Add git provenance labels

as per #1290

Signed-off-by: Christian Dupuis <cd@atomist.com>

build/git.go

@@ -0,0 +1,98 @@
+package build
+
+import (
+	"context"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+
+	ocispecs "github.com/opencontainers/image-spec/specs-go/v1"
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+)
+
+const DockerfileLabel = "com.docker.image.source.entrypoint"
+
+func addGitProvenance(ctx context.Context, contextPath string, dockerfilePath string) (map[string]string, error) {
+	v, ok := os.LookupEnv("BUILDX_GIT_LABELS")
+	if !ok || contextPath == "" {
+		return nil, nil
+	}
+	labels := make(map[string]string, 0)
+
+	// figure out in which directory the git command needs to run in
+	var wd string
+	if filepath.IsAbs(contextPath) {
+		wd = contextPath
+	} else {
+		cwd, _ := os.Getwd()
+		wd, _ = filepath.Abs(filepath.Join(cwd, contextPath))
+	}
+
+	// check if inside git working tree
+	cmd := exec.CommandContext(ctx, "git", "rev-parse", "--is-inside-work-tree")
+	cmd.Dir = wd
+	err := cmd.Run()
+	if err != nil {
+		logrus.Warnf("Unable to determine Git information")
+		return nil, nil
+	}
+
+	// obtain Git sha of current HEAD
+	cmd = exec.CommandContext(ctx, "git", "rev-parse", "HEAD")
+	cmd.Dir = wd
+	out, err := cmd.Output()
+	if err != nil {
+		return nil, errors.Wrap(err, "error obtaining git head")
+	}
+	sha := strings.TrimSpace(string(out))
+
+	// check if the current HEAD is clean
+	cmd = exec.CommandContext(ctx, "git", "status", "--porcelain", "--ignored")
+	cmd.Dir = wd
+	out, err = cmd.Output()
+	if err != nil {
+		return nil, errors.Wrap(err, "error obtaining git status")
+	}
+	if len(strings.TrimSpace(string(out))) != 0 {
+		sha += "-dirty"
+	}
+	labels[ocispecs.AnnotationRevision] = sha
+
+	// add a remote url if full Git details are requested; if there aren't any remotes don't fail
+	if v == "full" {
+		cmd = exec.CommandContext(ctx, "git", "ls-remote", "--get-url")
+		cmd.Dir = wd
+		out, _ := cmd.Output()
+		if len(out) > 0 {
+			labels[ocispecs.AnnotationSource] = strings.TrimSpace(string(out))
+		}
+	}
+
+	// add Dockerfile path; there is no org.opencontainers annotation for this
+	if dockerfilePath == "" {
+		dockerfilePath = filepath.Join(wd, "Dockerfile")
+	}
+
+	// obtain Git root directory
+	cmd = exec.CommandContext(ctx, "git", "rev-parse", "--show-toplevel")
+	cmd.Dir = wd
+	out, err = cmd.Output()
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to get git root")
+	}
+	root := strings.TrimSpace(string(out))
+
+	// record only Dockerfile paths that are within the Git root
+	if !filepath.IsAbs(dockerfilePath) {
+		cwd, _ := os.Getwd()
+		dockerfilePath = filepath.Join(cwd, dockerfilePath)
+	}
+	dockerfilePath, _ = filepath.Rel(root, dockerfilePath)
+	if !strings.HasPrefix(dockerfilePath, "..") {
+		labels[DockerfileLabel] = dockerfilePath
+	}
+
+	return labels, nil
+}