all: replace log15 with slog (#28187)

This PR replaces Geth's logger package (a fork of [log15](https://github.com/inconshreveable/log15)) with an implementation using slog, a logging library included as part of the Go standard library as of Go1.21.

Main changes are as follows:
* removes any log handlers that were unused in the Geth codebase.
* Json, logfmt, and terminal formatters are now slog handlers.
* Verbosity level constants are changed to match slog constant values.  Internal translation is done to make this opaque to the user and backwards compatible with existing `--verbosity` and `--vmodule` options.
* `--log.backtraceat` and `--log.debug` are removed.

The external-facing API is largely the same as the existing Geth logger.  Logger method signatures remain unchanged.

A small semantic difference is that a `Handler` can only be set once per `Logger` and not changed dynamically.  This just means that a new logger must be instantiated every time the handler of the root logger is changed.

----
For users of the `go-ethereum/log` module. If you were using this module for your own project, you will need to change the initialization. If you previously did 
```golang
log.Root().SetHandler(log.LvlFilterHandler(log.LvlInfo, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
```
You now instead need to do 
```golang
log.SetDefault(log.NewLogger(log.NewTerminalHandlerWithLevel(os.Stderr, log.LevelInfo, true)))
```
See more about reasoning here: https://github.com/ethereum/go-ethereum/issues/28558#issuecomment-1820606613

p2p/simulations/adapters/exec.go

@@ -41,6 +41,7 @@ import (
 	"github.com/ethereum/go-ethereum/p2p/enode"
 	"github.com/ethereum/go-ethereum/rpc"
 	"github.com/gorilla/websocket"
+	"golang.org/x/exp/slog"
 )
 
 func init() {
@@ -375,9 +376,11 @@ type execNodeConfig struct {
 
 func initLogging() {
 	// Initialize the logging by default first.
-	glogger := log.NewGlogHandler(log.StreamHandler(os.Stderr, log.LogfmtFormat()))
-	glogger.Verbosity(log.LvlInfo)
-	log.Root().SetHandler(glogger)
+	var innerHandler slog.Handler
+	innerHandler = slog.NewTextHandler(os.Stderr, nil)
+	glogger := log.NewGlogHandler(innerHandler)
+	glogger.Verbosity(log.LevelInfo)
+	log.SetDefault(log.NewLogger(glogger))
 
 	confEnv := os.Getenv(envNodeConfig)
 	if confEnv == "" {
@@ -395,14 +398,15 @@ func initLogging() {
 		}
 		writer = logWriter
 	}
-	var verbosity = log.LvlInfo
-	if conf.Node.LogVerbosity <= log.LvlTrace && conf.Node.LogVerbosity >= log.LvlCrit {
-		verbosity = conf.Node.LogVerbosity
+	var verbosity = log.LevelInfo
+	if conf.Node.LogVerbosity <= log.LevelTrace && conf.Node.LogVerbosity >= log.LevelCrit {
+		verbosity = log.FromLegacyLevel(int(conf.Node.LogVerbosity))
 	}
 	// Reinitialize the logger
-	glogger = log.NewGlogHandler(log.StreamHandler(writer, log.TerminalFormat(true)))
+	innerHandler = log.NewTerminalHandler(writer, true)
+	glogger = log.NewGlogHandler(innerHandler)
 	glogger.Verbosity(verbosity)
-	log.Root().SetHandler(glogger)
+	log.SetDefault(log.NewLogger(glogger))
 }
 
 // execP2PNode starts a simulation node when the current binary is executed with

p2p/simulations/adapters/types.go

@@ -34,6 +34,7 @@ import (
 	"github.com/ethereum/go-ethereum/p2p/enr"
 	"github.com/ethereum/go-ethereum/rpc"
 	"github.com/gorilla/websocket"
+	"golang.org/x/exp/slog"
 )
 
 // Node represents a node in a simulation network which is created by a
@@ -129,7 +130,7 @@ type NodeConfig struct {
 	// LogVerbosity is the log verbosity of the p2p node at runtime.
 	//
 	// The default verbosity is INFO.
-	LogVerbosity log.Lvl
+	LogVerbosity slog.Level
 }
 
 // nodeConfigJSON is used to encode and decode NodeConfig as JSON by encoding
@@ -197,7 +198,7 @@ func (n *NodeConfig) UnmarshalJSON(data []byte) error {
 	n.Port = confJSON.Port
 	n.EnableMsgEvents = confJSON.EnableMsgEvents
 	n.LogFile = confJSON.LogFile
-	n.LogVerbosity = log.Lvl(confJSON.LogVerbosity)
+	n.LogVerbosity = slog.Level(confJSON.LogVerbosity)
 
 	return nil
 }

p2p/simulations/examples/ping-pong.go

@@ -41,7 +41,7 @@ func main() {
 	flag.Parse()
 
 	// set the log level to Trace
-	log.Root().SetHandler(log.LvlFilterHandler(log.LvlTrace, log.StreamHandler(os.Stderr, log.TerminalFormat(false))))
+	log.SetDefault(log.NewLogger(log.NewTerminalHandlerWithLevel(os.Stderr, log.LevelTrace, false)))
 
 	// register a single ping-pong service
 	services := map[string]adapters.LifecycleConstructor{

p2p/simulations/http_test.go

@@ -37,14 +37,14 @@ import (
 	"github.com/ethereum/go-ethereum/p2p/simulations/adapters"
 	"github.com/ethereum/go-ethereum/rpc"
 	"github.com/mattn/go-colorable"
+	"golang.org/x/exp/slog"
 )
 
 func TestMain(m *testing.M) {
 	loglevel := flag.Int("loglevel", 2, "verbosity of logs")
 
 	flag.Parse()
-	log.PrintOrigins(true)
-	log.Root().SetHandler(log.LvlFilterHandler(log.Lvl(*loglevel), log.StreamHandler(colorable.NewColorableStderr(), log.TerminalFormat(true))))
+	log.SetDefault(log.NewLogger(log.NewTerminalHandlerWithLevel(colorable.NewColorableStderr(), slog.Level(*loglevel), true)))
 	os.Exit(m.Run())
 }