[#56779] Allow empty lines in rich text

[as-op]

Ticket

https://community.openproject.org/work_packages/56779

What are you trying to accomplish?

Allow empty lines everywhere in our rich text (markdown with html)

Screenshots

What approach did you choose and why?

Support blank lines on markdown root level

Markdown does not support multiple blank lines. So I adapted the format supported by most markdown parsers/renderers.

First line

<br>

<br>

Fourth line

(First line\n\n<br>\n\n<br>\n\nFourth line)

compatible with:

• GIthub
• markdown => HTML pipeline in OpenProject
• md-to-pdf
• markdown => html => CKeditor conversion support added
• CKeditor => html => markdown conversion support added

Support blank lines in table cells

We store tables as HTML, so we just need to preserve empty lines as paragraphs <p><br></p>

compatible with:

• GIthub
• markdown => HTML pipeline in OpenProject
• md-to-pdf support added
• markdown => html => CKeditor conversion support added
• CKeditor => html => markdown conversion support added

Support blank lines in lists

As for empty lines on root level, blank lines in lists are not supported by markdown, therefor we use the same method.

*  Start item

   <br>

   <br>

   End

*  Second item

compatible with:

• GIthub
• markdown => HTML pipeline in OpenProject
• md-to-pdf support added
• markdown => html => CKeditor conversion support added
• CKeditor => html => markdown conversion support added

Support blank lines in code blocks

Empty markdown code blocks are inflated to have at least one empty line

compatible with:

• GIthub

• markdown => HTML pipeline in OpenProject

• markdown => html => CKeditor conversion support added

• CKeditor => html => markdown conversion support added

• Check md-to-pdf

Merge checklist

• Added/updated tests
• Added/updated documentation in Lookbook (patterns, previews, etc)
• Tested major browsers (Chrome, Firefox, Edge, ...)