Enable shell auto completion. (opendistro-for-elasticsearch#40)

Add command to generate auto completion script for specified shell (bash/fish/zsh).

Author: VijayanB

commands/completion.go

@@ -0,0 +1,97 @@
+/*
+ * Copyright 2021 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+package commands
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+const (
+	CompletionCommandName = "completion"
+	BashShell             = "bash"
+	ZshShell              = "zsh"
+	FishShell             = "fish"
+	PowerShell            = "powershell"
+)
+
+var longText = `To enable shell autocompletion:
+
+Bash:
+
+$ source <(odfe-cli completion bash)
+
+# To enable auto completion for commands for each session, execute once:
+Linux:
+  $ odfe-cli completion bash > /etc/bash_completion.d/odfe-cli
+MacOS:
+  $ odfe-cli completion bash > /usr/local/etc/bash_completion.d/odfe-cli
+
+Zsh:
+
+# If shell completion is not already enabled in your environment you will need
+# to enable it.  You can execute the following once:
+
+$ echo "autoload -U compinit; compinit" >> ~/.zshrc
+
+# To enable auto completion for commands for each session, execute once:
+$ odfe-cli completion zsh > "${fpath[1]}/_odfe-cli"
+
+# You will need to start a new shell for this setup to take effect.
+
+Fish:
+
+$ odfe-cli completion fish | source
+
+# To enable auto completion for commands for each session, execute once:
+$ odfe-cli completion fish > ~/.config/fish/completions/odfe-cli.fish
+
+Powershell:
+
+PS> odfe-cli completion powershell | Out-String | Invoke-Expression
+
+# To enable auto completion for commands for each session, execute once:
+PS> odfe-cli completion powershell > odfe-cli.ps1
+# and source this file from your powershell profile.
+`
+
+var completionCmd = &cobra.Command{
+	Use:                   fmt.Sprintf("%s [ %s | %s | %s | %s ]", CompletionCommandName, BashShell, ZshShell, FishShell, PowerShell),
+	Short:                 "Generate completion script for your shell",
+	Long:                  longText,
+	DisableFlagsInUseLine: true,
+	ValidArgs:             []string{BashShell, ZshShell, FishShell, PowerShell},
+	Args:                  cobra.ExactValidArgs(1),
+	Run: func(cmd *cobra.Command, args []string) {
+		var err error
+		switch args[0] {
+		case BashShell:
+			err = cmd.Root().GenBashCompletion(os.Stdout)
+		case ZshShell:
+			err = cmd.Root().GenZshCompletion(os.Stdout)
+		case FishShell:
+			err = cmd.Root().GenFishCompletion(os.Stdout, true)
+		case PowerShell:
+			err = cmd.Root().GenPowerShellCompletion(os.Stdout)
+		}
+		DisplayError(err, CompletionCommandName)
+	},
+}
+
+func init() {
+	GetRoot().AddCommand(completionCmd)
+}