1 files changed, 40 insertions, 0 deletions
diff --git a/refstore/files/transaction_verify_refnames.go b/refstore/files/transaction_verify_refnames.go
new file mode 100644
index 00000000..2efc872a
--- /dev/null
+++ b/refstore/files/transaction_verify_refnames.go
@@ -0,0 +1,40 @@
+package files
+
+import (
+	"fmt"
+	"strings"
+)
+
+func verifyRefnameAvailable(name string, existing map[string]struct{}, writes []string, deleted map[string]struct{}) error {
+	for existingName := range existing {
+		if existingName == name {
+			continue
+		}
+
+		if _, skip := deleted[existingName]; skip {
+			continue
+		}
+
+		if refnamesConflict(name, existingName) {
+			return fmt.Errorf("refstore/files: reference name conflict between %q and %q", name, existingName)
+		}
+	}
+
+	for _, other := range writes {
+		if other == name {
+			continue
+		}
+
+		if refnamesConflict(name, other) {
+			return fmt.Errorf("refstore/files: reference name conflict between %q and %q", name, other)
+		}
+	}
+
+	return nil
+}
+
+func refnamesConflict(left, right string) bool {
+	return left == right ||
+		strings.HasPrefix(left, right+"/") ||
+		strings.HasPrefix(right, left+"/")
+}