fix(orderdList): preserve non-1 start numbers

Also fixes preserving `0` as first list number.

Fixes: #4828

Signed-off-by: Jonas <jonas@freesources.org>

Author: mejo-

src/nodes/OrderedList.ts

@@ -3,6 +3,9 @@
  * SPDX-License-Identifier: AGPL-3.0-or-later
  */
 
+import type { Node } from '@tiptap/pm/model'
+import type { MarkdownSerializerState } from 'prosemirror-markdown'
+
 import { OrderedList as TiptapOrderedList } from '@tiptap/extension-list'
 import { toggleListCommand } from '../commands'
 
@@ -23,6 +26,18 @@ const OrderedList = TiptapOrderedList.extend({
 			toggleOrderedList: toggleListCommand('orderedList', 'listItem'),
 		}
 	},
+
+	// Overwrite toMarkdown from prosemirror-markdown to preserve non-1 start numbers in lists
+	// @ts-expect-error - toMarkdown is a custom field not part of the official Tiptap API
+	toMarkdown(state: MarkdownSerializerState, node: Node) {
+		const start = node.attrs.start ?? 1
+		const maxW = String(start + node.childCount - 1).length
+		const space = state.repeat(' ', maxW + 2)
+		state.renderList(node, space, (i) => {
+			const nStr = String(start + i)
+			return state.repeat(' ', maxW - nStr.length) + nStr + '. '
+		})
+	},
 })
 
 export default OrderedList

src/tests/markdown.spec.js

@@ -55,6 +55,13 @@ describe('Markdown though editor', () => {
 	})
 	test('ol', () => {
 		expect(markdownThroughEditor('1. foo\n2. bar')).toBe('1. foo\n2. bar')
+		expect(markdownThroughEditor('0. foo\n1. bar')).toBe('0. foo\n1. bar')
+		// regression test for #4828
+		expect(markdownThroughEditor('42. foo\n43. bar')).toBe('42. foo\n43. bar')
+		// for now we enforce sequential order in ordered lists
+		expect(markdownThroughEditor('2. foo\n19. bar\n2. baz')).toBe(
+			'2. foo\n3. bar\n4. baz',
+		)
 	})
 	test('paragraph', () => {
 		// Test whitespace characters are untouched