build: Add versioning

This handles:
- builds from a git repository
- builds from a tarball
- builds using `go install ...`

.gitattributes

@@ -0,0 +1 @@
+/pkg/cmdline/version.go export-subst

Makefile

@@ -1,5 +1,8 @@
 .PHONY: all build check clean cross test
 
+GIT_VERSION ?= $(shell git describe --always --dirty)
+VERSION_LDFLAGS=-X github.com/crc-org/macadam/pkg/cmdline.gitVersion=$(GIT_VERSION)
+
 DEFAULT_GOOS=$(shell go env GOOS)
 DEFAULT_GOARCH=$(shell go env GOARCH)
 
@@ -23,27 +26,27 @@ clean:
 bin/macadam-darwin-amd64: GOOS=darwin
 bin/macadam-darwin-amd64: GOARCH=amd64
 bin/macadam-darwin-amd64: force-build
-	@go build -o bin/macadam-$(GOOS)-$(GOARCH) ./cmd/macadam
+	@go build -ldflags "$(VERSION_LDFLAGS)" -o bin/macadam-$(GOOS)-$(GOARCH) ./cmd/macadam
 
 bin/macadam-darwin-arm64: GOOS=darwin
 bin/macadam-darwin-arm64: GOARCH=arm64
 bin/macadam-darwin-arm64: force-build
-	@go build -o bin/macadam-$(GOOS)-$(GOARCH) ./cmd/macadam
+	@go build -ldflags "$(VERSION_LDFLAGS)" -o bin/macadam-$(GOOS)-$(GOARCH) ./cmd/macadam
 
 bin/macadam-linux-amd64: GOOS=linux
 bin/macadam-linux-amd64: GOARCH=amd64
 bin/macadam-linux-amd64: force-build
-	@go build -o bin/macadam-$(GOOS)-$(GOARCH) ./cmd/macadam
+	@go build -ldflags "$(VERSION_LDFLAGS)" -o bin/macadam-$(GOOS)-$(GOARCH) ./cmd/macadam
 
 bin/macadam-linux-arm64: GOOS=linux
 bin/macadam-linux-arm64: GOARCH=arm64
 bin/macadam-linux-arm64: force-build
-	@go build -o bin/macadam-$(GOOS)-$(GOARCH) ./cmd/macadam
+	@go build -ldflags "$(VERSION_LDFLAGS)" -o bin/macadam-$(GOOS)-$(GOARCH) ./cmd/macadam
 
 bin/macadam-windows-amd64: GOOS=windows
 bin/macadam-windows-amd64: GOARCH=amd64
 bin/macadam-windows-amd64: force-build
-	@go build -o bin/macadam-$(GOOS)-$(GOARCH) ./cmd/macadam
+	@go build -ldflags "$(VERSION_LDFLAGS)" -o bin/macadam-$(GOOS)-$(GOARCH) ./cmd/macadam
 
 .PHONY: lint
 lint: $(TOOLS_BINDIR)/golangci-lint

cmd/macadam/main.go

@@ -1,9 +1,12 @@
 package main
 
 import (
+	"fmt"
 	"log/slog"
+
+	"github.com/crc-org/macadam/pkg/cmdline"
 )
 
 func main() {
-	slog.Info("macadam")
+	slog.Info(fmt.Sprintf("macadam version %s", cmdline.Version()))
 }

pkg/cmdline/version.go

@@ -0,0 +1,40 @@
+package cmdline
+
+import (
+	"runtime/debug"
+	"strings"
+)
+
+var (
+	// set using the '-X github.com/crc-org/macadam/pkg/cmdline.gitVersion' linker flag
+	gitVersion = "unknown"
+
+	// set through .gitattributes when `git archive` is used
+	// see https://icinga.com/blog/2022/05/25/embedding-git-commit-information-in-go-binaries/
+	gitArchiveVersion = "$Format:%(describe)$"
+)
+
+func Version() string {
+	switch {
+	// This will be substituted when building from a GitHub tarball
+	case !strings.HasPrefix(gitArchiveVersion, "$Format:"):
+		return gitArchiveVersion
+	// This will be set when building from git using make
+	case gitVersion != "":
+		return gitVersion
+	// moduleVersionFromBuildInfo() will be set when using `go install`
+	default:
+		return moduleVersionFromBuildInfo()
+	}
+}
+
+func moduleVersionFromBuildInfo() string {
+	info, ok := debug.ReadBuildInfo()
+	if !ok {
+		return ""
+	}
+	if info.Main.Version == "(devel)" {
+		return ""
+	}
+	return info.Main.Version
+}