HTML API: Make get_attribute_names_with_prefix() agree with enqueued attribute updates

src/wp-includes/html-api/class-wp-html-tag-processor.php

@@ -2966,17 +2966,46 @@ public function get_attribute_names_with_prefix( $prefix ): ?array {
 			return null;
 		}
 
-		$comparable = strtolower( $prefix );
+		$this->class_name_updates_to_attributes_updates();
+
+		$comparable      = strtolower( $prefix );
+		$candidate_names = array_merge( $this->newly_added_attribute_names(), array_keys( $this->attributes ) );
 
 		$matches = array();
-		foreach ( array_keys( $this->attributes ) as $attr_name ) {
-			if ( str_starts_with( $attr_name, $comparable ) ) {
+		foreach ( $candidate_names as $attr_name ) {
+			if (
+				str_starts_with( $attr_name, $comparable ) &&
+				null !== $this->get_enqueued_attribute_value( $attr_name )
+			) {
 				$matches[] = $attr_name;
 			}
 		}
 		return $matches;
 	}
 
+	/**
+	 * Returns the comparable names of attributes enqueued by `set_attribute()`
+	 * that were not present in the original input document.
+	 *
+	 * @since 7.1.0
+	 *
+	 * @return string[] Comparable names of newly-added attributes.
+	 */
+	private function newly_added_attribute_names(): array {
+		$new_updates = array();
+		foreach ( $this->lexical_updates as $name => $update ) {
+			// The `modifiable text` key is reserved for enqueued text content updates, not an attribute name.
+			if ( is_string( $name ) && 'modifiable text' !== $name && ! isset( $this->attributes[ $name ] ) ) {
+				$new_updates[ $name ] = $update;
+			}
+		}
+
+		// Matches the order these attributes would appear in after `get_updated_html()`.
+		uasort( $new_updates, array( self::class, 'sort_start_ascending' ) );
+
+		return array_keys( $new_updates );
+	}
+
 	/**
 	 * Returns the namespace of the matched token.
 	 *

tests/phpunit/tests/html-api/wpHtmlTagProcessor.php

@@ -464,6 +464,114 @@ public function test_get_attribute_names_with_prefix_returns_attribute_added_by_
 		);
 	}
 
+	/**
+	 * @ticket 64567
+	 *
+	 * @covers WP_HTML_Tag_Processor::get_attribute_names_with_prefix
+	 */
+	public function test_get_attribute_names_with_prefix_finds_attribute_added_by_set_attribute_before_get_updated_html() {
+		$processor = new WP_HTML_Tag_Processor( '<div data-foo="bar">Test</div>' );
+		$processor->next_tag();
+		$processor->set_attribute( 'data-test-id', '14' );
+
+		$this->assertSame(
+			array( 'data-test-id', 'data-foo' ),
+			$processor->get_attribute_names_with_prefix( 'data-' ),
+			"Accessing attribute names doesn't find attribute added via set_attribute before get_updated_html() is called"
+		);
+	}
+
+	/**
+	 * @ticket 64567
+	 *
+	 * @covers WP_HTML_Tag_Processor::get_attribute_names_with_prefix
+	 */
+	public function test_get_attribute_names_with_prefix_finds_attribute_set_on_tag_with_no_original_attributes() {
+		$processor = new WP_HTML_Tag_Processor( '<div>' );
+		$processor->next_tag();
+		$processor->set_attribute( 'id', 'test' );
+
+		$this->assertSame(
+			array( 'id' ),
+			$processor->get_attribute_names_with_prefix( '' ),
+			"Accessing attribute names doesn't find an attribute added via set_attribute() on a tag with no original attributes, before get_updated_html() is called"
+		);
+	}
+
+	/**
+	 * @ticket 64567
+	 *
+	 * @covers WP_HTML_Tag_Processor::get_attribute_names_with_prefix
+	 */
+	public function test_get_attribute_names_with_prefix_excludes_attribute_removed_by_remove_attribute() {
+		$processor = new WP_HTML_Tag_Processor( '<div data-foo="bar" data-baz="quux">Test</div>' );
+		$processor->next_tag();
+		$processor->remove_attribute( 'data-foo' );
+
+		$this->assertSame(
+			array( 'data-baz' ),
+			$processor->get_attribute_names_with_prefix( 'data-' ),
+			"Accessing attribute names shouldn't find an attribute removed via remove_attribute(), before get_updated_html() is called"
+		);
+	}
+
+	/**
+	 * @ticket 64567
+	 *
+	 * @covers WP_HTML_Tag_Processor::get_attribute_names_with_prefix
+	 */
+	public function test_get_attribute_names_with_prefix_finds_class_attribute_created_by_add_class() {
+		$processor = new WP_HTML_Tag_Processor( '<div>Test</div>' );
+		$processor->next_tag();
+		$processor->add_class( 'main' );
+
+		$this->assertSame(
+			array( 'class' ),
+			$processor->get_attribute_names_with_prefix( 'c' ),
+			"Accessing attribute names doesn't find the class attribute created by add_class(), before get_updated_html() is called"
+		);
+	}
+
+	/**
+	 * @ticket 64567
+	 *
+	 * @covers WP_HTML_Tag_Processor::get_attribute_names_with_prefix
+	 */
+	public function test_get_attribute_names_with_prefix_excludes_class_attribute_emptied_by_remove_class() {
+		$processor = new WP_HTML_Tag_Processor( '<div class="main">Test</div>' );
+		$processor->next_tag();
+		$processor->remove_class( 'main' );
+
+		$this->assertSame(
+			array(),
+			$processor->get_attribute_names_with_prefix( 'c' ),
+			"Accessing attribute names shouldn't find the class attribute after remove_class() empties it, before get_updated_html() is called"
+		);
+	}
+
+	/**
+	 * @ticket 64567
+	 *
+	 * @covers WP_HTML_Tag_Processor::get_attribute_names_with_prefix
+	 */
+	public function test_get_attribute_names_with_prefix_orders_newly_added_attributes_to_match_get_updated_html() {
+		$processor = new WP_HTML_Tag_Processor( '<div>' );
+		$processor->next_tag();
+		$processor->set_attribute( 'zebra', '1' );
+		$processor->set_attribute( 'apple', '2' );
+
+		$this->assertSame(
+			array( 'apple', 'zebra' ),
+			$processor->get_attribute_names_with_prefix( '' ),
+			'Newly-added attribute names should be ordered as they will appear in the serialized output, not in call order'
+		);
+		$this->assertSame(
+			'<div apple="2" zebra="1">',
+			$processor->get_updated_html(),
+			'Sanity check: serialized attribute order should match the order asserted above'
+		);
+	}
+
 	/**
 	 * @ticket 56299
 	 *