comments_open() & pings_open() trigger PHP Notice when called on a page without a $post

[dd32]

Both comments_open() and pings_open() contain some slightly odd logic, that accounts for the $post not existing on one line, and assuming it does exist on the next. Causing a PHP Notice under some specific circumstances.

Calling comments_open( $post_id_that_does_not_exist ) would also trigger it.

See attached.

[audrasjb]

The patch doesn't apply anymore against trunk

[audrasjb]

patch refreshed against trunk

[hellofromTonya]

Though today is 5.9 Beta 1, assigning to me to check test coverage and get this one committed.

[costdev]

Test Report

Env

• WordPress 5.9-alpha-20211117.140912
• Chrome 95.0.4638.69
• Windows 10
• Theme: Twenty Twenty Two
• Gutenberg Editor
• Plugin: None activated

Steps to test

1. Add comments_open( 999999 ); to your theme's functions.php file.
2. Load any page. You should see a PHP notice.
3. Apply the patch.
4. Reload the page. You should not see a PHP notice.

Results

Without the patch: A PHP notice displays for Warning: Attempt to read property "comment_status" on null.
With the patch: The PHP notice no longer displays.

[hellofromTonya]

Marking for commit.

Adds unit tests for both functions. Confirms PHP notice.
Applies patch 54159.1.diff. Confirms notice is fixed.

Trac ticket: https://core.trac.wordpress.org/ticket/54159

[hellofromTonya]

In 52223:

Comments: Fix PHP Notice "trying to get property of non-object" in comments_open() and pings_open().

The post for the comments or pings is retrieved by get_post(). If the post exists, get_post() returns an instance of WP_Post; else, it returns null.

In both comments_open() and pings_open(), the returned value from get_post() is used without checking if the object returned, if the post exists. When the post does not exist, the following notices occur:

PHP Notice:  Trying to get property 'comment_status' of non-object in .../src/wp-includes/comment-template.php on line 1244

and

PHP Notice:  Trying to get property 'pings_open' of non-object in ../src/wp-includes/comment-template.php on line 1274

This commit fixes these notices by checking if the post has a non-falsey value before using it as an object to set the $open state. As the return from get_post() will only be an object or null, the truthy check is appropriate and slightly more performant.

Tests added to validate the fix.

Follow-up to [1964], [40666].

Props dd32, audrasjb, costdev, hellofromTonya, sergeybiryukov.
Fixes #54159.

Committed via changeset https://core.trac.wordpress.org/changeset/52223.