HTML API: Fix - avoid calling subclass method while internally scanning in Tag Processor

[dmsnell]

Trac ticket: Core-59607

After modifying tags in the HTML API, the Tag Processor backs up to before the tag being modified and then re-parses its attributes. This saves on the code-complexity involved in applying updates, which have already been transformed to "lexical updates" by the time they are applied.

In order to do that, get_updated_html() calls next_tag() to reuse its logic. Unfortunately, as a public method, subclasses may change the behavior of that method, and the HTML Processor does just this. It maintains an HTML stack of open elements and when the Tag Processor calls this method to re-scan a tag and its attributes, it leads to a broken stack.

To fix this, this patch replaces the call to next_tag() with a more appropriate reapplication of its internal parsing logic to rescan the tag name and its attributes. Given the limited nature of what's occurring in get_updated_html() this should bring with it certain guarantees that no HTML structure is being changed (that structure will only be changed by subclasses like the HTML Processor).

This patch resolves an issue discovered by @adamziel during testing of the HTML Processor.

There is no evidence that this makes a clear impact on performance

[dmsnell]

cc: @adamziel @westonruter @ockham

[adamziel]

Hey this is better than the previous implementation ❤️

[SergeyBiryukov]

Thanks for the PR! Merged in r56941.

[dmsnell]

thanks @SergeyBiryukov!

[andrewserong]

I'm not sure if it's related, but Gutenberg trunk PHP tests have started failing, in particular WP_Directive_Processor tests:

There were 2 failures:

1) WP_Directive_Processor_Test::test_set_inner_html_subsequent_updates_on_the_same_tag_work
Failed asserting that two strings are identical.
--- Expected
+++ Actual
@@ @@
-'<div>outside</div><section>This is the even newer section content.</section>'
+'<This is the even newer section content.</section>'

/var/www/html/wp-content/plugins/gutenberg/phpunit/experimental/interactivity-api/class-wp-directive-processor-test.php:90
phpvfscomposer:///var/www/html/wp-content/plugins/gutenberg/vendor/phpunit/phpunit/phpunit:60

2) WP_Directive_Processor_Test::test_set_inner_html_preceded_by_set_attribute_works
Failed asserting that two strings are identical.
--- Expected
+++ Actual
@@ @@
-'<div>outside</div><section id="thesection">This is the new section content.</section>'
+'<This is the new section content.</section>'

/var/www/html/wp-content/plugins/gutenberg/phpunit/experimental/interactivity-api/class-wp-directive-processor-test.php:108
phpvfscomposer:///var/www/html/wp-content/plugins/gutenberg/vendor/phpunit/phpunit/phpunit:60

Could that be related to this change, since WP_Directive_Processor extends WP_HTML_Tag_Processor?

There's also a bit of discussion over in the #core-editor Slack channel: https://wordpress.slack.com/archives/C02QB2JS7/p1697514694299429?thread_ts=1697471144.510409&cid=C02QB2JS7