feat: docker - added linker for extra directories

When adding extra files to docker using a hard link it is impossible
to add a directory because only files can be linked hard. For directories
I added a linker that recursively linkes all files in a directory and re-
creates the directory structure in the dist directory.

pipeline/docker/docker.go

@@ -16,6 +16,7 @@ import (
 	"github.com/goreleaser/goreleaser/context"
 	"github.com/goreleaser/goreleaser/internal/artifact"
 	"github.com/goreleaser/goreleaser/pipeline"
+	"io/ioutil"
 )
 
 // ErrNoDocker is shown when docker cannot be found in $PATH
@@ -127,7 +128,7 @@ func process(ctx *context.Context, docker config.Docker, artifact artifact.Artif
 		return errors.Wrap(err, "failed to link dockerfile")
 	}
 	for _, file := range docker.Files {
-		if err := os.Link(file, filepath.Join(root, filepath.Base(file))); err != nil {
+		if err := link(file, filepath.Join(root, filepath.Base(file))); err != nil {
 			return errors.Wrapf(err, "failed to link extra file '%s'", file)
 		}
 	}
@@ -143,6 +144,62 @@ func process(ctx *context.Context, docker config.Docker, artifact artifact.Artif
 	return publish(ctx, docker, image, latest)
 }
 
+// link a file or directory hard
+func link(src, dest string) error {
+	info, err := os.Stat(src)
+	if err != nil {
+		return err
+	}
+	if info.IsDir() {
+		return directoryLink(src, dest, info)
+	}
+	return fileLink(src, dest)
+}
+
+// directoryLink recursively creates all subdirectories and links all files hard
+func directoryLink(src, dest string, info os.FileInfo) error {
+	if info == nil {
+		i, err := os.Stat(src)
+		if err != nil {
+			return err
+		}
+		info = i
+	}
+	if err := os.MkdirAll(dest, info.Mode()); err != nil {
+		return err
+	}
+	infos, err := ioutil.ReadDir(src)
+	if err != nil {
+		return err
+	}
+	for _, info := range infos {
+		if info.IsDir() {
+			err := directoryLink(
+				filepath.Join(src, info.Name()),
+				filepath.Join(dest, info.Name()),
+				info,
+			)
+			if err != nil {
+				return err
+			}
+		} else {
+			err := fileLink(
+				filepath.Join(src, info.Name()),
+				filepath.Join(dest, info.Name()),
+			)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// fileLink links a file hard
+func fileLink(src, dest string) error {
+	return os.Link(src, dest)
+}
+
 func publish(ctx *context.Context, docker config.Docker, image, latest string) error {
 	// TODO: improve this so it can log it to stdout
 	if !ctx.Publish {

pipeline/docker/docker_test.go

@@ -12,6 +12,7 @@ import (
 	"github.com/goreleaser/goreleaser/internal/artifact"
 	"github.com/goreleaser/goreleaser/pipeline"
 	"github.com/stretchr/testify/assert"
+	"syscall"
 )
 
 func killAndRm(t *testing.T) {
@@ -236,3 +237,60 @@ func TestDefaultSet(t *testing.T) {
 	assert.Equal(t, "{{ .Version }}", docker.TagTemplate)
 	assert.Equal(t, "Dockerfile.foo", docker.Dockerfile)
 }
+
+func TestLinkFile(t *testing.T) {
+	const srcFile = "/tmp/test"
+	const dstFile = "/tmp/linked"
+	err := ioutil.WriteFile(srcFile, []byte("foo"), 0644)
+	if err != nil {
+		t.Log("Cannot setup test file")
+		t.Fail()
+	}
+	err = link(srcFile, dstFile)
+	if err != nil {
+		t.Log("Failed to link: ", err)
+		t.Fail()
+	}
+	if inode(srcFile) != inode(dstFile) {
+		t.Log("Inodes do not match, destination file is not a link")
+		t.Fail()
+	}
+	// cleanup
+	os.Remove(srcFile)
+	os.Remove(dstFile)
+}
+
+func TestLinkDirectory(t *testing.T) {
+	const srcDir = "/tmp/testdir"
+	const testFile = "test"
+	const dstDir = "/tmp/linkedDir"
+
+	os.Mkdir(srcDir, 0755)
+	err := ioutil.WriteFile(srcDir+"/"+testFile, []byte("foo"), 0644)
+	if err != nil {
+		t.Log("Cannot setup test file")
+		t.Fail()
+	}
+	err = directoryLink(srcDir, dstDir, nil)
+	if err != nil {
+		t.Log("Failed to link: ", err)
+		t.Fail()
+	}
+	if inode(srcDir+"/"+testFile) != inode(dstDir+"/"+testFile) {
+		t.Log("Inodes do not match, destination file is not a link")
+		t.Fail()
+	}
+
+	// cleanup
+	os.RemoveAll(srcDir)
+	os.RemoveAll(dstDir)
+}
+
+func inode(file string) uint64 {
+	fileInfo, err := os.Stat(file)
+	if err != nil {
+		return 0
+	}
+	stat := fileInfo.Sys().(*syscall.Stat_t)
+	return stat.Ino
+}