Support ecto config

Ecto has mix tasks that will attempt to start the repo. In some of these
scenarios, the application will not yet have been started. Most notable
are ecto.create and ecto.migrate. These are aliased for you in a brand
new phoenix project under `mix test`.

With this new `Provider.ecto_config/3` function, we ensure that the
given config process is running, and we will also shut it down
afterwards to ensure that when your application starts, we do not have
an issue with the process already being started.

Author: ankhers

README.md

@@ -97,16 +97,18 @@ defmodule MySystem.Repo do
     adapter: Ecto.Adapters.Postgres
 
   @impl Ecto.Repo
-  def init(_type, config) do
-    {:ok,
-      Keyword.merge(
-        config,
-        hostname: MySystem.Config.db_host(),
-        database_name: MySystem.Config.db_name(),
-        pool_size: MySystem.Config.db_pool_size(),
-        # ...
-      )
-    }
+  def init(context, config) do
+    Provider.ecto_config(MySystem.Config, context, fn ->
+      {:ok,
+        Keyword.merge(
+          config,
+          hostname: MySystem.Config.db_host(),
+          database_name: MySystem.Config.db_name(),
+          pool_size: MySystem.Config.db_pool_size(),
+          # ...
+        )
+      }
+    end)
   end
 end
 ```

lib/provider.ex

@@ -102,6 +102,7 @@ defmodule Provider do
   @type type :: :string | :integer | :float | :boolean
   @type value :: String.t() | number | boolean | nil
   @type data :: %{param_name => value}
+  @type ecto_context :: :supervisor | :runtime
 
   # ------------------------------------------------------------------------
   # API
@@ -129,6 +130,19 @@ defmodule Provider do
     end
   end
 
+  @spec ecto_config(module(), ecto_context(), (-> {:ok, Keyword.t()})) :: {:ok, Keyword.t()}
+  def ecto_config(mod, context, fun) do
+    mod.start_link(nil)
+
+    ret = fun.()
+
+    if context == :runtime do
+      GenServer.stop(mod)
+    end
+
+    ret
+  end
+
   # ------------------------------------------------------------------------
   # Private
   # ------------------------------------------------------------------------

mix.exs

@@ -1,7 +1,7 @@
 defmodule Provider.MixProject do
   use Mix.Project
 
-  @version "0.2.0"
+  @version "0.2.1"
 
   def project do
     [

test/provider_test.exs

@@ -37,6 +37,48 @@ defmodule ProviderTest do
     end
   end
 
+  describe "ecto_config" do
+    test "starts and stops the server when the context is :runtime" do
+      System.put_env("OPT_1", "some data")
+      System.put_env("OPT_2", "42")
+      System.put_env("OPT_6", "false")
+      System.put_env("OPT_7", "3.14")
+
+      pid = Process.whereis(TestModule)
+      assert is_nil(pid)
+
+      config =
+        Provider.ecto_config(TestModule, :runtime, fn ->
+          {:ok, [hostname: TestModule.opt_1()]}
+        end)
+
+      assert {:ok, [hostname: "some data"]} = config
+
+      pid = Process.whereis(TestModule)
+      assert is_nil(pid)
+    end
+
+    test "starts but not stops the server when the context is :supervisor" do
+      System.put_env("OPT_1", "some data")
+      System.put_env("OPT_2", "42")
+      System.put_env("OPT_6", "false")
+      System.put_env("OPT_7", "3.14")
+
+      pid = Process.whereis(TestModule)
+      assert is_nil(pid)
+
+      config =
+        Provider.ecto_config(TestModule, :supervisor, fn ->
+          {:ok, [hostname: TestModule.opt_1()]}
+        end)
+
+      assert {:ok, [hostname: "some data"]} = config
+
+      pid = Process.whereis(TestModule)
+      assert not is_nil(pid)
+    end
+  end
+
   describe "generated module" do
     setup do
       Enum.each(1..7, &System.delete_env("OPT_#{&1}"))