Use comment status and type to set $maybe_notify default

[adamsilverstein]

Trac ticket: https://core.trac.wordpress.org/ticket/64217

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Props adamsilverstein, westonruter, jorbin.

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[adamsilverstein]

@westonruter whenever you have a moment, this is ready for review again.

[adamsilverstein]

Draft dev note for the 7.1 field guide

The notify_post_author filter now has the final say on post author notifications

WordPress 7.1 changes when the comment approval status is checked in wp_new_comment_notify_postauthor(). See #64217.

Previously, the notify_post_author filter received a default value derived only from the comments_notify (or wp_notes_notify) option. The comment's approval status was checked after the filter ran, which had two consequences:

1. The filter received a misleading default of true for unapproved comments, even though no notification would be sent.
2. Returning true from the filter could not force a notification for an unapproved comment - the return value was silently discarded.

As of 7.1, the approval status is incorporated into the default value passed to the filter, and the filter's return value is final:

• The default is false for unapproved comments (including spam and trash).
• The default for notes continues to follow the wp_notes_notify option regardless of approval status, and the default for approved comments continues to follow the comments_notify option.
• Returning true from the filter now sends the notification, even for an unapproved comment.

In addition, the filter no longer fires when the passed comment ID does not resolve to a valid comment; the function returns false immediately.

Who is affected: Sites or plugins using a callback such as __return_true on notify_post_author to force notifications will now also receive emails for comments held in moderation, marked as spam, or trashed. If that is not desired, the callback should check the comment's approval status:

add_filter(
	'notify_post_author',
	function ( $maybe_notify, $comment_id ) {
		$comment = get_comment( $comment_id );

		// Only force notifications for approved comments.
		if ( $comment && '1' === $comment->comment_approved ) {
			return true;
		}

		return $maybe_notify;
	},
	10,
	2
);

Callbacks that only suppress notifications (returning false) are unaffected.