Display buildkit version in nerdctl

Fixes#1082

Signed-off-by: Manu Gupta <manugupt1@gmail.com>

cmd/nerdctl/version.go

@@ -21,8 +21,13 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"os/exec"
+	"strings"
 	"text/template"
 
+	"github.com/sirupsen/logrus"
+
+	"github.com/containerd/nerdctl/pkg/buildkitutil"
 	"github.com/containerd/nerdctl/pkg/infoutil"
 	"github.com/containerd/nerdctl/pkg/inspecttypes/dockercompat"
 	"github.com/spf13/cobra"
@@ -86,6 +91,8 @@ func versionAction(cmd *cobra.Command, args []string) error {
 			}
 		}
 	}
+	fmt.Fprintf(w, "\n")
+	fmt.Fprint(w, getBuildKitVersion())
 	return vErr
 }
 
@@ -102,3 +109,24 @@ func versionInfo(cmd *cobra.Command) (dockercompat.VersionInfo, error) {
 	v.Server, err = infoutil.ServerVersion(ctx, client)
 	return v, err
 }
+
+func getBuildKitVersion() string {
+	buildctlBinary, err := buildkitutil.BuildctlBinary()
+	if err != nil {
+		logrus.Warnf("unable to determine buildkit version: %s", err.Error())
+		return "buildkit: not installed"
+	}
+
+	stdout, err := exec.Command(buildctlBinary, "--version").Output()
+	if err != nil {
+		logrus.Warnf("unable to determine buildkit version: %s", err.Error())
+		return "buildkit: undetermined"
+	}
+
+	versionStr := strings.Fields(strings.TrimSpace(string(stdout)))
+	formattedStr := fmt.Sprintf("buildkit:\n"+
+		" Version: \t%s\n"+
+		" Git commit: \t%s\n", versionStr[2], versionStr[3])
+
+	return formattedStr
+}