Supply proper version information

This only adds the facilities to do so, the version information itself
is currently only a git hash, as we have not tagged any releases so far.

With this in place, let's set up some CI system, maybe a few test stubs
and then we can do a 1.0 release.

main.go

@@ -10,6 +10,7 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/prometheus/common/log"
+	"github.com/prometheus/common/version"
 	kingpin "gopkg.in/alecthomas/kingpin.v2"
 )
 
@@ -77,6 +78,7 @@ func updateConfiguration(w http.ResponseWriter, r *http.Request) {
 func main() {
 	log.AddFlags(kingpin.CommandLine)
 	kingpin.HelpFlag.Short('h')
+	kingpin.Version(version.Print("ipmi_exporter"))
 	kingpin.Parse()
 	log.Infoln("Starting ipmi_exporter")
 

vendor/github.com/prometheus/common/version/info.go

@@ -0,0 +1,89 @@
+// Copyright 2016 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package version
+
+import (
+	"bytes"
+	"fmt"
+	"runtime"
+	"strings"
+	"text/template"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// Build information. Populated at build-time.
+var (
+	Version   string
+	Revision  string
+	Branch    string
+	BuildUser string
+	BuildDate string
+	GoVersion = runtime.Version()
+)
+
+// NewCollector returns a collector which exports metrics about current version information.
+func NewCollector(program string) *prometheus.GaugeVec {
+	buildInfo := prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Namespace: program,
+			Name:      "build_info",
+			Help: fmt.Sprintf(
+				"A metric with a constant '1' value labeled by version, revision, branch, and goversion from which %s was built.",
+				program,
+			),
+		},
+		[]string{"version", "revision", "branch", "goversion"},
+	)
+	buildInfo.WithLabelValues(Version, Revision, Branch, GoVersion).Set(1)
+	return buildInfo
+}
+
+// versionInfoTmpl contains the template used by Info.
+var versionInfoTmpl = `
+{{.program}}, version {{.version}} (branch: {{.branch}}, revision: {{.revision}})
+  build user:       {{.buildUser}}
+  build date:       {{.buildDate}}
+  go version:       {{.goVersion}}
+`
+
+// Print returns version information.
+func Print(program string) string {
+	m := map[string]string{
+		"program":   program,
+		"version":   Version,
+		"revision":  Revision,
+		"branch":    Branch,
+		"buildUser": BuildUser,
+		"buildDate": BuildDate,
+		"goVersion": GoVersion,
+	}
+	t := template.Must(template.New("version").Parse(versionInfoTmpl))
+
+	var buf bytes.Buffer
+	if err := t.ExecuteTemplate(&buf, "version", m); err != nil {
+		panic(err)
+	}
+	return strings.TrimSpace(buf.String())
+}
+
+// Info returns version, branch and revision information.
+func Info() string {
+	return fmt.Sprintf("(version=%s, branch=%s, revision=%s)", Version, Branch, Revision)
+}
+
+// BuildContext returns goVersion, buildUser and buildDate information.
+func BuildContext() string {
+	return fmt.Sprintf("(go=%s, user=%s, date=%s)", GoVersion, BuildUser, BuildDate)
+}

vendor/modules.txt

@@ -19,6 +19,7 @@ github.com/prometheus/client_golang/prometheus/internal
 github.com/prometheus/client_model/go
 # github.com/prometheus/common v0.6.0
 github.com/prometheus/common/log
+github.com/prometheus/common/version
 github.com/prometheus/common/expfmt
 github.com/prometheus/common/model
 github.com/prometheus/common/internal/bitbucket.org/ww/goautoneg