Fix use of 'fields'=>'ids', which should return post IDs

[danielbachhuber]

No description provided.

[danielbachhuber]

@ataylorme We have a bit of a problem with this, unfortunately.

Solr Power fills in posts from Solr on the_posts filter: https://github.com/WordPress/WordPress/blob/06fa4161aa74619239cf27017d124081c825684a/wp-includes/class-wp-query.php#L3007

When we return an array of IDs in the_posts filter, they get transformed into proper post objects: https://github.com/WordPress/WordPress/blob/06fa4161aa74619239cf27017d124081c825684a/wp-includes/class-wp-query.php#L3010-L3020

The workaround would be to use the posts_pre_query filter, added in WordPress 4.6. But, we need to increase the minimum version to 4.6: https://github.com/WordPress/WordPress/blob/06fa4161aa74619239cf27017d124081c825684a/wp-includes/class-wp-query.php#L2781

I can't think of an alternative fix at this point.

I noticed this issue while working on #299. There are lots of tests like this:

[ataylorme]

@danielbachhuber per Josh's comment in #284 I think bumping minimum version is okay. Please proceed.

cc @joshkoenig

[danielbachhuber]

per Josh's comment in #284 I think bumping minimum version is okay. Please proceed.

I confirmed today with Josh. I'll do so in a separate PR.

[ataylorme]

@danielbachhuber what's the status of this work? I see the unit tests are failing. Wondering if we should try to get this into 1.4 which I'd like to release soon

[danielbachhuber]

what's the status of this work?

It's on my plate but I haven't started. I'll need to do a fair amount of refactoring to use posts_pre_query.

Wondering if we should try to get this into 1.4 which I'd like to release soon

Is 1.5 to 2 weeks fine? I can work on the refactor early next.

[ataylorme]

Saving it for 1.5 is fine. I'll be out on vacation until 9/5 starting next week but can review and cut a release when I return.

[ataylorme]

@danielbachhuber this seems to be the last thing in the 1.5 milestone. Still plan on getting this in for that release?

[danielbachhuber]

Closing in favor of #336