wp_insert_comment should require comment_post_ID

[markoheijnen]

At this moment there is no check for example comment_post_ID. Not sure if there are more checks needed. Reason I asked are a few notices on the unit tests caused by WP_UnitTest_Factory_For_Comment. Those comments don't add a post ID what should change.

Currently, if a null comment_post_ID is passed, the comment isn't connected to a post. This can create confusion. Also Unit tests should run with WP_Debug on.

Simplify construction of commentdata array for insertion with defaults

By refactoring the way that the commentdata is prepared for insertion into the DB, it now merges the passed-in data on top of a defaults array that includes a comment_post_ID, so there will be no undefined index.

Patch also includes a wp_insert_comment_data filter before insert to accompany the wp_insert_comment action which happens after insert.

See first attached patch, or see from branch on GitHub: ​https://github.com/x-team/WordPress/compare/87f9d11...7588a21

Update unit tests to always create comments with a valid comment_post_ID

Return WP_Error from wp_insert_comment if invalid comment_post_ID inserted

Also add assertions for unit tests to check for returned WP_Error instance when invalid comment_post_ID is supplied, and test the wp_insert_comment_data filter

All patches pushed to branch on GitHub: ​https://github.com/x-team/WordPress/compare/87f9d11...23931-require-comment_post_ID

BTW, the need for a wp_insert_comment_data filter came up while doing work on the Liveblog plugin: ​https://github.com/x-team/wp-liveblog/commit/94958de51f786e4eed6389cc0c3124fcdb8c5c29#L4R458

Something does need to happen here. At the very least, the tests should set comment_post_ID to 0 by default. That will keep it from erroring. If we're going to force comment_post_ID to be valid though, we should make WP_UnitTest_Factory_For_Comment automatically create a post if comment_post_ID isn't set. I think that makes more sense then having to create one each time like in ​your patch.