Allow snapshot to be created from empty local repo

Fixes #288

deb/snapshot.go

@@ -53,11 +53,7 @@ func NewSnapshotFromRepository(name string, repo *RemoteRepo) (*Snapshot, error)
 
 // NewSnapshotFromLocalRepo creates snapshot from current state of local repository
 func NewSnapshotFromLocalRepo(name string, repo *LocalRepo) (*Snapshot, error) {
-	if repo.packageRefs == nil {
-		return nil, errors.New("local repo doesn't have packages")
-	}
-
-	return &Snapshot{
+	snap := &Snapshot{
 		UUID:        uuid.New(),
 		Name:        name,
 		CreatedAt:   time.Now(),
@@ -65,7 +61,13 @@ func NewSnapshotFromLocalRepo(name string, repo *LocalRepo) (*Snapshot, error) {
 		SourceIDs:   []string{repo.UUID},
 		Description: fmt.Sprintf("Snapshot from local repo %s", repo),
 		packageRefs: repo.packageRefs,
-	}, nil
+	}
+
+	if snap.packageRefs == nil {
+		snap.packageRefs = NewPackageRefList()
+	}
+
+	return snap, nil
 }
 
 // NewSnapshotFromPackageList creates snapshot from PackageList

deb/snapshot_test.go

@@ -37,11 +37,17 @@ func (s *SnapshotSuite) TestNewSnapshotFromRepository(c *C) {
 func (s *SnapshotSuite) TestNewSnapshotFromLocalRepo(c *C) {
 	localRepo := NewLocalRepo("lala", "hoorah!")
 
-	_, err := NewSnapshotFromLocalRepo("snap2", localRepo)
-	c.Check(err, ErrorMatches, "local repo doesn't have packages")
+	snapshot, err := NewSnapshotFromLocalRepo("snap2", localRepo)
+	c.Assert(err, IsNil)
+	c.Check(snapshot.Name, Equals, "snap2")
+	c.Check(snapshot.NumPackages(), Equals, 0)
+	c.Check(snapshot.RefList().Len(), Equals, 0)
+	c.Check(snapshot.SourceKind, Equals, "local")
+	c.Check(snapshot.SourceIDs, DeepEquals, []string{localRepo.UUID})
 
 	localRepo.UpdateRefList(s.reflist)
-	snapshot, _ := NewSnapshotFromLocalRepo("snap1", localRepo)
+	snapshot, err = NewSnapshotFromLocalRepo("snap1", localRepo)
+	c.Assert(err, IsNil)
 	c.Check(snapshot.Name, Equals, "snap1")
 	c.Check(snapshot.NumPackages(), Equals, 3)
 	c.Check(snapshot.RefList().Len(), Equals, 3)