Use compile_env if available

lib/gettext.ex

@@ -584,10 +584,15 @@ defmodule Gettext do
 
   @doc false
   defmacro __using__(opts) do
+    env_fun =
+      if function_exported?(Application, :compile_env, 3), do: :compile_env, else: :get_env
+
     quote do
       require Logger
 
-      @gettext_opts unquote(opts)
+      opts = unquote(opts)
+      otp_app = Keyword.fetch!(opts, :otp_app)
+      @gettext_opts Keyword.merge(opts, Application.unquote(env_fun)(otp_app, __MODULE__, []))
       @before_compile Gettext.Compiler
 
       def handle_missing_bindings(exception, incomplete) do

lib/gettext/compiler.ex

@@ -16,21 +16,8 @@ defmodule Gettext.Compiler do
 
   @doc false
   defmacro __before_compile__(env) do
-    compile_time_opts = Module.get_attribute(env.module, :gettext_opts)
-
-    # :otp_app is only supported in "use Gettext" (because we need it to get the Mix config).
-    {otp_app, compile_time_opts} = Keyword.pop(compile_time_opts, :otp_app)
-
-    if is_nil(otp_app) do
-      # We're using Keyword.fetch!/2 to raise below.
-      Keyword.fetch!(compile_time_opts, :otp_app)
-    end
-
-    # Options given to "use Gettext" have higher precedence than options set
-    # throught Mix.Config.
-    mix_config_opts = Application.get_env(otp_app, env.module, [])
-    opts = Keyword.merge(mix_config_opts, compile_time_opts)
-
+    opts = Module.get_attribute(env.module, :gettext_opts)
+    otp_app = Keyword.fetch!(opts, :otp_app)
     priv = Keyword.get(opts, :priv, @default_priv)
     translations_dir = Application.app_dir(otp_app, priv)
     external_file = String.replace(Path.join(".compile", priv), "/", "_")

lib/gettext/plural.ex

@@ -70,6 +70,10 @@ defmodule Gettext.Plural do
         use Gettext, otp_app: :my_app, plural_forms: MyApp.Plural
       end
 
+  **Note**: set `:plural_forms` in your `config/config.exs` and
+  not in `config/runtime.exs`, as this configuration is read when
+  compiling your backends.
+
   Notice that tasks such as `mix gettext.merge` use the plural
   backend configured under the `:gettext` application, so generally
   speaking the first format is preferred.