Splice expression into appropriate stage during v2 metric expansion (#48800)

* Fix expression stage

* Add test

* Parallel test

* Adjust test

* Adjust test

src/metabase/query_processor/middleware/metrics.clj

@@ -64,8 +64,8 @@
          not-empty)))
 
 (defn- expression-with-name-from-source
-  [query [_ {:lib/keys [expression-name]} :as expression]]
-  (lib/expression query 0 expression-name expression))
+  [query agg-stage-index [_ {:lib/keys [expression-name]} :as expression]]
+  (lib/expression query agg-stage-index expression-name expression))
 
 (defn- update-metric-query-expression-names
   [metric-query unique-name-fn]
@@ -137,7 +137,8 @@
                                          (:qp/stage-had-source-card (lib.util/query-stage query agg-stage-index)))))
                            (let [metric-query (update-metric-query-expression-names metric-query unique-name-fn)]
                              (as-> query $q
-                               (reduce expression-with-name-from-source $q (lib/expressions metric-query -1))
+                               (reduce #(expression-with-name-from-source %1 agg-stage-index %2)
+                                       $q (lib/expressions metric-query -1))
                                (include-implicit-joins $q agg-stage-index metric-query)
                                (reduce #(lib/filter %1 agg-stage-index %2) $q (lib/filters metric-query -1))
                                (replace-metric-aggregation-refs $q agg-stage-index lookup)))

test/metabase/query_processor/middleware/metrics_test.clj

 (ns metabase.query-processor.middleware.metrics-test
   (:require
    [clojure.test :refer [deftest is testing]]
+   [java-time.api :as t]
    [mb.hawk.assert-exprs.approximately-equal :as =?]
    [medley.core :as m]
    [metabase.analytics.prometheus :as prometheus]
@@ -788,6 +789,30 @@
                  [u.date/temporal-str->iso8601-str int int 3.0]
                  (mt/rows (qp/process-query query)))))))))
 
+(deftest ^:parallel expressions-from-metrics-are-spliced-to-correct-stage-test
+  (testing "Integration test: Expression is spliced into correct stage during metric expansion (#48722)"
+    (mt/with-temp [:model/Card source-model {:dataset_query (mt/mbql-query orders {})
+                                             :database_id (mt/id)
+                                             :name "source model"
+                                             :type :model}
+                   :model/Card metric {:dataset_query
+                                       (mt/mbql-query
+                                         orders
+                                         {:source-table (str "card__" (:id source-model))
+                                          :expressions {"somedays" [:datetime-diff
+                                                                    [:field "CREATED_AT" {:base-type :type/DateTime}]
+                                                                    (t/offset-date-time 2024 10 16 0 0 0)
+                                                                    :day]}
+                                          :aggregation [[:median [:expression "somedays" {:base-type :type/Integer}]]]})
+                                       :database_id (mt/id)
+                                       :name "somedays median"
+                                       :type :metric}]
+      (let [mp (lib.metadata.jvm/application-database-metadata-provider (mt/id))
+            query (-> (lib/query mp (lib.metadata/card mp (:id source-model)))
+                      (lib/aggregate (lib.metadata/metric mp (:id metric))))]
+        (is (= 2162
+               (ffirst (mt/rows (qp/process-query query)))))))))
+
 (deftest ^:parallel ^:mb/once fetch-referenced-metrics-test
   (testing "Metric's aggregation `:name` is used in expanded aggregation (#48625)"
     (let [mp (lib.metadata.jvm/application-database-metadata-provider (mt/id))