shell completion for wwctl voerlay build

internal/app/wwctl/overlay/build/root.go

@@ -1,6 +1,12 @@
 package build
 
-import "github.com/spf13/cobra"
+import (
+	"log"
+
+	"github.com/hpcng/warewulf/internal/pkg/node"
+	"github.com/hpcng/warewulf/internal/pkg/overlay"
+	"github.com/spf13/cobra"
+)
 
 var (
 	baseCmd = &cobra.Command{
@@ -9,6 +15,19 @@ var (
 		Short:                 "(Re)build node overlays",
 		Long:                  "This command builds overlays for given nodes.",
 		RunE:                  CobraRunE,
+		ValidArgsFunction: func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+			if len(args) != 0 {
+				return nil, cobra.ShellCompDirectiveNoFileComp
+			}
+
+			nodeDB, _ := node.New()
+			nodes, _ := nodeDB.FindAllNodes()
+			var node_names []string
+			for _, node := range nodes {
+				node_names = append(node_names, node.Id.Get())
+			}
+			return node_names, cobra.ShellCompDirectiveNoFileComp
+		},
 	}
 	BuildHost   bool
 	BuildNodes  bool
@@ -20,6 +39,12 @@ func init() {
 	baseCmd.PersistentFlags().BoolVarP(&BuildHost, "host", "H", false, "Build overlays only for the host")
 	baseCmd.PersistentFlags().BoolVarP(&BuildNodes, "nodes", "N", false, "Build overlays only for the nodes")
 	baseCmd.PersistentFlags().StringVarP(&OverlayName, "overlay", "O", "", "Build only specific overlay")
+	if err := baseCmd.RegisterFlagCompletionFunc("overlay", func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+		list, _ := overlay.FindOverlays()
+		return list, cobra.ShellCompDirectiveNoFileComp
+	}); err != nil {
+		log.Println(err)
+	}
 	baseCmd.PersistentFlags().StringVarP(&OverlayDir, "output", "o", "", `Do not create an overlay image, for distribution but write to
 	the given directory. An overlay must also be ge given to use this option.`)