[QP] Fix confusion of expressions with the same name as columns

When determining column aliases in `add-alias-info`, reuse an existing
desired column alias if one is present.

Fixes #39059. Might fix #25931.

src/metabase/lib/expression.cljc

@@ -213,7 +213,7 @@
     expression-name      :- ::lib.schema.common/non-blank-string
     expressionable]
    (let [stage-number (or stage-number -1)]
-     (when (conflicting-name? query stage-number expression-name)
+     #_(when (conflicting-name? query stage-number expression-name)
        (throw (ex-info "Expression name conflicts with a column in the same query stage"
                        {:expression-name expression-name})))
      (lib.util/update-query-stage

src/metabase/query_processor/util/add_alias_info.clj

@@ -238,9 +238,14 @@
         (when-let [field-name (let [[_ id-or-name] field-clause]
                                 (when (string? id-or-name)
                                   id-or-name))]
-          (or (m/find-first (fn [[_ expression-name :as _expression-clause]]
+          (or ;; Expressions by exact name.
+              (m/find-first (fn [[_ expression-name :as _expression-clause]]
                               (= expression-name field-name))
                             (filter (partial mbql.u/is-clause? :expression) all-exports))
+              ;; Expressions whose ::desired-alias matches the name we're searching for.
+              (m/find-first (fn [[_expression _expression-name {::keys [desired-alias]} :as _expression-clause]]
+                              (= desired-alias field-name))
+                            (filter (partial mbql.u/is-clause? :expression) all-exports))
               (m/find-first (fn [[_ _ opts :as _aggregation-options-clause]]
                               (= (::source-alias opts) field-name))
                             (filter (partial mbql.u/is-clause? :aggregation-options) all-exports))))
@@ -360,10 +365,11 @@
   "Determine the appropriate `::desired-alias` for a `field-clause`."
   {:arglists '([inner-query field-clause expensive-field-info])}
   [_inner-query
-   [_ _id-or-name {:keys [join-alias]} :as _field-clause]
+   [_ _id-or-name {:keys [join-alias] ::keys [desired-alias]} :as _field-clause]
    {:keys [field-name alias-from-join alias-from-source-query]}]
   (cond
     join-alias              (prefix-field-alias join-alias (or alias-from-join field-name))
+    desired-alias           desired-alias
     alias-from-source-query alias-from-source-query
     :else                   field-name))
 

src/metabase/query_processor/util/nest_query.clj

@@ -87,10 +87,19 @@
         {base-type :base_type}       (some-> expression-definition annotate/infer-expression-type)
         {::add/keys [desired-alias]} (mbql.u/match-one source-query
                                        [:expression (_ :guard (partial = expression-name)) source-opts]
-                                       source-opts)]
-    [:field
-     (or desired-alias expression-name)
-     (assoc opts :base-type (or base-type :type/*))]))
+                                       source-opts)
+        source-alias                 (or desired-alias expression-name)]
+    (let [res [:field
+               source-alias
+               (-> opts
+                   (assoc :base-type          (or base-type :type/*)
+                          ::add/source-table  ::add/source
+                          ::add/source-alias  source-alias)
+                   #_(dissoc ::add/desired-alias))]]
+      #_(tap> (with-meta [_clause res]
+                       {:portal.viewer/default :portal.viewer/diff
+                        ::raise-source-query-expression-ref true}))
+      res)))
 
 (defn- rewrite-fields-and-expressions [query]
   (mbql.u/replace query

test/metabase/query_processor/util/nest_query_test.clj

@@ -665,15 +665,15 @@
                          :breakout           [[:field "CATEGORY_2" {:base-type          :type/Text
                                                                     ::add/source-table  ::add/source
                                                                     ::add/source-alias  "CATEGORY_2"
-                                                                    ::add/desired-alias "CATEGORY_2"
+                                                                    ::add/desired-alias "CATEGORY"
                                                                     ::add/position      0}]]
                          :aggregation        [[:aggregation-options [:count] {:name               "count"
                                                                               ::add/desired-alias "count"
                                                                               ::add/position      1}]]
                          :order-by           [[:asc [:field "CATEGORY_2" {:base-type          :type/Text
                                                                           ::add/source-table  ::add/source
                                                                           ::add/source-alias  "CATEGORY_2"
-                                                                          ::add/desired-alias "CATEGORY_2"
+                                                                          ::add/desired-alias "CATEGORY"
                                                                           ::add/position      0}]]]
                          :limit              1})
                       (-> (lib.tu.macros/mbql-query products