make unwatching when we hit "too many open files" deterministic

Also clarify in the log message that it's the number of directories watched,
not number of files watched. We don't actually know the number of files watched
since we only add directories to the watcher. On kqueue (macOS) that translates
to one file descriptor used per directory and one file decriptor used per file,
while on inotify (Linux) only needs one file descriptor per directory
(https://news.ycombinator.com/item?id=9063910).

Author: bokwoon95

wgo_cmd.go

@@ -14,6 +14,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"runtime"
+	"sort"
 	"strconv"
 	"strings"
 	"sync"
@@ -657,14 +658,15 @@ func (wgoCmd *WgoCmd) addDirsRecursively(watcher *fsnotify.Watcher, dir string)
 				if err != nil {
 					if errors.Is(err, syscall.EMFILE) {
 						watchList := watcher.WatchList()
+						sort.Strings(watchList)
 						unwatchCount := 256
 						if unwatchCount > len(watchList)/2 {
 							unwatchCount = int(0.2 * float64(len(watchList)))
 						}
 						for i := len(watchList) - 1; i >= unwatchCount; i-- {
 							watcher.Remove(watchList[i])
 						}
-						wgoCmd.Logger.Printf("ERROR too many open files (%d open files), not watching any more\n", len(watchList))
+						wgoCmd.Logger.Printf("ERROR too many open files (%d directories), not watching any more\n", len(watchList))
 						return fs.SkipAll
 					}
 					return fs.SkipDir
@@ -685,14 +687,15 @@ func (wgoCmd *WgoCmd) addDirsRecursively(watcher *fsnotify.Watcher, dir string)
 		if err != nil {
 			if errors.Is(err, syscall.EMFILE) {
 				watchList := watcher.WatchList()
+				sort.Strings(watchList)
 				unwatchCount := 256
 				if unwatchCount > len(watchList)/2 {
 					unwatchCount = int(0.2 * float64(len(watchList)))
 				}
 				for i := len(watchList) - 1; i >= unwatchCount; i-- {
 					watcher.Remove(watchList[i])
 				}
-				wgoCmd.Logger.Printf("ERROR too many open files (%d open files), not watching any more\n", len(watchList))
+				wgoCmd.Logger.Printf("ERROR too many open files (%d directories), not watching any more\n", len(watchList))
 				return fs.SkipAll
 			}
 			return fs.SkipDir