X.Layout: Don't draw zero-area windows in Tall

CHANGES.md

@@ -10,6 +10,8 @@
 
 * Exported `buildLaunch` from `XMonad.Main`.
 
+* `Tall` does not draw windows with zero area.
+
 ### Bug Fixes
 
 ## 0.17.1 (September 3, 2022)

src/XMonad/Layout.hs

@@ -62,9 +62,13 @@ data Tall a = Tall { tallNMaster :: !Int               -- ^ The default number o
 
 -- a nice pure layout, lots of properties for the layout, and its messages, in Properties.hs
 instance LayoutClass Tall a where
-    pureLayout (Tall nmaster _ frac) r s = zip ws rs
+    pureLayout (Tall nmaster _ frac) r s
+        | frac == 0 = drop nmaster layout
+        | frac == 1 = take nmaster layout
+        | otherwise = layout
       where ws = W.integrate s
             rs = tile frac r nmaster (length ws)
+            layout = zip ws rs
 
     pureMessage (Tall nmaster delta frac) m =
             msum [fmap resize     (fromMessage m)

tests/Properties.hs

@@ -166,11 +166,16 @@ tests =
   -- tall layout
 
   ,("tile 1 window fullsize", property prop_tile_fullscreen)
+  ,("tile max ratio",         property prop_tile_max_ratio)
+  ,("tile min ratio",         property prop_tile_min_ratio)
   ,("tiles never overlap",    property prop_tile_non_overlap)
   ,("split horizontal",       property prop_split_horizontal)
   ,("split vertical",         property prop_split_vertical)
 
   ,("pure layout tall",            property prop_purelayout_tall)
+    {- Following two test cases should be automatically generated by QuickCheck ideally, but it fails. -}
+  ,("pure layout tall: ratio = 0", property (\n d rect -> prop_purelayout_tall n d 0 rect))
+  ,("pure layout tall: ratio = 1", property (\n d rect -> prop_purelayout_tall n d 1 rect))
   ,("send shrink    tall",    property prop_shrink_tall)
   ,("send expand    tall",    property prop_expand_tall)
   ,("send incmaster tall",    property prop_incmaster_tall)

tests/Properties/Layout/Tall.hs

@@ -11,8 +11,9 @@ import XMonad.Layout
 
 import Graphics.X11.Xlib.Types (Rectangle(..))
 
-import Data.Maybe
+import Control.Applicative
 import Data.List (sort)
+import Data.Maybe
 import Data.Ratio
 
 ------------------------------------------------------------------------
@@ -27,6 +28,22 @@ prop_tile_non_overlap rect windows nmaster = noOverlaps (tile pct rect nmaster w
   where _ = rect :: Rectangle
         pct = 3 % 100
 
+-- with a ratio of 1, no stack windows are drawn of there is at least
+-- one master window around.
+prop_tile_max_ratio = extremeRatio 1 drop
+
+-- with a ratio of 0, no master windows are drawn at all if there are
+-- any stack windows around.
+prop_tile_min_ratio = extremeRatio 0 take
+
+extremeRatio amount getRects rect = do
+    w@(NonNegative windows) <- arbitrary `suchThat` (> NonNegative 0)
+    NonNegative nmaster     <- arbitrary `suchThat` (< w)
+    let tiled = tile amount rect nmaster windows
+    pure $ if   nmaster == 0
+           then prop_tile_non_overlap rect windows nmaster
+           else all ((== 0) . rect_width) $ getRects nmaster tiled
+
 -- splitting horizontally yields sensible results
 prop_split_horizontal (NonNegative n) x =
       noOverflows (+) (rect_x x) (rect_width x) ==>
@@ -49,13 +66,20 @@ prop_split_vertical (r :: Rational) x =
 
 
 -- pureLayout works.
-prop_purelayout_tall n r1 r2 rect = do
+prop_purelayout_tall n d r rect = do
   x <- (arbitrary :: Gen T) `suchThat` (isJust . peek)
-  let layout = Tall n r1 r2
+  let layout = Tall n d r
       st = fromJust . stack . workspace . current $ x
       ts = pureLayout layout rect st
+      ntotal = length (index x)
   return $
-        length ts == length (index x)
+       (if r == 0 then
+          -- (<=) for Bool is the logical implication
+          (0 <= n && n <= ntotal) <= (length ts == ntotal - n)
+        else if r == 1 then
+          (0 <= n && n <= ntotal) <= (length ts == n)
+        else
+          length ts == ntotal)
       &&
         noOverlaps (map snd ts)
       &&