Add MLv2 schema and functions for `:var` (#29961)

* Add QP test middleware to validate converted pMBQL queries against MLv2 schema

* Revert 'fix' for #29944

* Fix ups

* Hack

* Fix final test failure

* Remove unused namespace

* Fix Kondo warning

* Skip #29958

* Add MLv2 schema for `:var`

* Fix typo

* Additional tests.

src/metabase/lib/aggregation.cljc

 (ns metabase.lib.aggregation
-  (:refer-clojure :exclude [count distinct max min])
+  (:refer-clojure :exclude [count distinct max min var])
   (:require
    [metabase.lib.common :as lib.common]
    [metabase.lib.hierarchy :as lib.hierarchy]
@@ -195,6 +195,7 @@
 (lib.common/defop stddev      [x])
 (lib.common/defop sum         [x])
 (lib.common/defop sum-where   [x y])
+(lib.common/defop var         [x])
 
 (mu/defn aggregate :- ::lib.schema/query
   "Adds an aggregation to query."

src/metabase/lib/core.cljc

@@ -2,7 +2,7 @@
   "Currently this is mostly a convenience namespace for REPL and test usage. We'll probably have a slightly different
   version of this for namespace for QB and QP usage in the future -- TBD."
   (:refer-clojure :exclude [filter remove replace and or not = < <= > ->> >= not-empty case count distinct max min
-                            + - * / time abs concat replace ref])
+                            + - * / time abs concat replace ref var])
   (:require
    [metabase.lib.aggregation :as lib.aggregation]
    [metabase.lib.breakout :as lib.breakout]
@@ -63,7 +63,8 @@
    share
    stddev
    sum
-   sum-where]
+   sum-where
+   var]
   [lib.breakout
    breakout
    current-breakouts]

src/metabase/lib/schema/aggregation.cljc

@@ -56,6 +56,9 @@
 
 (lib.hierarchy/derive :sum-where :lib.type-of/type-is-type-of-first-arg)
 
+(mbql-clause/define-tuple-mbql-clause :var :- :type/Float
+  #_expr [:schema [:ref ::expression/number]])
+
 (mr/def ::aggregation
   ;; placeholder!
   [:or
@@ -71,6 +74,7 @@
    :mbql.clause/stddev
    :mbql.clause/sum
    :mbql.clause/sum-where
+   :mbql.clause/var
    any?])
 
 (mr/def ::aggregations

test/metabase/lib/aggregation_test.cljc

@@ -33,7 +33,8 @@
                         [lib/median :median]
                         [lib/sum :sum]
                         [lib/stddev :stddev]
-                        [lib/distinct :distinct]]]
+                        [lib/distinct :distinct]
+                        [lib/var :var]]]
         (is-fn? op tag [venues-category-id-metadata] [venue-field-check])))))
 
 (defn- aggregation-display-name [aggregation-clause]
@@ -252,3 +253,11 @@
                :display_name "Sum of Price"
                :lib/source   :source/aggregations}
               (lib.metadata.calculation/metadata query (first (lib/aggregations query -1))))))))
+
+(deftest ^:parallel var-test
+  (let [query (-> (lib/query-for-table-name meta/metadata-provider "VENUES")
+                  (lib/aggregate (lib/var (lib/field (meta/id :venues :price)))))]
+    (is (=? {:stages [{:aggregation [[:var {} [:field {} (meta/id :venues :price)]]]}]}
+            query))
+    (is (= "Venues, Variance of Price"
+           (lib.metadata.calculation/describe-query query)))))

test/metabase/query_processor_test/test_mlv2.clj

@@ -31,10 +31,6 @@
   [legacy-query]
   (or
    *skip-conversion-tests*
-   ;; #29745: missing schema for `:var`
-   (mbql.u/match-one legacy-query
-     :var
-     "#29745")
    ;; #29747: schema for `:relative-datetime` current without a unit is broken
    (mbql.u/match-one legacy-query
      [:relative-datetime :current]