linuxkit pkg: handle packages which are not in git

Detect if this is the case by checking if the given path is not in git and
conditionalising anything which would touch git.

Images built from outside git will, in the absence of options to force
otherwise, get tagged "latest".

Fixes: #2613

Signed-off-by: Ian Campbell <ijc@docker.com>

src/cmd/linuxkit/pkglib/build.go

@@ -70,7 +70,7 @@ func (p Pkg) Build(bos ...BuildOpt) error {
 		return fmt.Errorf("Unknown arch %q", arch)
 	}
 
-	if bo.release == "" {
+	if p.git != nil && bo.release == "" {
 		r, err := p.git.commitTag("HEAD")
 		if err != nil {
 			return err
@@ -97,10 +97,10 @@ func (p Pkg) Build(bos ...BuildOpt) error {
 
 	var args []string
 
-	if p.gitRepo != "" {
+	if p.git != nil && p.gitRepo != "" {
 		args = append(args, "--label", "org.opencontainers.image.source="+p.gitRepo)
 	}
-	if !p.dirty {
+	if p.git != nil && !p.dirty {
 		commit, err := p.git.commitHash("HEAD")
 		if err != nil {
 			return err

src/cmd/linuxkit/pkglib/git.go

@@ -24,8 +24,19 @@ type git struct {
 	dir string
 }
 
-func newGit(dir string) *git {
-	return &git{dir}
+// Returns git==nil and no error if the path is not within a git repository
+func newGit(dir string) (*git, error) {
+	g := &git{dir}
+
+	// Check if dir really is within a git directory
+	ok, err := g.isWorkTree(dir)
+	if err != nil {
+		return nil, err
+	}
+	if !ok {
+		return nil, nil
+	}
+	return g, nil
 }
 
 func (g git) mkCmd(args ...string) *exec.Cmd {
@@ -56,6 +67,25 @@ func (g git) command(args ...string) error {
 	return cmd.Run()
 }
 
+func (g git) isWorkTree(pkg string) (bool, error) {
+	tf, err := g.commandStdout(nil, "rev-parse", "--is-inside-work-tree")
+	if err != nil {
+		// If we executed git ok but it errored then that's because this isn't a git repo
+		if _, ok := err.(*exec.ExitError); ok {
+			return false, nil
+		}
+		return false, err
+	}
+
+	tf = strings.TrimSpace(tf)
+
+	if tf == "true" {
+		return true, nil
+	}
+
+	return false, fmt.Errorf("unexpected output from git rev-parse --is-inside-work-tree: %s", tf)
+}
+
 func (g git) treeHash(pkg, commit string) (string, error) {
 	out, err := g.commandStdout(os.Stderr, "ls-tree", "--full-tree", commit, "--", pkg)
 	if err != nil {

src/cmd/linuxkit/pkglib/pkglib.go

@@ -139,22 +139,27 @@ func NewFromCLI(fs *flag.FlagSet, args ...string) (Pkg, error) {
 		}
 	})
 
-	git := newGit(pkgPath)
-
-	gitDirty, err := git.isDirty(hashPath, hashCommit)
+	git, err := newGit(pkgPath)
 	if err != nil {
 		return Pkg{}, err
 	}
 
-	dirty = dirty || gitDirty
-
-	if hash == "" {
-		if hash, err = git.treeHash(hashPath, hashCommit); err != nil {
+	if git != nil {
+		gitDirty, err := git.isDirty(hashPath, hashCommit)
+		if err != nil {
 			return Pkg{}, err
 		}
 
-		if dirty {
-			hash += "-dirty"
+		dirty = dirty || gitDirty
+
+		if hash == "" {
+			if hash, err = git.treeHash(hashPath, hashCommit); err != nil {
+				return Pkg{}, err
+			}
+
+			if dirty {
+				hash += "-dirty"
+			}
 		}
 	}
 
@@ -193,7 +198,11 @@ func (p Pkg) ReleaseTag(release string) (string, error) {
 
 // Tag returns the tag to use for the package
 func (p Pkg) Tag() string {
-	return p.org + "/" + p.image + ":" + p.hash
+	r := p.org + "/" + p.image
+	if p.hash != "" {
+		r += ":" + p.hash
+	}
+	return r
 }
 
 // TrustEnabled returns true if trust is enabled