Update StatusBar library to use the X monad instead of IO.

This change allows dynamic status bars to pull information out of the
X monad, which can be really useful for status bars. For instance, you
can now query the screen width in order to set the width of status
bars appropriately.

Existing configurations may need to be updated in order to lift an
`IO StatusBarConfig` to an `X StatusBarConfig`. This can be done using
either the `io` function provided by `XMonad.Core`, or `liftIO` from
`base` in `Control.Monad.IO.Class`

- https://hackage.haskell.org/package/xmonad-0.18.0/docs/XMonad-Core.html#v:io
- https://hackage.haskell.org/package/base-4.19.1.0/docs/Control-Monad-IO-Class.html#v:liftIO

CHANGES.md

@@ -4,6 +4,15 @@
 
 ### Breaking Changes
 
+  * `XMonad.Hooks.StatusBars`
+
+    - Move status bar functions from the `IO` to the `X` monad to
+       allow them to look up information from `X`, like the screen
+       width. Existing configurations may need to use `io` from
+       `XMonad.Core` or `liftIO` from `Control.Monad.IO.Class` in
+       order to lift any existing `IO StatusBarConfig` values into
+       `X StatusBarConfig` values.
+
 ### New Modules
 
   * `XMonad.Actions.Profiles`.

XMonad/Hooks/StatusBar.hs

@@ -452,7 +452,7 @@ instance ExtensionClass ActiveSBs where
 -- 'avoidStruts', check 'dynamicEasySBs'.
 --
 -- Heavily inspired by "XMonad.Hooks.DynamicBars"
-dynamicSBs :: (ScreenId -> IO StatusBarConfig) -> XConfig l -> XConfig l
+dynamicSBs :: (ScreenId -> X StatusBarConfig) -> XConfig l -> XConfig l
 dynamicSBs f conf = addAfterRescreenHook (updateSBs f) $ conf
   { startupHook = startupHook conf >> killAllStatusBars >> updateSBs f
   , logHook     = logHook conf >> logSBs
@@ -462,7 +462,7 @@ dynamicSBs f conf = addAfterRescreenHook (updateSBs f) $ conf
 -- resulting config and adds 'avoidStruts' to the
 -- layout.
 dynamicEasySBs :: LayoutClass l Window
-               => (ScreenId -> IO StatusBarConfig)
+               => (ScreenId -> X StatusBarConfig)
                -> XConfig l
                -> XConfig (ModifiedLayout AvoidStruts l)
 dynamicEasySBs f conf =
@@ -471,7 +471,7 @@ dynamicEasySBs f conf =
 -- | Given the function to create status bars, update
 -- the status bars by killing those that shouldn't be
 -- visible anymore and creates any missing status bars
-updateSBs :: (ScreenId -> IO StatusBarConfig) -> X ()
+updateSBs :: (ScreenId -> X StatusBarConfig) -> X ()
 updateSBs f = do
   actualScreens    <- withWindowSet $ return . map W.screen . W.screens
   (toKeep, toKill) <-
@@ -480,7 +480,7 @@ updateSBs f = do
   cleanSBs (map snd toKill)
   -- Create new status bars if needed
   let missing = actualScreens \\ map fst toKeep
-  added <- io $ traverse (\s -> (s,) <$> f s) missing
+  added <- traverse (\s -> (s,) <$> f s) missing
   traverse_ (sbStartupHook . snd) added
   XS.put (ASB (toKeep ++ added))