refactor(syncer): filter hidden directories before the IsRepo check

ListDirs used `strings.Index(f.Name(), ".") != 0` to drop hidden
entries — a slightly indirect way of asking the same question that
strings.HasPrefix asks more idiomatically. Switch to HasPrefix.

While here, reorder the filter chain so the cheap HasPrefix check
runs before IsRepo. IsRepo now performs an os.Stat per call, so
short-circuiting on hidden directories avoids a syscall for each
.something entry in the parent. Rewrite the conjunction as a
sequence of early-continue guards so the intent of each step reads
top-down.

Pure refactor — for non-empty names, "name starts with ." and
"strings.Index(name, \".\") == 0" are exactly the same predicate, so
ListDirs returns the same set of paths it always did.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: takecy

syncer/dir.go

@@ -6,7 +6,10 @@ import (
 	"strings"
 )
 
-// ListDirs returns target directories
+// ListDirs returns the names of direct child directories that look like git
+// repositories, skipping hidden entries (those whose name starts with ".").
+// The order matters for efficiency: HasPrefix is a cheap string check, so we
+// filter out hidden directories before paying the os.Stat cost in IsRepo.
 func ListDirs() (dirs []string, err error) {
 	files, err := os.ReadDir("./")
 	if err != nil {
@@ -15,11 +18,17 @@ func ListDirs() (dirs []string, err error) {
 
 	dirs = make([]string, 0, len(files))
 	for _, f := range files {
-		if f.IsDir() && IsRepo(f.Name()) && strings.Index(f.Name(), ".") != 0 {
-			dirs = append(dirs, f.Name())
+		if !f.IsDir() {
+			continue
 		}
+		if strings.HasPrefix(f.Name(), ".") {
+			continue
+		}
+		if !IsRepo(f.Name()) {
+			continue
+		}
+		dirs = append(dirs, f.Name())
 	}
-
 	return
 }