count dirs while reading the parent dir

This commit moves directory counting with 'dircounts' option from ui
printing to dir reading to be run asynchronously without locking the ui.
On the other side, disadvantage of this approach is that if 'dircounts'
option is changed at runtime, then directory counts may not be available
requiring a manual 'reload'. Indicators for errors are changed to '!'
instead of '?' to distinguish them from missing values.

nav.go

@@ -101,12 +101,29 @@ func readdir(path string) ([]*file, error) {
 		// i.e. directories, filenames without extensions
 		ext := filepath.Ext(fpath)
 
+		dirCount := -1
+		if lstat.IsDir() && gOpts.dircounts {
+			d, err := os.Open(fpath)
+			if err != nil {
+				dirCount = -2
+			}
+
+			names, err := d.Readdirnames(1000)
+			d.Close()
+
+			if names == nil && err != io.EOF {
+				dirCount = -2
+			} else {
+				dirCount = len(names)
+			}
+		}
+
 		files = append(files, &file{
 			FileInfo:   lstat,
 			linkState:  linkState,
 			linkTarget: linkTarget,
 			path:       fpath,
-			dirCount:   -1,
+			dirCount:   dirCount,
 			dirSize:    -1,
 			accessTime: at,
 			changeTime: ct,

ui.go

@@ -3,7 +3,6 @@ package main
 import (
 	"bytes"
 	"fmt"
-	"io"
 	"log"
 	"os"
 	"path/filepath"
@@ -287,8 +286,6 @@ func infotimefmt(t time.Time) string {
 func fileInfo(f *file, d *dir) string {
 	var info string
 
-	path := filepath.Join(d.path, f.Name())
-
 	for _, s := range gOpts.info {
 		switch s {
 		case "size":
@@ -303,23 +300,9 @@ func fileInfo(f *file, d *dir) string {
 				continue
 			}
 
-			if f.dirCount == -1 {
-				d, err := os.Open(path)
-				if err != nil {
-					f.dirCount = -2
-				}
-
-				names, err := d.Readdirnames(1000)
-				d.Close()
-
-				if names == nil && err != io.EOF {
-					f.dirCount = -2
-				} else {
-					f.dirCount = len(names)
-				}
-			}
-
 			switch {
+			case f.dirCount < -1:
+				info = fmt.Sprintf("%s    !", info)
 			case f.dirCount < 0:
 				info = fmt.Sprintf("%s    ?", info)
 			case f.dirCount < 1000: