Whitespace can trip up `WP_Interactivity_API::_process_directives()` when there is a `core/button` `text` block binding

[wongjn]

Steps to reproduce

1. Set WP_DEBUG to true in wp-config.php.
2. Install clean WordPress 6.7.1.
3. Activate Twenty Twenty-Four theme.
4. Replace /wp-content/themes/twentytwentyfour/templates/single.html with:

   <!-- wp:query {"queryId":0,"query":{"perPage":10,"pages":"0","offset":0,"postType":"post","order":"desc","orderBy":"date","author":"","search":"","exclude":[],"sticky":"","inherit":false,"parents":[],"format":[]},"enhancedPagination":true,"layout":{"type":"constrained"}} -->
   <div class="wp-block-query">
   	<!-- wp:post-template {"layout":{"type":"default","columnCount":3}} -->
   		<!-- wp:buttons -->
   		<div class="wp-block-buttons"><!-- wp:button {"metadata":{"bindings":{"text":{"source":"core/post-meta","args":{"key":"foo"}}}}} -->
   			<div class="wp-block-button"><a class="wp-block-button__link wp-element-button">Get Tickets</a></div>
   			<!-- /wp:button -->
   		</div>
   		<!-- /wp:buttons -->
   	<!-- /wp:post-template -->
   </div>
   <!-- /wp:query -->
   

5. Append the following to /wp-content/themes/twentytwentyfour/functions.php:

   function _test() {
           $args = array(
                   'type'              => 'string',
                   'single'            => true,
                   'sanitize_callback' => '',
                   'show_in_rest'      => true,
                   'revisions_enabled' => true,
           );
           register_post_meta( 'post', 'foo', $args );
           update_post_meta(1, 'foo', 'test' );
   }
   add_action( 'init', '_test' );
   

6. Navigate to /index.php?p=1 (the Hello World post) in your browser.
7. Notice no errors.
8. Replace /wp-content/themes/twentytwentyfour/templates/single.html with:

   <!-- wp:query {"queryId":0,"query":{"perPage":10,"pages":"0","offset":0,"postType":"post","order":"desc","orderBy":"date","author":"","search":"","exclude":[],"sticky":"","inherit":false,"parents":[],"format":[]},"enhancedPagination":true,"layout":{"type":"constrained"}} -->
   <div class="wp-block-query">
   	<!-- wp:post-template {"layout":{"type":"default","columnCount":3}} -->
   		<!-- wp:buttons -->
   		<div class="wp-block-buttons">
   <!-- wp:button {"metadata":{"bindings":{"text":{"source":"core/post-meta","args":{"key":"foo"}}}}} -->
   			<div class="wp-block-button"><a class="wp-block-button__link wp-element-button">Get Tickets</a></div>
   			<!-- /wp:button -->
   		</div>
   		<!-- /wp:buttons -->
   	<!-- /wp:post-template -->
   </div>
   <!-- /wp:query -->
   

9. Navigate to /index.php?p=1 (the Hello World post) in your browser.
10. Notice an error displayed:

    Notice: Function WP_Interactivity_API::_process_directives was called <strong>incorrectly</strong>. Interactivity directives failed to process in "" due to a missing "LI" end tag. Please see <a href="https://developer.wordpress.org/advanced-administration/debug/debug-wordpress/">Debugging in WordPress</a> for more information. (This message was added in version 6.6.0.) in /path/to/wordpress/wp-includes/functions.php on line 6114
    

Other remarkables

• When the error is displayed, the markup has some HTML in uppercase:

  <DIV class="wp-block-button"><a class="wp-block-button__link wp-element-button">test</a></DIV>
  

• Any amount of newline/whitespace seems to cause the error:

  <!-- wp:query {"queryId":0,"query":{"perPage":10,"pages":"0","offset":0,"postType":"post","order":"desc","orderBy":"date","author":"","search":"","exclude":[],"sticky":"","inherit":false,"parents":[],"format":[]},"enhancedPagination":true,"layout":{"type":"constrained"}} -->
  <div class="wp-block-query">
  	<!-- wp:post-template {"layout":{"type":"default","columnCount":3}} -->
  		<!-- wp:buttons -->
  		<div class="wp-block-buttons">
  			<!-- wp:button {"metadata":{"bindings":{"text":{"source":"core/post-meta","args":{"key":"foo"}}}}} -->
  			<div class="wp-block-button"><a class="wp-block-button__link wp-element-button">Get Tickets</a></div>
  			<!-- /wp:button -->
  		</div>
  		<!-- /wp:buttons -->
  	<!-- /wp:post-template -->
  </div>
  <!-- /wp:query -->
  

• Including the same snippet from _Copy All Blocks_ command in the editor, but with a newline before the opening core/button comment:

  <!-- wp:query {"queryId":0,"query":{"perPage":10,"pages":"0","offset":0,"postType":"post","order":"desc","orderBy":"date","author":"","search":"","exclude":[],"sticky":"","inherit":false,"parents":[],"format":[]},"enhancedPagination":true,"layout":{"type":"constrained"}} -->
  <div class="wp-block-query"><!-- wp:post-template {"layout":{"type":"default","columnCount":3}} -->
  	<!-- wp:buttons {"layout":{"type":"flex"}} -->
  	<div class="wp-block-buttons">
  <!-- wp:button {"metadata":{"bindings":{"text":{"source":"core/post-meta","args":{"key":"foo"}}}}} -->
  	<div class="wp-block-button"><a class="wp-block-button__link wp-element-button">Get Tickets</a></div>
  	<!-- /wp:button --></div>
  	<!-- /wp:buttons -->
  	<!-- /wp:post-template --></div>
  	<!-- /wp:query -->
  

Trac ticket: https://core.trac.wordpress.org/ticket/62522

Fixes a bug where processing the button block with bindings returns the HTML wrapper DIV in uppercase, which breaks other processing, like the Interactivity API directives.

Ensure uppercase tag names are matched correctly by the tag processor.

Ticket 62522 describes an issue where a whitespace-prefixed tag was causing problems. With the help of @SantosGuillamot and @cbravobernal, this was narrowed down to an uppercase open tag name prefixed by whitespace not being found in the tag processor.

There was a missing "D" in the character list used by strspn to find tag openers, causing tags starting with D to be skipped by the tag processor in some circumstances.

Add tests to ensure variations of uppper and lowercase tag names openers and closers are recognized.

This only appears in rare cases because the tag name must appear in the correct position (preceded by whitespace) and must start with an uppercase D. Casing is not relevant for tag names, and most tag names are lowercase in the wild.

Trac ticket: https://core.trac.wordpress.org/ticket/62522

Closes ​https://github.com/WordPress/wordpress-develop/pull/7893 (supersedes).

[jonsurrell]

I'm changing the milestone to 6.7.2, I'd like ​https://github.com/WordPress/wordpress-develop/pull/7897 to be considered for inclusion.

[cbravobernal]

In 59464:

HTML API: Recognize all uppercase tag names in tag processor.

Fixes a missing "D" in the character list used by strspn to find tag openers, causing tags starting with D to be skipped by the tag processor in some circumstances.

Follow-up to [58613].

Props jonsurrell, santosguillamot, wongjn, cbravobernal.
Fixes #62522.

Committed in https://core.trac.wordpress.org/changeset/59464

Superseeded by ​https://github.com/WordPress/wordpress-develop/pull/7897

[jonsurrell]

Reopening to consider for 6.7.2.