Make mix tasks work in a release

lib/pleroma/release_tasks.ex

@@ -0,0 +1,38 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.ReleaseTasks do
+  def run(args) do
+    [task | args] = String.split(args)
+
+    case task do
+      "migrate" -> migrate(args)
+      task -> mix_task(task, args)
+    end
+  end
+
+  defp mix_task(task, args) do
+    # Modules are not loaded before application starts
+    Mix.Tasks.Pleroma.Common.start_pleroma()
+    {:ok, modules} = :application.get_key(:pleroma, :modules)
+
+    module =
+      Enum.find(modules, fn module ->
+        module = Module.split(module)
+
+        match?(["Mix", "Tasks", "Pleroma" | _], module) and
+          String.downcase(List.last(module)) == task
+      end)
+
+    if module do
+      module.run(args)
+    else
+      IO.puts("The task #{task} does not exist")
+    end
+  end
+
+  defp migrate(_args) do
+    :noop
+  end
+end