deal with group layer in existence checks properly

(before it would fail to find e.g. the start layer if it wasn't a
top-level layer)

lib/Properties.hs

@@ -50,19 +50,20 @@ import           Uris          (SubstError (..), applySubst)
 checkMap :: LintWriter Tiledmap
 checkMap = do
   tiledmap <- askContext
-  let unlessLayer = unlessElement (tiledmapLayers tiledmap)
+  let layers = collectLayers tiledmap
+  let unlessLayer = unlessElement layers
 
   -- test custom map properties
   mapM_ checkMapProperty (fromMaybe mempty $ tiledmapProperties tiledmap)
 
   -- can't have these with the rest of layer/tileset lints since they're
   -- not specific to any one of them
-  refuseDoubledNames (tiledmapLayers tiledmap)
+  refuseDoubledNames layers
   refuseDoubledNames (tiledmapTilesets tiledmap)
   refuseDoubledNames (getProperties tiledmap)
 
   -- some layers should exist
-  unlessElementNamed (tiledmapLayers tiledmap) "start"
+  unlessElementNamed layers "start"
     $ complain "The map must have one layer named \"start\"."
   unlessLayer (\l -> getName l == "floorLayer" && layerType l == "objectgroup")
     $ complain "The map must have one layer named \"floorLayer\" of type \"objectgroup\"."
@@ -79,9 +80,17 @@ checkMap = do
     $ suggest "document the map's copyright via the \"mapCopyright\" property."
 
   -- TODO: this doesn't catch collisions with the default start layer!
-  whenLayerCollisions (\(Property name _) -> name == "exitUrl" || name == "startLayer")
+  whenLayerCollisions layers (\(Property name _) -> name == "exitUrl" || name == "startLayer")
     $ \cols -> warn $ "collisions between entry and / or exit layers: " <> prettyprint cols
 
+  where
+    -- recursively find all layers (to deal with nested group layers)
+    collectLayers :: Tiledmap -> V.Vector Layer
+    collectLayers tiledmap = tiledmapLayers tiledmap <>
+      V.fromList (concatMap groupmembers (tiledmapLayers tiledmap))
+     where groupmembers :: Layer -> [Layer]
+           groupmembers layer = concatMap groupmembers layers <> layers
+            where layers = fromMaybe [] $ layerLayers layer
 
 -- | Checks a single property of a map.
 checkMapProperty :: Property -> LintWriter Tiledmap
@@ -122,7 +131,7 @@ checkTileset = do
 
   when (isJust (tilesetSource tileset))
     $ complain "Tilesets must be embedded and cannot be loaded from external files."
-  -- TODO: check copyright!
+
   unlessHasProperty "tilesetCopyright"
     $ forbid "property \"tilesetCopyright\" for tilesets must be set."
 
@@ -423,12 +432,12 @@ containsProperty props name = any
 
 -- | should the layers fulfilling the given predicate collide, then perform andthen.
 whenLayerCollisions
-  :: (Property -> Bool)
-  -> (Set Collision -> LintWriter Tiledmap)
-  -> LintWriter Tiledmap
-whenLayerCollisions f andthen = do
-  tiledmap <- askContext
-  let collisions = layerOverlaps . V.filter (any f . getProperties) $ tiledmapLayers tiledmap
+  :: V.Vector Layer
+  -> (Property -> Bool)
+  -> (Set Collision -> LintWriter a)
+  -> LintWriter a
+whenLayerCollisions layers f andthen = do
+  let collisions = layerOverlaps . V.filter (any f . getProperties) $ layers
   unless (null collisions)
     $ andthen collisions