1 files changed, 79 insertions, 0 deletions
diff --git a/config-model/src/main/java/com/yahoo/schema/DocumentGraphValidator.java b/config-model/src/main/java/com/yahoo/schema/DocumentGraphValidator.java
new file mode 100644
index 00000000000..648cdf18c5b
--- /dev/null
+++ b/config-model/src/main/java/com/yahoo/schema/DocumentGraphValidator.java
@@ -0,0 +1,79 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.schema;
+
+import com.yahoo.schema.document.SDDocumentType;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+import java.util.List;
+
+import static java.util.stream.Collectors.joining;
+
+/**
+ * Validates that there are no cycles between document types (exception: self-reference is allowed).
+ * Example: if document B inherits A, then A cannot have a document reference to B.
+ *
+ * @author bjorncs
+ */
+public class DocumentGraphValidator {
+
+    public void validateDocumentGraph(List<SDDocumentType> documents) {
+        for (SDDocumentType document : documents) {
+            validateRoot(document);
+        }
+    }
+
+    private static void validateRoot(SDDocumentType root) {
+        validateChildren(root, root);
+    }
+
+    private static void validateChildren(SDDocumentType root, SDDocumentType currentDocument) {
+        try {
+            currentDocument.getDocumentReferences().get()
+                    .forEach(entry -> {
+                        SDDocumentType referencedDocument = entry.getValue().targetSearch().getDocument();
+                        validateDocument(root, referencedDocument);
+                    });
+            currentDocument.getInheritedTypes()
+                    .forEach(inheritedDocument -> {
+                        if (!isRootDocument(inheritedDocument)) {
+                            validateDocument(root, inheritedDocument);
+                        }
+                    });
+        } catch (DocumentGraphException e) {
+            e.addParentDocument(currentDocument);
+            throw e;
+        }
+    }
+
+    private static void validateDocument(SDDocumentType root, SDDocumentType currentDocument) {
+        if (root.equals(currentDocument)) {
+            throw new DocumentGraphException(currentDocument);
+        }
+        validateChildren(root, currentDocument);
+    }
+
+    private static boolean isRootDocument(SDDocumentType doc) {
+        return doc.getName().equals("document");
+    }
+
+    public static class DocumentGraphException extends IllegalArgumentException {
+        private final Deque<SDDocumentType> deque = new ArrayDeque<>();
+
+        public DocumentGraphException(SDDocumentType document) {
+            deque.addLast(document);
+        }
+
+        public void addParentDocument(SDDocumentType document) {
+            deque.addFirst(document);
+        }
+
+        @Override
+        public String getMessage() {
+            return deque.stream()
+                    .map(SDDocumentType::getName)
+                    .collect(joining("->", "Document dependency cycle detected: ", "."));
+        }
+    }
+
+}