Add a polyfill for Application.put_all_env/2

lib/mix/tasks/pleroma/instance.ex

@@ -5,6 +5,7 @@
 defmodule Mix.Tasks.Pleroma.Instance do
   use Mix.Task
   import Mix.Pleroma
+  alias Pleroma.Polyfill
 
   @shortdoc "Manages Pleroma instance"
   @moduledoc """
@@ -226,15 +227,17 @@ defmodule Mix.Tasks.Pleroma.Instance do
       shell_info("Writing the postgres script to #{psql_path}.")
       File.write(psql_path, result_psql)
 
-      Config.Reader.read!(config_path)
-      |> Enum.map(fn {application, config} ->
-        config =
-          Application.get_all_env(application)
-          |> Config.Reader.merge(config)
+      new_config =
+        Config.Reader.read!(config_path)
+        |> Enum.map(fn {application, config} ->
+          config =
+            Application.get_all_env(application)
+            |> Config.Reader.merge(config)
 
-        {application, config}
-      end)
-      |> Application.put_all_env()
+          {application, config}
+        end)
+
+      Polyfill.apply_or_fallback(Application, :put_all_env, [new_config])
 
       write_robots_txt(indexable, template_dir)
 

lib/pleroma/polyfill.ex

@@ -0,0 +1,19 @@
+defmodule Pleroma.Polyfill do
+  @doc "Provides fallbacks for features not available on Elixir versions supported"
+
+  def apply_or_fallback(module, function_name, args) do
+    if function_exported?(module, function_name, length(args)) do
+      apply(module, function_name, args)
+    else
+      if fallback_available?(module, function_name, length(args)) do
+        apply(Module.concat(__MODULE__, module), function_name, args)
+      else
+        raise "No fallback for #{module}.#{to_string(function_name)} found!"
+      end
+    end
+  end
+
+  def fallback_available?(module, function_name, arity) do
+    function_exported?(Module.concat(__MODULE__, module), function_name, arity)
+  end
+end

lib/pleroma/polyfill/application.ex

@@ -0,0 +1,23 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.Polyfill.Application do
+  # Taken from https://github.com/elixir-lang/elixir/blob/b50e0f4ea7d1d6860bc8d9081f5dbe16047375ef/lib/elixir/lib/application.ex 
+  # Copyright 2012 Plataformatec
+  def put_all_env(config, opts \\ []) when is_list(config) and is_list(opts) do
+    if function_exported?(:application, :set_env, 2) do
+      # Directly calling it would result in a compilation warning on OTP <22
+      apply(:application, :set_env, [config, opts])
+    else
+      for app_keyword <- config,
+          {app, keyword} = app_keyword,
+          key_value <- keyword,
+          {key, value} = key_value do
+        :application.set_env(app, key, value, opts)
+      end
+
+      :ok
+    end
+  end
+end

test/tasks/instance_test.exs

@@ -4,6 +4,7 @@
 
 defmodule Pleroma.InstanceTest do
   use ExUnit.Case, async: true
+  alias Pleroma.Polyfill
 
   setup do
     File.mkdir_p!(tmp_path())
@@ -16,7 +17,7 @@ defmodule Pleroma.InstanceTest do
 
     on_exit(fn ->
       File.rm_rf(tmp_path())
-      Application.put_all_env(config)
+      Polyfill.apply_or_fallback(Application, :put_all_env, [config])
     end)
 
     :ok