WP_DEBUG "undefined index" notices in get_metadata() for empty arrays

[doublesharp]

When the WP_DEBUG constant is set, calling get_metadata() in /wp-includes/meta.php with $single==true can cause "undefined index" notices when the meta data value is an empty array. As null is an acceptable return value for this function, silencing the notice with @ will remove noise when debugging without the overhead of checking the array length or that the 0 index isset().

[doublesharp]

silences undefined index notice with @$check[0]

[doublesharp]

silences undefined index notice with @$check[0]

[JD55]

I think there is really a larger issue here. I don't think that the logic behind this is correct:

if ( $single && is_array( $check ) )
       return $check[0];

This makes it impossible to return an array for the single meta value, which is a real problem if your meta value is stored as an array. I've attached a some code that demonstrates this. I think that this check should be removed completely, and $check should be returned 'raw'. As nacin said in a related ticket:

In many locations throughout core, we simply trust the plugin to return the right data, and if they don't, then the sky may fall on their head.

So it should just be this:

if ( null !== $check )
      return $check;

It should be up to the plugin to return an appropriate value based on $single. It has to be, because we have no way of knowing whether a value is appropriate.

[nacin]

While I am not a huge fan of how this is implemented, I don't think there is a bug here, and it's not impossible to return an array.

It seems the onus is on the plugin author to look at the $single argument passed to the get_{$meta_type}_metadata filter, and obey it. As in, if you want to return an array, then do so if $single, but wrap it in an array (with key 0 being your array) if not $single.

[JD55]

Replying to nacin:

if you want to return an array, then do so if $single, but wrap it in an array (with key 0 being your array) if not $single.

I hadn't thought of that hack. But it still seems like, well, a hack, to me. If its going to stay this way it should be mentioned in the codex so people know this is a 'feature' and not a bug.

[jdgrimes]

I've made ​a note of this in the codex, so if it changes that needs to be updated.

[nacin]

Thanks for adding a note to the Codex, jdgrimes.