Add index option to change-tab

This allows selection of a tab using its index. It attempts to parse the
given argument as a number, if it fails then it uses it as a name.

Also supports relative indexes using prefixed + or -.

commands/ct.go

@@ -3,6 +3,7 @@ package commands
 import (
 	"errors"
 	"fmt"
+	"strconv"
 	"strings"
 
 	"git.sr.ht/~sircmpwn/aerc/widgets"
@@ -35,16 +36,34 @@ func (_ ChangeTab) Execute(aerc *widgets.Aerc, args []string) error {
 	if len(args) != 2 {
 		return errors.New(fmt.Sprintf("Usage: %s <tab>", args[0]))
 	}
-
 	if args[1] == "-" {
 		ok := aerc.SelectPreviousTab()
 		if !ok {
 			return errors.New("No previous tab to return to")
 		}
 	} else {
-		ok := aerc.SelectTab(args[1])
-		if !ok {
-			return errors.New("No tab with that name")
+		n, err := strconv.Atoi(args[1])
+		if err == nil {
+			if strings.HasPrefix(args[1], "+") {
+				for ; n > 0; n-- {
+					aerc.NextTab()
+				}
+			} else if strings.HasPrefix(args[1], "-") {
+				for ; n < 0; n++ {
+					aerc.PrevTab()
+				}
+			} else {
+				ok := aerc.SelectTabIndex(n)
+				if !ok {
+					return errors.New(
+						"No tab with that index")
+				}
+			}
+		} else {
+			ok := aerc.SelectTab(args[1])
+			if !ok {
+				return errors.New("No tab with that name")
+			}
 		}
 	}
 	return nil

doc/aerc.1.scd

@@ -36,8 +36,10 @@ These commands work in any context.
 *cd* <directory>
 	Changes aerc's current working directory.
 
-*change-tab* <tabname>
-	Changes the focus to the tab with the name.
+*change-tab* [+|-]<tab name or index>
+	Changes the focus to the tab with the given name. If a number is given,
+	it's treated as an index. If + or - is specified, the number is interpreted
+	as a delta from the selected tab.
 
 *exec* <command...>
 	Executes an arbitrary command in the background.

widgets/aerc.go

@@ -268,6 +268,16 @@ func (aerc *Aerc) SelectTab(name string) bool {
 	return false
 }
 
+func (aerc *Aerc) SelectTabIndex(index int) bool {
+	for i, _ := range aerc.tabs.Tabs {
+		if i == index {
+			aerc.tabs.Select(i)
+			return true
+		}
+	}
+	return false
+}
+
 func (aerc *Aerc) TabNames() []string {
 	var names []string
 	for _, tab := range aerc.tabs.Tabs {