Rich Text: Void blocks are considered plain-text, aren't converted

[aduth]

Describe the bug

A void block (a block with no content, self-closing), when pasted, is not converted to a block (at least in macOS Chrome). The root cause is that ClipboardData#getData considers the comment-only markup as plain-text, not HTML. This could be considered a browser bug, though it has the practical impact of preventing blocks from being converted correctly.

Example void block:

<!-- wp:latest-posts /-->

To Reproduce

Steps to reproduce the behavior:

1. Copy the block markup above
2. Navigate to Posts > Add New
3. Click on the writing prompt
4. Paste the block markup

Expected behavior

The pasted text is converted into a Latest Posts block.

Alternatively, if it was interpreted as plain-text, the plain text of the markup should be inserted into the paragraph.

Actual behavior

Nothing happens.

Desktop:

• OS: macOS Mojave Version 10.14.3 (18D109)
• Browser: Chrome Version 73.0.3683.75 (Official Build) (64-bit)

Additional context

Both HTML and plain text data are retrieved from the clipboard and passed to clipboardData.

gutenberg/packages/block-editor/src/components/rich-text/index.js

Lines 236 to 237 in 27c0d00

	plainText = clipboardData.getData( 'text/plain' );
	html = clipboardData.getData( 'text/html' );

For this reason, if it's not possible to have the browser consider the comment markup as HTML, an alternative to consider may be to update the following condition to consider plainText, in addition to HTML:

gutenberg/packages/blocks/src/api/raw-handling/paste-handler.js

Lines 130 to 133 in 27c0d00

	// If we detect block delimiters, parse entirely as blocks.
	if ( mode !== 'INLINE' && HTML.indexOf( '<!-- wp:' ) !== -1 ) {
	return parseWithGrammar( HTML );
	}

cc @ellatrix

[ellatrix]

Fixed in #14536.