Fix iex -S mix on Windows

Author: José Valim

lib/elixir/lib/kernel/cli.ex

@@ -271,7 +271,7 @@ defmodule Kernel.CLI do
   end
 
   defp process_command({:script, file}, _config) when is_binary(file) do
-    if exec = System.find_executable(file) do
+    if exec = find_elixir_executable(file) do
       Code.require_file(exec)
       :ok
     else
@@ -330,4 +330,19 @@ defmodule Kernel.CLI do
       { :error, "--compile : No files matched patterns #{Enum.join(patterns, ",")}" }
     end
   end
+
+  defp find_elixir_executable(file) do
+    if exec = System.find_executable(file) do
+      # If we are on Windows, the executable is going to be
+      # a .bat file that must be in the same directory as
+      # the actual Elixir executable.
+      case :os.type() do
+        { :win32, _ } ->
+          exec = Path.rootname(exec)
+          if File.regular?(exec), do: exec
+        _ ->
+          exec
+      end
+    end
+  end
 end

lib/elixir/lib/system.ex

@@ -204,21 +204,23 @@ defmodule System do
   end
 
   @doc """
-  This functions looks up an executable program given
+  This function looks up an executable program given
   its name using the environment variable PATH on Unix
-  and Windows.
+  and Windows. It also considers the proper executable
+  extension for each OS, so for Windows it will try to
+  lookup files with `.com`, `.cmd` or similar extensions.
 
-  If `command` is a char list, a char list is returned.
+  If `program` is a char list, a char list is returned.
   Returns a binary otherwise.
   """
   @spec find_executable(char_list) :: char_list | nil
   @spec find_executable(String.t) :: String.t | nil
-  def find_executable(command) when is_list(command) do
-    :os.find_executable(command) || nil
+  def find_executable(program) when is_list(program) do
+    :os.find_executable(program) || nil
   end
 
-  def find_executable(command) do
-    case :os.find_executable(to_char_list(command)) do
+  def find_executable(program) do
+    case :os.find_executable(to_char_list(program)) do
       false -> nil
       other -> list_to_binary(other)
     end