Enable bash completion for podman commands

I added a command completion that generates
the bash script that would enable the shell
completion, using the cobra function GenBashCompletion.

Closes containers#3878

Signed-off-by: Neville Cain <[email protected]>

CONTRIBUTING.md

@@ -103,6 +103,13 @@ Well, you can now create your own branch, apply changes on it, and then submitti
 
 For further reading about branching [you can read this document](https://herve.beraud.io/containers/linux/podman/isolate/environment/2019/02/06/how-to-hack-on-podman.html).
 
+### Adding/Updating a new command
+
+When you add/update a new command, dont't forget to run 'make completion' to update
+the bash completion script.
+
+There is no need to update zsh completion script as it autogenerates completion.
+
 ## Submitting Pull Requests
 
 No Pull Request (PR) is too small! Typos, additional comments in the code,

Makefile

@@ -120,6 +120,9 @@ CROSS_BUILD_TARGETS := \
 
 all: binaries docs
 
+completion: binaries
+	bin/podman completion bash > completions/bash/podman
+
 default: help
 
 define PRINT_HELP_PYSCRIPT

cmd/podman/build.go

@@ -196,7 +196,7 @@ func buildCmd(c *cliconfig.BuildValues) error {
 	}
 
 	if len(cliArgs) > 0 {
-		// The context directory could be a URL.  Try to handle that.
+		// The context directory could be a URL. Try to handle that.
 		tempDir, subDir, err := imagebuildah.TempDirForURL("", "buildah", cliArgs[0])
 		if err != nil {
 			return errors.Wrapf(err, "error prepping temporary context directory")

cmd/podman/main.go

@@ -31,6 +31,7 @@ var (
 // implemented.
 var mainCommands = []*cobra.Command{
 	_attachCommand,
+	_bashCompletionCommand,
 	_buildCommand,
 	_commitCommand,
 	_diffCommand,

cmd/podman/shell_auto_completion.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+const (
+	bashAutoCompletionDescription = `To load completion run
+
+podman completion bash >>~/.bashrc
+
+Reload your shell.
+
+To make it available in all your bash session, add this to your ~/.bashrc file:
+echo 'source <(podman completion bash)' >>~/.bashrc
+
+As an alternative, if 'bash-completion' is installed on your system, you can add it in:
+/etc/bash_completion.d/{your_file_name}
+`
+)
+
+var _bashCompletionCommand = &cobra.Command{
+	Use:   "completion",
+	Short: "Generates shell scripts for auto-completion",
+	// We do not intend to show this command to the user so
+	// we marked it as hidden. We should use them by using
+	// the "make completion" target to update the shell scripts
+	// enabling the auto-completion for podman.
+	Hidden:  true,
+	Example: `podman completion --help`,
+}
+
+func init() {
+	_bashCompletionCommand.AddCommand(
+		&cobra.Command{
+			Use:   "bash",
+			Short: "generate auto-completion for bash",
+			Long:  bashAutoCompletionDescription,
+			RunE: func(cmd *cobra.Command, args []string) error {
+				// Writing the shell script to stdout allows the most flexible use
+				// as the user can redirect the outputt where it needs it.
+				return rootCmd.GenBashCompletion(os.Stdout)
+			},
+			Example: `podman completion bash >>~/.bashrc`,
+		},
+	)
+}