Tax Query: Allow querying for all posts with any term of a given taxonomy

src/wp-includes/class-wp-query.php

@@ -1169,7 +1169,16 @@ public function parse_tax_query( &$q ) {
 				continue; // Handled further down in the $q['tag'] block.
 			}
 
-			if ( $t->query_var && ! empty( $q[ $t->query_var ] ) ) {
+			if ( ! $t->query_var || ! isset( $q[ $t->query_var ] ) ) {
+				continue;
+			}
+
+			if ( empty( $q[ $t->query_var ] ) && ! $t->root_taxonomy_archive ) {
+				// We only allow the term to be empty if the taxonomy is set up to
+				// show its root archive.
+				continue;
+			}
+
 			$tax_query_defaults = array(
 				'taxonomy' => $taxonomy,
 				'field'    => 'slug',
@@ -1195,14 +1204,20 @@ public function parse_tax_query( &$q ) {
 						)
 					);
 				}
-				} else {
+			} elseif ( ! empty( $term ) ) {
 				$tax_query[] = array_merge(
 					$tax_query_defaults,
 					array(
 						'terms' => preg_split( '/[,]+/', $term ),
 					)
 				);
-				}
+			} else {
+				$tax_query[] = array_merge(
+					$tax_query_defaults,
+					array(
+						'operator' => 'EXISTS',
+					)
+				);
 			}
 		}
 

src/wp-includes/class-wp-taxonomy.php

@@ -245,6 +245,15 @@ final class WP_Taxonomy {
 	 */
 	public $default_term;
 
+	/**
+	 * Whether to show a page for the root taxonomy route, displaying all
+	 * posts that have any term from the taxonomy assigned.
+	 *
+	 * @since 6.8.0
+	 * @var bool
+	 */
+	public $root_taxonomy_archive = false;
+
 	/**
 	 * Whether terms in this taxonomy should be sorted in the order they are provided to `wp_set_object_terms()`.
 	 *
@@ -359,6 +368,7 @@ public function set_props( $object_type, $args ) {
 			'rest_namespace'        => false,
 			'rest_controller_class' => false,
 			'default_term'          => null,
+			'root_taxonomy_archive' => false,
 			'sort'                  => null,
 			'args'                  => null,
 			'_builtin'              => false,
@@ -510,7 +520,12 @@ public function add_rewrite_rules() {
 				$tag = '([^/]+)';
 			}
 
-			add_rewrite_tag( "%$this->name%", $tag, $this->query_var ? "{$this->query_var}=" : "taxonomy=$this->name&term=" );
+			$query = $this->query_var ? "{$this->query_var}=" : "taxonomy=$this->name&term=";
+
+			add_rewrite_tag( "%taxonomy-$this->name%", "$this->name()", $query );
+			add_permastruct( "taxonomy-$this->name", "%taxonomy-$this->name%", $this->rewrite );
+
+			add_rewrite_tag( "%$this->name%", $tag, $query );
 			add_permastruct( $this->name, "{$this->rewrite['slug']}/%$this->name%", $this->rewrite );
 		}
 	}
@@ -535,6 +550,9 @@ public function remove_rewrite_rules() {
 		if ( false !== $this->rewrite ) {
 			remove_rewrite_tag( "%$this->name%" );
 			remove_permastruct( $this->name );
+
+			remove_rewrite_tag( "%taxonomy-$this->name%" );
+			remove_permastruct( "taxonomy-$this->name" );
 		}
 	}
 

src/wp-includes/taxonomy.php

@@ -426,6 +426,7 @@ function is_taxonomy_hierarchical( $taxonomy ) {
  * @since 5.4.0 Added the registered taxonomy object as a return value.
  * @since 5.5.0 Introduced `default_term` argument.
  * @since 5.9.0 Introduced `rest_namespace` argument.
+ * @since 6.8.0 Introduced `root_taxonomy_archive` argument.
  *
  * @global WP_Taxonomy[] $wp_taxonomies Registered taxonomies.
  *
@@ -506,6 +507,8 @@ function is_taxonomy_hierarchical( $taxonomy ) {
  *         @type string $slug         Slug for default term. Default empty.
  *         @type string $description  Description for default term. Default empty.
  *     }
+ *     @type bool          $root_taxonomy_archive Whether to show a page at the root taxonomy route, displaying all
+ *                                                posts that have any term from the taxonomy assigned. Default false.
  *     @type bool          $sort                  Whether terms in this taxonomy should be sorted in the order they are
  *                                                provided to `wp_set_object_terms()`. Default null which equates to false.
  *     @type array         $args                  Array of arguments to automatically use inside `wp_get_object_terms()`

tests/phpunit/tests/canonical.php

@@ -87,13 +87,32 @@ public function data_canonical() {
 			array( '?cat=%d', array( 'url' => '/category/parent/' ), 15256 ),
 			array( '?cat=%d', array( 'url' => '/category/parent/child-1/' ), 15256 ),
 			array( '?cat=%d', array( 'url' => '/category/parent/child-1/child-2/' ) ), // No children.
+			array(
+				'/category/',
+				array(
+					'url' => '/category/',
+					'qv'  => array( 'category_name' => '' ),
+				),
+				61957,
+			),
 			array(
 				'/category/uncategorized/',
 				array(
 					'url' => '/category/uncategorized/',
 					'qv'  => array( 'category_name' => 'uncategorized' ),
 				),
 			),
+			array(
+				'/category/page/2/',
+				array(
+					'url' => '/category/page/2/',
+					'qv'  => array(
+						'category_name' => '',
+						'paged'         => 2,
+					),
+				),
+				61957,
+			),
 			array(
 				'/category/uncategorized/page/2/',
 				array(
@@ -104,6 +123,17 @@ public function data_canonical() {
 					),
 				),
 			),
+			array(
+				'/category/?paged=2',
+				array(
+					'url' => '/category/page/2/',
+					'qv'  => array(
+						'category_name' => '',
+						'paged'         => 2,
+					),
+				),
+				61957,
+			),
 			array(
 				'/category/uncategorized/?paged=2',
 				array(
@@ -127,6 +157,17 @@ public function data_canonical() {
 			),
 
 			// Categories & intersections with other vars.
+			array(
+				'/category/?tag=post-formats',
+				array(
+					'url' => '/category/?tag=post-formats',
+					'qv'  => array(
+						'category_name' => '',
+						'tag'           => 'post-formats',
+					),
+				),
+				61957,
+			),
 			array(
 				'/category/uncategorized/?tag=post-formats',
 				array(
@@ -146,6 +187,7 @@ public function data_canonical() {
 			),
 
 			// Taxonomies with extra query vars.
+			array( '/category/page/1/?test=one%20two', '/category/?test=one%20two', 61957 ), // Extra query vars should stay encoded.
 			array( '/category/cat-a/page/1/?test=one%20two', '/category/cat-a/?test=one%20two', 18086 ), // Extra query vars should stay encoded.
 
 			// Categories with dates.

tests/phpunit/tests/taxonomy.php

@@ -917,7 +917,7 @@ public function test_unregister_taxonomy_removes_rewrite_rules() {
 		$this->assertTrue( unregister_taxonomy( 'foo' ) );
 		$this->assertNotContains( '%foo%', $wp_rewrite->rewritecode );
 		$this->assertNotContains( 'bar=', $wp_rewrite->queryreplace );
-		$this->assertCount( --$count_before, $wp_rewrite->rewritereplace ); // Array was reduced by one value.
+		$this->assertCount( $count_before - 2, $wp_rewrite->rewritereplace ); // Array was reduced by two values.
 	}
 
 	/**