Add filesystem completions for :attach and :cd

Tab-completions now cycle through filesystem paths when using :attach or
:cd commands.

commands/cd.go

@@ -3,6 +3,7 @@ package commands
 import (
 	"errors"
 	"os"
+	"strings"
 
 	"git.sr.ht/~sircmpwn/aerc/widgets"
 	"github.com/mitchellh/go-homedir"
@@ -23,7 +24,22 @@ func (_ ChangeDirectory) Aliases() []string {
 }
 
 func (_ ChangeDirectory) Complete(aerc *widgets.Aerc, args []string) []string {
-	return nil
+	path := ""
+	if len(args) >= 1 {
+		path = args[0]
+	}
+
+	completions := CompletePath(path)
+
+	var dirs []string
+	for _, c := range completions {
+		// filter out non-directories
+		if strings.HasSuffix(c, "/") {
+			dirs = append(dirs, c)
+		}
+	}
+
+	return dirs
 }
 
 func (_ ChangeDirectory) Execute(aerc *widgets.Aerc, args []string) error {

commands/compose/attach.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"time"
 
+	"git.sr.ht/~sircmpwn/aerc/commands"
 	"git.sr.ht/~sircmpwn/aerc/widgets"
 	"github.com/gdamore/tcell"
 	"github.com/mitchellh/go-homedir"
@@ -21,7 +22,12 @@ func (_ Attach) Aliases() []string {
 }
 
 func (_ Attach) Complete(aerc *widgets.Aerc, args []string) []string {
-	return nil
+	path := ""
+	if len(args) >= 1 {
+		path = args[0]
+	}
+
+	return commands.CompletePath(path)
 }
 
 func (_ Attach) Execute(aerc *widgets.Aerc, args []string) error {