WP_Query(array( 'p' => 0)) will return posts

[ChiefAlchemist]

Long to short, I was presuming that if the $args were such that no rows exist then WP_Query would return nothing.

Not so.

If by chance, 'p' => 0, you do get results.

Perhaps the 0 is interpreted as false? Even so, an ID == false should return no row, yes? Or one might argue "well, that query doesn't make sense. it's not really valid." again, all the more reason to return nothing.

[boonebgorges]

I agree that it's counterintuitive, and that, in theory, 'p' => 0 should return no results.

However, it's likely that such a change would introduce backward compatibility concerns. See #35090 and [36381] for a similar issue, where it was quickly discovered that people were passing 0 to disable the parameter, rather than to match 0 as a value.

In order to consider a change like this (which applies equally to page_id, year, monthnum, day, w, paged, and maybe others), we need a couple things:

1. Unit tests describing the changed behavior
2. A review of the plugin repo to see the circumstances in which people are passing 'p' => 0 to WP_Query. If it's widely used as a way to disable the p check, then we probably can't change it. (This is a good task for anyone wanting to help with the ticket.)
3. Assuming it's not being widely exploited, we should drop it in at the very beginning of a dev cycle, with some related publicity, so we have time to see what breaks.

35820.diff is what the patch would look like.