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<title>[57768] trunk: HTML API: Ensure that breadcrumbs are properly retained after seeking.</title>
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<dt style="float: left; width: 6em; font-weight: bold">Revision</dt> <dd><a style="font-weight: bold" href="https://core.trac.wordpress.org/changeset/57768">57768</a><script type="application/ld+json">{"@context":"http://schema.org","@type":"EmailMessage","description":"Review this Commit","action":{"@type":"ViewAction","url":"https://core.trac.wordpress.org/changeset/57768","name":"Review Commit"}}</script></dd>
<dt style="float: left; width: 6em; font-weight: bold">Author</dt> <dd>dmsnell</dd>
<dt style="float: left; width: 6em; font-weight: bold">Date</dt> <dd>2024-03-05 05:32:19 +0000 (Tue, 05 Mar 2024)</dd>
</dl>
<pre style='padding-left: 1em; margin: 2em 0; border-left: 2px solid #ccc; line-height: 1.25; font-size: 105%; font-family: sans-serif'>HTML API: Ensure that breadcrumbs are properly retained after seeking.
In some cases, it's possible to seek back into a location found inside
an element which has been closed before the point in the document where
the `seek()` was made. In these cases the breadcrumb stack is lost, and
calling `get_breadcrumbs()` after the seek will return the wrong information.
In this patch, the HTML Processor takes a conservative approach and
moves to the front of the document, then reparses the document until
it reaches the sought-after location. This ensures consistency on
the stack of open elements and active formats, and preserves
breadcrumbs.
Developed in https://github.com/WordPress/wordpress-develop/pull/6185
Discussed in https://core.trac.wordpress.org/ticket/60687
Props jonsurrell.
Follow-up to <a href="https://core.trac.wordpress.org/changeset/60687">[60687]</a>.
See <a href="https://core.trac.wordpress.org/ticket/58517">#58517</a>.
Fixes <a href="https://core.trac.wordpress.org/ticket/60687">#60687</a>.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunksrcwpincludeshtmlapiclasswphtmlprocessorphp">trunk/src/wp-includes/html-api/class-wp-html-processor.php</a></li>
<li><a href="#trunktestsphpunittestshtmlapiwpHtmlProcessorBreadcrumbsphp">trunk/tests/phpunit/tests/html-api/wpHtmlProcessorBreadcrumbs.php</a></li>
</ul>
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<h3>Diff</h3>
<a id="trunksrcwpincludeshtmlapiclasswphtmlprocessorphp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/src/wp-includes/html-api/class-wp-html-processor.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/src/wp-includes/html-api/class-wp-html-processor.php 2024-03-05 03:01:09 UTC (rev 57767)
+++ trunk/src/wp-includes/html-api/class-wp-html-processor.php 2024-03-05 05:32:19 UTC (rev 57768)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -241,15 +241,15 @@
</span><span class="cx" style="display: block; padding: 0 10px"> return null;
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- $p = new self( $html, self::CONSTRUCTOR_UNLOCK_CODE );
- $p->state->context_node = array( 'BODY', array() );
- $p->state->insertion_mode = WP_HTML_Processor_State::INSERTION_MODE_IN_BODY;
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $processor = new self( $html, self::CONSTRUCTOR_UNLOCK_CODE );
+ $processor->state->context_node = array( 'BODY', array() );
+ $processor->state->insertion_mode = WP_HTML_Processor_State::INSERTION_MODE_IN_BODY;
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> // @todo Create "fake" bookmarks for non-existent but implied nodes.
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- $p->bookmarks['root-node'] = new WP_HTML_Span( 0, 0 );
- $p->bookmarks['context-node'] = new WP_HTML_Span( 0, 0 );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $processor->bookmarks['root-node'] = new WP_HTML_Span( 0, 0 );
+ $processor->bookmarks['context-node'] = new WP_HTML_Span( 0, 0 );
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- $p->state->stack_of_open_elements->push(
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $processor->state->stack_of_open_elements->push(
</ins><span class="cx" style="display: block; padding: 0 10px"> new WP_HTML_Token(
</span><span class="cx" style="display: block; padding: 0 10px"> 'root-node',
</span><span class="cx" style="display: block; padding: 0 10px"> 'HTML',
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -257,15 +257,15 @@
</span><span class="cx" style="display: block; padding: 0 10px"> )
</span><span class="cx" style="display: block; padding: 0 10px"> );
</span><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- $p->state->stack_of_open_elements->push(
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $processor->state->stack_of_open_elements->push(
</ins><span class="cx" style="display: block; padding: 0 10px"> new WP_HTML_Token(
</span><span class="cx" style="display: block; padding: 0 10px"> 'context-node',
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- $p->state->context_node[0],
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $processor->state->context_node[0],
</ins><span class="cx" style="display: block; padding: 0 10px"> false
</span><span class="cx" style="display: block; padding: 0 10px"> )
</span><span class="cx" style="display: block; padding: 0 10px"> );
</span><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- return $p;
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ return $processor;
</ins><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> /**
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -1226,6 +1226,10 @@
</span><span class="cx" style="display: block; padding: 0 10px"> /**
</span><span class="cx" style="display: block; padding: 0 10px"> * Moves the internal cursor in the HTML Processor to a given bookmark's location.
</span><span class="cx" style="display: block; padding: 0 10px"> *
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ * Be careful! Seeking backwards to a previous location resets the parser to the
+ * start of the document and reparses the entire contents up until it finds the
+ * sought-after bookmarked location.
+ *
</ins><span class="cx" style="display: block; padding: 0 10px"> * In order to prevent accidental infinite loops, there's a
</span><span class="cx" style="display: block; padding: 0 10px"> * maximum limit on the number of times seek() can be called.
</span><span class="cx" style="display: block; padding: 0 10px"> *
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -1247,44 +1251,73 @@
</span><span class="cx" style="display: block; padding: 0 10px"> $bookmark_starts_at = $this->bookmarks[ $actual_bookmark_name ]->start;
</span><span class="cx" style="display: block; padding: 0 10px"> $direction = $bookmark_starts_at > $processor_started_at ? 'forward' : 'backward';
</span><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- switch ( $direction ) {
- case 'forward':
- // When moving forwards, reparse the document until reaching the same location as the original bookmark.
- while ( $this->step() ) {
- if ( $bookmark_starts_at === $this->bookmarks[ $this->state->current_token->bookmark_name ]->start ) {
- return true;
- }
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ /*
+ * If seeking backwards, it's possible that the sought-after bookmark exists within an element
+ * which has been closed before the current cursor; in other words, it has already been removed
+ * from the stack of open elements. This means that it's insufficient to simply pop off elements
+ * from the stack of open elements which appear after the bookmarked location and then jump to
+ * that location, as the elements which were open before won't be re-opened.
+ *
+ * In order to maintain consistency, the HTML Processor rewinds to the start of the document
+ * and reparses everything until it finds the sought-after bookmark.
+ *
+ * There are potentially better ways to do this: cache the parser state for each bookmark and
+ * restore it when seeking; store an immutable and idempotent register of where elements open
+ * and close.
+ *
+ * If caching the parser state it will be essential to properly maintain the cached stack of
+ * open elements and active formatting elements when modifying the document. This could be a
+ * tedious and time-consuming process as well, and so for now will not be performed.
+ *
+ * It may be possible to track bookmarks for where elements open and close, and in doing so
+ * be able to quickly recalculate breadcrumbs for any element in the document. It may even
+ * be possible to remove the stack of open elements and compute it on the fly this way.
+ * If doing this, the parser would need to track the opening and closing locations for all
+ * tokens in the breadcrumb path for any and all bookmarks. By utilizing bookmarks themselves
+ * this list could be automatically maintained while modifying the document. Finding the
+ * breadcrumbs would then amount to traversing that list from the start until the token
+ * being inspected. Once an element closes, if there are no bookmarks pointing to locations
+ * within that element, then all of these locations may be forgotten to save on memory use
+ * and computation time.
+ */
+ if ( 'backward' === $direction ) {
+ /*
+ * Instead of clearing the parser state and starting fresh, calling the stack methods
+ * maintains the proper flags in the parser.
+ */
+ foreach ( $this->state->stack_of_open_elements->walk_up() as $item ) {
+ if ( 'context-node' === $item->bookmark_name ) {
+ break;
</ins><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- return false;
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $this->state->stack_of_open_elements->remove_node( $item );
+ }
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- case 'backward':
- /*
- * When moving backwards, clear out all existing stack entries which appear after the destination
- * bookmark. These could be stored for later retrieval, but doing so would require additional
- * memory overhead and also demand that references and bookmarks are updated as the document
- * changes. In time this could be a valuable optimization, but it's okay to give up that
- * optimization in exchange for more CPU time to recompute the stack, to re-parse the
- * document that may have already been parsed once.
- */
- foreach ( $this->state->stack_of_open_elements->walk_up() as $item ) {
- if ( $bookmark_starts_at >= $this->bookmarks[ $item->bookmark_name ]->start ) {
- break;
- }
-
- $this->state->stack_of_open_elements->remove_node( $item );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ foreach ( $this->state->active_formatting_elements->walk_up() as $item ) {
+ if ( 'context-node' === $item->bookmark_name ) {
+ break;
</ins><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- foreach ( $this->state->active_formatting_elements->walk_up() as $item ) {
- if ( $bookmark_starts_at >= $this->bookmarks[ $item->bookmark_name ]->start ) {
- break;
- }
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $this->state->active_formatting_elements->remove_node( $item );
+ }
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- $this->state->active_formatting_elements->remove_node( $item );
- }
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ parent::seek( 'context-node' );
+ $this->state->insertion_mode = WP_HTML_Processor_State::INSERTION_MODE_IN_BODY;
+ $this->state->frameset_ok = true;
+ }
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- return parent::seek( $actual_bookmark_name );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ // When moving forwards, reparse the document until reaching the same location as the original bookmark.
+ if ( $bookmark_starts_at === $this->bookmarks[ $this->state->current_token->bookmark_name ]->start ) {
+ return true;
</ins><span class="cx" style="display: block; padding: 0 10px"> }
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+
+ while ( $this->step() ) {
+ if ( $bookmark_starts_at === $this->bookmarks[ $this->state->current_token->bookmark_name ]->start ) {
+ return true;
+ }
+ }
+
+ return false;
</ins><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> /**
</span></span></pre></div>
<a id="trunktestsphpunittestshtmlapiwpHtmlProcessorBreadcrumbsphp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/tests/phpunit/tests/html-api/wpHtmlProcessorBreadcrumbs.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/tests/phpunit/tests/html-api/wpHtmlProcessorBreadcrumbs.php 2024-03-05 03:01:09 UTC (rev 57767)
+++ trunk/tests/phpunit/tests/html-api/wpHtmlProcessorBreadcrumbs.php 2024-03-05 05:32:19 UTC (rev 57768)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -545,4 +545,26 @@
</span><span class="cx" style="display: block; padding: 0 10px"> $processor->seek( 'second' );
</span><span class="cx" style="display: block; padding: 0 10px"> $this->assertTrue( $processor->get_attribute( 'two' ) );
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+
+ /**
+ * Ensures that breadcrumbs are properly reported after seeking backward to a location
+ * inside an element which has been fully closed before the seek.
+ *
+ * @ticket 60687
+ */
+ public function test_retains_proper_bookmarks_after_seeking_back_to_closed_element() {
+ $processor = WP_HTML_Processor::create_fragment( '<div><img></div><div><hr></div>' );
+
+ $processor->next_tag( 'IMG' );
+ $processor->set_bookmark( 'first' );
+
+ $processor->next_tag( 'HR' );
+
+ $processor->seek( 'first' );
+ $this->assertSame(
+ array( 'HTML', 'BODY', 'DIV', 'IMG' ),
+ $processor->get_breadcrumbs(),
+ 'Should have retained breadcrumbs from bookmarked location after seeking backwards to it.'
+ );
+ }
</ins><span class="cx" style="display: block; padding: 0 10px"> }
</span></span></pre>
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