Fix MultiToggle crashes with decorated layouts

Ignore-this: 9208f5da9f0de95464ea62cb45e8f291

The problem was that certain layouts keep their "world" state in their value,
which was thrown away and forgotten after ReleaseResources during toggle.

In particular, decorated layouts store some X11 handles in them and
allocate/deallocate it as appropriate. If any modification to their state is
ignored, they may try to deallocate already deallocated memory, which results
in a crash somewhere inside Xlib.

This patch makes Transformers reversible so that nothing is ever ignored. As a
side effect, layout transformers now do receive messages and messages for the
base layout do not need the undo/reapply cycle -- we just pass messages to the
current transformed layout and unapply the transformer when needed.
(This, however, doesn't mean that the base layout is not asked to release
resources on a transformer change -- we still need the transformer to release
its resources and there's no way to do this without asking the base layout as
well.)

darcs-hash:20091220004733-c9ff5-34670f3db8ab715d8f334973d6ea2a3e7f3aed7a.gz

1 files changed, 6 insertions, 5 deletions

diff --git a/XMonad/Layout/MultiToggle/Instances.hs b/XMonad/Layout/MultiToggle/Instances.hs
index a409aa8..b8112f1 100644
--- a/XMonad/Layout/MultiToggle/Instances.hs
+++ b/XMonad/Layout/MultiToggle/Instances.hs
@@ -22,6 +22,7 @@ import XMonad.Layout.MultiToggle
 
 import XMonad
 import XMonad.Layout.NoBorders
+import XMonad.Layout.LayoutModifier
 
 data StdTransformers = FULL          -- ^ switch to Full layout
                      | NBFULL        -- ^ switch to Full with no borders
@@ -31,8 +32,8 @@ data StdTransformers = FULL          -- ^ switch to Full layout
   deriving (Read, Show, Eq, Typeable)
 
 instance Transformer StdTransformers Window where
-    transform FULL         _ k = k Full
-    transform NBFULL       _ k = k (noBorders Full)
-    transform MIRROR       x k = k (Mirror x)
-    transform NOBORDERS    x k = k (noBorders x)
-    transform SMARTBORDERS x k = k (smartBorders x)
+    transform FULL         x k = k Full (const x)
+    transform NBFULL       x k = k (noBorders Full) (const x)
+    transform MIRROR       x k = k (Mirror x) (\(Mirror x') -> x')
+    transform NOBORDERS    x k = k (noBorders x) (\(ModifiedLayout _ x') -> x')
+    transform SMARTBORDERS x k = k (smartBorders x) (\(ModifiedLayout _ x') -> x')