try to set a more matching version number

Makefile

@@ -1,6 +1,6 @@
 .PHONY: runtime
 
-VERSION = $(shell git describe --tags --abbrev=0)
+VERSION = $(shell go run tools/build-version.go)
 HASH = $(shell git rev-parse --short HEAD)
 DATE = $(shell go run tools/build-date.go)
 

tools/build-version.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"fmt"
+	"os/exec"
+	"strings"
+
+	"github.com/blang/semver"
+)
+
+func getTag(match ...string) (string, *semver.PRVersion) {
+	args := append([]string{
+		"describe", "--tags",
+	}, match...)
+	if tag, err := exec.Command("git", args...).Output(); err != nil {
+		return "", nil
+	} else {
+		tagParts := strings.Split(string(tag), "-")
+		if len(tagParts) == 3 {
+			if ahead, err := semver.NewPRVersion(tagParts[1]); err == nil {
+				return tagParts[0], &ahead
+			}
+		}
+
+		return tagParts[0], nil
+	}
+}
+
+func main() {
+	// Find the last vX.X.X Tag and get how many builds we are ahead of it.
+	versionStr, ahead := getTag("--match", "v*")
+	version, err := semver.ParseTolerant(versionStr)
+	if err != nil {
+		// no version tag found so just return what ever we can find.
+		fmt.Println(getTag())
+		return
+	}
+	// Get the tag of the current revision.
+	tag, _ := getTag("--exact-match")
+	if tag == versionStr {
+		// Seems that we are going to build a release.
+		// So the version number should already be correct.
+		fmt.Println(version.String())
+		return
+	}
+
+	// If we don't have any tag assume "dev"
+	if tag == "" {
+		tag = "dev"
+	}
+	// Get the most likely next version:
+	version.Patch = version.Patch + 1
+
+	if pr, err := semver.NewPRVersion(tag); err == nil {
+		// append the tag as pre-release name
+		version.Pre = append(version.Pre, pr)
+	}
+
+	if ahead != nil {
+		// if we know how many commits we are ahead of the last release, append that too.
+		version.Pre = append(version.Pre, *ahead)
+	}
+
+	fmt.Println(version.String())
+}