main: Add a --version flag to show the build version

This embeds the version at build time and displays it when passed the
--version flag.

Makefile

@@ -98,7 +98,7 @@ $(BUILDDIR)/%/:
 
 .PHONY: build
 build: $(BUILDDIR)/bin/  ## build the binary from source
-	go build -o $<image-builder ./cmd/image-builder/
+	go build -ldflags="-X main.BuildVersion=${VERSION}" -o $<image-builder ./cmd/image-builder/
 
 .PHONY: clean
 clean:  ## Remove all built binaries

cmd/image-builder/main.go

@@ -25,8 +25,9 @@ import (
 )
 
 var (
-	osStdout io.Writer = os.Stdout
+	osStdout     io.Writer = os.Stdout
-	osStderr io.Writer = os.Stderr
+	osStderr     io.Writer = os.Stderr
+	BuildVersion           = "DEVEL"
 )
 
 // basenameFor returns the basename for directory and filenames
@@ -378,6 +379,7 @@ image-type and blueprint.
 Image-builder builds operating system images for a range of predefined
 operating systems like Fedora, CentOS and RHEL with easy customizations support.`,
 		SilenceErrors: true,
+		Version:       BuildVersion,
 	}
 	rootCmd.PersistentFlags().String("data-dir", "", `Override the default data directory for e.g. custom repositories/*.json data`)
 	rootCmd.PersistentFlags().StringArray("extra-repo", nil, `Add an extra repository during build (will *not* be gpg checked and not be part of the final image)`)

image-builder.spec

@@ -85,6 +85,7 @@ export GOFLAGS+=" -mod=vendor"
 GOTAGS="exclude_graphdriver_btrfs"
 %endif
 
+export LDFLAGS="${LDFLAGS} -X 'main.BuildVersion=%{version}'"
 %gobuild ${GOTAGS:+-tags=$GOTAGS} -o %{gobuilddir}/bin/image-builder %{goipath}/cmd/image-builder
 
 %install