Fix version info string.

Broken by the following commit
e38bb7c Use Makefile.COMMON and add generated files.go

Makefile

@@ -16,6 +16,18 @@ TARGET   := alertmanager
 
 include Makefile.COMMON
 
+REV        := $(shell git rev-parse --short HEAD 2> /dev/null  || echo 'unknown')
+BRANCH     := $(shell git rev-parse --abbrev-ref HEAD 2> /dev/null  || echo 'unknown')
+HOSTNAME   := $(shell hostname -f)
+BUILD_DATE := $(shell date +%Y%m%d-%H:%M:%S)
+GOFLAGS    := -ldflags \
+	"-X=main.buildVersion $(VERSION)\
+	-X=main.buildRevision $(REV)\
+	-X=main.buildBranch $(BRANCH)\
+	-X=main.buildUser $(USER)@$(HOSTNAME)\
+	-X=main.buildDate $(BUILD_DATE)\
+	-X=main.goVersion $(GO_VERSION)"
+
 web: web/blob/files.go
 
 web/blob/files.go: $(shell find web/templates/ web/static/ -type f)

build_info.go

@@ -19,17 +19,19 @@ import (
 
 // Build information. Populated by Makefile.
 var (
-	buildVersion string
-	buildBranch  string
-	buildUser    string
-	buildDate    string
-	goVersion    string
+	buildVersion  string
+	buildRevision string
+	buildBranch   string
+	buildUser     string
+	buildDate     string
+	goVersion     string
 )
 
 // BuildInfo encapsulates compile-time metadata about Prometheus made available
 // via go tool ld such that this can be reported on-demand.
 var BuildInfo = map[string]string{
 	"version":    buildVersion,
+	"revision":   buildRevision,
 	"branch":     buildBranch,
 	"user":       buildUser,
 	"date":       buildDate,
@@ -37,7 +39,7 @@ var BuildInfo = map[string]string{
 }
 
 var versionInfoTmpl = template.Must(template.New("version").Parse(
-	`alertmanager, version {{.version}} ({{.branch}})
+	`alertmanager, version {{.version}} ({{.branch}}@{{.revision}})
   build user:       {{.user}}
   build date:       {{.date}}
   go version:       {{.go_version}}