Fix /api/latestbuilds ordering.

Evaluations are added sequentially to database but builds are not always
registered nor performed in order. This means that a build corresponding to an
older evaluation can be returned first if it was completed last. Order by
descending evaluation id to prevent it.

* src/cuirass/database.scm (db-get-builds): Add "evaluation" order.
* src/cuirass/http.scm (url-handler): Order latestbuilds by descending
evaluation number.

src/cuirass/database.scm

@@ -926,6 +926,7 @@ FILTERS is an assoc list whose possible keys are 'derivation | 'id | 'jobset |
     (lambda (inner)
       (match (assq 'order filters)
         (('order . 'build-id) "Builds.id ASC")
+        (('order . 'evaluation) "Builds.evaluation DESC")
         (('order . 'finish-time) "stoptime DESC")
         (('order . 'finish-time+build-id)
          (if inner

src/cuirass/http.scm

@@ -490,12 +490,16 @@ Hydra format."
         ((> limit 1000)
          (respond-json-with-error 500 "Maximum limit exceeded"))
         (else
-         ;; Limit results to builds that are "done".
+         ;; Limit results to builds that are "done".  Order the builds by
+         ;; descending evaluation numbers.  This ensures that the builds that
+         ;; were last registered are first returned even if they take more
+         ;; time to complete.  Ordering by timestamp wouldn't work as
+         ;; evaluations are not always performed sequentially.
          (respond-json
           (object->json-string
            (handle-builds-request `((status . done)
                                     ,@params
-                                    (order . finish-time)))))))))
+                                    (order . evaluation)))))))))
     (('GET "api" "queue")
      (let* ((params (request-parameters request))
             ;; 'nr parameter is mandatory to limit query size.