[QP] Fix query caching for pivot queries (#48962) (#49028)

This was throwing errors trying to `nippy/freeze!` an Atom.

That was because in certain circumstances a pMBQL query can end up in
`(:json_query metadata)` for a query, and those can contain an atom
due to `metabase.lib.cache` and both `CachedMetadataProvider` and
`InvocationTracker`.

I added `lib.query/serializable` as a single location to strip out
anything that isn't serializable, such as atoms. (And the entire
`:lib/metadata`, which is a wasted effort to serialize.)

Co-authored-by: Braden Shepherdson <braden@metabase.com>

src/metabase/lib/cache.cljc

@@ -62,6 +62,13 @@
                                 (not (contains? mmeta :lib/__cache))
                                 (assoc :lib/__cache (Collections/synchronizedMap (WeakHashMap.))))))))
 
+(defn discard-query-cache
+  "Removes the cache from the given query. Does nothing if no cache is present."
+  [query]
+  #?(:cljs query
+     :clj  (when query
+             (vary-meta query dissoc :lib/__cache))))
+
 (defn- side-channel-cache*
   "(CLJS only; this is a pass-through in CLJ.)
 

src/metabase/lib/query.cljc

@@ -421,3 +421,12 @@
   [a-query stage-number card-id f & args]
   (let [{q :query, n :stage-number} (wrap-native-query-with-mbql a-query stage-number card-id)]
     (apply f q n args)))
+
+(defn serializable
+  "Given a query, ensure it doesn't have any keys or structures that aren't safe for serialization.
+
+  For example, any Atoms or Delays or should be removed."
+  [a-query]
+  (-> a-query
+      (dissoc a-query :lib/metadata)
+      lib.cache/discard-query-cache))

src/metabase/query_processor/middleware/cache.clj

@@ -11,6 +11,7 @@
    [java-time.api :as t]
    [medley.core :as m]
    [metabase.config :as config]
+   [metabase.lib.query :as lib.query]
    [metabase.public-settings :as public-settings]
    [metabase.query-processor.middleware.cache-backend.db :as backend.db]
    [metabase.query-processor.middleware.cache-backend.interface :as i]
@@ -57,7 +58,8 @@
   "Add `object` (e.g. a result row or metadata) to the current cache entry."
   [object]
   (when *in-fn*
-    (*in-fn* object)))
+    (*in-fn* (cond-> object
+               (map? object) (m/update-existing :json_query lib.query/serializable)))))
 
 (def ^:private ^:dynamic *result-fn*
   "The `result-fn` provided by [[impl/do-with-serialization]]."
@@ -136,7 +138,7 @@
          (let [normal-format? (and (map? (unreduced result))
                                    (seq (get-in (unreduced result) [:data :cols])))
                result*        (-> (if normal-format?
-                                    (merge-with merge @final-metadata (unreduced result))
+                                    (m/deep-merge @final-metadata (unreduced result))
                                     (unreduced result))
                                   (assoc :cache/details {:hash query-hash :cached true :updated_at last-ran}))]
            (rf (cond-> result*