Add String.valid?

lib/elixir/lib/string.ex

@@ -458,6 +458,34 @@ defmodule String do
   @spec next_codepoint(t) :: {codepoint, t} | :no_codepoint
   defdelegate next_codepoint(string), to: String.Unicode
 
+  @doc %B"""
+  Checks whether `str` is a valid UTF-8 string.
+
+  ## Examples
+
+      iex> String.valid?("a")
+      true
+      iex> String.valid?("ø")
+      true
+      iex> String.valid?(<<0xffff :: 16>>)
+      false
+      iex> String.valid?("asd" <> <<0xffff :: 16>>)
+      false
+
+  """
+  @spec valid?(t) :: boolean
+  def valid?(<<_ :: utf8, t :: binary>>) do
+    valid?(t)
+  end
+
+  def valid?(<<>>) do
+    true
+  end
+
+  def valid?(_) do
+    false
+  end
+
   @doc %B"""
   Checks whether `str` is a valid codepoint.
 
@@ -470,7 +498,7 @@ defmodule String do
       true
       iex> String.valid_codepoint?("ø")
       true
-      iex> String.valid_codepoint?("\xffff")
+      iex> String.valid_codepoint?(<<0xffff :: 16>>)
       false
       iex> String.valid_codepoint?("asdf")
       false

lib/elixir/test/elixir/string_test.exs

@@ -228,12 +228,21 @@ defmodule StringTest do
     assert String.slice("", 0, 1) == nil
   end
 
+  test :valid? do
+    assert String.valid?("afds")
+    assert String.valid?("øsdfh")
+    assert String.valid?("dskfjあska")
+
+    refute String.valid?(<<0xffff :: 16>>)
+    refute String.valid?("asd" <> <<0xffff :: 16>>)
+  end
+
   test :valid_codepoint? do
     assert String.valid_codepoint?("a")
     assert String.valid_codepoint?("ø")
     assert String.valid_codepoint?("あ")
 
-    refute String.valid_codepoint?("\xffff")
+    refute String.valid_codepoint?(<<0xffff :: 16>>)
     refute String.valid_codepoint?("ab")
   end