`get_terms()` falsely assumes that legacy arguments are used

[flixos90]

As stated by @wonderboymusic on Slack (​https://wordpress.slack.com/archives/core/p1470289963002086), get_terms() under some conditions assumes that legacy arguments are used when they actually aren't. This can cause the taxonomy argument to have some weird values.

[flixos90]

37568.diff​ fixes that problem by introducing a new static method to WP_Meta_Query which returns the default values for it. These default values are then included in the query var defaults in WP_Term_Query. They could alternatively be placed directly in WP_Term_Query, but I think this approach makes more sense since several classes use WP_Meta_Query and could use its new method.

[ocean90]

Related: [36614]

[flixos90]

In 37568.2.diff​ I added a unit tests to verify the issue is fixed.

[boonebgorges]

@flixos90 - Thanks for the debugging and the patches.

Adding the meta-related query params to the $query_var_defaults array seems like the right approach to me.

They could alternatively be placed directly in WP_Term_Query, but I think this approach makes more sense since several classes use WP_Meta_Query and could use its new method.

This feels off to me. First, the naming is weird: what's really being provided here is the "default top-level query params that are supported by parse_query_vars()". (IMO, meta_query is a different kind of thing from meta_key, meta_type, etc.) This is hard to capture in a method name, which suggests to me that it's not a discrete enough concept to abstract in the way you've suggested. I'd like to explore a better way to centralize the definition and processing of WP_*_Query parameters, but this should be tackled as a larger project. Since get_terms() is the only place where the defaults are being used in this way, let's hold off on the additional abstraction. See 37568.3.diff​.

As @ocean90 notes, this dates to [36614], which means it's a regression in 4.5, not 4.6. For this reason, I don't think it's necessary to put it into the 4.6 RC, but I'll let @ocean90 make the call there. @wonderboymusic In the meantime, you should be able to work around by passing any additional parameter to get_terms() - something redundant like:

$terms = get_terms( [
    'meta_key' => 'foo',
    'meta_value' => 1,
    'orderby' => 'name',
] );

[wonderboymusic]

that was an accident

[wonderboymusic]

In 38337:

Taxonomy: in get_terms(), do not assume that legacy args are being passed when the only params are top-level meta_* values. Add keys in WP_Term_Query::__construct().

Adds unit tests.

Props flixos90, boonebgorges.
Fixes #37568.