lib/fs: Introduce walkfs debug facility (#4712)

lib/fs/filesystem.go

@@ -160,7 +160,7 @@ func NewFilesystem(fsType FilesystemType, uri string) Filesystem {
 	var fs Filesystem
 	switch fsType {
 	case FilesystemTypeBasic:
-		fs = NewWalkFilesystem(newBasicFilesystem(uri))
+		fs = newBasicFilesystem(uri)
 	default:
 		l.Debugln("Unknown filesystem", fsType, uri)
 		fs = &errorFilesystem{
@@ -170,10 +170,15 @@ func NewFilesystem(fsType FilesystemType, uri string) Filesystem {
 		}
 	}
 
-	if l.ShouldDebug("fs") {
-		fs = &logFilesystem{fs}
+	if l.ShouldDebug("walkfs") {
+		return NewWalkFilesystem(&logFilesystem{fs})
 	}
-	return fs
+
+	if l.ShouldDebug("fs") {
+		return &logFilesystem{NewWalkFilesystem(fs)}
+	}
+
+	return NewWalkFilesystem(fs)
 }
 
 // IsInternal returns true if the file, as a path relative to the folder