Improve Error on bad_return from Application.Behaviour.Start

Author: Jason S

lib/mix/lib/mix/tasks/app.start.ex

@@ -27,14 +27,16 @@ defmodule Mix.Tasks.App.Start do
     end
 
     unless opts[:no_start] do
-      start_app(project)
+      start(project)
     end
   end
 
-  defp start_app(project) do
+  def start(project) do
     if app = project[:app] do
       case Application.Behaviour.start(app) do
         :ok -> :ok
+        { :error, {:bad_return, err}} ->
+          raise Exception.normalize(err)
         { :error, reason } ->
           raise Mix.Error, message: "Could not start application #{app}: #{inspect reason}"
       end

lib/mix/test/mix/tasks/app.start_test.exs

@@ -9,6 +9,24 @@ defmodule Mix.Tasks.App.StartTest do
     end
   end
 
+  defmodule BadReturnSample do
+    def project do
+      [app: :bad_return_app, version: "0.1.0"]
+    end
+    # Configuration for the OTP application
+    def application do
+      [mod: { Mix.Tasks.App.StartTest.BadReturnApp, [] }]
+    end
+  end
+
+  defmodule BadReturnApp do
+    use Application.Behaviour
+
+    def start(_type, _args) do
+      :bar # Bad return
+    end
+  end
+
   defmodule WrongElixirProject do
     def project do
       [app: :error, version: "0.1.0", elixir: "~> 0.8.1"]
@@ -76,4 +94,41 @@ defmodule Mix.Tasks.App.StartTest do
   after
     purge [A, B, C]
   end
+
+  test "start does nothing if project[:app] is nil" do
+    project = Mix.project
+    assert Mix.Tasks.App.Start.start(project) == nil
+  end
+
+  test "start runs successfully in okay case" do
+    Mix.Project.push MixTest.Case.Sample
+    in_fixture "no_mixfile", fn ->
+      Mix.Tasks.Compile.run []
+      project = Mix.project
+      assert Mix.Tasks.App.Start.start(project) == :ok
+    end
+  end
+
+  test "start raises an exception on :error" do
+    Mix.Project.push AppStartSample
+
+    in_fixture "no_mixfile", fn ->
+      project = Mix.project
+      assert_raise Mix.Error, fn ->
+        Mix.Tasks.App.Start.start(project)
+      end
+    end
+  end
+
+  test "start raises a stacktrace on bad_return" do
+    Mix.Project.push BadReturnSample
+
+    in_fixture "no_mixfile", fn ->
+      Mix.Tasks.Compile.run []
+      project = Mix.project
+      assert_raise ErlangError, fn ->
+        Mix.Tasks.App.Start.start(project)
+      end
+    end
+  end
 end