From ac6305943444102a209f0f3bf4e48e111bf805b3 Mon Sep 17 00:00:00 2001
From: Petyo Ivanov <underlog@gmail.com>
Date: Sat, 14 Sep 2024 09:18:06 +0300
Subject: [PATCH] fix: deeply nested lists don't throw an error

Fixes #583
---
 src/examples/nested-lists.tsx               | 32 +++++++++++++++++++++
 src/plugins/lists/LexicalListItemVisitor.ts | 11 +++++--
 2 files changed, 41 insertions(+), 2 deletions(-)
 create mode 100644 src/examples/nested-lists.tsx

diff --git a/src/examples/nested-lists.tsx b/src/examples/nested-lists.tsx
new file mode 100644
index 00000000..fde570e4
--- /dev/null
+++ b/src/examples/nested-lists.tsx
@@ -0,0 +1,32 @@
+import React from 'react'
+import { MDXEditor, listsPlugin, diffSourcePlugin, toolbarPlugin, DiffSourceToggleWrapper, UndoRedo } from '..'
+
+const listsMarkdown = `
+* hello
+* world
+    * indented
+  * more
+* back
+`
+
+export function NestedLists() {
+  return (
+    <MDXEditor
+      markdown={listsMarkdown}
+      onChange={(md) => {
+        console.log(md)
+      }}
+      plugins={[
+        listsPlugin(),
+        diffSourcePlugin(),
+        toolbarPlugin({
+          toolbarContents: () => (
+            <DiffSourceToggleWrapper>
+              <UndoRedo />
+            </DiffSourceToggleWrapper>
+          )
+        })
+      ]}
+    />
+  )
+}
diff --git a/src/plugins/lists/LexicalListItemVisitor.ts b/src/plugins/lists/LexicalListItemVisitor.ts
index 601f6536..d82c6e47 100644
--- a/src/plugins/lists/LexicalListItemVisitor.ts
+++ b/src/plugins/lists/LexicalListItemVisitor.ts
@@ -10,8 +10,15 @@ export const LexicalListItemVisitor: LexicalExportVisitor<ListItemNode, Mdast.Li
 
     if (children.length === 1 && $isListNode(firstChild)) {
       // append the list after the paragraph of the previous list item
-      const prevListItemNode = mdastParent.children.at(-1) as Mdast.ListItem
-      actions.visitChildren(lexicalNode, prevListItemNode)
+      const prevListItemNode = mdastParent.children.at(-1) as Mdast.ListItem | undefined
+      // XXX: this is a hack to avoid errors with deeply nested lists - the approach will flatten them.
+      // Deeply nested lists are still not supported, but at least no error will be thrown.
+      if (!prevListItemNode) {
+        // @ts-expect-error - MDAST type is incorrect
+        actions.visitChildren(firstChild, mdastParent)
+      } else {
+        actions.visitChildren(lexicalNode, prevListItemNode)
+      }
     } else {
       const parentList = lexicalNode.getParent()! as ListNode
       // nest the children in a paragraph for MDAST compatibility