Fix versioned namespace clears

When using namespace versioning to achieve atomic cache clears, only delete cache keys matching the old/current version. This resolves tag inconsistency issues whereby the process running the clear would delete keys set against the new version by more recently spawned concurreny processes. Most seriously this could result in newly set data keys remaining, but with empty associated tag sets meaning the invalidation via tags was no longer possible. Clearing specific prefixes is not supported when using versioned namespaces as it is desirable to clear all old keys as they will no longer be used and would otherwise eventually fill cache memory.
symfony · nicolas-grekas · Feb 24, 2020 · Feb 20, 2020 · Feb 20, 2020 · 971b177d27ec43fca1ed6c027971190508bc5063
commit 971b177d27ec43fca1ed6c027971190508bc5063
diff --git a/src/Symfony/Component/Cache/Traits/AbstractTrait.php b/src/Symfony/Component/Cache/Traits/AbstractTrait.php
@@ -111,9 +111,14 @@ public function hasItem($key)
     */
    public function clear(/*string $prefix = ''*/)
    {
-        $prefix = 0 < \func_num_args() ? (string) func_get_arg(0) : '';
        $this->deferred = [];
        if ($cleared = $this->versioningIsEnabled) {
+            if ('' === $namespaceVersionToClear = $this->namespaceVersion) {
+                foreach ($this->doFetch([static::NS_SEPARATOR.$this->namespace]) as $v) {
+                    $namespaceVersionToClear = $v;
+                }
+            }
+            $namespaceToClear = $this->namespace.$namespaceVersionToClear;
            $namespaceVersion = substr_replace(base64_encode(pack('V', mt_rand())), static::NS_SEPARATOR, 5);
            try {
                $cleared = $this->doSave([static::NS_SEPARATOR.$this->namespace => $namespaceVersion], 0);
@@ -124,10 +129,13 @@ public function clear(/*string $prefix = ''*/)
                $this->namespaceVersion = $namespaceVersion;
                $this->ids = [];
            }
+        } else {
+            $prefix = 0 < \func_num_args() ? (string) func_get_arg(0) : '';
+            $namespaceToClear = $this->namespace.$prefix;
        }

        try {
-            return $this->doClear($this->namespace.$prefix) || $cleared;
+            return $this->doClear($namespaceToClear) || $cleared;
        } catch (\Exception $e) {
            CacheItem::log($this->logger, 'Failed to clear the cache: '.$e->getMessage(), ['exception' => $e]);