Persist log level to app env in Logger.configure/1

lib/logger/lib/logger.ex

@@ -738,9 +738,15 @@ defmodule Logger do
   def configure(options) do
     for {k, v} <- options do
       cond do
-        k == :level -> :logger.set_primary_config(:level, elixir_level_to_erlang_level(v))
-        k in @valid_options -> Application.put_env(:logger, k, v)
-        true -> :ok
+        k == :level ->
+          :ok = :logger.set_primary_config(:level, elixir_level_to_erlang_level(v))
+          Application.put_env(:logger, :level, v)
+
+        k in @valid_options ->
+          Application.put_env(:logger, k, v)
+
+        true ->
+          :ok
       end
     end
 

lib/logger/test/logger_test.exs

@@ -650,6 +650,30 @@ defmodule LoggerTest do
     Logger.configure(translator_inspect_opts: [])
   end
 
+  test "configure/1 persists :level to the application environment across restarts" do
+    previous = Application.get_env(:logger, :level)
+
+    try do
+      Application.delete_env(:logger, :level)
+      Logger.configure(level: :error)
+      assert Logger.level() == :error
+      assert Application.get_env(:logger, :level) == :error
+
+      Logger.App.stop()
+      Application.start(:logger)
+      assert Logger.level() == :error
+      assert Application.get_env(:logger, :level) == :error
+    after
+      Logger.configure(level: previous || :debug)
+
+      if previous do
+        Application.put_env(:logger, :level, previous)
+      else
+        Application.delete_env(:logger, :level)
+      end
+    end
+  end
+
   @tag formatter: [metadata: [:module, :meta]]
   test "always evaluate messages" do
     Logger.configure(