Do not rely on conditional module definition

The downside of conditional module definition is that
it may not work as expected in umbrellas. Given the
Sentry Logger configuration in an umbrella project is
shared across all apps, if we do:

    config :logger, :backends, [Sentry.LoggerBackend]

then `:sentry` needs to be defined on all dependencies.
However, if a dependency is not a web application,
Sentry may be compiled before Plug! And if it is compiled
before Plug, it wouldn't define Sentry.PlugCapture and
friends, which means the web app in the umbrella wouldn't
have those modules available.

Author: josevalim

lib/sentry/plug_capture.ex

@@ -1,51 +1,49 @@
-if Code.ensure_loaded?(Plug) do
-  defmodule Sentry.PlugCapture do
-    @moduledoc """
-    Provides basic functionality to handle and send errors occurring within
-    Plug applications, including Phoenix.
-    It is intended for usage with `Sentry.PlugContext`.
-
-    #### Usage
-    In a Phoenix application, it is important to use this module before
-    the Phoenix endpoint itself. It should be added to your endpoint.ex:
-
-
-        defmodule MyApp.Endpoint
-          use Sentry.PlugCapture
-          use Phoenix.Endpoint, otp_app: :my_app
-          # ...
-        end
+defmodule Sentry.PlugCapture do
+  @moduledoc """
+  Provides basic functionality to handle and send errors occurring within
+  Plug applications, including Phoenix.
+  It is intended for usage with `Sentry.PlugContext`.
 
-    In a Plug application, it can be added below your router:
+  #### Usage
+  In a Phoenix application, it is important to use this module before
+  the Phoenix endpoint itself. It should be added to your endpoint.ex:
 
-        defmodule MyApp.PlugRouter do
-          use Plug.Router
-          use Sentry.PlugCapture
-          # ...
-        end
-    """
-    defmacro __using__(_opts) do
-      quote do
-        @before_compile Sentry.PlugCapture
+
+      defmodule MyApp.Endpoint
+        use Sentry.PlugCapture
+        use Phoenix.Endpoint, otp_app: :my_app
+        # ...
       end
+
+  In a Plug application, it can be added below your router:
+
+      defmodule MyApp.PlugRouter do
+        use Plug.Router
+        use Sentry.PlugCapture
+        # ...
+      end
+  """
+  defmacro __using__(_opts) do
+    quote do
+      @before_compile Sentry.PlugCapture
     end
+  end
 
-    defmacro __before_compile__(_) do
-      quote do
-        defoverridable call: 2
-
-        def call(conn, opts) do
-          try do
-            super(conn, opts)
-          rescue
-            e in Plug.Conn.WrapperError ->
-              Sentry.capture_exception(e.reason, stacktrace: e.stack, event_source: :plug)
-              Plug.Conn.WrapperError.reraise(e)
-
-            e ->
-              Sentry.capture_exception(e, stacktrace: __STACKTRACE__, event_source: :plug)
-              :erlang.raise(:error, e, __STACKTRACE__)
-          end
+  defmacro __before_compile__(_) do
+    quote do
+      defoverridable call: 2
+
+      def call(conn, opts) do
+        try do
+          super(conn, opts)
+        rescue
+          e in Plug.Conn.WrapperError ->
+            Sentry.capture_exception(e.reason, stacktrace: e.stack, event_source: :plug)
+            Plug.Conn.WrapperError.reraise(e)
+
+          e ->
+            Sentry.capture_exception(e, stacktrace: __STACKTRACE__, event_source: :plug)
+            :erlang.raise(:error, e, __STACKTRACE__)
         end
       end
     end