string is split into as many parts as possible by
   default, unless the `global` option is set to `false`.
 
+  Empty strings are removed from the result, unless the
+  `trim` option is set to `false`.
+
   ## Examples
 
       iex> String.split("a,b,c", ",")
       ["a", "b", "c"]
       iex> String.split("a,b,c", ",", global: false)
       ["a", "b,c"]
+      iex> String.split(" a b c ", " ", trim: false)
+      ["", "a", "b", "c", ""]
 
       iex> String.split("1,2 3,4", [" ", ","])
       ["1", "2", "3", "4"]
@@ -188,12 +193,19 @@ defmodule String do
   def split("", _pattern, _options), do: [""]
 
   def split(binary, pattern, options) when is_regex(pattern) do
-    Regex.split(pattern, binary, global: options[:global])
+    Regex.split(pattern, binary, options)
   end
 
   def split(binary, pattern, options) do
-    opts = if options[:global] != false, do: [:global], else: []
-    :binary.split(binary, pattern, opts)
+    defaults = [global: true, trim: true]
+    options = Keyword.merge(defaults, options)
+
+    option_keys = Enum.filter_map(options, &elem(&1, 1), &elem(&1, 0))
+    splits = :binary.split(binary, pattern, option_keys)
+
+    if options[:trim], do: splits = Enum.filter(splits, &(&1 != ""))
+
+    splits
   end
 
   @doc """

lib/elixir/test/elixir/string_test.exs

@@ -29,9 +29,13 @@ defmodule StringTest do
     assert String.split("a,b,c", ",") == ["a", "b", "c"]
     assert String.split("a,b", ".") == ["a,b"]
     assert String.split("1,2 3,4", [" ", ","]) == ["1", "2", "3", "4"]
+    assert String.split(" a b c ", " ") == ["a", "b", "c"]
 
     assert String.split("a,b,c", ",", global: false) == ["a", "b,c"]
     assert String.split("1,2 3,4", [" ", ","], global: false) == ["1", "2 3,4"]
+
+    assert String.split(" a b c ", " ", trim: false) == ["", "a", "b", "c", ""]
+    assert String.split(" a b c ", " ", trim: false, global: false) == ["", "a b c "]
   end
 
   test :split_with_regex do