sort: show warning when sort is not supported

Use the capabilities returned by the backend to check whether sort is
implemented when the user tries to use the sort command. Print a warning
to the log when a sort request is silently dropped by the backend.

Suggested-by: |cos|
Signed-off-by: Koni Marti <koni.marti@gmail.com>
Acked-by: Robin Jarry <robin@jarry.cc>

commands/account/sort.go

@@ -72,6 +72,12 @@ func (Sort) Execute(aerc *widgets.Aerc, args []string) error {
 		return errors.New("Messages still loading.")
 	}
 
+	if c := store.Capabilities(); c != nil {
+		if !c.Sort {
+			return errors.New("Sorting is not available for this backend.")
+		}
+	}
+
 	var err error
 	var sortCriteria []*types.SortCriterion
 	if len(args[1:]) == 0 {