refactor(logging): replace the logrus backend with log/slog (#1304)

Log through `log/slog`, with a console `slog.Handler` that writes the text the runner has always written (sorted `key=value` fields on a plain stream, a colored prefix on a terminal), so nothing changes for users. I compared its output byte for byte with logrus's `TextFormatter` over plain, colored, timestamped and caller cases.

Why not `slog.TextHandler`: its output differs from what users and their log parsers see today, and `ReplaceAttr` cannot close the gap.
- level is `WARN` where logrus wrote `warning`, and time has milliseconds and no quotes
- fields keep call order instead of being sorted
- the caller is one `source=` key, where the runner writes `func=` and `file=` (reshaped by `callPrettyfier`), and `ReplaceAttr` returns a single attribute
- no colored prefix on a terminal
- no hook to rewrite a whole formatted line, which the process-wide secret masking relies on

Libraries that log through logrus's global logger (the workflow model, the Docker client) are forwarded to the process-wide logger, so they keep following its level, format and secret masking. This is why logrus stays in `go.mod`.

Stacked on https://gitea.com/gitea/runner/pulls/1303.

Assisted-by: Codet
Co-authored-by: bircni <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1304
Reviewed-by: bircni <[email protected]>

act/common/logging/global.go

@@ -5,15 +5,32 @@ package logging
 
 import (
 	"io"
+	"log/slog"
+	"os"
+	"runtime"
 	"sync/atomic"
 
 	"github.com/sirupsen/logrus"
 )
 
-var std atomic.Pointer[Logger]
+// TextOptions describes how the process-wide Logger writes a record as text.
+type TextOptions struct {
+	DisableColors    bool
+	DisableTimestamp bool
+	FullTimestamp    bool
+	// CallerPrettyfier renames the function and file reported with a record when ReportCaller is on.
+	CallerPrettyfier func(*runtime.Frame) (function, file string)
+	// Filter rewrites each formatted line, for example to mask secrets.
+	Filter func(line []byte) []byte
+}
+
+var (
+	std      atomic.Pointer[Logger]
+	stdState = newConsole(os.Stderr)
+)
 
 func init() {
-	std.Store(New(NewLogrusHandler(logrus.StandardLogger())))
+	std.Store(New(NewSlogHandler(&consoleHandler{c: stdState})))
 }
 
 // Default returns the process-wide Logger.
@@ -21,20 +38,42 @@ func Default() *Logger { return std.Load() }
 
 // SetDefault replaces the process-wide Logger, which tests use to capture what the package
 // functions log. SetLevel, GetLevel, SetOutput and the format functions keep configuring the
-// initial logrus-backed Logger.
+// initial console Logger.
 func SetDefault(l *Logger) { std.Store(l) }
 
-// SetLevel sets the minimum level of the process-wide Logger.
-func SetLevel(level Level) { logrus.SetLevel(toLogrusLevel(level)) }
+// SetLevel sets the minimum level of the initial process-wide Logger and of what libraries log through logrus.
+func SetLevel(level Level) {
+	stdState.level.Set(slog.Level(level))
+	logrus.SetLevel(toLogrusLevel(level))
+}
 
-// GetLevel returns the minimum level of the process-wide Logger.
-func GetLevel() Level { return fromLogrusLevel(logrus.GetLevel()) }
+// GetLevel returns the minimum level of the initial process-wide Logger.
+func GetLevel() Level { return Level(stdState.level.Level()) }
 
-// SetOutput sets where the process-wide Logger writes.
-func SetOutput(w io.Writer) { logrus.SetOutput(w) }
+// SetOutput sets where the initial process-wide Logger writes.
+func SetOutput(w io.Writer) { stdState.setOutput(w) }
 
-// Output returns where the process-wide Logger writes.
-func Output() io.Writer { return logrus.StandardLogger().Out }
+// Output returns where the initial process-wide Logger writes.
+func Output() io.Writer {
+	stdState.mu.Lock()
+	defer stdState.mu.Unlock()
+	return stdState.out
+}
+
+// SetTextFormat sets the text format of the initial process-wide Logger.
+func SetTextFormat(o TextOptions) {
+	stdState.mu.Lock()
+	defer stdState.mu.Unlock()
+	stdState.opts = o
+}
+
+// SetReportCaller makes the initial process-wide Logger record where each call came from, which costs time.
+func SetReportCaller(on bool) {
+	stdState.mu.Lock()
+	defer stdState.mu.Unlock()
+	stdState.reportCaller = on
+	logrus.SetReportCaller(on)
+}
 
 func Enabled(level Level) bool { return Default().Enabled(level) }