feat: show RootlessKit version in nerdctl version output

When running in rootless mode, nerdctl version now includes the
RootlessKit version as a server component, matching the format used
by docker version. The version is retrieved via the RootlessKit API
socket (rootlessutil.NewRootlessKitClient + Info(ctx)) rather than
shelling out to rootlesskit --version, which is more robust and
avoids PATH issues.

The version is only shown when rootless mode is active (i.e. when
rootlessutil.IsRootless() is true). If the API socket is unavailable
or the Info call fails, a warning is logged and the component is
shown without a version string.

Fixes #4936

Signed-off-by: Aaron Mark <64331623+amarkdotdev@users.noreply.github.com>

Author: amarkdotdev

pkg/infoutil/infoutil.go

@@ -35,6 +35,7 @@ import (
 	"github.com/containerd/nerdctl/v2/pkg/buildkitutil"
 	"github.com/containerd/nerdctl/v2/pkg/inspecttypes/dockercompat"
 	"github.com/containerd/nerdctl/v2/pkg/inspecttypes/native"
+	"github.com/containerd/nerdctl/v2/pkg/rootlessutil"
 	"github.com/containerd/nerdctl/v2/pkg/version"
 )
 
@@ -142,6 +143,9 @@ func ServerVersion(ctx context.Context, client *containerd.Client) (*dockercompa
 			runcVersion(),
 		},
 	}
+	if rootlessutil.IsRootless() {
+		v.Components = append(v.Components, rootlessKitVersion(ctx))
+	}
 	return v, nil
 }
 
@@ -233,6 +237,35 @@ func parseRuncVersion(runcVersionStdout []byte) (*dockercompat.ComponentVersion,
 }
 
 // getMobySysInfo returns the moby system info for the given cgroup manager
+
+func rootlessKitVersion(ctx context.Context) dockercompat.ComponentVersion {
+	rc, err := rootlessutil.NewRootlessKitClient()
+	if err != nil {
+		log.L.WithError(err).Warnf("unable to connect to RootlessKit API socket")
+		return dockercompat.ComponentVersion{Name: "rootlesskit"}
+	}
+	info, err := rc.Info(ctx)
+	if err != nil {
+		log.L.WithError(err).Warnf("unable to retrieve RootlessKit version via API")
+		return dockercompat.ComponentVersion{Name: "rootlesskit"}
+	}
+	details := map[string]string{
+		"ApiVersion": info.APIVersion,
+		"StateDir":   info.StateDir,
+	}
+	if info.NetworkDriver != nil {
+		details["NetworkDriver"] = info.NetworkDriver.Driver
+	}
+	if info.PortDriver != nil {
+		details["PortDriver"] = info.PortDriver.Driver
+	}
+	return dockercompat.ComponentVersion{
+		Name:    "rootlesskit",
+		Version: info.Version,
+		Details: details,
+	}
+}
+
 func getMobySysInfo(cgroupManager string) *sysinfo.SysInfo {
 	var info dockercompat.Info
 	info.CgroupVersion = CgroupsVersion()