TinyMCE: empty paragraphs are created from HTML comments on separate lines

[azaozz]

Follow up from ​https://github.com/WordPress/gutenberg/issues/6385. To test: ​http://fiddle.tinymce.com/Ctgaab/5.

To fix this we will need to remove any line breaks from between HTML comments, and insert them again (when wpautop is disabled).

[azaozz]

In 44308.patch:

• Remove any white space between two or more HTML comments when wpautop is not used. Fixes a bug where TinyMCE may insert empty paragraph tags.
• When saving, add back the two line breaks between HTML comments if they are Gutenberg block markers.

[danielbachhuber]

I've confirmed 44308.patch works as expected.

I've also confirmed the post content is saved to the database as expected:

$ wp post get 1 --field=content
<!-- wp:heading -->
<h2>This is a heading block</h2>
<!-- /wp:heading -->

<!-- wp:paragraph -->
<p>This is my paragraph text.</p>
<!-- /wp:paragraph -->

Does it make sense to land this in 4.9.7 or 4.9.8?

[azaozz]

Does it make sense to land this in 4.9.7

Think so. This is an edge case bugfix for HTML comments when wpautop is disabled in the editor.

[azaozz]

In 43336:

TinyMCE: prevent creation of paragraphs from multiple HTML comments when wpautop is disabled.

Fixes #44308.