version: Add moduleVersionFromBuildInfo

This adds correct version information for `gvproxy -version` when
it's installed using:
```
go install github.com/containers/gvisor-tap-vsock/cmd/gvproxy
```

Signed-off-by: Christophe Fergeau <[email protected]>

pkg/types/version.go

@@ -3,6 +3,7 @@ package types
 import (
 	"flag"
 	"fmt"
+	"runtime/debug"
 )
 
 var ModuleVersion = ""
@@ -19,7 +20,7 @@ func NewVersion(binaryName string) *version { //nolint:revive
 }
 
 func (ver *version) String() string {
-	return fmt.Sprintf("%s version %s", ver.binaryName, ModuleVersion)
+	return fmt.Sprintf("%s version %s", ver.binaryName, moduleVersion())
 }
 
 func (ver *version) AddFlag() {
@@ -29,3 +30,25 @@ func (ver *version) AddFlag() {
 func (ver *version) ShowVersion() bool {
 	return ver.showVersion
 }
+
+func moduleVersion() string {
+	switch {
+	// This will be set when building from git using make
+	case ModuleVersion != "":
+		return ModuleVersion
+	// moduleVersionFromBuildInfo() will be set when using `go install`
+	default:
+		return moduleVersionFromBuildInfo()
+	}
+}
+
+func moduleVersionFromBuildInfo() string {
+	info, ok := debug.ReadBuildInfo()
+	if !ok {
+		return ""
+	}
+	if info.Main.Version == "(devel)" {
+		return ""
+	}
+	return info.Main.Version
+}