feat(core): support cycles in deep cloning (#3322)

Before this change, deepClone function supported
directed acyclic trees. With this change the
function will handle directed cyclic graphs.

Refs #3290

Author: char0n

packages/apidom-core/src/clone/index.ts

@@ -6,26 +6,78 @@ import ShallowCloneError from './errors/ShallowCloneError';
 
 type FinalCloneTypes = KeyValuePair | ArraySlice | ObjectSlice;
 
-const invokeClone = <T extends Element | FinalCloneTypes>(value: T): T => {
-  if (typeof value?.clone === 'function') {
-    return value.clone() as T;
-  }
-  return value;
+type DeepCloneOptions<T extends Element | FinalCloneTypes> = {
+  visited?: WeakMap<T, T>;
 };
 
-export const cloneDeep = <T extends Element | FinalCloneTypes>(value: T): T => {
+export const cloneDeep = <T extends Element | FinalCloneTypes>(
+  value: T,
+  options: DeepCloneOptions<T> = {},
+): T => {
+  const { visited = new WeakMap<T, T>() } = options;
+  const passThroughOptions = { ...options, visited };
+
+  // detect cycle and return memoized value
+  if (visited.has(value)) {
+    return visited.get(value) as T;
+  }
+
+  if (value instanceof KeyValuePair) {
+    const { key, value: val } = value;
+    const keyCopy = isElement(key)
+      ? cloneDeep(key, passThroughOptions as DeepCloneOptions<Element>)
+      : key;
+    const valueCopy = isElement(val)
+      ? cloneDeep(val, passThroughOptions as DeepCloneOptions<Element>)
+      : val;
+    const copy = new KeyValuePair(keyCopy, valueCopy) as T;
+    visited.set(value, copy);
+    return copy;
+  }
+
   if (value instanceof ObjectSlice) {
-    const items = [...(value as ObjectSlice)].map(invokeClone) as T[];
-    return new ObjectSlice(items) as T;
+    const mapper = (element: T) => cloneDeep(element, passThroughOptions);
+    const items = [...(value as ObjectSlice)].map(mapper) as T[];
+    const copy = new ObjectSlice(items) as T;
+    visited.set(value, copy);
+    return copy;
   }
 
   if (value instanceof ArraySlice) {
-    const items = [...(value as ArraySlice)].map(invokeClone) as T[];
-    return new ArraySlice(items) as T;
+    const mapper = (element: T) => cloneDeep(element, passThroughOptions);
+    const items = [...(value as ArraySlice)].map(mapper) as T[];
+    const copy = new ArraySlice(items) as T;
+    visited.set(value, copy);
+    return copy;
   }
 
-  if (typeof value?.clone === 'function') {
-    return value.clone() as T;
+  if (isElement(value)) {
+    const copy = cloneShallow(value); // eslint-disable-line @typescript-eslint/no-use-before-define
+
+    visited.set(value, copy);
+
+    if (value.content) {
+      if (isElement(value.content)) {
+        copy.content = cloneDeep(
+          value.content,
+          passThroughOptions as DeepCloneOptions<Element>,
+        ) as any;
+      } else if ((value.content as unknown) instanceof KeyValuePair) {
+        copy.content = cloneDeep(
+          value.content as unknown as KeyValuePair,
+          passThroughOptions as DeepCloneOptions<KeyValuePair>,
+        ) as any;
+      } else if (Array.isArray(value.content)) {
+        const mapper = (element: unknown) => cloneDeep(element as T, passThroughOptions);
+        copy.content = value.content.map(mapper);
+      } else {
+        copy.content = value.content;
+      }
+    } else {
+      copy.content = value.content;
+    }
+
+    return copy;
   }
 
   throw new DeepCloneError("Value provided to cloneDeep function couldn't be cloned", {

packages/apidom-core/test/clone/index.ts

@@ -119,28 +119,48 @@ describe('clone', function () {
   });
 
   context('cloneDeep', function () {
-    specify('should deep clone ObjectElement', function () {
-      const valueElement = new ArrayElement([1]);
-      const objectElement = new ObjectElement({ a: valueElement });
-      const clone = cloneDeep(objectElement);
+    context('given ObjectElement', function () {
+      specify('should deep clone', function () {
+        const valueElement = new ArrayElement([1]);
+        const objectElement = new ObjectElement({ a: valueElement });
+        const clone = cloneDeep(objectElement);
 
-      objectElement.set('c', 'd');
-      valueElement.push(2);
+        objectElement.set('c', 'd');
+        valueElement.push(2);
 
-      assert.notStrictEqual(clone, objectElement);
-      assert.deepEqual(toValue(clone), { a: [1] });
+        assert.notStrictEqual(clone, objectElement);
+        assert.deepEqual(toValue(clone), { a: [1] });
+      });
+
+      specify('should deep clone with cycles', function () {
+        const objectElement = new ObjectElement({ a: 'b' });
+        objectElement.set('c', objectElement);
+        const clone = cloneDeep(objectElement);
+
+        assert.strictEqual(clone, clone.get('c'));
+      });
     });
 
-    specify('should deep clone ArrayElement', function () {
-      const firstItemElement = new ObjectElement({ a: 'b' });
-      const arrayElement = new ArrayElement([firstItemElement, 2, 3]);
-      const clone = cloneDeep(arrayElement);
+    context('given ArrayElement', function () {
+      specify('should deep clone', function () {
+        const firstItemElement = new ObjectElement({ a: 'b' });
+        const arrayElement = new ArrayElement([firstItemElement, 2, 3]);
+        const clone = cloneDeep(arrayElement);
 
-      arrayElement.push(4);
-      firstItemElement.set('a', 'c');
+        arrayElement.push(4);
+        firstItemElement.set('a', 'c');
 
-      assert.notStrictEqual(clone, arrayElement);
-      assert.deepEqual(toValue(clone), [{ a: 'b' }, 2, 3]);
+        assert.notStrictEqual(clone, arrayElement);
+        assert.deepEqual(toValue(clone), [{ a: 'b' }, 2, 3]);
+      });
+
+      specify('should deep clone with cycles', function () {
+        const arrayElement = new ArrayElement([1]);
+        arrayElement.push(arrayElement);
+        const clone = cloneDeep(arrayElement);
+
+        assert.strictEqual(clone, clone.get(1));
+      });
     });
 
     specify('should deep clone NumberElement', function () {