Show note about federation being disabled, and list other known instances

config/settings-default.yaml

@@ -165,3 +165,6 @@ retry-delivery-every:
 # activities received in local inboxes and the result of their processing.
 # 'null' means disable the report page entirely.
 #activity-debug-reports: 10
+
+# List of (hosts of) other known federating instances.
+#instances:              []

src/Vervis/Foundation.hs

@@ -222,11 +222,14 @@ instance Yesod App where
         pc <- widgetToPageContent $ do
             setTitle $ toHtml $
                 T.intercalate " → " (map snd bcs) <> " → " <> title
-            let instanceHost = appInstanceHost $ appSettings master
+            let settings = appSettings master
+                instanceHost = appInstanceHost settings
                 federationPage :: Text
                 federationPage =
                     "https://dev.angeley.es\
                     \/s/fr33domlover/r/vervis/s/FEDERATION.md"
+                federationDisabled = not $ appFederation settings
+                federatedServers = appInstances settings
             $(widgetFile "default-layout")
         withUrlRenderer $(hamletFile "templates/default-layout-wrapper.hamlet")
 

src/Vervis/Settings.hs

@@ -152,6 +152,8 @@ data AppSettings = AppSettings
       -- latest activities received in local inboxes and the result of their
       -- processing. 'Nothing' means disable the report page entirely.
     , appInboxDebugReportLength   :: Maybe Int
+      -- | List of (hosts of) other known federating instances.
+    , appInstances                :: [Text]
     }
 
 instance FromJSON AppSettings where
@@ -201,6 +203,7 @@ instance FromJSON AppSettings where
         appDropDeliveryAfter        <- ndt <$> o .: "drop-delivery-after"
         appDeliveryRetryFreq        <- interval <$> o .: "retry-delivery-every"
         appInboxDebugReportLength   <- o .:? "activity-debug-reports"
+        appInstances                <- o .:? "instances" .!= []
 
         return AppSettings {..}
         where

templates/default-layout.hamlet

@@ -32,6 +32,22 @@ $nothing
 <p>
   Federation status: See <a href="#{federationPage}">here</a>!
 
+$if federationDisabled
+  <p>
+    <span>
+      NOTE: Federation is disabled on this instance!
+  $if null federatedServers
+    <span>
+      You can test federation between other instances.
+  $else
+    <span>
+      You can test federation between the following instances:
+    <ul>
+      $forall h <- federatedServers
+        <li>
+          <code>
+            #{h}
+
 <.instance>
   Vervis @ #{instanceHost}