fix(checkout): checkout fails early if link exists

fsi/fsi.go

@@ -99,29 +99,51 @@ func (fsi *FSI) LinkedRefs(offset, limit int) ([]reporef.DatasetRef, error) {
 	return refs, nil
 }
 
-// CreateLink links a working directory to a dataset. Returns the reference alias, and a
-// rollback function if no error occurs
-func (fsi *FSI) CreateLink(dirPath, refStr string) (alias string, rollback func(), err error) {
-	rollback = func() {}
-
+// HasLink checks if a refString already has an existing link on the file system
+func (fsi *FSI) HasLink(refStr string) (hasLink bool, err error) {
 	ref, err := repo.ParseDatasetRef(refStr)
 	if err != nil {
-		return "", rollback, err
+		return false, err
 	}
 	err = repo.CanonicalizeDatasetRef(fsi.repo, &ref)
 	if err != nil && err != repo.ErrNotFound && err != repo.ErrNoHistory {
-		return ref.String(), rollback, err
+		return false, err
 	}
 
+	return fsi.RefHasLink(ref)
+}
+
+// RefHasLink checks if a ref already has an existing link on the file system
+func (fsi *FSI) RefHasLink(ref reporef.DatasetRef) (hasLink bool, err error) {
 	if stored, err := fsi.repo.GetRef(ref); err == nil {
 		if stored.FSIPath != "" {
 			// There is already a link for this dataset, see if that link still exists.
 			targetPath := filepath.Join(stored.FSIPath, QriRefFilename)
 			if _, err := os.Stat(targetPath); err == nil {
-				return "", rollback, fmt.Errorf("'%s' is already linked to %s", ref.AliasString(), stored.FSIPath)
+				return true, fmt.Errorf("'%s' is already linked to %s", ref.AliasString(), stored.FSIPath)
 			}
 		}
 	}
+	return false, nil
+}
+
+// CreateLink links a working directory to a dataset. Returns the reference alias, and a
+// rollback function if no error occurs
+func (fsi *FSI) CreateLink(dirPath, refStr string) (alias string, rollback func(), err error) {
+	rollback = func() {}
+
+	ref, err := repo.ParseDatasetRef(refStr)
+	if err != nil {
+		return "", rollback, err
+	}
+	err = repo.CanonicalizeDatasetRef(fsi.repo, &ref)
+	if err != nil && err != repo.ErrNotFound && err != repo.ErrNoHistory {
+		return ref.String(), rollback, err
+	}
+
+	if _, err := fsi.RefHasLink(ref); err != nil {
+		return "", rollback, err
+	}
 
 	// Link the FSIPath to the reference before putting it into the repo
 	log.Debugf("fsi.CreateLink: linking ref=%q, FSIPath=%q", ref, dirPath)

lib/fsi.go

@@ -197,6 +197,11 @@ func (m *FSIMethods) Checkout(p *CheckoutParams, out *string) (err error) {
 	}
 	log.Debugf("Checkout loaded dataset %q", ref)
 
+	// Fail early if link already exists
+	if _, err := m.inst.fsi.HasLink(p.Ref); err != nil {
+		return err
+	}
+
 	// Create a directory.
 	if err := os.Mkdir(p.Dir, os.ModePerm); err != nil {
 		log.Debugf("Checkout, Mkdir failed, error: %s", ref)