Preserve comments when removing style declarations

Author: sirreal

src/wp-includes/html-api/class-wp-html-style-attribute-processor.php

@@ -202,18 +202,14 @@ public function remove_declaration(): bool {
 			return false;
 		}
 
-		if ( '' === trim( substr( $this->style, 0, $declaration['leading_start'] ), self::WHITESPACE ) ) {
-			$remove_start = $declaration['leading_start'];
-			$remove_end   = $declaration['trailing_end'];
-		} else {
-			$remove_start = $declaration['leading_start'];
-			$remove_end   = $declaration['after'];
-		}
+		$remove_start = $this->get_offset_before_preceding_whitespace( $declaration['start'] );
+		$remove_end   = $this->get_offset_after_following_whitespace( $declaration['after'] );
+		$replacement  = ( $remove_start > 0 && $remove_end < strlen( $this->style ) ) ? ' ' : '';
 
 		$this->queue_lexical_update(
 			$remove_start,
 			$remove_end - $remove_start,
-			'',
+			$replacement,
 			$this->current_declaration
 		);
 
@@ -681,6 +677,36 @@ private function is_ignored_token( array $token ): bool {
 		);
 	}
 
+	/**
+	 * Gets the byte offset before contiguous whitespace ending at an offset.
+	 *
+	 * @param int $offset Byte offset.
+	 * @return int Offset before preceding whitespace.
+	 */
+	private function get_offset_before_preceding_whitespace( int $offset ): int {
+		while ( $offset > 0 && false !== strpos( self::WHITESPACE, $this->style[ $offset - 1 ] ) ) {
+			--$offset;
+		}
+
+		return $offset;
+	}
+
+	/**
+	 * Gets the byte offset after contiguous whitespace beginning at an offset.
+	 *
+	 * @param int $offset Byte offset.
+	 * @return int Offset after following whitespace.
+	 */
+	private function get_offset_after_following_whitespace( int $offset ): int {
+		$length = strlen( $this->style );
+
+		while ( $offset < $length && false !== strpos( self::WHITESPACE, $this->style[ $offset ] ) ) {
+			++$offset;
+		}
+
+		return $offset;
+	}
+
 	/**
 	 * Gets the current declaration metadata.
 	 *

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

@@ -183,6 +183,30 @@ public function test_remove_declaration_removes_adjacent_duplicate_declarations(
 		$this->assertSame( 'background: white;', $processor->get_updated_style() );
 	}
 
+	/**
+	 * @covers ::remove_declaration
+	 * @covers ::get_updated_style
+	 */
+	public function test_remove_declaration_preserves_surrounding_comments() {
+		$processor = new WP_HTML_Style_Attribute_Processor( '/*keep*/ color: red; background: white;' );
+
+		$this->assertTrue( $processor->next_declaration( 'color' ) );
+		$this->assertTrue( $processor->remove_declaration() );
+		$this->assertSame( '/*keep*/ background: white;', $processor->get_updated_style() );
+
+		$processor = new WP_HTML_Style_Attribute_Processor( 'color: red; /*keep*/ background: white;' );
+
+		$this->assertTrue( $processor->next_declaration( 'color' ) );
+		$this->assertTrue( $processor->remove_declaration() );
+		$this->assertSame( '/*keep*/ background: white;', $processor->get_updated_style() );
+
+		$processor = new WP_HTML_Style_Attribute_Processor( 'color: red; /*keep*/ background: white;' );
+
+		$this->assertTrue( $processor->next_declaration( 'background' ) );
+		$this->assertTrue( $processor->remove_declaration() );
+		$this->assertSame( 'color: red; /*keep*/', $processor->get_updated_style() );
+	}
+
 	/**
 	 * @covers ::append_declaration
 	 * @covers ::get_updated_style