Avoid PHP notice in get_comment_reply_link() for null comment

[birgire]

When I was working on tests for get_comment_reply_link() I got a PHP notice:

Notice	Trying to get property of non-object ...

with inputs like:

get_comment_reply_link( array( 'depth' => 1, 'max_depth' => 2 ) );

when there's no current global comment available and the input comment is null.

That's because of this part:

$comment = get_comment( $comment );

if ( empty( $post ) ) {
    $post = $comment->comment_post_ID;
}

where there's no validation for $comment.

[birgire]

In 41846.patch​ we added a comment validation, similar to the existing one for the post.

Included is a test.

[birgire]

Related #38925

[earnjam]

Thanks @birgire! This looks good.

In 41846.diff​ I just made a few small whitespace CS fixes to the unit test and added the ticket number to the @ticket annotation in the docblock.

I'm going to go ahead and milestone this for the next release.

[whyisjake]

When I run phpunit --group comment I am getting the following error.

1) Tests_Comment_GetCommentReplyLink::test_should_return_null_when_depth_less_than_max_depth_and_comment_null_and_no_current_global_comment
TypeError: Argument 2 passed to PHPUnit\Framework\Assert::assertNull() must be of the type string, null given, called in /tests/phpunit/tests/comment/getCommentReplyLink.php on line 89

/tests/phpunit/tests/comment/getCommentReplyLink.php:89

[birgire]

@whyisjake thanks for testing

41846-2.diff​ is a refreshed patch that runs successfully through the comment group tests.

[whyisjake]

In 46335:

Comments: Avoid PHP notice in get_comment_reply_link() for null comment.

If there is no global comment, or the input comment is null, return early to prevent warnings.

Fixes #41846
Props birgire, earnjam

[SergeyBiryukov]

Related: #40143

[johnbillion]

@birgire @whyisjake What bug does this fix? Returning early when there's no global comment silences the error which, in my eyes, seems to be a legitimate one. Calling this function in a context where there's no global comment is incorrect.

[birgire]

@johnbillion good question

At the time I think I might have looked at the validation on some of the other input arguments, that also returns null when invalid, correpsonding to the existing void part of the docs:

 * @return void|false|string Link to show comment form, if successful. False, if comments are closed.

I might have also looked into get_post() as a reference point too, for a typical WordPress practice, as it returns null on failure of finding a global post object:

https://core.trac.wordpress.org/browser/tags/5.2/src/wp-includes/post.php#L726

But I'm all in for helping devs to better debug their code.