API ThreadItemsHTML: improve generation of othercontent

Othercontent would often contain the opening tag of the next heading /
section. By looking for the closest node with a previousSibling we can
more-reliably escape the heading.

Also, only add the initial placeholder if there's content before the
first heading. We do this by testing for any siblings before the
startContainer of the first heading -- if there are any, assume this
means there's some sort of content. (This can still result in a
placeholder with `othercontent:""` if there's only whitespace before
the first heading.)

Bug: T313850
Change-Id: I080205b74413c46d3cf3442e79276145aaa9439c

includes/ApiDiscussionToolsPageInfo.php

@@ -9,6 +9,8 @@ use MediaWiki\Extension\DiscussionTools\ThreadItem\ContentThreadItem;
 use MediaWiki\Extension\VisualEditor\ApiParsoidTrait;
 use Title;
 use Wikimedia\ParamValidator\ParamValidator;
+use Wikimedia\Parsoid\DOM\Element;
+use Wikimedia\Parsoid\DOM\Text;
 use Wikimedia\Parsoid\Utils\DOMUtils;
 
 class ApiDiscussionToolsPageInfo extends ApiBase {
@@ -92,13 +94,25 @@ class ApiDiscussionToolsPageInfo extends ApiBase {
 	 * @return array
 	 */
 	private static function getThreadItemsHtml( ContentThreadItemSet $threadItemSet ): array {
+		// This function assumes that the start of the ranges associated with
+		// HeadingItems are going to be at the start of their associated
+		// heading node (`<h2>^heading</h2>`), i.e. in the position generated
+		// by getHeadlineNodeAndOffset.
 		$threads = $threadItemSet->getThreads();
-		if ( count( $threads ) > 0 ) {
+		if ( count( $threads ) > 0 && !$threads[0]->isPlaceholderHeading() ) {
 			$firstHeading = $threads[0];
-			if ( !$firstHeading->isPlaceholderHeading() ) {
-				$range = new ImmutableRange( $firstHeading->getRootNode(), 0, $firstHeading->getRootNode(), 0 );
+			$firstRange = $firstHeading->getRange();
+			$rootNode = $firstHeading->getRootNode();
+			// We need a placeholder if there's content between the beginning
+			// of rootnode and the start of firstHeading. An ancestor of the
+			// first heading with a previousSibling is evidence that there's
+			// probably content. If this is giving false positives we could
+			// perhaps use linearWalkBackwards and DomUtils::isContentNode.
+			$closest = CommentUtils::closestElementWithSibling( $firstRange->startContainer, 'previous' );
+			if ( $closest && !$rootNode->isSameNode( $closest ) ) {
+				$range = new ImmutableRange( $rootNode, 0, $rootNode, 0 );
 				$fakeHeading = new ContentHeadingItem( $range, null );
-				$fakeHeading->setRootNode( $firstHeading->getRootNode() );
+				$fakeHeading->setRootNode( $rootNode );
 				$fakeHeading->setName( 'h-' );
 				$fakeHeading->setId( 'h-' );
 				array_unshift( $threads, $fakeHeading );
@@ -113,19 +127,54 @@ class ApiDiscussionToolsPageInfo extends ApiBase {
 			// need to loop over this to fix up empty sections, because we
 			// need context that's not available inside the array map
 			if ( $item instanceof ContentHeadingItem && count( $item->getReplies() ) === 0 ) {
+				// If there are no replies we want to include whatever's
+				// inside this section as "othercontent". We create a range
+				// that's between the end of this section's heading and the
+				// start of next section's heading. The main difficulty here
+				// is avoiding catching any of the heading's tags within the
+				// range.
 				$nextItem = $threads[ $index + 1 ] ?? false;
 				$startRange = $item->getRange();
+				if ( $item->isPlaceholderHeading() ) {
+					// Placeholders don't have any heading to avoid
+					$startNode = $startRange->startContainer;
+					$startOffset = $startRange->startOffset;
+				} else {
+					$startNode = CommentUtils::closestElementWithSibling( $startRange->endContainer, 'next' );
+					$startNode = $startNode->nextSibling;
+					$startOffset = 0;
+				}
+
+				if ( !$startNode ) {
+					 $startNode = $startRange->endContainer;
+					 $startOffset = $startRange->endOffset;
+				}
+
 				if ( $nextItem ) {
-					$nextRange = $nextItem->getRange();
-					$nextStart = $nextRange->startContainer->previousSibling ?: $nextRange->startContainer;
+					$nextStart = $nextItem->getRange()->startContainer;
+					$endContainer = CommentUtils::closestElementWithSibling( $nextStart, 'previous' );
+					$endContainer = $endContainer && $endContainer->previousSibling ?
+						$endContainer->previousSibling : $nextStart;
+					$endOffset = CommentUtils::childIndexOf( $endContainer );
+					if ( $endContainer instanceof Text ) {
+						// This probably means that there's a wrapping node
+						// e.g. <div>foo\n==heading==\nbar</div>
+						$endOffset += $endContainer->length;
+					} elseif ( $endContainer instanceof Element && $endContainer->tagName === 'section' ) {
+						// if we're in sections, make sure we're selecting the
+						// end of the previous section
+						$endOffset = $endContainer->childNodes->length;
+					} elseif ( $endContainer->parentNode ) {
+						$endContainer = $endContainer->parentNode;
+					}
 					$betweenRange = new ImmutableRange(
-						$startRange->endContainer->nextSibling ?: $startRange->endContainer, 0,
-						$nextStart, $nextStart->childNodes->length ?? 0
+						$startNode, $startOffset,
+						$endContainer ?: $nextStart, $endOffset
 					);
 				} else {
 					// This is the last section, so we want to go to the end of the rootnode
 					$betweenRange = new ImmutableRange(
-						$startRange->endContainer->nextSibling ?: $startRange->endContainer, 0,
+						$startNode, $startOffset,
 						$item->getRootNode(), $item->getRootNode()->childNodes->length
 					);
 				}

includes/CommentUtils.php

@@ -229,6 +229,28 @@ class CommentUtils {
 		return null;
 	}
 
+	/**
+	 * Find closest ancestor element that has sibling nodes
+	 *
+	 * @param Node $node
+	 * @param string $direction Can be 'next', 'previous', or 'either'
+	 * @return Element|null
+	 */
+	public static function closestElementWithSibling( Node $node, string $direction ): ?Element {
+		do {
+			if (
+				$node instanceof Element && (
+					( $node->nextSibling && ( $direction === 'next' || $direction == 'either' ) ) ||
+					( $node->previousSibling && ( $direction === 'previous' || $direction == 'either' ) )
+				)
+			) {
+				return $node;
+			}
+			$node = $node->parentNode;
+		} while ( $node );
+		return null;
+	}
+
 	/**
 	 * Find the transclusion node which rendered the current node, if it exists.
 	 *