Make sure lazy seqs get realized during CSV exports (#26327)

* realize lazy seqs during exports

* add test & helper

* update based on tamas's comment

* use mapv

* remove unused import

* try to fix test

* switch to using just a LocalDate for the second test since the ZonedDateTime test was failing for certain drivers and not others, and that isnt relevant to this test

src/metabase/query_processor/streaming/common.clj

@@ -4,7 +4,8 @@
             [metabase.query-processor.store :as qp.store]
             [metabase.query-processor.timezone :as qp.timezone]
             [metabase.util.date-2 :as u.date])
-  (:import [java.time LocalDate LocalDateTime LocalTime OffsetDateTime OffsetTime ZonedDateTime]))
+  (:import clojure.lang.ISeq
+           [java.time LocalDate LocalDateTime LocalTime OffsetDateTime OffsetTime ZonedDateTime]))
 
 (defn in-result-time-zone
   "Set the time zone of a temporal value `t` to result timezone without changing the actual moment in time. e.g.
@@ -29,6 +30,10 @@
   Object
   (format-value [this] this)
 
+  ISeq
+  (format-value [this]
+    (mapv format-value this))
+
   LocalDate
   (format-value [t]
     (u.date/format t))

test/metabase/query_processor/streaming/csv_test.clj

@@ -2,8 +2,10 @@
   (:require [cheshire.core :as json]
             [clojure.data.csv :as csv]
             [clojure.test :refer :all]
+            [metabase.query-processor.streaming.interface :as qp.si]
             [metabase.test :as mt]
-            [metabase.test.data.dataset-definitions :as defs]))
+            [metabase.test.data.dataset-definitions :as defs])
+  (:import [java.io BufferedOutputStream ByteArrayOutputStream]))
 
 (defn- parse-and-sort-csv [response]
   (assert (some? response))
@@ -55,3 +57,27 @@
             ["4" "Simcha Yan"          "2014-01-01T08:30:00"]
             ["5" "Quentin Sören"       "2014-10-03T17:30:00"]]
            (parse-and-sort-csv result)))))
+
+(defn- csv-export
+  "Given a seq of result rows, write it as a CSV, then read the CSV and return the resulting data."
+  [rows]
+  (with-open [bos (ByteArrayOutputStream.)
+              os  (BufferedOutputStream. bos)]
+    (let [results-writer (qp.si/streaming-results-writer :csv os)]
+      (qp.si/begin! results-writer {:data {:ordered-cols []}} {})
+      (doall (map-indexed
+              (fn [i row] (qp.si/write-row! results-writer row i [] {}))
+              rows))
+      (qp.si/finish! results-writer {:row_count (count rows)}))
+    (let [bytea (.toByteArray bos)]
+      (rest (csv/read-csv (String. bytea))))))
+
+(deftest lazy-seq-realized-test
+  (testing "Lazy seqs within rows are automatically realized during exports (#26261)"
+    (let [row (first (csv-export [[(lazy-seq [1 2 3])]]))]
+      (is (= ["[1 2 3]"] row))))
+
+  (testing "LocalDate in a lazy seq (checking that elements in a lazy seq are formatted correctly as strings)"
+   (mt/with-everything-store
+     (let [row (first (csv-export [[(lazy-seq [#t "2021-03-30T"])]]))]
+       (is (= ["[\"2021-03-30\"]"] row))))))

test/metabase/query_processor/streaming_test.clj

@@ -131,7 +131,7 @@
 ;; see also `metabase.query-processor.streaming.xlsx-test/report-timezone-test`
 ;; TODO this test doesn't seem to run?
 (deftest report-timezone-test
-  (testing "Export downloads should format stuff with the report timezone rather than UTC (#13677)\n"
+  (testing "Export downloads should format stuff with the report timezone rather than UTC (#13677)"
     (mt/test-driver :postgres
       (let [query     (mt/dataset attempted-murders
                         (mt/mbql-query attempts