Add URL handling to raw handler

[ellatrix]

Description

This PR changes several things regarding the pasting of URLs.

1. Instead of using TinyMCE's link-over-word paste, add it to Gutenberg, and add the behaviour of core which ignores whitespace and empty/wrapping HTML tags.

   https://github.com/WordPress/WordPress/blob/06fa4161aa74619239cf27017d124081c825684a/wp-includes/js/tinymce/plugins/wplink/plugin.js#L320-L336

2. Remove the 'paste' transformation type from the patterns plugin, and instead use the raw handler. This will allow URLs to be embedded from paste and raw handling in general, not just pasting a URL on an empty line. The paste transform was kind of an odd hack in the patterns plugin.

One thing that is a bit awkward is that the order of registration matters. This is similar to the <pre> and <pre><code> tags. I'm not sure what the best solution is other than ensuring the right order (also register plugins first), or adding a condition to the paragraph block to ignore ones with a URL (bad imo).

How Has This Been Tested?

• Paste a (e.g. YouTube) URL on an empty line. Should embed.
• Create an old post (or similar) with a URL on its own line. Paste in Gutenberg. Should embed.
• Paste a URL in the classic editor block. Convert to blocks. Should keep embed.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows has proper inline documentation.

[codecov]

Codecov Report

Merging #3326 into master will decrease coverage by 0.03%.
The diff coverage is 15%.

@@            Coverage Diff             @@
##           master    #3326      +/-   ##
==========================================
- Coverage   34.65%   34.61%   -0.04%     
==========================================
  Files         260      260              
  Lines        6741     6757      +16     
  Branches     1220     1226       +6     
==========================================
+ Hits         2336     2339       +3     
- Misses       3719     3728       +9     
- Partials      686      690       +4

Impacted Files	Coverage Δ
blocks/editable/patterns.js	1.85% <ø> (+0.03%)	⬆️
blocks/editable/index.js	10.23% <0%> (-0.56%)	⬇️
blocks/api/raw-handling/index.js	84.21% <100%> (+0.87%)	⬆️
blocks/library/embed/index.js	46.15% <100%> (+0.59%)	⬆️

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[mcsf]

One thing that is a bit awkward is that the order of registration matters. This is similar to the <pre> and <pre><code> tags. I'm not sure what the best solution is other than ensuring the right order (also register plugins first), or adding a condition to the paragraph block to ignore ones with a URL (bad imo).

This seems normal to me. I agree we shouldn't try to have extra rules in Paragraph to ignore URLs. As with any parsable system, expressions will match multiple constructs and precedence rules will be needed. Take basic algebra and precedence rules for +, -, ⨯, ÷, for instance. For now, relying on import order for the core library seems acceptable. As we start focusing on extensibility across Gutenberg, however, something more flexible will be needed—plugins will sometimes want to act before core blocks, and sometimes after them. One of the most obvious solutions would be a priority system as known in WordPress core (add_action( 'tag', 'function', 10 )).

[mcsf]

As for the PR, LGTM! Soon we should work on documentation for the whole paste / patterns / transforms stack.

[vedranmiletic]

Is this in 1.9.1? I have a blocks that has:

• a paragraph
• YouTube iframe embed code
• a paragraph

And YouTube iframe embed code gets deleted upon "Convert to blocks".

[mcsf]

@vedranmiletic, do you mean classic (pre-Gutenberg) content? If so, I've logged issue #4125.