Fix broken Tracer.configure(disabled?: true) (#71)

Author: sekiyama58

lib/tracer.ex

@@ -102,7 +102,7 @@ defmodule Spandex.Tracer do
       def configure(opts) do
         case config(opts, @otp_app) do
           :disabled ->
-            :ok
+            Application.put_env(@otp_app, __MODULE__, merge_config(opts, @otp_app))
 
           config ->
             Application.put_env(@otp_app, __MODULE__, config)
@@ -223,14 +223,17 @@ defmodule Spandex.Tracer do
         Spandex.distributed_context(conn, config(opts, @otp_app))
       end
 
+      defp merge_config(opts, otp_app) do
+        otp_app
+        |> Application.get_env(__MODULE__)
+        |> Kernel.||([])
+        |> Keyword.merge(opts || [])
+        |> Optimal.validate!(@opts)
+        |> Keyword.put(:tracer, __MODULE__)
+      end
+
       defp config(opts, otp_app) do
-        config =
-          otp_app
-          |> Application.get_env(__MODULE__)
-          |> Kernel.||([])
-          |> Keyword.merge(opts || [])
-          |> Optimal.validate!(@opts)
-          |> Keyword.put(:tracer, __MODULE__)
+        config = merge_config(opts, otp_app)
 
         if config[:disabled?] do
           :disabled
@@ -242,7 +245,7 @@ defmodule Spandex.Tracer do
       defp validate_update_config(opts, otp_app) do
         env = Application.get_env(otp_app, __MODULE__)
 
-        if env[:disabled] do
+        if env[:disabled?] do
           :disabled
         else
           schema = %{@opts | defaults: [], required: []}

test/configure_test.exs

@@ -0,0 +1,21 @@
+defmodule Spandex.Test.ConfigureTest do
+  use ExUnit.Case, async: false
+
+  alias Spandex.Test.Util
+  require Spandex.Test.Support.Tracer
+  alias Spandex.Test.Support.Tracer
+
+  test "disabled tracer should not have results" do
+    original_env = Application.get_env(:spandex, Tracer)
+    assert :ok = Tracer.configure(disabled?: true)
+
+    Tracer.trace "my_trace" do
+    end
+
+    span = Util.can_fail(fn -> Util.find_span("my_trace") end)
+
+    assert(span == nil)
+
+    Tracer.configure(original_env)
+  end
+end