Conveniently fallback to using en-US if no match for locale

Hermes tries to make it easy by building a cache of preferred descriptions for search and autocompletion. This isn't necessary, but helpful. It usually uses the default locale to choose, but we can now define the locale to use at time of index creation. However, if we do not have a map from locale to a set of language reference sets for a specific locale, this now falls back to using en-US rather than failing with what might appear to be a weird exception.

src/com/eldrix/hermes/impl/search.clj

@@ -134,15 +134,19 @@
   (let [ch (async/chan 1 (partition-all 1000))]             ;; chunk concepts into batches
     (with-open [store (store/open-store store-filename)
                 writer (open-index-writer search-filename)]
-      (let [langs (lang/match store language-priority-list)]
-        (when-not (seq langs) (throw (ex-info "No language refset for any locale listed in priority list"
+      (let [langs (lang/match store language-priority-list)
+            langs' (if (seq langs) langs
+                                   (do (log/warn "No language refset for any locale in requested priority list" {:priority-list language-priority-list :store-filename store-filename})
+                                       (log/warn "Falling back to default of 'en-US'")
+                                       (lang/match store "en-US")))]
+        (when-not (seq langs') (throw (ex-info "No language refset for any locale listed in priority list"
                                               {:priority-list language-priority-list :store-filename store-filename})))
         (store/stream-all-concepts store ch)                ;; start streaming all concepts
         (async/<!!                                          ;; block until pipeline complete
           (async/pipeline                                   ;; pipeline for side-effects
             (.availableProcessors (Runtime/getRuntime))     ;; Parallelism factor
             (doto (async/chan) (async/close!))              ;; Output channel - /dev/null
-            (map (partial write-batch! store writer langs))
+            (map (partial write-batch! store writer langs'))
             ch))
         (.forceMerge writer 1)))))