version: Move vX.Y.Z to version.go so it works with go get, add git info

Previously, building with `make` was required for `version` command to
output v0.15.0; `go get` or `go build` would always tell you v0.0.0-unset.

Now the basic vX.Y.Z is always available, and when building with `make`
git information is appended:

$ go run . version
v0.15.0 built from git (unknown)
$ out/container-diff version
v0.15.0 built from git v0.15.0-1-gcd5a837-dirty

Author: cben

Makefile

@@ -12,12 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# Bump these on release
-VERSION_MAJOR ?= 0
-VERSION_MINOR ?= 15
-VERSION_BUILD ?= 0
-
-VERSION ?= v$(VERSION_MAJOR).$(VERSION_MINOR).$(VERSION_BUILD)
+# On release, remember to also bump const in version/version.go
+GIT_VERSION ?= $(shell git describe --always --tags --long --dirty)
 
 GOOS ?= $(shell go env GOOS)
 GOARCH = amd64
@@ -31,11 +27,11 @@ SUPPORTED_PLATFORMS := linux-$(GOARCH) darwin-$(GOARCH) windows-$(GOARCH).exe
 BUILD_PACKAGE = $(REPOPATH)
 
 # These build tags are from the containers/image library.
-# 
+#
 # container_image_ostree_stub allows building the library without requiring the libostree development libraries
 # container_image_openpgp forces a Golang-only OpenPGP implementation for signature verification instead of the default cgo/gpgme-based implementation
 GO_BUILD_TAGS := "container_image_ostree_stub containers_image_openpgp"
-GO_LDFLAGS := "-X $(REPOPATH)/version.version=$(VERSION)"
+GO_LDFLAGS := "-X $(REPOPATH)/version.gitVersion=$(GIT_VERSION)"
 GO_FILES := $(shell go list  -f '{{join .Deps "\n"}}' $(BUILD_PACKAGE) | grep $(ORG) | xargs go list -f '{{ range $$file := .GoFiles }} {{$$.Dir}}/{{$$file}}{{"\n"}}{{end}}')
 
 $(BUILD_DIR)/$(PROJECT): $(BUILD_DIR)/$(PROJECT)-$(GOOS)-$(GOARCH)
@@ -68,7 +64,7 @@ integration: $(BUILD_DIR)/$(PROJECT)
 
 .PHONY: release
 release: cross
-	gsutil cp $(BUILD_DIR)/$(PROJECT)-* gs://$(RELEASE_BUCKET)/$(VERSION)/
+	gsutil cp $(BUILD_DIR)/$(PROJECT)-* gs://$(RELEASE_BUCKET)/$(shell $(BUILD_DIR)/$(PROJECT) version --short)/
 	gsutil cp $(BUILD_DIR)/$(PROJECT)-* gs://$(RELEASE_BUCKET)/latest/
 
 .PHONY: clean

cmd/version.go

@@ -29,10 +29,18 @@ var versionCmd = &cobra.Command{
 	Long:  `Print the version of container-diff.`,
 	Args:  cobra.ExactArgs(0),
 	Run: func(command *cobra.Command, args []string) {
-		fmt.Println(version.GetVersion())
+		if shortVersion {
+			fmt.Println(version.GetShortVersion())
+		} else {
+			fmt.Println(version.GetVersion())
+		}
 	},
 }
 
+// `version --short` is useful for `make release`
+var shortVersion bool
+
 func init() {
+	versionCmd.Flags().BoolVarP(&shortVersion, "short", "", false, "Output single vX.Y.Z word")
 	RootCmd.AddCommand(versionCmd)
 }

version/version.go

@@ -16,8 +16,19 @@ limitations under the License.
 
 package version
 
-var version = "v0.0.0-unset"
+import "fmt"
 
-func GetVersion() string {
+// Bump this on release
+var version = "v0.15.0"
+
+// When built using `make` this is overridden via -ldflags
+var gitVersion = "(unknown)"
+
+// returns just the vX.Y.Z version suitable for `make release`
+func GetShortVersion() string {
 	return version
 }
+
+func GetVersion() string {
+	return fmt.Sprintf("%s built from git %s", version, gitVersion)
+}