When focus was separated from the stack order on each workspace, we
forgot to update the Arbitrary instance to set random focus. As spotted
by David R, this then invalidates 4 of our QC properties. In particular,
the property involving where focus goes after a random transient
(annoying behaviour) appeared to be correct, but wasn't, due to
inadequate coverage.
This patch sets focus to a random window on each workspace. As a result,
we now catch the focus/raise/delete issue people have been complaining
about.
Lesson: make sure your QuickCheck generators are doing what you think
they are.
Using Typeables as the only constraint on layout messages is a bit
scary, as a user can send arbitrary values to layoutMsg, whether they
make sense or not: there's basically no type feedback on the values you
supply to layoutMsg.
Folloing Simon Marlow's dynamically extensible exceptions paper, we use
an existential type, and a Message type class, to constrain valid
arguments to layoutMsg to be valid members of Message.
That is, a user writes some data type for messages their layout
algorithm accepts:
data MyLayoutEvent = Zoom
| Explode
| Flaming3DGlassEffect
deriving (Typeable)
and they then add this to the set of valid message types:
instance Message MyLayoutEvent
Done. We also reimplement the dynamic type check while we're here, to
just directly use 'cast', rather than expose a raw fromDynamic/toDyn.
With this, I'm much happier about out dynamically extensible layout
event subsystem.
This also fixes a bug where xmonad was assuming a 24-bit display, and just
using, eg, 0xff0000 as an index into a colormap without querying the X server
to determine the proper pixel value for "red".
