The empty lines before an inline editable macro are removed

Follow these steps to reproduce with the WYSIWYG editor:

• Set the content of a wiki page to:

  before
  
  
  
  
  
  {{info}}test{{/info}}
  

• Edit the page with the WYSIWYG editor.
• Notice that the empty lines are present.
• Edit the parameters of the info macro and modify some parameter (e.g. set a CSS class, doesn't matter)
• The empty lines disappear after the content is re-rendered due to the macro parameter change

With the network tab I can see that the HTML converter is called with something like:

<p>before</p><div class="wikimodel-emptyline"></div><div class="wikimodel-emptyline"></div><div class="wikimodel-emptyline"></div><div class="wikimodel-emptyline"></div><!--startmacro:info|-|--><div data-xwiki-non-generated-content="java.util.List&lt;org.xwiki.rendering.block.Block&gt;" class="xwiki-metadata-container"><p>test</p></div><!--stopmacro-->

and the result of parsing to XDOM and rendering back to XWiki 2.1 syntax is:

<p>before</p><!--startmacro:info|-||-|test--><div class="box infomessage"><div data-xwiki-non-generated-content="java.util.List&lt;org.xwiki.rendering.block.Block&gt;" class="xwiki-metadata-container"><p>test</p></div></div><!--stopmacro-->

As you can see the empty lines are missing.

Note that the problem doesn't reproduce when the macro is initially inserted, where the HTML converter is called with:

<p>before</p><div class="wikimodel-emptyline"></div><div class="wikimodel-emptyline"></div><div class="wikimodel-emptyline"></div><div class="wikimodel-emptyline"></div><p><!--startmacro:info|-||-|test--><!--stopmacro--></p>

and correctly produces:

<p>before</p><div class="wikimodel-emptyline"></div><div class="wikimodel-emptyline"></div><div class="wikimodel-emptyline"></div><div class="wikimodel-emptyline"></div><!--startmacro:info|-||-|test--><div class="box infomessage"><div data-xwiki-non-generated-content="java.util.List&lt;org.xwiki.rendering.block.Block&gt;" class="xwiki-metadata-container"><p>test</p></div></div><!--stopmacro-->

This suggests that the problem is in the code that handles the "data-xwiki-non-generated-content", i.e. the content of macros editable inline.

Note that this issue is very annoying when editing in realtime because realtime editing makes it reproduce more easily:

• Alice inserts some empty lines and then inserts an info box
• While Alice is typing inside the info box:
  • the changes are propagated to Bob and since there's a new macro, the content is re-rendered for Bob, but due to the realtime sync the "data-xwiki-non-generated-content" DIV is present, and thus the empty lines are removed for Bob, which produces a change that gets propagated to Alice
  • Alice sees the empty lines (she just entered) disappear and blames it on Bob