WIP PoC dynamic shell completion for 'kubectl-argo-rollouts get rollo…

…ut [TAB]'

works toward #2015

use ValidArgsFunction from cobra to list candidates for completion: https://github.com/spf13/cobra/blob/main/shell_completions.md#dynamic-completion-of-nouns
- filtering on 'toComplete' doesn't seem necessary, at least on
  bash (most probably bash-completion handles that itself), not sure
  for the others; I could not find cobra documentation about that

use v2 of GenBashCompletion from cobra: https://github.com/spf13/cobra/blob/main/shell_completions.md#bash-completion-v2
- I chose to disable descriptions for completion (as a bash user I'm not
  used to that), but it's enabled for fish it seems, we can enable it
  if desired, I have no strong opinion on it

pkg/kubectl-argo-rollouts/cmd/completion/completion.go

@@ -54,7 +54,7 @@ func NewCmdCompletion(o *options.ArgoRolloutsOptions) *cobra.Command {
 		Run: func(cmd *cobra.Command, args []string) {
 			switch args[0] {
 			case "bash":
-				cmd.Root().GenBashCompletion(o.Out)
+				cmd.Root().GenBashCompletionV2(o.Out, false)
 			case "zsh":
 				cmd.Root().GenZshCompletion(o.Out)
 			case "fish":

pkg/kubectl-argo-rollouts/cmd/get/get_rollout.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/juju/ansiterm"
 	"github.com/spf13/cobra"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 
 	"github.com/argoproj/argo-rollouts/pkg/apiclient/rollout"
 	"github.com/argoproj/argo-rollouts/pkg/kubectl-argo-rollouts/cmd/signals"
@@ -75,6 +76,26 @@ func NewCmdGetRollout(o *options.ArgoRolloutsOptions) *cobra.Command {
 			}
 			return nil
 		},
+		ValidArgsFunction: func(c *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+			if len(args) != 0 {
+				return nil, cobra.ShellCompDirectiveNoFileComp
+			}
+			// list rollouts names
+			ctx := c.Context()
+			opts := metav1.ListOptions{}
+			rolloutIf := o.RolloutsClientset().ArgoprojV1alpha1().Rollouts(o.Namespace())
+			rolloutList, err := rolloutIf.List(ctx, opts)
+			if err != nil {
+				return []string{}, cobra.ShellCompDirectiveError
+			}
+
+			rolloutNames := make([]string, len(rolloutList.Items))
+			for i, ro := range rolloutList.Items {
+				rolloutNames[i] = ro.Name
+			}
+
+			return rolloutNames, cobra.ShellCompDirectiveNoFileComp
+		},
 	}
 	cmd.Flags().BoolVarP(&getOptions.Watch, "watch", "w", false, "Watch live updates to the rollout")
 	cmd.Flags().BoolVar(&getOptions.NoColor, "no-color", false, "Do not colorize output")