fix: lazy init default logger (#111)

* fix: lazy init default logger

The default logger will try to query background et al on startup, which
might conflict with other libs trying to query it too.

It's easily reproducible with some of our tools that use the log
package, e.g., VHS:

```sh
faketty vhs --help
```

It slows down the program quite a bit, and print some ansi escape
sequences as well.

This patch changes it so it only inits the default logger when/if the
default logger is used.

Per my testing, it seems to fix the original issue.

* fix: var name

context.go

@@ -14,7 +14,7 @@ func FromContext(ctx context.Context) *Logger {
 	if logger, ok := ctx.Value(ContextKey).(*Logger); ok {
 		return logger
 	}
-	return defaultLogger
+	return Default()
 }
 
 type contextKey struct{ string }

pkg.go

@@ -17,11 +17,19 @@ var (
 	registry = sync.Map{}
 
 	// defaultLogger is the default global logger instance.
-	defaultLogger = NewWithOptions(os.Stderr, Options{ReportTimestamp: true})
+	defaultLoggerOnce sync.Once
+	defaultLogger     *Logger
 )
 
 // Default returns the default logger. The default logger comes with timestamp enabled.
 func Default() *Logger {
+	defaultLoggerOnce.Do(func() {
+		if defaultLogger != nil {
+			// already set via SetDefault.
+			return
+		}
+		defaultLogger = NewWithOptions(os.Stderr, Options{ReportTimestamp: true})
+	})
 	return defaultLogger
 }
 
@@ -74,165 +82,165 @@ func NewWithOptions(w io.Writer, o Options) *Logger {
 
 // SetReportTimestamp sets whether to report timestamp for the default logger.
 func SetReportTimestamp(report bool) {
-	defaultLogger.SetReportTimestamp(report)
+	Default().SetReportTimestamp(report)
 }
 
 // SetReportCaller sets whether to report caller location for the default logger.
 func SetReportCaller(report bool) {
-	defaultLogger.SetReportCaller(report)
+	Default().SetReportCaller(report)
 }
 
 // SetLevel sets the level for the default logger.
 func SetLevel(level Level) {
-	defaultLogger.SetLevel(level)
+	Default().SetLevel(level)
 }
 
 // GetLevel returns the level for the default logger.
 func GetLevel() Level {
-	return defaultLogger.GetLevel()
+	return Default().GetLevel()
 }
 
 // SetTimeFormat sets the time format for the default logger.
 func SetTimeFormat(format string) {
-	defaultLogger.SetTimeFormat(format)
+	Default().SetTimeFormat(format)
 }
 
 // SetTimeFunction sets the time function for the default logger.
 func SetTimeFunction(f TimeFunction) {
-	defaultLogger.SetTimeFunction(f)
+	Default().SetTimeFunction(f)
 }
 
 // SetOutput sets the output for the default logger.
 func SetOutput(w io.Writer) {
-	defaultLogger.SetOutput(w)
+	Default().SetOutput(w)
 }
 
 // SetFormatter sets the formatter for the default logger.
 func SetFormatter(f Formatter) {
-	defaultLogger.SetFormatter(f)
+	Default().SetFormatter(f)
 }
 
 // SetCallerFormatter sets the caller formatter for the default logger.
 func SetCallerFormatter(f CallerFormatter) {
-	defaultLogger.SetCallerFormatter(f)
+	Default().SetCallerFormatter(f)
 }
 
 // SetCallerOffset sets the caller offset for the default logger.
 func SetCallerOffset(offset int) {
-	defaultLogger.SetCallerOffset(offset)
+	Default().SetCallerOffset(offset)
 }
 
 // SetPrefix sets the prefix for the default logger.
 func SetPrefix(prefix string) {
-	defaultLogger.SetPrefix(prefix)
+	Default().SetPrefix(prefix)
 }
 
 // SetColorProfile force sets the underlying Lip Gloss renderer color profile
 // for the TextFormatter.
 func SetColorProfile(profile termenv.Profile) {
-	defaultLogger.SetColorProfile(profile)
+	Default().SetColorProfile(profile)
 }
 
 // SetStyles sets the logger styles for the TextFormatter.
 func SetStyles(s *Styles) {
-	defaultLogger.SetStyles(s)
+	Default().SetStyles(s)
 }
 
 // GetPrefix returns the prefix for the default logger.
 func GetPrefix() string {
-	return defaultLogger.GetPrefix()
+	return Default().GetPrefix()
 }
 
 // With returns a new logger with the given keyvals.
 func With(keyvals ...interface{}) *Logger {
-	return defaultLogger.With(keyvals...)
+	return Default().With(keyvals...)
 }
 
 // WithPrefix returns a new logger with the given prefix.
 func WithPrefix(prefix string) *Logger {
-	return defaultLogger.WithPrefix(prefix)
+	return Default().WithPrefix(prefix)
 }
 
 // Helper marks the calling function as a helper
 // and skips it for source location information.
 // It's the equivalent of testing.TB.Helper().
 func Helper() {
-	defaultLogger.helper(1)
+	Default().helper(1)
 }
 
 // Log logs a message with the given level.
 func Log(level Level, msg interface{}, keyvals ...interface{}) {
-	defaultLogger.Log(level, msg, keyvals...)
+	Default().Log(level, msg, keyvals...)
 }
 
 // Debug logs a debug message.
 func Debug(msg interface{}, keyvals ...interface{}) {
-	defaultLogger.Log(DebugLevel, msg, keyvals...)
+	Default().Log(DebugLevel, msg, keyvals...)
 }
 
 // Info logs an info message.
 func Info(msg interface{}, keyvals ...interface{}) {
-	defaultLogger.Log(InfoLevel, msg, keyvals...)
+	Default().Log(InfoLevel, msg, keyvals...)
 }
 
 // Warn logs a warning message.
 func Warn(msg interface{}, keyvals ...interface{}) {
-	defaultLogger.Log(WarnLevel, msg, keyvals...)
+	Default().Log(WarnLevel, msg, keyvals...)
 }
 
 // Error logs an error message.
 func Error(msg interface{}, keyvals ...interface{}) {
-	defaultLogger.Log(ErrorLevel, msg, keyvals...)
+	Default().Log(ErrorLevel, msg, keyvals...)
 }
 
 // Fatal logs a fatal message and exit.
 func Fatal(msg interface{}, keyvals ...interface{}) {
-	defaultLogger.Log(FatalLevel, msg, keyvals...)
+	Default().Log(FatalLevel, msg, keyvals...)
 	os.Exit(1)
 }
 
 // Print logs a message with no level.
 func Print(msg interface{}, keyvals ...interface{}) {
-	defaultLogger.Log(noLevel, msg, keyvals...)
+	Default().Log(noLevel, msg, keyvals...)
 }
 
 // Logf logs a message with formatting and level.
 func Logf(level Level, format string, args ...interface{}) {
-	defaultLogger.Logf(level, format, args...)
+	Default().Logf(level, format, args...)
 }
 
 // Debugf logs a debug message with formatting.
 func Debugf(format string, args ...interface{}) {
-	defaultLogger.Log(DebugLevel, fmt.Sprintf(format, args...))
+	Default().Log(DebugLevel, fmt.Sprintf(format, args...))
 }
 
 // Infof logs an info message with formatting.
 func Infof(format string, args ...interface{}) {
-	defaultLogger.Log(InfoLevel, fmt.Sprintf(format, args...))
+	Default().Log(InfoLevel, fmt.Sprintf(format, args...))
 }
 
 // Warnf logs a warning message with formatting.
 func Warnf(format string, args ...interface{}) {
-	defaultLogger.Log(WarnLevel, fmt.Sprintf(format, args...))
+	Default().Log(WarnLevel, fmt.Sprintf(format, args...))
 }
 
 // Errorf logs an error message with formatting.
 func Errorf(format string, args ...interface{}) {
-	defaultLogger.Log(ErrorLevel, fmt.Sprintf(format, args...))
+	Default().Log(ErrorLevel, fmt.Sprintf(format, args...))
 }
 
 // Fatalf logs a fatal message with formatting and exit.
 func Fatalf(format string, args ...interface{}) {
-	defaultLogger.Log(FatalLevel, fmt.Sprintf(format, args...))
+	Default().Log(FatalLevel, fmt.Sprintf(format, args...))
 	os.Exit(1)
 }
 
 // Printf logs a message with formatting and no level.
 func Printf(format string, args ...interface{}) {
-	defaultLogger.Log(noLevel, fmt.Sprintf(format, args...))
+	Default().Log(noLevel, fmt.Sprintf(format, args...))
 }
 
 // StandardLog returns a standard logger from the default logger.
 func StandardLog(opts ...StandardLogOptions) *log.Logger {
-	return defaultLogger.StandardLog(opts...)
+	return Default().StandardLog(opts...)
 }