From 6961426665222d6087b5b360d8bd2fe3682779e6 Mon Sep 17 00:00:00 2001
From: dmsnell <dmsnell@git.wordpress.org>
Date: Mon, 11 Mar 2024 23:55:09 +0000
Subject: [PATCH] HTML API: Defer applying attribute updates until necessary.

When making repeated updates to a document, the Tag Processor will end
up copying the entire document once for every update. This can lead to
catastrophic behavior in the worse case.

However, when batch-applying updates it's able to copy chunks of the
document in one thread and only end up copying the entire document once
for the entire batch.

Previously the Tag Processor has been eagerly applying udpates, but in
this patch it defers applying those updates as long as is possible.

Developed in https://github.com/WordPress/wordpress-develop/pull/6120
Discussed in https://core.trac.wordpress.org/ticket/60697

Props: dmsnell, bernhard-reiter, jonsurrell, westonruter.
Fixes #60697.
Follow-up to [55706], [56941], [57348].


Built from https://develop.svn.wordpress.org/trunk@57805


git-svn-id: http://core.svn.wordpress.org/trunk@57306 1a063a9b-81f0-0310-95a4-ce76da25c4cd
---
 .../html-api/class-wp-html-tag-processor.php  | 72 ++++++++++++++++---
 wp-includes/version.php                       |  2 +-
 2 files changed, 62 insertions(+), 12 deletions(-)

diff --git a/wp-includes/html-api/class-wp-html-tag-processor.php b/wp-includes/html-api/class-wp-html-tag-processor.php
index d5e43251af25..c540ea96c111 100644
--- a/wp-includes/html-api/class-wp-html-tag-processor.php
+++ b/wp-includes/html-api/class-wp-html-tag-processor.php
@@ -837,8 +837,27 @@ public function next_tag( $query = null ) {
 	 * @return bool Whether a token was parsed.
 	 */
 	public function next_token() {
+		return $this->base_class_next_token();
+	}
+
+	/**
+	 * Internal method which finds the next token in the HTML document.
+	 *
+	 * This method is a protected internal function which implements the logic for
+	 * finding the next token in a document. It exists so that the parser can update
+	 * its state without affecting the location of the cursor in the document and
+	 * without triggering subclass methods for things like `next_token()`, e.g. when
+	 * applying patches before searching for the next token.
+	 *
+	 * @since 6.5.0
+	 *
+	 * @access private
+	 *
+	 * @return bool Whether a token was parsed.
+	 */
+	private function base_class_next_token() {
 		$was_at = $this->bytes_already_parsed;
-		$this->get_updated_html();
+		$this->after_tag();
 
 		// Don't proceed if there's nothing more to scan.
 		if (
@@ -2041,6 +2060,45 @@ private function skip_whitespace() {
 	 * @since 6.2.0
 	 */
 	private function after_tag() {
+		/*
+		 * There could be lexical updates enqueued for an attribute that
+		 * also exists on the next tag. In order to avoid conflating the
+		 * attributes across the two tags, lexical updates with names
+		 * need to be flushed to raw lexical updates.
+		 */
+		$this->class_name_updates_to_attributes_updates();
+
+		/*
+		 * Purge updates if there are too many. The actual count isn't
+		 * scientific, but a few values from 100 to a few thousand were
+		 * tests to find a practially-useful limit.
+		 *
+		 * If the update queue grows too big, then the Tag Processor
+		 * will spend more time iterating through them and lose the
+		 * efficiency gains of deferring applying them.
+		 */
+		if ( 1000 < count( $this->lexical_updates ) ) {
+			$this->get_updated_html();
+		}
+
+		foreach ( $this->lexical_updates as $name => $update ) {
+			/*
+			 * Any updates appearing after the cursor should be applied
+			 * before proceeding, otherwise they may be overlooked.
+			 */
+			if ( $update->start >= $this->bytes_already_parsed ) {
+				$this->get_updated_html();
+				break;
+			}
+
+			if ( is_int( $name ) ) {
+				continue;
+			}
+
+			$this->lexical_updates[] = $update;
+			unset( $this->lexical_updates[ $name ] );
+		}
+
 		$this->token_starts_at      = null;
 		$this->token_length         = null;
 		$this->tag_name_starts_at   = null;
@@ -2230,7 +2288,7 @@ private function apply_attributes_updates( $shift_this_point = 0 ) {
 			$shift = strlen( $diff->text ) - $diff->length;
 
 			// Adjust the cursor position by however much an update affects it.
-			if ( $diff->start <= $this->bytes_already_parsed ) {
+			if ( $diff->start < $this->bytes_already_parsed ) {
 				$this->bytes_already_parsed += $shift;
 			}
 
@@ -3164,15 +3222,7 @@ public function get_updated_html() {
 		 *                 └←─┘ back up by strlen("em") + 1 ==> 3
 		 */
 		$this->bytes_already_parsed = $before_current_tag;
-		$this->parse_next_tag();
-		// Reparse the attributes.
-		while ( $this->parse_next_attribute() ) {
-			continue;
-		}
-
-		$tag_ends_at                = strpos( $this->html, '>', $this->bytes_already_parsed );
-		$this->token_length         = $tag_ends_at - $this->token_starts_at;
-		$this->bytes_already_parsed = $tag_ends_at;
+		$this->base_class_next_token();
 
 		return $this->html;
 	}
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 98c9866f1296..76116aa6ff2f 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.6-alpha-57804';
+$wp_version = '6.6-alpha-57805';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.