Drop support for Go older than 1.18

We don't support Go older than 1.21 in the Go modules file, so we can
drop the special handling for older Go in the version package.

Signed-off-by: SuperQ <superq@gmail.com>

version/info.go

@@ -17,6 +17,7 @@ import (
 	"bytes"
 	"fmt"
 	"runtime"
+	"runtime/debug"
 	"strings"
 	"text/template"
 )
@@ -31,6 +32,9 @@ var (
 	GoVersion = runtime.Version()
 	GoOS      = runtime.GOOS
 	GoArch    = runtime.GOARCH
+
+	computedRevision string
+	computedTags     string
 )
 
 // versionInfoTmpl contains the template used by Info.
@@ -74,3 +78,48 @@ func Info() string {
 func BuildContext() string {
 	return fmt.Sprintf("(go=%s, platform=%s, user=%s, date=%s, tags=%s)", GoVersion, GoOS+"/"+GoArch, BuildUser, BuildDate, GetTags())
 }
+
+func GetRevision() string {
+	if Revision != "" {
+		return Revision
+	}
+	return computedRevision
+}
+
+func GetTags() string {
+	return computedTags
+}
+
+func init() {
+	computedRevision, computedTags = computeRevision()
+}
+
+func computeRevision() (string, string) {
+	var (
+		rev      = "unknown"
+		tags     = "unknown"
+		modified bool
+	)
+
+	buildInfo, ok := debug.ReadBuildInfo()
+	if !ok {
+		return rev, tags
+	}
+	for _, v := range buildInfo.Settings {
+		if v.Key == "vcs.revision" {
+			rev = v.Value
+		}
+		if v.Key == "vcs.modified" {
+			if v.Value == "true" {
+				modified = true
+			}
+		}
+		if v.Key == "-tags" {
+			tags = v.Value
+		}
+	}
+	if modified {
+		return rev + "-modified", tags
+	}
+	return rev, tags
+}