Add `make tidy` to check for up-to-date go.mod

This commit adds the `tidy` target. This target will fail if the go.mod
or go.sum files are not up to date with the code. It will also be a
prerequisite to the `lint` command, implying that it will also be caught
by the Zuul gates.

Change-Id: Ie33de2d793beca100435670346eb0e2ea7b3b0dd

Makefile

@@ -53,11 +53,18 @@ cover: unit-tests
 	@./tools/coverage_check $(COVER_PROFILE)
 
 .PHONY: lint
+lint: tidy
 lint: $(LINTER)
 	@echo "Performing linting step..."
 	@./$(LINTER) run --config $(LINTER_CONFIG)
 	@echo "Linting completed successfully"
 
+.PHONY: tidy
+tidy:
+	@echo "Checking that go.mod is up to date..."
+	@./tools/gomod_check
+	@echo "go.mod is up to date"
+
 .PHONY: docker-image
 docker-image:
 	@docker build . --build-arg MAKE_TARGET=$(DOCKER_MAKE_TARGET) --tag $(DOCKER_IMAGE) --target $(DOCKER_TARGET_STAGE)

tools/gomod_check

@@ -0,0 +1,22 @@
+#!/bin/bash
+set -e
+
+backup_dir=$(mktemp -d)
+
+revert() {
+  cp "$backup_dir/go.mod" "go.mod"
+  cp "$backup_dir/go.sum" "go.sum"
+}
+
+cp go.mod go.sum "$backup_dir"
+if [[ $(go mod tidy 2>&1) ]]; then
+  printf "FAIL: error in go.mod. Please run 'go mod tidy' and fix any issues\n"
+  revert
+  exit 1
+fi
+
+if [[ $(diff "go.mod" "$backup_dir/go.mod") ]] || [[ $(diff "go.sum" "$backup_dir/go.sum") ]]; then
+  printf "FAIL: go.mod/go.sum are not up to date. Please run 'go mod tidy'\n"
+  revert
+  exit 1
+fi