Cannot mention post with deleted author

[clarkwinkelmann]

Bug Report

Current Behavior
If you try mentioning a post whose author is [deleted], the preview will render correctly, but after saving the mention will stay as plain text.

Steps to Reproduce

1. Create post and delete author, either by deleting the user or setting user_id null in the database
2. Use reply button or @ syntax to mention the post with deleted author
3. Preview shows mention as expected
4. Submit post
5. Final post doesn't contain mention

Expected Behavior
It should be possible to mention those posts. In fact it works fine if the author is deleted after the reply is created. But if the reply is created afterwards, it doesn't work.

Screenshots
Preview:

Submitted:

Environment

• Flarum version: 1.2.1, likely still in 1.3.0 because the master code still contains the issue right now

Possible Solution
The problem is in

framework/extensions/mentions/src/ConfigureMentions.php

Lines 124 to 135 in 471947d

	public static function addPostId($tag)
	{
	$post = CommentPost::find($tag->getAttribute('id'));
	if ($post && $post->user) {
	$tag->setAttribute('discussionid', (int) $post->discussion_id);
	$tag->setAttribute('number', (int) $post->number);
	$tag->setAttribute('displayname', $post->user->display_name);
	return true;
	}
	}

which only saves a mention if both the post and author exist.

I think we should just move $tag->setAttribute('displayname', $post->user->display_name); to a separate if( $post->user). Not sure if we should put a different default value for displayname. Its value will already be set to [deleted] in Formatter/FormatPostMentions anyway.

The preview JavaScript code doesn't have that limitation

framework/extensions/mentions/js/src/forum/utils/textFormatter.js

Lines 23 to 33 in 471947d

	export function filterPostMentions(tag) {
	const post = app.store.getById('posts', tag.getAttribute('id'));
	if (post) {
	tag.setAttribute('discussionid', post.discussion().id());
	tag.setAttribute('number', post.number());
	tag.setAttribute('displayname', extractText(username(post.user())));
	return true;
	}
	}