Fix render order of LayoutHints and MultiColumns

Before this fix, when using layoutHintsToCenter together with
MultiColumns, in certain situations XMonad would render the border of
the focused window below a border of unfocused windows. This looks odd
and is here fixed by changing MultiColumns to always place the focused
window in front (even though they should not really overlap) and making
LayoutHints preserve the order returned from the underlying layout,
except for the focused window that is placed on top.

This is a good idea since layoutHintsToCenter requires the focused
window to be on top for good rendering, even if that is not really
required when the underlying layout is used on its own. This way
layoutHintsToCenter requires less of the layout that is modified and
MultiColumns is more compatible with future layout modifiers that are
not so considerate.

CHANGES.md

@@ -58,6 +58,19 @@
 
 ### Bug Fixes and Minor Changes
 
+  * `XMonad.Layout.LayoutHints`
+
+    Preserve the window order of the modified layout, except for the focused
+    window that is placed on top. This fixes an issue where the border of the
+    focused window in certain situations could be rendered below borders of
+    unfocused windows. It also has a lower risk of interfering with the
+    modified layout.
+
+  * `XMonad.Layout.MultiColumns`
+
+    The focused window is placed above the other windows if they would be made to
+    overlap due to a layout modifier. (As long as it preserves the window order.)
+
   * `XMonad.Actions.GridSelect`
 
     - The vertical centring of text in each cell has been improved.

XMonad/Layout/LayoutHints.hs

@@ -44,6 +44,7 @@ import Data.Monoid(All(..))
 
 import Data.Set (Set)
 import qualified Data.Set as Set
+import Data.Maybe(fromJust)
 
 -- $usage
 -- You can use this module with the following in your @~\/.xmonad\/xmonad.hs@:
@@ -147,10 +148,15 @@ instance LayoutModifier LayoutHintsToCenter Window where
     modifyLayout _ ws@(W.Workspace _ _ (Just st)) r = do
         (arrs,ol) <- runLayout ws r
         flip (,) ol
+            . changeOrder (W.focus st : (filter (/= W.focus st) $ map fst arrs))
             . head . reverse . sortBy (compare `on` (fitting . map snd))
             . map (applyHints st r) . applyOrder r
             <$> mapM (\x -> fmap ((,) x) $ mkAdjust (fst x)) arrs
 
+changeOrder :: [Window] -> [(Window, Rectangle)] -> [(Window, Rectangle)]
+changeOrder w wr = zip w' $ map (fromJust . flip lookup wr) w'
+    where w' = filter (`elem` map fst wr) w
+
 -- apply hints to first, grow adjacent windows
 applyHints :: W.Stack Window -> Rectangle -> [((Window, Rectangle),(D -> D))] -> [(Window, Rectangle)]
 applyHints _ _ [] = []

XMonad/Layout/MultiColumns.hs

@@ -77,10 +77,9 @@ data MultiCol a = MultiCol
   } deriving (Show,Read,Eq)
 
 instance LayoutClass MultiCol a where
-    doLayout l r s = return (zip w rlist, resl)
+    doLayout l r s = return (combine s rlist, resl)
         where rlist = doL (multiColNWin l') (multiColSize l') r wlen
-              w = W.integrate s
+              wlen = length $ W.integrate s
-              wlen = length w
               -- Make sure the list of columns is big enough and update active column
               nw = multiColNWin l ++ repeat (multiColDefWin l)
               l' = l { multiColNWin = take (max (length $ multiColNWin l) $ getCol (wlen-1) nw + 1) nw
@@ -90,6 +89,7 @@ instance LayoutClass MultiCol a where
               resl = if l'==l
                      then Nothing
                      else Just l'
+              combine (W.Stack foc left right) rs = zip (foc : reverse left ++ right) $ raiseFocused (length left) rs
     handleMessage l m =
         return $ msum [fmap resize     (fromMessage m)
                       ,fmap incmastern (fromMessage m)]
@@ -104,6 +104,10 @@ instance LayoutClass MultiCol a where
                   a = multiColActive l
     description _ = "MultiCol"
 
+raiseFocused :: Int -> [a] -> [a]
+raiseFocused n xs = actual ++ before ++ after
+    where (before,rest) = splitAt n xs
+          (actual,after) = splitAt 1 rest
 
 -- | Get which column a window is in, starting at 0.
 getCol :: Int -> [Int] -> Int