main.go

package main

import (
	"errors"
	"fmt"
	"os"
	"os/exec"
	"strings"
	"text/template"
)

func sysCmd(name string, arg ...string) (string, error) {
	cmd := exec.Command(name, arg...)
	out, err := cmd.CombinedOutput()
	splitted := strings.Split(string(out), "\n")
	lines := make([]string, 0, len(splitted))
	for _, l := range splitted {
		l = strings.TrimSpace(l)
		if l == "" {
			continue
		}
		lines = append(lines, l)
	}
	if len(lines) != 1 {
		fmt.Println(string(out))

		return "", errors.New("Expects a single line")
	}

	return lines[0], err
}

func mustSysCmd(name string, arg ...string) string {
	out, err := sysCmd(name, arg...)
	if err != nil {
		panic(err)
	}

	return out
}

func getVersionTag(tags string) string {
	var candidates []string
	for _, t := range strings.Split(tags, " ") {
		if strings.HasPrefix(t, "v") {
			candidates = append(candidates, t)
		}
	}
	if len(candidates) == 0 {
		return ""
	}

	return candidates[0]
}

var outTemplate = template.Must(template.New("").Parse(`package {{ .package }}

var Version = "{{ .version }}"
var HgSha = "{{ .sha }}"
var HgTopic = "{{ .topic }}"
var HgBranch = "{{ .branch }}"
var Build = "{{ .build }}"
`))

func main() {
	sha := mustSysCmd("hg", "id", "--id")
	curVersion := getVersionTag(mustSysCmd("hg", "id", "--tags"))
	lastVersion := getVersionTag(mustSysCmd("hg", "id", "--tags", "-r", "limit(last(ancestors(.)&tag('re:v.*'))|.,1)"))
	modified := strings.HasSuffix(sha, "+")
	jobID := os.Getenv("CI_JOB_ID")

	topic, err := sysCmd("hg", "topic", "--current")
	if topic == "no active topic" {
		topic = ""
	} else if err != nil {
		panic(err)
	}
	branch := mustSysCmd("hg", "id", "--branch")

	var version string

	switch {
	case modified && lastVersion != "":
		version = lastVersion + ""
	case curVersion != "":
		version = curVersion
	case lastVersion != "":
		version = lastVersion + "-" + sha
	default:
		version = "v0.0.0-" + sha
	}

	vars := map[string]string{
		"package": "main",
		"sha":     sha,
		"version": version,
		"build":   jobID,
		"topic":   topic,
		"branch":  branch,
	}

	out, err := os.Create("version.go")
	if err != nil {
		panic(err)
	}

	if err := outTemplate.Execute(out, vars); err != nil {
		panic(err)
	}
}