Fix trend widget for years (#10722)

* fix issue preventing insights on year-grouped data

* remove (probably) unnecessary function

* formatting/style

* years are timestamps now

src/metabase/sync/analyze/fingerprint/insights.clj

@@ -206,16 +206,6 @@
                    :col            (:name number-col)
                    :unit           unit})))))))
 
-(defn- datetime-truncated-to-year?
-  "This is hackish as hell, but we change datetimes with year granularity to strings upstream and
-   this is the only way to recover the information they were once datetimes."
-  [{:keys [base_type unit fingerprint] :as field}]
-  (and (= base_type :type/Text)
-       (contains? field :unit)
-       (nil? unit)
-       (or (nil? (:type fingerprint))
-           (-> fingerprint :type :type/DateTime))))
-
 (defn insights
   "Based on the shape of returned data construct a transducer to statistically analyize data."
   [cols]
@@ -225,7 +215,7 @@
                           (group-by (fn [{:keys [base_type special_type unit] :as field}]
                                       (cond
                                         (#{:type/FK :type/PK} special_type)          :others
-                                        (datetime-truncated-to-year? field)          :datetimes
+                                        (= unit :year)                               :datetimes
                                         (metabase.util.date/date-extract-units unit) :numbers
                                         (field/unix-timestamp? field)                :datetimes
                                         (isa? base_type :type/Number)                :numbers

test/metabase/sync/analyze/fingerprint/insights_test.clj

@@ -34,6 +34,12 @@
       first
       :last-value))
 
+(expect
+  (transduce identity
+             (insights [{:base_type :type/DateTime :unit :year}
+                        {:base_type :type/Integer}])
+             [["2014-01-01T00:00:00Z" 100]
+              ["2015-01-01T00:00:00Z" 200]]))
 
 (defn- inst->day
   [inst]