When building with dev flag, disable the approot host check middleware

This allows to browse via e.g. localhost:3000 even if the instance host is
something else and the rendered URLs don't have a port number. It still makes
many things impossible or inconvenient, but at least you can launch Vervis
locally for development and see pages. Right now even CSS doesn't work because
of the URLs not matching the actual localhost:3000 access. Maybe gradually I'll
figure it out.

src/Vervis/Foundation.hs

@@ -193,12 +193,15 @@ instance Yesod App where
                 defaultCsrfHeaderName
                 defaultCsrfParamName
           )
-        . ( \ handler -> do
-                host <- getsYesod $ appInstanceHost . appSettings
-                bs <- lookupHeaders hHost
-                case bs of
-                    [b] | b == encodeUtf8 host -> handler
-                    _ -> invalidArgs [hostMismatch host bs]
+        . ( \ handler ->
+                if developmentMode
+                    then handler
+                    else do
+                        host <- getsYesod $ appInstanceHost . appSettings
+                        bs <- lookupHeaders hHost
+                        case bs of
+                            [b] | b == encodeUtf8 host -> handler
+                            _ -> invalidArgs [hostMismatch host bs]
           )
         . defaultYesodMiddleware
         where

src/Vervis/Settings.hs

@@ -164,14 +164,17 @@ data AppSettings = AppSettings
     , appHighlightStyle           :: Text
     }
 
+developmentMode :: Bool
+developmentMode =
+#if DEVELOPMENT
+    True
+#else
+    False
+#endif
+
 instance FromJSON AppSettings where
     parseJSON = withObject "AppSettings" $ \ o -> do
-        let defaultDev =
-#if DEVELOPMENT
-                True
-#else
-                False
-#endif
+        let defaultDev = developmentMode
         appStaticDir              <- o .: "static-dir"
         appDatabaseConf           <- o .: "database"
         appMaxInstanceKeys        <- o .:? "max-instance-keys"