Fix Range validation

- checks for lists when defining range
- replace (left .. right) with (first .. last) in error messages
  to use the same terminology used in the function definition
- add guards to Range.new/2
- add specs to Range.range?/1
- test added to check for lists in range.

lib/elixir/lib/kernel.ex

@@ -2444,16 +2444,18 @@ defmodule Kernel do
   defmacro first .. last do
     case is_float(first) or is_float(last) or
          is_atom(first) or is_atom(last) or
-         is_binary(first) or is_binary(last) do
+         is_binary(first) or is_binary(last) or
+         is_list(first) or is_list(last) do
       true ->
         raise ArgumentError,
-          "ranges (left .. right) expect both sides to be integers, " <>
+          "ranges (first .. last) expect both sides to be integers, " <>
           "got: #{Macro.to_string({:.., [], [first, last]})}"
       false ->
         {:%{}, [], [__struct__: Elixir.Range, first: first, last: last]}
     end
   end
 
+
   @doc """
   Provides a short-circuit operator that evaluates and returns
   the second expression only if the first one evaluates to `true`
@@ -2677,7 +2679,7 @@ defmodule Kernel do
       {:%{}, [], [__struct__: Elixir.Range, first: first, last: last]} ->
         in_range(left, Macro.expand(first, __CALLER__), Macro.expand(last, __CALLER__))
       _ ->
-        raise ArgumentError, <<"invalid args for operator in, it expects a compile time list ",
+        raise ArgumentError, <<"invalid args for operator \"in\", it expects a compile time list ",
                                "or range on the right side when used in guard expressions, got: ",
                                Macro.to_string(right) :: binary>>
     end

lib/elixir/lib/range.ex

@@ -31,12 +31,13 @@ defmodule Range do
   @doc """
   Creates a new range.
   """
-  def new(first, last) do
+  @spec new(integer, integer) :: t
+  def new(first, last) when is_integer(first) and is_integer(last) do
     %Range{first: first, last: last}
   end
 
   @doc """
-  Returns `true` if the given argument is a range.
+  Returns `true` if the given `term` is a range.
 
   ## Examples
 
@@ -47,6 +48,12 @@ defmodule Range do
       false
 
   """
+  # @spec range?(term) :: boolean
+  @spec range?(arg) :: false when arg: %Range{first: nil, last: nil}
+  @spec range?(arg) :: true when arg: %Range{}
+  @spec range?(term) :: false
+  def range?(term)
+  def range?(%Range{first: nil, last: nil}), do: false
   def range?(%Range{}), do: true
   def range?(_), do: false
 end
@@ -95,10 +102,14 @@ defimpl Enumerable, for: Range do
     end
   end
 
-  defp validate_range!(first, last) when is_integer(first) and is_integer(last), do: :ok
+  defp validate_range!(first, last) when is_integer(first)
+    and is_integer(last),
+    do: :ok
+
   defp validate_range!(first, last) do
     raise ArgumentError,
-          "ranges (left .. right) expect both sides to be integers, got: #{inspect first..last}"
+      "ranges (first .. last) expect both sides to be integers, " <>
+      "got: #{Macro.to_string({:.., [], [first, last]})}"
   end
 end
 

lib/elixir/test/elixir/range_test.exs

@@ -42,9 +42,18 @@ defmodule RangeTest do
   test "integer only" do
     x = 1.0
     y = 3.0
-    message = "ranges (left .. right) expect both sides to be integers, got: 1.0..3.0"
+    message = "ranges (first .. last) expect both sides to be integers, got: 1.0..3.0"
     assert_raise ArgumentError, message, fn ->
       Enum.map(x..y, &(&1 * 2))
     end
+
+    first = []
+    last = []
+    message = "ranges (first .. last) expect both sides to be integers, got: []..[]"
+    assert_raise ArgumentError, message, fn ->
+      first..last
+      Enum.map(first..last, &(&1))
+    end
+
   end
 end