Update to drupal 8.0.0-rc1. For more information, see https://www.drupal.org/node/2582663

core/lib/Drupal/Core/Cache/ApcuBackend.php

@@ -166,7 +166,7 @@ class ApcuBackend implements CacheBackendInterface {
    * {@inheritdoc}
    */
   public function set($cid, $data, $expire = CacheBackendInterface::CACHE_PERMANENT, array $tags = array()) {
-    Cache::validateTags($tags);
+    assert('\Drupal\Component\Assertion\Inspector::assertAllStrings($tags)', 'Cache tags must be strings.');
     $tags = array_unique($tags);
     $cache = new \stdClass();
     $cache->cid = $cid;

core/lib/Drupal/Core/Cache/Cache.php

@@ -34,7 +34,7 @@ class Cache {
    */
   public static function mergeContexts(array $a = [], array $b = []) {
     $cache_contexts = array_unique(array_merge($a, $b));
-    \Drupal::service('cache_contexts_manager')->validateTokens($cache_contexts);
+    assert('\Drupal::service(\'cache_contexts_manager\')->assertValidTokens($cache_contexts)');
     sort($cache_contexts);
     return $cache_contexts;
   }
@@ -59,8 +59,9 @@ class Cache {
    *   The merged array of cache tags.
    */
   public static function mergeTags(array $a = [], array $b = []) {
+    assert('\Drupal\Component\Assertion\Inspector::assertAllStrings($a) && \Drupal\Component\Assertion\Inspector::assertAllStrings($b)', 'Cache tags must be valid strings');
+
     $cache_tags = array_unique(array_merge($a, $b));
-    static::validateTags($cache_tags);
     sort($cache_tags);
     return $cache_tags;
   }
@@ -99,6 +100,9 @@ class Cache {
    * @param string[] $tags
    *   An array of cache tags.
    *
+   * @deprecated
+   *   Use assert('\Drupal\Component\Assertion\Inspector::assertAllStrings($tags)');
+   *
    * @throws \LogicException
    */
   public static function validateTags(array $tags) {

core/lib/Drupal/Core/Cache/CacheCollector.php

@@ -115,7 +115,7 @@ abstract class CacheCollector implements CacheCollectorInterface, DestructableIn
    *   (optional) The tags to specify for the cache item.
    */
   public function __construct($cid, CacheBackendInterface $cache, LockBackendInterface $lock, array $tags = array()) {
-    Cache::validateTags($tags);
+    assert('\Drupal\Component\Assertion\Inspector::assertAllStrings($tags)', 'Cache tags must be strings.');
     $this->cid = $cid;
     $this->cache = $cache;
     $this->tags = $tags;

core/lib/Drupal/Core/Cache/CacheTagsInvalidator.php

@@ -27,8 +27,7 @@ class CacheTagsInvalidator implements CacheTagsInvalidatorInterface {
    * {@inheritdoc}
    */
   public function invalidateTags(array $tags) {
-    // Validate the tags.
-    Cache::validateTags($tags);
+    assert('Drupal\Component\Assertion\Inspector::assertAllStrings($tags)', 'Cache tags must be strings.');
 
     // Notify all added cache tags invalidators.
     foreach ($this->invalidators as $invalidator) {

core/lib/Drupal/Core/Cache/Context/CacheContextsManager.php

@@ -103,11 +103,9 @@ class CacheContextsManager {
    *   The ContextCacheKeys object containing the converted cache keys and
    *   cacheability metadata.
    *
-   * @throws \LogicException
-   *   Thrown if any of the context tokens or parameters are not valid.
    */
   public function convertTokensToKeys(array $context_tokens) {
-    $this->validateTokens($context_tokens);
+    assert('$this->assertValidTokens($context_tokens)');
     $cacheable_metadata = new CacheableMetadata();
     $optimized_tokens = $this->optimizeTokens($context_tokens);
     // Iterate over cache contexts that have been optimized away and get their
@@ -299,4 +297,33 @@ class CacheContextsManager {
     }
   }
 
+  /**
+   * Asserts the context tokens are valid
+   *
+   * Similar to ::validateTokens, this method returns boolean TRUE when the
+   * context tokens are valid, and FALSE when they are not instead of returning
+   * NULL when they are valid and throwing a \LogicException when they are not.
+   * This function should be used with the assert() statement.
+   *
+   * @param mixed $context_tokens
+   *   Variable to be examined - should be array of context_tokens.
+   *
+   * @return bool
+   *   TRUE if context_tokens is an array of valid tokens.
+   */
+  public function assertValidTokens($context_tokens) {
+    if (!is_array($context_tokens)) {
+      return FALSE;
+    }
+
+    try {
+      $this->validateTokens($context_tokens);
+    }
+    catch (\LogicException $e) {
+      return FALSE;
+    }
+
+    return TRUE;
+  }
+
 }

core/lib/Drupal/Core/Cache/DatabaseBackend.php

@@ -199,7 +199,7 @@ class DatabaseBackend implements CacheBackendInterface {
         'tags' => array(),
       );
 
-      Cache::validateTags($item['tags']);
+      assert('\Drupal\Component\Assertion\Inspector::assertAllStrings($item[\'tags\'])', 'Cache Tags must be strings.');
       $item['tags'] = array_unique($item['tags']);
       // Sort the cache tags so that they are stored consistently in the DB.
       sort($item['tags']);

core/lib/Drupal/Core/Cache/MemoryBackend.php

@@ -107,7 +107,7 @@ class MemoryBackend implements CacheBackendInterface, CacheTagsInvalidatorInterf
    * Implements Drupal\Core\Cache\CacheBackendInterface::set().
    */
   public function set($cid, $data, $expire = Cache::PERMANENT, array $tags = array()) {
-    Cache::validateTags($tags);
+    assert('\Drupal\Component\Assertion\Inspector::assertAllStrings($tags)', 'Cache Tags must be strings.');
     $tags = array_unique($tags);
     // Sort the cache tags so that they are stored consistently in the database.
     sort($tags);

core/lib/Drupal/Core/Cache/PhpBackend.php

@@ -148,7 +148,7 @@ class PhpBackend implements CacheBackendInterface {
    * {@inheritdoc}
    */
   public function set($cid, $data, $expire = Cache::PERMANENT, array $tags = array()) {
-    Cache::validateTags($tags);
+    assert('\Drupal\Component\Assertion\Inspector::assertAllStrings($tags)', 'Cache Tags must be strings.');
     $item = (object) array(
       'cid' => $cid,
       'data' => $data,

core/lib/Drupal/Core/Cache/RefinableCacheableDependencyTrait.php

@@ -33,6 +33,27 @@ trait RefinableCacheableDependencyTrait {
    */
   protected $cacheMaxAge = Cache::PERMANENT;
 
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheTags() {
+    return $this->cacheTags;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheContexts() {
+    return $this->cacheContexts;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheMaxAge() {
+    return $this->cacheMaxAge;
+  }
+
   /**
    * {@inheritdoc}
    */