Exclude non-cacheable meta keys from keyless meta_value queries

When a WP_Query uses meta_value without meta_key, the query matches
across all meta keys. Non-cacheable meta keys must be excluded from
these results, otherwise stale cached results would be served since
cache invalidation is skipped for those keys.

Adds a NOT IN clause to exclude registered non-cacheable keys when
a meta query clause has a value but no key.

Adds tests based on the cases raised in PR review.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ellatrix

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

@@ -776,6 +776,21 @@ public function get_sql_for_clause( &$clause, $parent_query, $clause_key = '' )
 			}
 		}
 
+		// When querying by meta_value without a specific key, exclude
+		// non-cacheable meta keys so their rows never appear in results.
+		// This is necessary because cache invalidation is skipped for these
+		// keys, so including them would produce stale cached query results.
+		if ( 'post' === $this->object_type
+			&& ! array_key_exists( 'key', $clause )
+			&& array_key_exists( 'value', $clause )
+		) {
+			$excluded_keys = $this->get_non_cacheable_meta_keys();
+			if ( ! empty( $excluded_keys ) ) {
+				$placeholders              = implode( ',', array_fill( 0, count( $excluded_keys ), '%s' ) );
+				$sql_chunks['where'][]     = $wpdb->prepare( "$alias.meta_key NOT IN ($placeholders)", $excluded_keys ); // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared
+			}
+		}
+
 		// meta_value.
 		if ( array_key_exists( 'value', $clause ) ) {
 			$meta_value = $clause['value'];
@@ -895,6 +910,33 @@ protected function is_non_cacheable_meta_key( $meta_key ) {
 		return false;
 	}
 
+	/**
+	 * Returns all post meta keys registered with invalidates_query_cache false.
+	 *
+	 * @since 7.0.0
+	 *
+	 * @return string[] Array of non-cacheable meta keys.
+	 */
+	protected function get_non_cacheable_meta_keys() {
+		global $wp_meta_keys;
+
+		$keys = array();
+
+		if ( ! is_array( $wp_meta_keys ) || ! isset( $wp_meta_keys['post'] ) ) {
+			return $keys;
+		}
+
+		foreach ( $wp_meta_keys['post'] as $registered_keys ) {
+			foreach ( $registered_keys as $meta_key => $args ) {
+				if ( isset( $args['invalidates_query_cache'] ) && ! $args['invalidates_query_cache'] ) {
+					$keys[] = $meta_key;
+				}
+			}
+		}
+
+		return array_unique( $keys );
+	}
+
 	/**
 	 * Identifies an existing table alias that is compatible with the current
 	 * query clause.

tests/phpunit/tests/meta/invalidatesQueryCache.php

@@ -373,4 +373,60 @@ public function test_subtype_registration_does_not_skip_cache_for_different_post
 		$after = wp_cache_get_last_changed( 'posts' );
 		$this->assertNotSame( $before, $after, 'last_changed should still change when writing to a post type where the key is cacheable.' );
 	}
+
+	/**
+	 * A WP_Query using meta_value without meta_key should not return posts
+	 * matched via a non-cacheable meta key.
+	 */
+	public function test_wp_query_meta_value_excludes_non_cacheable_keys() {
+		register_post_meta(
+			'post',
+			'nocache_meta',
+			array( 'invalidates_query_cache' => false )
+		);
+
+		add_post_meta( self::$post_id, 'nocache_meta', 'nocache_value' );
+
+		$query = new WP_Query(
+			array(
+				'fields'     => 'ids',
+				'meta_value' => 'nocache_value',
+			)
+		);
+
+		$this->assertEmpty( $query->posts, 'WP_Query by meta_value should not match non-cacheable meta keys.' );
+	}
+
+	/**
+	 * A WP_Query using meta_value without meta_key should not return stale
+	 * cached results after non-cacheable meta is deleted.
+	 */
+	public function test_wp_query_meta_value_no_stale_cache_after_delete() {
+		register_post_meta(
+			'post',
+			'nocache_meta',
+			array( 'invalidates_query_cache' => false )
+		);
+
+		add_post_meta( self::$post_id, 'nocache_meta', 'nocache_value' );
+
+		// Run the query once to prime the cache.
+		$query1 = new WP_Query(
+			array(
+				'fields'     => 'ids',
+				'meta_value' => 'nocache_value',
+			)
+		);
+
+		delete_post_meta( self::$post_id, 'nocache_meta' );
+
+		$query2 = new WP_Query(
+			array(
+				'fields'     => 'ids',
+				'meta_value' => 'nocache_value',
+			)
+		);
+
+		$this->assertEmpty( $query2->posts, 'WP_Query should not return stale cached results for non-cacheable meta.' );
+	}
 }