Add custom sorting for folders

A new config options for accounts.conf (folders-sort) was added to
allow a user to choose which folders should be shown on top.
My use case was to avoid stepping into heavy, but rarely viewed folders
when cycling through other often accessed ones.

To test add this to your account.conf:

folders-sort  = INBOX,Sent,Archive

INBOX, Sent and Archive should then show at the top of your dirlist,
and all other folders should come next in alphabetical order.

config/config.go

@@ -61,6 +61,7 @@ type AccountConfig struct {
 	OutgoingCredCmd string
 	SignatureFile   string
 	SignatureCmd    string
+	FoldersSort     []string `ini:"folders-sort" delim:","`
 }
 
 type BindingConfig struct {

doc/aerc-config.5.scd

@@ -301,6 +301,12 @@ Note that many of these configuration options are written for you, such as
 
 	Default: all folders
 
+*folders-sort*
+	Specifies a comma separated list of folders to be shown at the top of the
+	list in the provided order. Remaining folders will be sorted alphabetically.
+
+	Default: none
+
 *from*
 	The default value to use for the From header in new emails. This should be
 	an RFC 5322-compatible string, such as "Your Name <you@example.org>".

widgets/dirlist.go

@@ -5,6 +5,7 @@ import (
 	"log"
 	"regexp"
 	"sort"
+	"strings"
 
 	"github.com/gdamore/tcell"
 	"github.com/mattn/go-runewidth"
@@ -61,9 +62,10 @@ func (dirlist *DirectoryList) UpdateList(done func(dirs []string)) {
 			case *types.Directory:
 				dirs = append(dirs, msg.Dir.Name)
 			case *types.Done:
-				sort.Strings(dirs)
 				dirlist.store.Update(dirs)
 				dirlist.filterDirsByFoldersConfig()
+				dirlist.sortDirsByFoldersSortConfig()
+				dirlist.store.Update(dirlist.dirs)
 				dirlist.spinner.Stop()
 				dirlist.Invalidate()
 				if done != nil {
@@ -94,6 +96,7 @@ func (dirlist *DirectoryList) Select(name string) {
 					dirlist.dirs = append(dirlist.dirs, dirlist.selected)
 				}
 				sort.Strings(dirlist.dirs)
+				dirlist.sortDirsByFoldersSortConfig()
 			}
 			dirlist.Invalidate()
 		})
@@ -261,7 +264,7 @@ func (dirlist *DirectoryList) Clicked(x int, y int) (string, bool) {
 }
 
 func (dirlist *DirectoryList) NextPrev(delta int) {
-	curIdx := sort.SearchStrings(dirlist.dirs, dirlist.selected)
+	curIdx := findString(dirlist.dirs, dirlist.selected)
 	if curIdx == len(dirlist.dirs) {
 		return
 	}
@@ -297,6 +300,26 @@ func folderMatches(folder string, pattern string) bool {
 	return pattern == folder
 }
 
+// sortDirsByFoldersSortConfig sets dirlist.dirs to be sorted based on the
+// AccountConfig.FoldersSort option. Folders not included in the option
+// will be appended at the end in alphabetical order
+func (dirlist *DirectoryList) sortDirsByFoldersSortConfig() {
+	sort.Slice(dirlist.dirs, func(i, j int) bool {
+		iInFoldersSort := findString(dirlist.acctConf.FoldersSort, dirlist.dirs[i])
+		jInFoldersSort := findString(dirlist.acctConf.FoldersSort, dirlist.dirs[j])
+		if iInFoldersSort >= 0 && jInFoldersSort >= 0 {
+			return iInFoldersSort < jInFoldersSort
+		}
+		if iInFoldersSort >= 0 {
+			return true
+		}
+		if jInFoldersSort >= 0 {
+			return false
+		}
+		return strings.Compare(dirlist.dirs[i], dirlist.dirs[j]) == -1
+	})
+}
+
 // filterDirsByFoldersConfig sets dirlist.dirs to the filtered subset of the
 // dirstore, based on the AccountConfig.Folders option
 func (dirlist *DirectoryList) filterDirsByFoldersConfig() {
@@ -331,3 +354,12 @@ func (dirlist *DirectoryList) SetMsgStore(name string, msgStore *lib.MessageStor
 		dirlist.Invalidate()
 	})
 }
+
+func findString(slice []string, str string) int {
+	for i, s := range slice {
+		if str == s {
+			return i
+		}
+	}
+	return -1
+}