Preserve Markdown emphasis delimiters when joining lines

[lingyaochu]

Objective

When joining lines, Zed checks the next line and strips comment, documentation-comment, and unordered-list delimiters. The logic trims whitespace from these delimiters, then checks whether the next line starts with the trimmed delimiter. If it does, Zed removes the delimiter before joining the lines.

This works for comment and documentation-comment delimiters, where trailing whitespace does not affect their meaning. However, it causes unexpected behavior for unordered-list delimiters, which, as far as I know, are unique to Markdown.

In Markdown, * is an unordered-list marker, while * is also used as an emphasis delimiter, such as *italics* and **bold**. The current logic strips the leading * from these emphasis cases, which it should not.

Solution

For unordered-list delimiters, Zed should strip the exact delimiter, such as * , rather than the trimmed *. It should strip a bare * only when the next line contains only *.

Testing

Tested locally and new GPUI tests were added.

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content adheres to Zed's UI standards (UX/UI and icon guidelines)
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

---

Release Notes:

• Fixed markdown emphasis delimiters being removed when joining lines.

[ChristopherBiscardi]

thanks!

[lingyaochu]

Apologies, I forgot to reference the issue in the PR description before merging 😅 . This PR was intended to fix #56358, so that issue can now be closed. Thanks!