switch from hslogger to purpose-built Utility.Debug

This uses a DebugSelector, rather than debug levels, which will allow
for a later option like --debug-from=Process to only
see debuging about running processes.

The module name that contains the thing being debugged is used as the
DebugSelector (in most cases; does not need to be a hard and fast rule).
Debug calls were changed to add that. hslogger did not display
that first parameter to debugM, but the DebugSelector does get
displayed.

Also fastDebug will allow doing debugging in places that are used in
tight loops, with the DebugSelector coming from the Annex Reader
essentially for free. Not done yet.

Messages.hs

@@ -1,6 +1,6 @@
 {- git-annex output messages
  -
- - Copyright 2010-2020 Joey Hess <id@joeyh.name>
+ - Copyright 2010-2021 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -43,7 +43,6 @@ module Messages (
 	setupConsole,
 	enableDebugOutput,
 	disableDebugOutput,
-	debugEnabled,
 	commandProgressDisabled,
 	jsonOutputEnabled,
 	outputMessage,
@@ -52,10 +51,6 @@ module Messages (
 	mkPrompter,
 ) where
 
-import System.Log.Logger
-import System.Log.Formatter
-import System.Log.Handler (setFormatter)
-import System.Log.Handler.Simple
 import Control.Concurrent
 import Control.Monad.IO.Class
 import qualified Data.ByteString as S
@@ -69,6 +64,7 @@ import Types.Command (StartMessage(..), SeekInput)
 import Types.Transfer (transferKey)
 import Messages.Internal
 import Messages.Concurrent
+import Utility.Debug
 import Annex.Concurrent.Utility
 import qualified Messages.JSON as JSON
 import qualified Annex
@@ -254,31 +250,33 @@ showRaw s = outputMessage JSON.none (s <> "\n")
 
 setupConsole :: IO ()
 setupConsole = do
-	s <- setFormatter
-		<$> streamHandler stderr DEBUG
-		<*> pure preciseLogFormatter
-	updateGlobalLogger rootLoggerName (setLevel NOTICE . setHandlers [s])
+	dd <- debugDisplayer
+	configureDebug dd (DebugSelector (\_ -> False))
 	{- Force output to be line buffered. This is normally the case when
 	 - it's connected to a terminal, but may not be when redirected to
 	 - a file or a pipe. -}
 	hSetBuffering stdout LineBuffering
 	hSetBuffering stderr LineBuffering
 
-{- Log formatter with precision into fractions of a second. -}
-preciseLogFormatter :: LogFormatter a
-preciseLogFormatter = tfLogFormatter "%F %X%Q" "[$time] $msg"
-
 enableDebugOutput :: IO ()
-enableDebugOutput = updateGlobalLogger rootLoggerName $ setLevel DEBUG
+enableDebugOutput = do
+	dd <- debugDisplayer
+	configureDebug dd (DebugSelector (\_ -> True))
 
 disableDebugOutput :: IO ()
-disableDebugOutput = updateGlobalLogger rootLoggerName $ setLevel NOTICE
+disableDebugOutput = do
+	dd <- debugDisplayer
+	configureDebug dd (DebugSelector (\_ -> False))
 
-{- Checks if debugging is enabled. -}
-debugEnabled :: IO Bool
-debugEnabled = do
-	l <- getRootLogger
-	return $ getLevel l <= Just DEBUG
+debugDisplayer :: IO (S.ByteString -> IO ())
+debugDisplayer = do
+	-- Debug output will get mixed in with any other output
+	-- made by git-annex, but use a lock to prevent two debug lines
+	-- that are displayed at the same time from mixing together.
+	lock <- newMVar ()
+	return $ \s -> withMVar lock $ \() -> do
+		S.putStr (s <> "\n")
+		hFlush stderr
 
 {- Should commands that normally output progress messages have that
  - output disabled? -}