[wp-trac] [WordPress Trac] #43977: Fix error-prone string to array parsing

[WordPress Trac]

#43977: Fix error-prone string to array parsing
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 Reporter:  flixos90      |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  5.0
Component:  General       |    Version:
 Severity:  normal        |   Keywords:  needs-patch needs-unit-tests
  Focuses:  rest-api      |
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 In the REST API (and sometimes in other areas of core too) it's a common
 procedure to parse a string into an array, splitting at comma characters.
 I noticed an issue that can easily lead to unexpected behavior when an
 empty value is passed.

 Several functions in core use this behavior: `$list = preg_split(
 '/[\s,]+/', $list );`

 However, it causes empty strings to be parsed into an array containing an
 empty string, where I would expect it to just be an empty array. In the
 REST API, this can cause strange behavior:

 * If you call `wp/v2/posts/?include=`, WordPress will search for posts
 with ID 0 (which won't change the response, but is still somewhat clunky).
 * If you call `wp/v2/posts/?slug=`, WordPress will search for posts with
 an empty slug (which won't change the response, but is still somewhat
 clunky).
 * More importantly though: If you call `wp/v2/posts/?status=`, you will
 get a strange error saying "Status is forbidden". That is because it
 validates the empty string in the parsed array against the enum whitelist,
 with that check obviously failing. It's not a required parameter, so in
 this case, it should instead just be ignored.

 We should look for functions that perform the above parsing procedure and
 fix them.

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Ticket URL: <https://core.trac.wordpress.org/ticket/43977>
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