Add vendor/.git exists check in SafeWriter.Write

txn_writer.go

@@ -294,6 +294,14 @@ func (sw *SafeWriter) Write(root string, sm gps.SourceManager) error {
 		}
 	}
 
+	// Ensure vendor/.git is preserved if present
+	if hasDotGit(vpath) {
+		err = os.Rename(filepath.Join(vpath, ".git"), filepath.Join(td, "vendor/.git"))
+		if _, ok := err.(*os.LinkError); ok {
+			return errors.Wrap(err, "failed to preserve vendor/.git")
+		}
+	}
+
 	// Move the existing files and dirs to the temp dir while we put the new
 	// ones in, to provide insurance against errors for as long as possible.
 	type pathpair struct {
@@ -526,6 +534,16 @@ func deleteDirs(toDelete []string) error {
 	return nil
 }
 
+// hasDotGit checks if a given path has .git file or directory in it.
+func hasDotGit(path string) bool {
+	gitfilepath := filepath.Join(path, ".git")
+	_, err := os.Stat(gitfilepath)
+	if err != nil {
+		return false
+	}
+	return true
+}
+
 type byLen []string
 
 func (a byLen) Len() int           { return len(a) }

txn_writer_test.go

@@ -5,6 +5,8 @@
 package dep
 
 import (
+	"io/ioutil"
+	"os"
 	"path/filepath"
 	"strings"
 	"testing"
@@ -522,3 +524,17 @@ func TestSafeWriter_DiffLocks(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestHasDotGit(t *testing.T) {
+	// Create a tempdir with .git file
+	td, err := ioutil.TempDir(os.TempDir(), "dotGitFile")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(td)
+
+	os.OpenFile(td+string(filepath.Separator)+".git", os.O_CREATE, 0777)
+	if !hasDotGit(td) {
+		t.Fatal("Expected hasDotGit to find .git")
+	}
+}