Use erlang log level if none is set

lib/logger/lib/logger.ex

@@ -601,7 +601,6 @@ defmodule Logger do
     Logger.Config.configure(options)
 
     # Then we can read from the writes
-    Logger.Config.load_log_level()
     :ok = :logger.set_handler_config(Logger, %{config: %{}})
   end
 

lib/logger/lib/logger/app.ex

@@ -57,8 +57,8 @@ defmodule Logger.App do
   end
 
   @doc false
-  def config_change(_changed, _new, _removed) do
-    Logger.configure([])
+  def config_change(changed, _new, _removed) do
+    Logger.configure(changed)
   end
 
   @doc """
@@ -81,15 +81,34 @@ defmodule Logger.App do
         end
     }
 
-    %{level: level} = primary_config = :logger.get_primary_config()
+    %{level: erl_level} = primary_config = :logger.get_primary_config()
+
+    # Elixir's logger level is no longer set by default.
+    #
+    # If it is set, it always has higher precedence, but we warn
+    # in case of mismatches.
+    #
+    # If it is not set, we revert Erlang's kernel to debug, if it
+    # has its default value, otherwise we keep it as is.
+    case Application.fetch_env(:logger, :level) do
+      {:ok, level} ->
+        if erl_level != :notice and erl_level != level do
+          IO.warn(
+            "the level for Erlang's logger was set to #{inspect(erl_level)}, " <>
+              "but Elixir's logger was set to #{inspect(level)}. " <>
+              "Elixir's logger value will take higher precedence"
+          )
+        end
+
+        :ok = :logger.set_primary_config(:level, level)
+
+      :error when erl_level == :notice ->
+        :ok = :logger.set_primary_config(:level, :debug)
 
-    if level != :notice and Application.fetch_env!(:logger, :level) != level do
-      IO.warn "the level for Erlang's logger was set to #{inspect(level)}, " <>
-                "but Elixir's logger was set to #{inspect(Application.fetch_env!(:logger, :level))}. " <>
-                "Elixir's logger value will take higher precedence"
+      :error ->
+        :ok
     end
 
-    Logger.Config.load_log_level()
     :ok = :logger.add_primary_filter(:process_disabled, {&Logger.Filter.process_disabled/2, []})
     :ok = :logger.add_handler(Logger, Logger.Handler, config)
     primary_config

lib/logger/lib/logger/config.ex

@@ -7,16 +7,6 @@ defmodule Logger.Config do
 
   alias Logger.Counter
 
-  def load_log_level do
-    level =
-      case Application.fetch_env!(:logger, :level) do
-        :warn -> :warning
-        level -> level
-      end
-
-    :ok = :logger.set_primary_config(:level, level)
-  end
-
   def configure(options) do
     :gen_event.call(Logger, @name, {:configure, options})
   end
@@ -55,8 +45,16 @@ defmodule Logger.Config do
   end
 
   def handle_call({:configure, options}, {counter, _, _, _}) do
-    Enum.each(options, fn {key, value} ->
-      Application.put_env(:logger, key, value)
+    Enum.each(options, fn
+      # TODO: Warn on deprecated level
+      {:level, :warn} ->
+        :ok = :logger.set_primary_config(:level, :warning)
+
+      {:level, level} ->
+        :ok = :logger.set_primary_config(:level, level)
+
+      {key, value} ->
+        Application.put_env(:logger, key, value)
     end)
 
     {:ok, :ok, load_state(counter)}

lib/logger/lib/logger/handler.ex

@@ -75,7 +75,6 @@ defmodule Logger.Handler do
             metadata = erlang_metadata_to_elixir_metadata(metadata)
             %{truncate: truncate, utc_log: utc_log?} = config
 
-            # TODO: Use `time` field of `erl_metadata` for timestamp
             event = {
               level,
               gl,
@@ -165,7 +164,9 @@ defmodule Logger.Handler do
 
   ## Metadata helpers
 
-  # TODO: We should only do this for legacy handlers
+  # TODO: We should only do this for legacy handlers.
+  # The new handlers should accept all metadata as is
+  # and receive the system time unit rather than tuples.
   defp erlang_metadata_to_elixir_metadata(metadata) do
     metadata =
       case metadata do

lib/logger/mix.exs

@@ -14,7 +14,6 @@ defmodule Logger.MixProject do
       registered: [Logger, Logger.BackendSupervisor, Logger.Supervisor, Logger.Watcher],
       mod: {Logger.App, []},
       env: [
-        level: :debug,
         utc_log: false,
         truncate: 8096,
         backends: [:console],

lib/logger/test/logger_test.exs

@@ -452,7 +452,6 @@ defmodule LoggerTest do
     :ok = Logger.configure(level: :debug)
 
     try do
-      Application.put_env(:logger, :level, :error)
       assert Logger.App.config_change([level: :error], [], []) === :ok
       assert Logger.level() === :error
     after