Force non-public taxonomies to have a query_var of false.

[35333] implemented `public=false` for taxonomies. The implementation prevented
non-public taxonomies from having their archives accessed via query_var during
a normal request. But it didn't prevent non-public taxonomies from registering
their query vars in the `$wp_taxonomies` global. The latter implementation
details causes problems specifically when a taxonomy is registered with
`query_var=true`; for public taxonomies, `register_taxonomy()` translates this
into a query_var equivalent to the taxonomy name, but in the case of non-public
taxonomies, the query_var was set to the boolean itself. The boolean then
causes problems when using non-strict comparison to filter taxonomy objects by
query_var, as when using `get_taxonomies()`.

This changeset addresses the issue by forcing the query_var property of
non-public taxonomies to `false`.

Fixes #35089.

git-svn-id: https://develop.svn.wordpress.org/trunk@36108 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/taxonomy.php

@@ -517,4 +517,17 @@ class Tests_Taxonomy extends WP_UnitTestCase {
 
 		$this->assertFalse( is_tax( 'wptests_tax' ) );
 	}
+
+	/**
+	 * @ticket 35089
+	 */
+	public function test_query_var_should_be_forced_to_false_for_non_public_taxonomy() {
+		register_taxonomy( 'wptests_tax', 'post', array(
+			'public' => false,
+			'query_var' => true,
+		) );
+
+		$tax = get_taxonomy( 'wptests_tax' );
+		$this->assertFalse( $tax->query_var );
+	}
 }