fix(cmd): register the --version flag, and report a real version on go install

internal/cmd/root.go

@@ -49,6 +49,10 @@ var (
 // Execute adds all child commands to the root command and sets flags appropriately.
 // This is called by main.main(). It only needs to happen once to the rootCmd.
 func Execute() {
+	// Cobra only registers the --version flag when Version is non-empty.
+	// Setting the template alone left --version and -v undefined, even though
+	// the man page and the shell completions both advertised them.
+	RootCmd.Version = version.GetVersion()
 	RootCmd.SetVersionTemplate("y509 version {{.Version}}\nBuild: " + version.GetFullVersion() + "\n")
 
 	if err := RootCmd.Execute(); err != nil {

internal/version/version.go

@@ -2,6 +2,7 @@
 package version
 
 import (
+	"runtime/debug"
 	"strings"
 )
 
@@ -14,6 +15,41 @@ var (
 	BuildDate = "unknown"
 )
 
+// Release builds get these values from -ldflags. A `go install` build gets no
+// ldflags at all, so it reported itself as "dev" forever -- even though the
+// toolchain had already stamped the module version and the VCS revision into
+// the binary. Read them back out.
+func init() {
+	info, ok := debug.ReadBuildInfo()
+	if !ok {
+		return
+	}
+
+	// Each value falls back on its own. A build that sets only Version through
+	// -ldflags should still pick up the commit and the build time the toolchain
+	// recorded, rather than being left reporting "unknown" for both.
+	if Version == "dev" {
+		// "(devel)" is what a build from a local working tree reports.
+		if info.Main.Version != "" && info.Main.Version != "(devel)" {
+			Version = info.Main.Version
+		}
+	}
+	for _, setting := range info.Settings {
+		switch setting.Key {
+		case "vcs.revision":
+			// An empty value must not overwrite "unknown" -- it would render as
+			// "y509 version dev ()".
+			if GitCommit == "unknown" && setting.Value != "" {
+				GitCommit = setting.Value
+			}
+		case "vcs.time":
+			if BuildDate == "unknown" && setting.Value != "" {
+				BuildDate = setting.Value
+			}
+		}
+	}
+}
+
 // GetVersion returns the version string
 func GetVersion() string {
 	return Version