feat: add version subcommand (#197)

The `version` subcommand without any flags prints out a general version
information, good to check what version we have.

    ❯ ./bin/flintlockd_amd64 version
    flintlock v0.1.0-alpha.1-11-af7a1a9

The `version` subcommand with `--short` flag prints out only the
version, useful for scripting.

    ❯ ./bin/flintlockd_amd64 version --short
    v0.1.0-alpha.1-11-af7a1a9

The `version` subcommand with `--long` flag prints out a detailed version
information, useful for bug reports.

    ❯ ./bin/flintlockd_amd64 version --long
    flintlock
      Version:    v0.1.0-alpha.1-12-gaf7a1a9
      CommitHash: af7a1a9
      BuildDate:  2021-11-03T11:38:43Z

== Why a subcommand and not a `-v` or `-V` flag?

Because it can be confusing. Some applications are using `-v` for
version, some are using `-V` for version because `-v` is the verbose
flag. Go, kubectl, and Helm follows the same logic, they have a
`version` subcommand.

== Different flags

* I find it annoying to parse version information from `version`
  subcommands all the time when I want to automate something, that's the
  `--short`.
* I find it useful to print out everything we have for debugging or
  filing bug reports, that's the `--long` flag.
* I find it useful to print out the package/application name, so even if
  the binary was renamed I can see what is the name of the application,
  but without extra information like commit hash or build date.  That's
  the no-flag option.

== Moved the log.Info call

In general, it's useful to print out the info log on `run` and `gw`, but
not for `version`.

Fixes #163

internal/command/gw/gw.go

@@ -15,6 +15,7 @@ import (
 	mvmv1 "github.com/weaveworks/flintlock/api/services/microvm/v1alpha1"
 	cmdflags "github.com/weaveworks/flintlock/internal/command/flags"
 	"github.com/weaveworks/flintlock/internal/config"
+	"github.com/weaveworks/flintlock/internal/version"
 	"github.com/weaveworks/flintlock/pkg/flags"
 	"github.com/weaveworks/flintlock/pkg/log"
 )
@@ -27,6 +28,14 @@ func NewCommand(cfg *config.Config) *cobra.Command {
 		PreRunE: func(c *cobra.Command, _ []string) error {
 			flags.BindCommandToViper(c)
 
+			logger := log.GetLogger(c.Context())
+			logger.Infof(
+				"flintlockd, version=%s, built_on=%s, commit=%s",
+				version.Version,
+				version.BuildDate,
+				version.CommitHash,
+			)
+
 			return nil
 		},
 		RunE: func(c *cobra.Command, _ []string) error {

internal/command/root.go

@@ -29,9 +29,6 @@ func NewRootCommand() (*cobra.Command, error) {
 				return fmt.Errorf("configuring logging: %w", err)
 			}
 
-			logger := log.GetLogger(cmd.Context())
-			logger.Infof("flintlockd, version=%s, built_on=%s, commit=%s", version.Version, version.BuildDate, version.CommitHash)
-
 			return nil
 		},
 		RunE: func(c *cobra.Command, _ []string) error {
@@ -63,7 +60,7 @@ func initCobra() {
 		viper.AddConfigPath("$HOME/.config/flintlockd/")
 	}
 
-	viper.ReadInConfig() //nolint: errcheck
+	_ = viper.ReadInConfig()
 }
 
 func addRootSubCommands(cmd *cobra.Command, cfg *config.Config) error {
@@ -73,9 +70,59 @@ func addRootSubCommands(cmd *cobra.Command, cfg *config.Config) error {
 	}
 
 	cmd.AddCommand(runCmd)
+	cmd.AddCommand(versionCommand())
 
 	gwCmd := gw.NewCommand(cfg)
 	cmd.AddCommand(gwCmd)
 
 	return nil
 }
+
+func versionCommand() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "version",
+		Short: "Print the version number of flintlock",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			var (
+				long, short bool
+				err         error
+			)
+
+			if long, err = cmd.Flags().GetBool("long"); err != nil {
+				return nil
+			}
+
+			if short, err = cmd.Flags().GetBool("short"); err != nil {
+				return nil
+			}
+
+			if short {
+				fmt.Fprintln(cmd.OutOrStdout(), version.Version)
+
+				return nil
+			}
+
+			if long {
+				fmt.Fprintf(
+					cmd.OutOrStdout(),
+					"%s\n  Version:    %s\n  CommitHash: %s\n  BuildDate:  %s\n",
+					version.PackageName,
+					version.Version,
+					version.CommitHash,
+					version.BuildDate,
+				)
+
+				return nil
+			}
+
+			fmt.Fprintf(cmd.OutOrStdout(), "%s %s\n", version.PackageName, version.Version)
+
+			return nil
+		},
+	}
+
+	_ = cmd.Flags().Bool("long", false, "Print long version information")
+	_ = cmd.Flags().Bool("short", false, "Print short version information")
+
+	return cmd
+}

internal/command/run/run.go

@@ -19,6 +19,7 @@ import (
 	cmdflags "github.com/weaveworks/flintlock/internal/command/flags"
 	"github.com/weaveworks/flintlock/internal/config"
 	"github.com/weaveworks/flintlock/internal/inject"
+	"github.com/weaveworks/flintlock/internal/version"
 	"github.com/weaveworks/flintlock/pkg/defaults"
 	"github.com/weaveworks/flintlock/pkg/flags"
 	"github.com/weaveworks/flintlock/pkg/log"
@@ -32,6 +33,14 @@ func NewCommand(cfg *config.Config) (*cobra.Command, error) {
 		PreRunE: func(c *cobra.Command, _ []string) error {
 			flags.BindCommandToViper(c)
 
+			logger := log.GetLogger(c.Context())
+			logger.Infof(
+				"flintlockd, version=%s, built_on=%s, commit=%s",
+				version.Version,
+				version.BuildDate,
+				version.CommitHash,
+			)
+
 			return nil
 		},
 		RunE: func(c *cobra.Command, _ []string) error {

internal/version/version.go

@@ -1,5 +1,9 @@
 package version
 
+// PackageName is the name of the package, not just FlintlockD,
+// all commands fall under this name.
+const PackageName = "flintlock"
+
 var (
 	Version    = "undefined" // Specifies the app version
 	BuildDate  = "undefined" // Specifies the build date