免责声明：我还没有测试过这个解决方案，也没有Xmonad env来测试它，但是这不适合放在评论部分。
对于这种“扩展布局”，我不知道你是否必须使用gaps，spacingRaw或两者都用。无论如何，下面有一些片段，我认为你应该配置每一种方式。
gaps应该使用关联列表[(screen border, num of pixels)]进行配置。在文档之前，这应该足够了。

import XMonad.Layout.Gaps

-- Set up, down, left and right screen gaps to 0
expandedL = gaps [(U,0), (D,0), (L,0), (R,0) ]

myConfig = def
    ...
    , layoutHook = expandedL $ myLayout
    ...

另一个可能性是使用细粒度的窗口间距函数spacingRaw。它有很多参数，我想你应该禁用屏幕边框。注意你可以设置边框为一些像素，然后禁用它。这有助于发送消息toggleScreenSpacingEnabled，如果你愿意

import XMonad.Layout.Spacing

--           |- fine grained constructor for spacing
--           |         |- Enable Smart border
--           |         |     |- Set screen border to 10 pixel except for the top one
--           |         |     |                  |- Disable screen borders
--           |         |     |                  |      |- Add a 10 pixel border to windows
--           |         |     |      T  B  R  L  |      |       T  B  R  L  |- Enable window borders
expandedL = spacingRaw True (Border 0 10 10 10) False (Border 10 10 10 10) True

myConfig = def
    ...
    , layoutHook = expandedL $ myLayout
    ...

也许你需要同时修改这两个修饰符。我想你可以简单地把它们连在一起

import XMonad.Layout.Spacing
import XMonad.Layout.Gaps

noGaps = gaps [(U,0), (D,0), (L,0), (R,0)]
noSpace = spacingRaw True (Border 0 10 10 10) False (Border 10 10 10 10) True

-- chain both mods
expandedL = noSpace  . noGaps 

myConfig = def
    ...
    , layoutHook = expandedL $ myLayout
    ...

在OP版本之后编辑

我发现您遇到了间距无法检测边缘是“内部”还是“外部”（在窗口内或窗口与屏幕之间）的问题。请注意，检测这样的问题可能很困难，例如，如果您有收缩的可用窗口或浮动窗口。
尽管如此，我认为您可以编写自己的LayoutModifier，只实现pureModifier。我不太喜欢xmonad库，所以下面的代码只是一个草图（我只从文档中构建它，并查看Spacing源代码，我手边甚至没有编译器，所以不要期待任何工作代码）

import qualified XMonad.Util.Rectangle as R
import           XMonad.Layout.LayoutModifier
import           Data.Function (on)
import           Data.List (minimumBy)

-- Probably you need to enable some compiler extension.
-- It will warn you with the right one
data Expanded a = Expanded

-- expand is defined as "add 10 pixel space to each window; then expand outer borders"
-- Notice you can define expand = ModifiedLayout Expanded but this way you ensure expand is applied to spaced windows.
expand :: l a -> ModifiedLayout Expanded (ModifiedLayout Spacing l) a
expand = ModifiedLayout Expanded . spacing 10

instance Eq a => LayoutModifier Expanded a where
  -- the last parameter of this function is the window list and rectangles
  -- returned by the underlying layout (the spacing layout in your case)
  pureModifier Expanded screen_rectangle window_stack window_list = 
     let rectangle_coords = fmap (pixelsToCoordinates . snd) window_list
         -- Notice that this may fail on runtime if no windows are on the stack...
         minimum_x = minimumBy (compare `on` point_x1) rectangle_coords 
         minimum_y = minimumBy (compare `on` point_y1) rectangle_coords 
         maximum_x = maximumBy (compare `on` point_x2) rectangle_coords 
         maximum_y = maximumBy (compare `on` point_y2) rectangle_coords
         -- this function takes a rectangle and change the borders to match the screen borders if the rectangle border is outer
         extend_border rect = 
            case pixelsToCoordinates rect of
              PointRectangle x1 y1 x2 y2 = 
                 let new_x1 = if x1 == minimum_x then point_x1 (pixelsToCoordinates screen_rectangle) else x1
                     new_y1 = if y1 == minimum_y then point_y1 (pixelsToCoordinates screen_rectangle) else y1
                     new_x2 = if x2 == maximum_x then point_x2 (pixelsToCoordinates screen_rectangle) else x2 
                     new_y2 = if y2 == maximum_y then point_y2 (pixelsToCoordinates screen_rectangle) else y2 
                 in coordinatesToRectangle (PointRectangle new_x1 new_y2 new_x2 new_y2)
         extended_rectangles = fmap (\(w, r) -> (w, extend_border r)) window_list 
      in if null window_list
          then ([], Nothing)
          else (extended_rectangles, Nothing)

-- then you can expand your layouts with this
myConfig = def
    ...
    , layoutHook = expand $ myLayout
    ...