Eliminate AMP validation from Classic Editor

[westonruter]

Summary

AMP validation in the Classic Editor is very poor. Since the Classic Editor requires a full page reload for each save, the synchronous validation performed during that request makes saving painfully long. And then if there was a validation error in the content, the presentation of the errors is poor since the specific content that has the error(s) can't be pinpointed:

Also, since the Block Editor is the future and the Classic Editor is the past, we should move along. A lot of legacy technical debt can be paid off by eliminating this integration. The Classic Editor integration was not being maintained and it is doubtful it provided any value for users. If a user is using the Classic Editor, they will still be able to discover validation errors via the admin bar when viewing the post on the frontend.

This is part of #2069.

Before

Time to save: 5 seconds

before.mov

After

Time to save: 1 second

after.mov

Checklist

• Make sure the AMP Async Validation mini plugin doesn't start breaking with the these changes: https://gist.github.com/westonruter/31ac0e056b8b1278c98f8a9f548fcc1a
• My code is tested and passes existing tests.
• My code follows the Engineering Guidelines (updates are often made to the guidelines, check it out periodically).

[codecov]

Codecov Report

Merging #5996 (9a69705) into develop (bcd47bf) will decrease coverage by 0.07%.
The diff coverage is n/a.

❗ Current head 9a69705 differs from pull request most recent head fec0b8d. Consider uploading reports for the commit fec0b8d to get more accurate results

@@              Coverage Diff              @@
##             develop    #5996      +/-   ##
=============================================
- Coverage      75.41%   75.34%   -0.08%     
+ Complexity      5735     5700      -35     
=============================================
  Files            218      218              
  Lines          17362    17277      -85     
=============================================
- Hits           13094    13017      -77     
+ Misses          4268     4260       -8     

Flag	Coverage Δ	Complexity Δ
javascript	80.05% <ø> (ø)	0.00 <ø> (ø)
php	75.14% <ø> (-0.08%)	0.00 <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ	Complexity Δ
...cludes/validation/class-amp-validation-manager.php	80.56% <ø> (-0.96%)	274.00 <0.00> (-35.00)

[github-actions]

Plugin builds for fec0b8d are ready 🛎️!

• Download development build
• Download production build

[amedina]

This is a great path to move forward on. Although it would seem users of the Classic Editor would have less visibility into validation issues right from the editor, actually the UX is much better this way.

[amedina]

This is great. Love to see all that code being cut.

Ship it.

[pierlon]

This variable can now be removed, no? Unless it was being referenced directly by themes/plugins.

[pierlon]

I can see that two plugins are making use of this variable, but in those cases they rely on the AMP plugin as a library so removing this variable shouldn't affect them.

[westonruter]

It can't be removed because it's being used by this mini plugin: https://gist.github.com/westonruter/31ac0e056b8b1278c98f8a9f548fcc1a

[pierlon]

Oh I see. Maybe we could add a note about that also so it isn't accidentally removed in the future.

[westonruter]

Added

[jwold]

I tried to reproduce for QA, but couldn't validate.

1. Installed Classic editor in Standard mode
2. On new page, in text mode, typed:

<script>document.write('Test.');</script>
<div attr="attr1">Div attribute error test</div>

3. When viewing on frontend I could see zero errors displayed in admin bar. Not sure if it's functioning correctly.

[jwold]

Something was wrong with my local instance of AMP. I did a clean install and validated that this issue is working. When I type an invalid entry into Classic editor, then go to frontend, I now see the error displaying in the admin bar. Passes QA.