fix: 🐛 preserve empty line exception and behavior

✅ Closes: #1811

Author: Saul-Mirone

Diff for: .prettierignore

@@ -1,4 +1,5 @@
 pnpm-lock.yaml
 **/storybook-static
 **/lib
-**/.storybook
+**/.storybook
+**/tests/data/*.md

Diff for: e2e/tests/data/preserve-empty-line.md

@@ -1,9 +1,11 @@
+#
+
 123
 
 <br />
 
 456
 
-<br />
+* <br />
 
-789
+> <br />

Diff for: e2e/tests/transform/preserve-empty-line.spec.ts

@@ -16,8 +16,23 @@ test('preserve empty line', async ({ page }) => {
   expect(await page.locator('p').nth(1).textContent()).toBe('')
   expect(await page.locator('p').nth(2).textContent()).toBe('456')
   expect(await page.locator('p').nth(3).textContent()).toBe('')
-  expect(await page.locator('p').nth(4).textContent()).toBe('789')
+  expect(await page.locator('li').nth(0).textContent()).toBe('')
+  expect(await page.locator('blockquote').nth(0).textContent()).toBe('')
 
   const markdownOutput = await getMarkdown(page)
   expect(markdownOutput.trim()).toBe(markdown.trim())
 })
+
+test('should not preserve last empty line', async ({ page }) => {
+  await focusEditor(page)
+
+  await page.keyboard.press('Enter')
+  await page.keyboard.press('Backspace')
+
+  let markdownOutput = await getMarkdown(page)
+  expect(markdownOutput.trim()).toBe('')
+
+  await page.keyboard.press('Enter')
+  markdownOutput = await getMarkdown(page)
+  expect(markdownOutput.trim()).toBe('<br />')
+})

Diff for: packages/plugins/preset-commonmark/src/node/paragraph.ts

@@ -1,6 +1,6 @@
 import type { Ctx } from '@milkdown/ctx'
 
-import { commandsCtx } from '@milkdown/core'
+import { commandsCtx, editorViewCtx } from '@milkdown/core'
 import { setBlockType } from '@milkdown/prose/commands'
 import { $command, $nodeAttr, $nodeSchema, $useKeymap } from '@milkdown/utils'
 
@@ -34,9 +34,13 @@ export const paragraphSchema = $nodeSchema('paragraph', (ctx) => ({
   toMarkdown: {
     match: (node) => node.type.name === 'paragraph',
     runner: (state, node) => {
+      const view = ctx.get(editorViewCtx)
+      const lastNode = view.state?.doc.lastChild
+
       state.openNode('paragraph')
       if (
         (!node.content || node.content.size === 0) &&
+        node !== lastNode &&
         shouldPreserveEmptyLine(ctx)
       ) {
         state.addNode('html', undefined, '<br />')

Diff for: packages/plugins/preset-commonmark/src/plugin/remark-preserve-empty-line.ts

@@ -5,8 +5,8 @@ import { visit } from 'unist-util-visit'
 
 import { withMeta } from '../__internal__'
 
-function visitImage(ast: Node) {
-  return visit(ast, 'paragraph', (node: Node & { children?: Node[] }) => {
+function visitEmptyLine(ast: Node) {
+  return visit(ast, (node: Node & { children?: Node[] }) => {
     if (node.children?.length !== 1) return
     const firstChild = node.children?.[0]
     if (!firstChild || firstChild.type !== 'html') return
@@ -30,7 +30,7 @@ function visitImage(ast: Node) {
 /// This plugin should be used with `linebreakSchema` to work.
 export const remarkPreserveEmptyLinePlugin = $remark(
   'remark-preserve-empty-line',
-  () => () => visitImage
+  () => () => visitEmptyLine
 )
 
 withMeta(remarkPreserveEmptyLinePlugin.plugin, {