refactor(Makefile): allow overriding default go program

Makefile

@@ -1,13 +1,14 @@
 DIST := dist
 EXECUTABLE := drone-packer
 GOFMT ?= gofmt "-s"
+GO ?= go
 
 # for dockerhub
 DEPLOY_ACCOUNT := appleboy
 DEPLOY_IMAGE := $(EXECUTABLE)
 
 TARGETS ?= linux darwin windows
-PACKAGES ?= $(shell go list ./... | grep -v /vendor/)
+PACKAGES ?= $(shell $(GO) list ./... | grep -v /vendor/)
 GOFILES := $(shell find . -name "*.go" -type f -not -path "./vendor/*")
 SOURCES ?= $(shell find . -name "*.go" -type f)
 TAGS ?=
@@ -32,43 +33,42 @@ fmt:
 	$(GOFMT) -w $(GOFILES)
 
 vet:
-	go vet $(PACKAGES)
+	$(GO) vet $(PACKAGES)
 
 errcheck:
 	@which errcheck > /dev/null; if [ $$? -ne 0 ]; then \
-		go get -u github.com/kisielk/errcheck; \
+		$(GO) get -u github.com/kisielk/errcheck; \
 	fi
 	errcheck $(PACKAGES)
 
 lint:
 	@which golint > /dev/null; if [ $$? -ne 0 ]; then \
-		go get -u golang.org/x/lint/golint; \
+		$(GO) get -u golang.org/x/lint/golint; \
 	fi
 	for PKG in $(PACKAGES); do golint -set_exit_status $$PKG || exit 1; done;
 
 unconvert:
 	@which unconvert > /dev/null; if [ $$? -ne 0 ]; then \
-		go get -u github.com/mdempsky/unconvert; \
+		$(GO) get -u github.com/mdempsky/unconvert; \
 	fi
 	for PKG in $(PACKAGES); do unconvert -v $$PKG || exit 1; done;
 
 .PHONY: misspell-check
 misspell-check:
 	@hash misspell > /dev/null 2>&1; if [ $$? -ne 0 ]; then \
-		go get -u github.com/client9/misspell/cmd/misspell; \
+		$(GO) get -u github.com/client9/misspell/cmd/misspell; \
 	fi
 	misspell -error $(GOFILES)
 
 .PHONY: misspell
 misspell:
 	@hash misspell > /dev/null 2>&1; if [ $$? -ne 0 ]; then \
-		go get -u github.com/client9/misspell/cmd/misspell; \
+		$(GO) get -u github.com/client9/misspell/cmd/misspell; \
 	fi
 	misspell -w $(GOFILES)
 
 .PHONY: fmt-check
 fmt-check:
-	# get all go files and run go fmt on them
 	@diff=$$($(GOFMT) -d $(GOFILES)); \
 	if [ -n "$$diff" ]; then \
 		echo "Please run 'make fmt' and commit the result:"; \
@@ -79,7 +79,7 @@ fmt-check:
 .PHONY: test-vendor
 test-vendor:
 	@hash govendor > /dev/null 2>&1; if [ $$? -ne 0 ]; then \
-		go get -u github.com/kardianos/govendor; \
+		$(GO) get -u github.com/kardianos/govendor; \
 	fi
 	govendor list +unused | tee "$(TMPDIR)/wc-gitea-unused"
 	[ $$(cat "$(TMPDIR)/wc-gitea-unused" | wc -l) -eq 0 ] || echo "Warning: /!\\ Some vendor are not used /!\\"
@@ -90,18 +90,18 @@ test-vendor:
 	govendor status || exit 1
 
 test: fmt-check
-	for PKG in $(PACKAGES); do go test -cover -coverprofile $$GOPATH/src/$$PKG/coverage.txt $$PKG || exit 1; done;
+	for PKG in $(PACKAGES); do $(GO) test -cover -coverprofile $$GOPATH/src/$$PKG/coverage.txt $$PKG || exit 1; done;
 
 html:
-	go tool cover -html=coverage.txt
+	$(GO) tool cover -html=coverage.txt
 
 install: $(SOURCES)
-	go install -v -tags '$(TAGS)' -ldflags '$(EXTLDFLAGS)-s -w $(LDFLAGS)'
+	$(GO) install -v -tags '$(TAGS)' -ldflags '$(EXTLDFLAGS)-s -w $(LDFLAGS)'
 
 build: $(EXECUTABLE)
 
 $(EXECUTABLE): $(SOURCES)
-	go build -v -tags '$(TAGS)' -ldflags '$(EXTLDFLAGS)-s -w $(LDFLAGS)' -o $@
+	$(GO) build -v -tags '$(TAGS)' -ldflags '$(EXTLDFLAGS)-s -w $(LDFLAGS)' -o $@
 
 release: release-dirs release-build release-copy release-check
 
@@ -110,7 +110,7 @@ release-dirs:
 
 release-build:
 	@which gox > /dev/null; if [ $$? -ne 0 ]; then \
-		go get -u github.com/mitchellh/gox; \
+		$(GO) get -u github.com/mitchellh/gox; \
 	fi
 	gox -os="$(TARGETS)" -arch="amd64 386" -tags="$(TAGS)" -ldflags="-s -w $(LDFLAGS)" -output="$(DIST)/binaries/$(EXECUTABLE)-$(VERSION)-{{.OS}}-{{.Arch}}"
 
@@ -121,16 +121,16 @@ release-check:
 	cd $(DIST)/release; $(foreach file,$(wildcard $(DIST)/release/$(EXECUTABLE)-*),sha256sum $(notdir $(file)) > $(notdir $(file)).sha256;)
 
 build_linux_amd64:
-	CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -a -tags '$(TAGS)' -ldflags '$(EXTLDFLAGS)-s -w $(LDFLAGS)' -o release/linux/amd64/$(DEPLOY_IMAGE)
+	CGO_ENABLED=0 GOOS=linux GOARCH=amd64 $(GO) build -a -tags '$(TAGS)' -ldflags '$(EXTLDFLAGS)-s -w $(LDFLAGS)' -o release/linux/amd64/$(DEPLOY_IMAGE)
 
 build_linux_i386:
-	CGO_ENABLED=0 GOOS=linux GOARCH=386 go build -a -tags '$(TAGS)' -ldflags '$(EXTLDFLAGS)-s -w $(LDFLAGS)' -o release/linux/i386/$(DEPLOY_IMAGE)
+	CGO_ENABLED=0 GOOS=linux GOARCH=386 $(GO) build -a -tags '$(TAGS)' -ldflags '$(EXTLDFLAGS)-s -w $(LDFLAGS)' -o release/linux/i386/$(DEPLOY_IMAGE)
 
 build_linux_arm64:
-	CGO_ENABLED=0 GOOS=linux GOARCH=arm64 go build -a -tags '$(TAGS)' -ldflags '$(EXTLDFLAGS)-s -w $(LDFLAGS)' -o release/linux/arm64/$(DEPLOY_IMAGE)
+	CGO_ENABLED=0 GOOS=linux GOARCH=arm64 $(GO) build -a -tags '$(TAGS)' -ldflags '$(EXTLDFLAGS)-s -w $(LDFLAGS)' -o release/linux/arm64/$(DEPLOY_IMAGE)
 
 build_linux_arm:
-	CGO_ENABLED=0 GOOS=linux GOARCH=arm GOARM=7 go build -a -tags '$(TAGS)' -ldflags '$(EXTLDFLAGS)-s -w $(LDFLAGS)' -o release/linux/arm/$(DEPLOY_IMAGE)
+	CGO_ENABLED=0 GOOS=linux GOARCH=arm GOARM=7 $(GO) build -a -tags '$(TAGS)' -ldflags '$(EXTLDFLAGS)-s -w $(LDFLAGS)' -o release/linux/arm/$(DEPLOY_IMAGE)
 
 docker_image:
 	docker build -t $(DEPLOY_ACCOUNT)/$(DEPLOY_IMAGE) .
@@ -150,7 +150,7 @@ coverage:
 	sed -i '/main.go/d' coverage.txt
 
 clean:
-	go clean -x -i ./...
+	$(GO) clean -x -i ./...
 	rm -rf coverage.txt $(EXECUTABLE) $(DIST) vendor
 
 version: