dev: Add Makefile with common commands (#516)

We can later update CONTRIBUTING.md and Actions workflows to use "make"
targets as the source of truth.

CONTRIBUTING.md

@@ -72,6 +72,8 @@ $ go test -race -coverprofile=coverage.txt -covermode=atomic && go tool cover -h
 
 ## Linting
 
+Lint with [`golangci-lint`](https://github.com/golangci/golangci-lint):
+
 ```console
 $ golangci-lint run
 ```

Makefile

@@ -0,0 +1,38 @@
+.DEFAULT_GOAL := help
+
+# Parse Makefile and display the help
+help: ## Show help
+	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'
+.PHONY: help
+
+build: ## Build everything
+	go build ./...
+.PHONY: build
+
+vet: ## Run "go vet"
+	go vet ./...
+.PHONY: vet
+
+test: ## Run tests
+	go test -count=1 ./...
+.PHONY: test
+
+test-with-race-detection: ## Run tests with data race detector
+	go test -count=1 -race ./...
+.PHONY: test-with-race-detection
+
+test-with-coverage: ## Test with coverage enabled
+	go test -count=1 -race -coverprofile=coverage.txt -covermode=atomic ./...
+.PHONY: test-with-coverage
+
+coverage-report: test-with-coverage ## Test with coverage and open the produced HTML report
+	go tool cover -html coverage.txt
+.PHONY: coverage-report
+
+lint: ## Lint (using "golangci-lint")
+	golangci-lint run
+.PHONY: lint
+
+fmt: ## Format all Go files
+	gofmt -l -w -s .
+.PHONY: fmt