Prettier 3.6.2
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# Options (if any):
--parser markdown

Input:

- a

  - b

Output:

- a
  - b

Expected output:

- a

  - b

Why?

According to the CommonMark spec:

A list is loose if any of its constituent list items are separated by blank lines, or if any of its constituent list items directly contain two block-level elements with a blank line between them. Otherwise a list is tight. (The difference in HTML output is that paragraphs in a loose list are wrapped in <p> tags, while paragraphs in a tight list are not.)

In this example, the loose version renders as

<ul>
  <li>
    <p>a</p>
    <ul>
      <li>b</li>
    </ul>
  </li>
</ul>

• a

  • b

while the tight version renders as

<ul>
  <li>
    a
    <ul>
      <li>b</li>
    </ul>
  </li>
</ul>

• a
  • b

The removed <p> visibly changes the vertical spacing. Prettier should not change the meaning of Markdown code by switching loose lists to tight or vice versa.

• Cc @byplayer (Fix markdown inserts unexpected newline in lists #16637)