Comments: Allow changing a comment's parent from the Edit Comment screen

src/js/_enqueues/admin/comment.js

@@ -99,4 +99,78 @@ jQuery( function($) {
 		$edittimestamp.show().trigger( 'focus' );
 		$timestampdiv.slideUp( 'fast' );
 	});
+
+	var $commentparentdiv = $( '#comment-parent-div' ),
+		$commentparentdisplay = $( '#comment-parent-display' ),
+		originalcommentparentdisplay = $commentparentdisplay.html(),
+		$editcommentparent = $commentparentdiv.siblings( 'a.edit-comment-parent' );
+
+	/**
+	 * Adds event that opens the parent comment form if the form is hidden.
+	 *
+	 * @since 7.1.0
+	 *
+	 * @listens $editcommentparent:click
+	 *
+	 * @param {Event} event The event object.
+	 * @return {void}
+	 */
+	$editcommentparent.on( 'click', function( event ) {
+		if ( $commentparentdiv.is( ':hidden' ) ) {
+			// Slide down the form and set focus on the parent field.
+			$commentparentdiv.slideDown( 'fast', function() {
+				$( '#comment_parent' ).trigger( 'focus' );
+			} );
+			$(this).hide();
+		}
+		event.preventDefault();
+	});
+
+	/**
+	 * Resets the parent comment value when the cancel button is clicked.
+	 *
+	 * @since 7.1.0
+	 *
+	 * @listens .cancel-comment-parent:click
+	 *
+	 * @param {Event} event The event object.
+	 * @return {void}
+	 */
+	$commentparentdiv.find( '.cancel-comment-parent' ).on( 'click', function( event ) {
+		// Move focus back to the Edit link.
+		$editcommentparent.show().trigger( 'focus' );
+		$commentparentdiv.slideUp( 'fast' );
+		$( '#comment_parent' ).val( $( '#hidden_comment_parent' ).val() );
+		$commentparentdisplay.html( originalcommentparentdisplay );
+		event.preventDefault();
+	});
+
+	/**
+	 * Updates the parent comment display when the ok button is clicked.
+	 *
+	 * @since 7.1.0
+	 *
+	 * @listens .save-comment-parent:click
+	 *
+	 * @param {Event} event The event object.
+	 * @return {void}
+	 */
+	$commentparentdiv.find( '.save-comment-parent' ).on( 'click', function( event ) {
+		var $selected = $( '#comment_parent option:selected' ),
+			parentLabel = $selected.data( 'author' ) || $selected.text();
+
+		event.preventDefault();
+
+		$commentparentdisplay.html(
+			wp.i18n.sprintf(
+				/* translators: %s: Parent comment author. */
+				wp.i18n.__( 'In reply to: %s' ),
+				$( '<b />' ).text( parentLabel ).prop( 'outerHTML' )
+			)
+		);
+
+		// Move focus back to the Edit link.
+		$editcommentparent.show().trigger( 'focus' );
+		$commentparentdiv.slideUp( 'fast' );
+	});
 });

src/wp-admin/css/edit.css

@@ -554,6 +554,16 @@ form#tags-filter {
 	line-height: 1.76923076;
 }
 
+#comment-parent-div {
+	padding-top: 5px;
+	/* Fieldsets cannot shrink below their content by default, allow it so the select cannot cause overflow. */
+	min-width: 0;
+}
+
+#comment-parent-div select {
+	width: 100%;
+}
+
 #timestampdiv p {
 	margin: 8px 0 6px;
 }

src/wp-admin/edit-form-comment.php

@@ -201,25 +201,183 @@
 </div>
 
 <?php
-if ( $comment->comment_parent ) :
+$parent_display = __( 'None' );
+
+if ( $comment->comment_parent ) {
 	$parent = get_comment( $comment->comment_parent );
-	if ( $parent ) :
-		$parent_link = esc_url( get_comment_link( $parent ) );
-		$name        = get_comment_author( $parent );
-		?>
-	<div class="misc-pub-section misc-pub-reply-to">
+
+	if ( $parent ) {
+		$parent_display = sprintf(
+			'<a href="%s">%s</a>',
+			esc_url( get_comment_link( $parent ) ),
+			esc_html( get_comment_author( $parent ) )
+		);
+	}
+}
+
+// The parent can only be changed when threaded comments are enabled.
+$comment_threading_enabled = get_option( 'thread_comments' );
+
+if ( $comment_threading_enabled ) {
+	$max_thread_depth = (int) get_option( 'thread_comments_depth' );
+
+	// Limit the number of comments to keep memory usage and the size of the dropdown reasonable on busy posts.
+	$post_comments = get_comments(
+		array(
+			'post_id' => $comment->comment_post_ID,
+			'type'    => 'comment',
+			'status'  => array( 'approve', 'hold' ),
+			'orderby' => 'comment_date_gmt',
+			'order'   => 'DESC',
+			'number'  => 100,
+		)
+	);
+
+	// Restore chronological order for display.
+	$post_comments = array_reverse( $post_comments );
+
+	// Index the comments by ID and by parent, to compute depths and find descendants.
+	$post_comments_by_id = array();
+	$comments_by_parent  = array();
+
+	foreach ( $post_comments as $post_comment ) {
+		$post_comments_by_id[ (int) $post_comment->comment_ID ]      = $post_comment;
+		$comments_by_parent[ (int) $post_comment->comment_parent ][] = (int) $post_comment->comment_ID;
+	}
+
+	// Walk the descendants level by level, which also gives the height of the subtree that moves with the comment.
+	$comment_descendants    = array();
+	$comment_subtree_height = 1;
+	$comment_level          = array( (int) $comment->comment_ID );
+
+	while ( $comment_level ) {
+		$next_level = array();
+
+		foreach ( $comment_level as $level_comment_id ) {
+			if ( isset( $comments_by_parent[ $level_comment_id ] ) ) {
+				foreach ( $comments_by_parent[ $level_comment_id ] as $descendant_id ) {
+					$comment_descendants[ $descendant_id ] = true;
+					$next_level[]                          = $descendant_id;
+				}
+			}
+		}
+
+		if ( $next_level ) {
+			++$comment_subtree_height;
+		}
+
+		$comment_level = $next_level;
+	}
+
+	// Compute each comment's depth, since comments at the maximum threading depth cannot become a parent.
+	$comment_depths = array();
+
+	foreach ( $post_comments as $post_comment ) {
+		$depth       = 1;
+		$ancestor_id = (int) $post_comment->comment_parent;
+
+		while ( $ancestor_id && isset( $post_comments_by_id[ $ancestor_id ] ) ) {
+			++$depth;
+			$ancestor_id = (int) $post_comments_by_id[ $ancestor_id ]->comment_parent;
+		}
+
+		$comment_depths[ (int) $post_comment->comment_ID ] = $depth;
+	}
+}
+?>
+<div class="misc-pub-section misc-pub-reply-to">
+<span id="comment-parent-display">
+<?php
+printf(
+	/* translators: %s: Parent comment link, or 'None'. */
+	__( 'In reply to: %s' ),
+	'<b>' . $parent_display . '</b>'
+);
+?>
+</span>
+<?php if ( $comment_threading_enabled ) : ?>
+<a href="#edit_comment_parent" class="edit-comment-parent hide-if-no-js"><span aria-hidden="true"><?php _e( 'Edit' ); ?></span> <span class="screen-reader-text">
+	<?php
+	/* translators: Hidden accessibility text. */
+	_e( 'Edit parent comment' );
+	?>
+</span></a>
+<fieldset id="comment-parent-div" class="hide-if-js">
+<legend class="screen-reader-text">
+	<?php
+	/* translators: Hidden accessibility text. */
+	_e( 'Parent comment' );
+	?>
+</legend>
+<label for="comment_parent"><?php _e( 'Parent comment' ); ?></label>
+<select name="comment_parent" id="comment_parent">
+	<option value="0"<?php selected( 0, (int) $comment->comment_parent ); ?>>
 		<?php
+		/* translators: Option in the parent comment dropdown, meaning the comment has no parent. */
+		_e( 'None (top-level comment)' );
+		?>
+	</option>
+	<?php
+	$current_parent_listed = false;
+
+	foreach ( $post_comments as $post_comment ) {
+		$post_comment_id = (int) $post_comment->comment_ID;
+
+		if ( $post_comment_id === (int) $comment->comment_ID || isset( $comment_descendants[ $post_comment_id ] ) ) {
+			continue;
+		}
+
+		// The comment and the replies that move with it must stay within the maximum threading depth.
+		if ( $max_thread_depth && $comment_depths[ $post_comment_id ] + $comment_subtree_height > $max_thread_depth ) {
+			continue;
+		}
+
+		if ( $post_comment_id === (int) $comment->comment_parent ) {
+			$current_parent_listed = true;
+		}
+
+		$option_label = sprintf(
+			/* translators: 1: Comment author, 2: Comment excerpt. */
+			__( '%1$s: %2$s' ),
+			get_comment_author( $post_comment ),
+			wp_html_excerpt( get_comment_excerpt( $post_comment ), 50, '…' )
+		);
+
 		printf(
-			/* translators: %s: Comment link. */
-			__( 'In reply to: %s' ),
-			'<b><a href="' . $parent_link . '">' . $name . '</a></b>'
+			"\t<option value='%d' data-author='%s'%s>%s</option>\n",
+			$post_comment_id,
+			esc_attr( get_comment_author( $post_comment ) ),
+			selected( $post_comment_id, (int) $comment->comment_parent, false ),
+			esc_html( $option_label )
 		);
-		?>
-	</div>
-		<?php
-endif;
-endif;
-?>
+	}
+
+	// The current parent may not be listed, e.g. a pingback or a comment no longer publicly visible.
+	if ( $comment->comment_parent && ! $current_parent_listed && isset( $parent ) ) {
+		$option_label = sprintf(
+			/* translators: 1: Comment author, 2: Comment excerpt. */
+			__( '%1$s: %2$s' ),
+			get_comment_author( $parent ),
+			wp_html_excerpt( get_comment_excerpt( $parent ), 50, '…' )
+		);
+
+		printf(
+			"\t<option value='%d' data-author='%s' selected>%s</option>\n",
+			(int) $comment->comment_parent,
+			esc_attr( get_comment_author( $parent ) ),
+			esc_html( $option_label )
+		);
+	}
+	?>
+</select>
+<input type="hidden" id="hidden_comment_parent" value="<?php echo esc_attr( $comment->comment_parent ); ?>" />
+<p>
+<a href="#edit_comment_parent" class="save-comment-parent hide-if-no-js button"><?php _e( 'OK' ); ?></a>
+<a href="#edit_comment_parent" class="cancel-comment-parent hide-if-no-js button-cancel"><?php _e( 'Cancel' ); ?></a>
+</p>
+</fieldset>
+<?php endif; ?>
+</div>
 
 <?php
 	/**

src/wp-admin/includes/comment.php

@@ -46,6 +46,7 @@ function comment_exists( $comment_author, $comment_date, $timezone = 'blog' ) {
  *
  * @since 2.0.0
  * @since 5.5.0 A return value was added.
+ * @since 7.1.0 The comment parent can be updated via `$_POST['comment_parent']`.
  *
  * @return int|WP_Error The value 1 if the comment was updated, 0 if not updated.
  *                      A WP_Error object on failure.
@@ -74,6 +75,85 @@ function edit_comment() {
 		$_POST['comment_ID'] = (int) $_POST['comment_ID'];
 	}
 
+	if ( isset( $_POST['comment_parent'] ) ) {
+		$comment_id     = (int) $_POST['comment_ID'];
+		$comment_parent = (int) $_POST['comment_parent'];
+
+		$_POST['comment_parent'] = $comment_parent;
+
+		$comment = get_comment( $comment_id );
+
+		if ( $comment && $comment_parent && $comment_parent !== (int) $comment->comment_parent ) {
+			if ( ! get_option( 'thread_comments' ) ) {
+				return new WP_Error( 'comment_parent_invalid', __( 'The comment parent cannot be changed because threaded comments are disabled.' ) );
+			}
+
+			if ( $comment_parent === $comment_id ) {
+				return new WP_Error( 'comment_parent_invalid', __( 'A comment cannot be a reply to itself.' ) );
+			}
+
+			$parent = get_comment( $comment_parent );
+
+			// The parent must be a comment of the same type, on the same post, and not in the Trash or marked as spam.
+			if (
+				! $parent
+				|| (int) $parent->comment_post_ID !== (int) $comment->comment_post_ID
+				|| $parent->comment_type !== $comment->comment_type
+				|| in_array( wp_get_comment_status( $parent ), array( 'spam', 'trash' ), true )
+			) {
+				return new WP_Error( 'comment_parent_invalid', __( 'Invalid parent comment.' ) );
+			}
+
+			// Walk up the new parent's ancestors to prevent creating a threading loop.
+			$ancestors    = array();
+			$ancestor     = $parent;
+			$parent_depth = 1;
+
+			while ( $ancestor && $ancestor->comment_parent && ! isset( $ancestors[ $ancestor->comment_ID ] ) ) {
+				if ( (int) $ancestor->comment_parent === $comment_id ) {
+					return new WP_Error( 'comment_parent_invalid', __( 'A comment cannot be a reply to one of its own replies.' ) );
+				}
+
+				$ancestors[ $ancestor->comment_ID ] = true;
+				++$parent_depth;
+
+				$ancestor = get_comment( $ancestor->comment_parent );
+			}
+
+			$max_thread_depth = (int) get_option( 'thread_comments_depth' );
+
+			if ( $max_thread_depth ) {
+				/*
+				 * The comment's replies move with it, so the whole subtree must stay within
+				 * the maximum depth. Measure its height one level of replies at a time,
+				 * stopping as soon as the subtree cannot fit, which also bounds the loop
+				 * should the stored comment hierarchy contain a cycle.
+				 */
+				$subtree_height = 1;
+				$level_ids      = array( $comment_id );
+
+				while ( $level_ids && $parent_depth + $subtree_height <= $max_thread_depth ) {
+					$level_ids = get_comments(
+						array(
+							'parent__in' => $level_ids,
+							'fields'     => 'ids',
+							'status'     => 'any',
+							'orderby'    => 'none',
+						)
+					);
+
+					if ( $level_ids ) {
+						++$subtree_height;
+					}
+				}
+
+				if ( $parent_depth + $subtree_height > $max_thread_depth ) {
+					return new WP_Error( 'comment_parent_invalid', __( 'The comment cannot be moved there because it or its replies would exceed the maximum threading depth.' ) );
+				}
+			}
+		}
+	}
+
 	foreach ( array( 'aa', 'mm', 'jj', 'hh', 'mn' ) as $timeunit ) {
 		if ( ! empty( $_POST[ 'hidden_' . $timeunit ] ) && $_POST[ 'hidden_' . $timeunit ] !== $_POST[ $timeunit ] ) {
 			$_POST['edit_date'] = '1';