internal/witcli, wit/logging: add basic Logger type

internal/witcli/logger.go

@@ -0,0 +1,18 @@
+package witcli
+
+import (
+	"os"
+
+	"github.com/bytecodealliance/wasm-tools-go/wit/logging"
+)
+
+// Logger returns a [logging.Logger] that outputs to stdout.
+func Logger(verbose, debug bool) logging.Logger {
+	level := logging.LevelWarn
+	if debug {
+		level = logging.LevelDebug
+	} else if verbose {
+		level = logging.LevelInfo
+	}
+	return logging.NewLogger(os.Stderr, level)
+}

wit/logging/logging.go

@@ -0,0 +1,91 @@
+package logging
+
+import (
+	"io"
+	"log"
+	"math"
+)
+
+// Level represents a logging level, identical to [slog.Level].
+type Level int
+
+const (
+	LevelDebug Level = -4
+	LevelInfo  Level = 0
+	LevelWarn  Level = 4
+	LevelError Level = 8
+	LevelNever Level = math.MaxInt
+)
+
+// Logger represents a simple logging interface.
+type Logger interface {
+	// Level returns the current logging level for this Logger.
+	Level() Level
+
+	// Logf logs a message with a logging level.
+	Logf(level Level, format string, v ...any)
+
+	// Debugf logs a message with level debug.
+	Debugf(format string, v ...any)
+
+	// Infof logs a message with level info.
+	Infof(format string, v ...any)
+
+	// Printf is an alias for Infof.
+	Printf(format string, v ...any)
+
+	// Warnf logs a message with level warn.
+	Warnf(format string, v ...any)
+
+	// Errorf logs a message with level error.
+	Errorf(format string, v ...any)
+}
+
+// DiscardLogger returns a logger that discards all output.
+func DiscardLogger() Logger {
+	return &logger{level: LevelNever}
+}
+
+// NewLogger returns a new leveled logger that writes to out.
+func NewLogger(out io.Writer, level Level) Logger {
+	return &logger{
+		level:  level,
+		logger: log.New(out, "", 0),
+	}
+}
+
+type logger struct {
+	level  Level
+	logger *log.Logger
+}
+
+func (l *logger) Level() Level {
+	return l.level
+}
+
+func (l *logger) Logf(level Level, format string, v ...any) {
+	if l.level > level || l.logger == nil {
+		return
+	}
+	l.logger.Printf(format, v...)
+}
+
+func (l *logger) Debugf(format string, v ...any) {
+	l.Logf(LevelDebug, format, v...)
+}
+
+func (l *logger) Infof(format string, v ...any) {
+	l.Logf(LevelInfo, format, v...)
+}
+
+func (l *logger) Printf(format string, v ...any) {
+	l.Logf(LevelInfo, format, v...)
+}
+
+func (l *logger) Warnf(format string, v ...any) {
+	l.Logf(LevelWarn, format, v...)
+}
+
+func (l *logger) Errorf(format string, v ...any) {
+	l.Logf(LevelError, format, v...)
+}