Introduce default_formatter and default_handler config for Logger (#12400)

We now fully integrate with Erlang/OTP logger.

  * Logger.Formatter can now instantiate a compatible Erlamg/OTP logger formatter

  * The default_handler configures the default handler

  * The default_formatter configures the default formatter

  * Backends front-end will be moved to logger_backends package,
    but the implementation will still be shipped as part of Elixir

Author: josevalim

lib/elixir/lib/kernel/cli.ex

@@ -57,9 +57,8 @@ defmodule Kernel.CLI do
       {_, status} = at_exit({ok_or_shutdown, status})
 
       # Ensure Logger messages are flushed before halting
-      case :erlang.whereis(Logger) do
-        pid when is_pid(pid) -> Logger.flush()
-        _ -> :ok
+      if Code.loaded?(Logger) do
+        Logger.flush()
       end
 
       System.halt(status)

lib/ex_unit/lib/ex_unit/capture_log.ex

@@ -39,7 +39,7 @@ defmodule ExUnit.CaptureLog do
 
   alias Logger.Backends.Console
 
-  @compile {:no_warn_undefined, Logger}
+  @compile {:no_warn_undefined, [Logger, Logger.Backends.Internal]}
 
   @doc """
   Captures Logger messages generated when evaluating `fun`.
@@ -138,24 +138,27 @@ defmodule ExUnit.CaptureLog do
 
   @doc false
   def init_proxy(pid, opts, parent) do
-    case :gen_event.add_sup_handler(Logger, {Console, pid}, {Console, [device: pid] ++ opts}) do
-      :ok ->
-        ref = Process.monitor(parent)
-        :proc_lib.init_ack(:ok)
-
-        receive do
-          {:DOWN, ^ref, :process, ^parent, _reason} -> :ok
-          {:gen_event_EXIT, {Console, ^pid}, _reason} -> :ok
-        end
+    Logger.Backends.Internal.configure([])
+  catch
+    _, _ -> :proc_lib.init_ack(:noproc)
+  else
+    _ ->
+      case :gen_event.add_sup_handler(Logger, {Console, pid}, {Console, [device: pid] ++ opts}) do
+        :ok ->
+          ref = Process.monitor(parent)
+          :proc_lib.init_ack(:ok)
+
+          receive do
+            {:DOWN, ^ref, :process, ^parent, _reason} -> :ok
+            {:gen_event_EXIT, {Console, ^pid}, _reason} -> :ok
+          end
 
-      {:EXIT, reason} ->
-        :proc_lib.init_ack({:error, reason})
+        {:EXIT, reason} ->
+          :proc_lib.init_ack({:error, reason})
 
-      {:error, reason} ->
-        :proc_lib.init_ack({:error, reason})
-    end
-  catch
-    :exit, :noproc -> :proc_lib.init_ack(:noproc)
+        {:error, reason} ->
+          :proc_lib.init_ack({:error, reason})
+      end
   end
 
   defp remove_capture(pid) do

lib/ex_unit/lib/ex_unit/capture_server.ex

@@ -36,7 +36,7 @@ defmodule ExUnit.CaptureServer do
     state = %{
       devices: %{},
       log_captures: %{},
-      log_status: nil
+      log_status: :error
     }
 
     {:ok, state}
@@ -64,7 +64,14 @@ defmodule ExUnit.CaptureServer do
     refs = Map.put(config.log_captures, ref, true)
 
     if map_size(refs) == 1 do
-      status = Logger.remove_backend(:console)
+      status =
+        with {:ok, config} <- :logger.get_handler_config(:default),
+             :ok <- :logger.remove_handler(:default) do
+          {:ok, config}
+        else
+          _ -> :error
+        end
+
       {:reply, ref, %{config | log_captures: refs, log_status: status}}
     else
       {:reply, ref, %{config | log_captures: refs}}
@@ -189,9 +196,11 @@ defmodule ExUnit.CaptureServer do
     end
   end
 
-  defp maybe_add_console(refs, status) do
-    if status == :ok and map_size(refs) == 0 do
-      Logger.add_backend(:console, flush: true)
-    end
+  defp maybe_add_console(refs, {:ok, %{module: module} = config}) when map_size(refs) == 0 do
+    :logger.add_handler(:default, module, config)
+  end
+
+  defp maybe_add_console(_refs, _config) do
+    :ok
   end
 end

lib/ex_unit/test/ex_unit/capture_log_test.exs

@@ -4,14 +4,8 @@ defmodule ExUnit.CaptureLogTest do
   use ExUnit.Case
 
   require Logger
-
   import ExUnit.CaptureLog
 
-  setup_all do
-    :ok = Logger.remove_backend(:console)
-    on_exit(fn -> Logger.add_backend(:console, flush: true) end)
-  end
-
   test "no output" do
     assert capture_log(fn -> nil end) == ""
   end
@@ -96,7 +90,7 @@ defmodule ExUnit.CaptureLogTest do
 
   defp wait_capture_removal() do
     case :gen_event.which_handlers(Logger) do
-      [Logger.Config] ->
+      [Logger.Backends.Config] ->
         :ok
 
       _otherwise ->

lib/ex_unit/test/ex_unit_test.exs

@@ -316,14 +316,8 @@ defmodule ExUnitTest do
   test "log capturing" do
     defmodule LogCapturingTest do
       use ExUnit.Case
-
       require Logger
 
-      setup_all do
-        :ok = Logger.remove_backend(:console)
-        on_exit(fn -> Logger.add_backend(:console, flush: true) end)
-      end
-
       @tag :capture_log
       test "one" do
         Logger.debug("one")
@@ -341,18 +335,12 @@ defmodule ExUnitTest do
         Logger.debug("three")
         assert 1 == 2
       end
-
-      test "four" do
-        Logger.debug("four")
-        assert 1 == 2
-      end
     end
 
     output = capture_io(&ExUnit.run/0)
-    assert output =~ "[debug] two\n"
     refute output =~ "[debug] one\n"
+    assert output =~ "[debug] two\n"
     assert output =~ "[debug] three\n"
-    refute output =~ "[debug] four\n"
   end
 
   test "supports multi errors" do