version: use buildinfo vcs revision

version.go

@@ -6,15 +6,47 @@ import (
 	"runtime/debug"
 	"strings"
 
+	"github.com/jzelinskie/stringz"
 	"github.com/spf13/cobra"
 	"github.com/spf13/pflag"
 )
 
+func findBuildSetting(bi *debug.BuildInfo, key string) string {
+	for _, setting := range bi.Settings {
+		if setting.Key == key {
+			return setting.Value
+		}
+	}
+	return ""
+}
+
+func vcsRevision(bi *debug.BuildInfo) string {
+	revision := findBuildSetting(bi, "vcs.revision")
+	if revision == "" {
+		return ""
+	}
+
+	revision = revision[:12] // Short SHA
+
+	if findBuildSetting(bi, "vcs.modified") == "true" {
+		revision = revision + "-dirty"
+	}
+
+	return revision
+}
+
 // Version is variable that holds program's version string.
 // This should be set with the follow flags to the `go build` command:
 // -ldflags '-X github.com/jzelinskie/cobrautil.Version=$YOUR_VERSION_HERE'
 var Version string
 
+// VersionWithFallbacks returns a string of the program version.
+// If the version wasn't set by ldflags, falls back to the VCS revision, and
+// finally Go module version.
+func VersionWithFallbacks(bi *debug.BuildInfo) string {
+	return stringz.DefaultEmpty(stringz.DefaultEmpty(Version, vcsRevision(bi)), bi.Main.Version)
+}
+
 // UsageVersion introspects the process debug data for Go modules to return a
 // version string.
 func UsageVersion(programName string, includeDeps bool) string {
@@ -23,21 +55,17 @@ func UsageVersion(programName string, includeDeps bool) string {
 		panic("failed to read BuildInfo because the program was compiled with Go " + runtime.Version())
 	}
 
-	if Version == "" {
-		// The version wasn't set by ldflags, so fallback to the Go module version.
-		// Although, this value is pretty much guaranteed to just be "(devel)".
-		Version = bi.Main.Version
-	}
+	version := VersionWithFallbacks(bi)
 
 	if !includeDeps {
 		if Version == "(devel)" {
 			return fmt.Sprintf("%s development build (unknown exact version)", programName)
 		}
-		return fmt.Sprintf("%s %s", programName, Version)
+		return fmt.Sprintf("%s %s", programName, version)
 	}
 
 	var b strings.Builder
-	fmt.Fprintf(&b, "%s %s", bi.Path, Version)
+	fmt.Fprintf(&b, "%s %s", bi.Path, version)
 	for _, dep := range bi.Deps {
 		fmt.Fprintf(&b, "\n\t%s %s", dep.Path, dep.Version)
 	}