Improve error message for IEx.pry/1

Author: José Valim

lib/iex/lib/iex.ex

@@ -391,25 +391,41 @@ defmodule IEx do
   Setting variables or importing modules in IEx does not
   affect the caller the environment (hence it is called `pry`).
   """
-  defmacro pry(timeout \\ 1000) do
+  defmacro pry(timeout \\ 5000) do
     quote do
-      env  = __ENV__
-      meta = "#{inspect self} at #{Path.relative_to_cwd(env.file)}:#{env.line}"
-      opts = [binding: binding, dot_iex_path: "", env: env, prefix: "pry"]
-      res  = IEx.Server.take_over("Request to pry #{meta}", opts, unquote(timeout))
-
-      # We cannot use colors because IEx may be off.
-      case res do
-        {:error, :self} = err ->
-          IO.puts :stdio, "IEx cannot pry itself."
-        {:error, :no_iex} = err ->
-          IO.puts :stdio, "Cannot pry #{meta}. Is an IEx shell running?"
-        _ ->
-          :ok
-      end
+      IEx.pry(binding, __ENV__, unquote(timeout))
+    end
+  end
 
-      res
+  @doc """
+  Callback for `IEx.pry/1`.
+
+  You can invoke this function directly when you are not able to invoke
+  `IEx.pry/1` as a macro. This function expects the binding (from
+  `Kernel.binding/0`), the environment (from `__ENV__`) and the timeout
+  (a sensible default is 5000).
+  """
+  def pry(binding, env, timeout) do
+    meta = "#{inspect self} at #{Path.relative_to_cwd(env.file)}:#{env.line}"
+    opts = [binding: binding, dot_iex_path: "", env: env, prefix: "pry"]
+    res  = IEx.Server.take_over("Request to pry #{meta}", opts, timeout)
+
+    # We cannot use colors because IEx may be off.
+    case res do
+      {:error, :self} ->
+        IO.puts :stdio, "IEx cannot pry the shell itself."
+      {:error, :no_iex} ->
+        extra =
+          case :os.type do
+            {:win32, _} -> " If you are Windows, you may need to start IEx with the --werl flag."
+            _           -> ""
+          end
+        IO.puts :stdio, "Cannot pry #{meta}. Is an IEx shell running?" <> extra
+      _ ->
+        :ok
     end
+
+    res
   end
 
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