feat(cli): --version using ldflags

The go-modules approach is a bit broken: https://github.com/golang/go/issues/29228
To resolve that, we now compute that version using `git describe` and
set it using `ldflags`.

While this is not as nice/builtin as the other approach, it at least
works all the time and across go versions.

Furthermore, I did refactor the Makefile in preparation for an AUR
package that builds from source and for building release artifacts in CI.

Makefile

@@ -1,31 +1,35 @@
-all: check-license build generate test
+.PHONY: all check-license crossbuild build install test generate embedmd
 
 GITHUB_URL=github.com/jsonnet-bundler/jsonnet-bundler
-GOOS?=$(shell uname -s | tr A-Z a-z)
-GOARCH?=$(subst x86_64,amd64,$(patsubst i%86,386,$(shell uname -m)))
+VERSION := $(shell git describe --tags --dirty --always)
 OUT_DIR=_output
 BIN?=jb
-VERSION?=$(shell cat VERSION)
 PKGS=$(shell go list ./... | grep -v /vendor/)
 
-check-license:
-	@echo ">> checking license headers"
-	@./scripts/check_license.sh
+all: check-license build generate test
 
-crossbuild:
-	@GOOS=linux ARCH=amd64 $(MAKE) -s build
+
+# Binaries
+LDFLAGS := '-s -w -extldflags "-static" -X main.Version=${VERSION}'
+cross: clean
+	CGO_ENABLED=0 gox \
+	  -output="$(OUT_DIR)/jb-{{.OS}}-{{.Arch}}" \
+	  -ldflags=$(LDFLAGS) \
+	  -arch="amd64 arm64 arm" -os="linux" \
+	  -osarch="darwin/amd64" \
+	  ./cmd/$(BIN)
+
+static:
+	CGO_ENABLED=0 go build -ldflags=${LDFLAGS} -o $(OUT_DIR)/$(BIN) ./cmd/$(BIN)
 
 build:
-	@$(eval OUTPUT=$(OUT_DIR)/$(GOOS)/$(GOARCH)/$(BIN))
-	@echo ">> building for $(GOOS)/$(GOARCH) to $(OUTPUT)"
-	@mkdir -p $(OUT_DIR)/$(GOOS)/$(GOARCH)
-	@CGO_ENABLED=0 go build --installsuffix cgo -o $(OUTPUT) $(GITHUB_URL)/cmd/$(BIN)
+	CGO_ENABLED=0 go build ./cmd/$(BIN)
 
-install: build
-	@$(eval OUTPUT=$(OUT_DIR)/$(GOOS)/$(GOARCH)/$(BIN))
+install: static
 	@echo ">> copying $(BIN) into $(GOPATH)/bin/$(BIN)"
-	@cp $(OUTPUT) $(GOPATH)/bin/$(BIN)
+	cp $(OUT_DIR)/$(BIN) $(GOPATH)/bin/$(BIN)
 
+# Tests
 test:
 	@echo ">> running all unit tests"
 	go test -v $(PKGS)
@@ -34,12 +38,22 @@ test-integration:
 	@echo ">> running all integration tests"
 	go test -v -tags=integration $(PKGS)
 
+# Documentation
 generate: embedmd
 	@echo ">> generating docs"
 	@./scripts/generate-help-txt.sh
 	@$(GOPATH)/bin/embedmd -w `find ./ -path ./vendor -prune -o -name "*.md" -print`
 
-embedmd:
-	@go get github.com/campoy/embedmd
+check-license:
+	@echo ">> checking license headers"
+	@./scripts/check_license.sh
 
-.PHONY: all check-license crossbuild build install test generate embedmd
+embedmd:
+	pushd /tmp && GO111MODULES=on go get github.com/campoy/embedmd && popd
+
+# Other
+clean:
+	rm -rf $(OUT_DIR) $(BIN)
+
+drone:
+	drone jsonnet --format