Fix to deep clone unknown nodes

lib/index.js

@@ -48,12 +48,13 @@
  *   User configuration.
  */
 
-import {Parser, Token, TokenizerMode, html} from 'parse5'
-import {pointStart, pointEnd} from 'unist-util-position'
-import {visit} from 'unist-util-visit'
+import extend from 'extend'
 import {fromParse5} from 'hast-util-from-parse5'
 import {toParse5} from 'hast-util-to-parse5'
 import {htmlVoidElements} from 'html-void-elements'
+import {Parser, Token, TokenizerMode, html} from 'parse5'
+import {pointStart, pointEnd} from 'unist-util-position'
+import {visit} from 'unist-util-visit'
 import {zwitch} from 'zwitch'
 
 /** @type {ParserOptions} */
@@ -282,23 +283,18 @@ function stitch(node, state) {
   state.stitches = true
 
   /** @type {Node} */
-  let clone
+  const clone = cloneWithoutChildren(node)
 
   // Recurse, because to somewhat handle `[<x>]</x>` (where `[]` denotes the
   // passed through node).
-  if ('children' in node) {
-    // To do: deep clone.
-    clone = {
-      ...node,
-      children: raw(
-        {type: 'root', children: node.children},
-        state.file,
-        state.options
-        // @ts-expect-error Assume a given parent yields a parent.
-      ).children
-    }
-  } else {
-    clone = {...node}
+  if ('children' in node && 'children' in clone) {
+    const fakeRoot = raw(
+      {type: 'root', children: node.children},
+      state.file,
+      state.options
+    )
+    // @ts-expect-error Assume a given parent yields a parent.
+    clone.children = fakeRoot.children
   }
 
   // Hack: `value` is supposed to be a string, but as none of the tools
@@ -641,3 +637,17 @@ function createParse5Location(node) {
 function isOptions(value) {
   return Boolean(value && !('message' in value && 'messages' in value))
 }
+
+/**
+ * @template {Node} NodeType
+ *   Node type.
+ * @param {NodeType} node
+ *   Node to clone.
+ * @returns {NodeType}
+ *   Cloned node, without children.
+ */
+function cloneWithoutChildren(node) {
+  return 'children' in node
+    ? extend(true, {}, {...node, children: []})
+    : extend(true, {}, node)
+}

package.json

@@ -36,6 +36,7 @@
   ],
   "dependencies": {
     "@types/hast": "^2.0.0",
+    "extend": "^3.0.0",
     "hast-util-from-parse5": "^7.0.0",
     "hast-util-to-parse5": "^7.0.0",
     "html-void-elements": "^2.0.0",