fix(xanthous): Only use alphabetic chars for menu items r/2682

Previously, we were using `smallestNotIn` for selecting new characters
for menu items with duplicate chatacters - this uses the 'Bounded'
instance for the type, which for Char meant the first character we would
always select was \NUL - making it look like the menu item had no
character, and making it impossible to actually select the menu item.
This introduces an AlphaChar newtype, which is a wrapper around Char
whose Bounded and Enum instances only use alphabetic characters (a-ZA-Z)
and uses that for menu characters instead.

Change-Id: If34ed9e9ce84f2bcb1cb87432cc6273f40b69f72
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3229
Reviewed-by: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI

1 files changed, 3 insertions, 0 deletions

diff --git a/users/grfn/xanthous/test/Xanthous/UtilSpec.hs b/users/grfn/xanthous/test/Xanthous/UtilSpec.hs
index 0d6b718bc351..684a03b2c7a0 100644
--- a/users/grfn/xanthous/test/Xanthous/UtilSpec.hs
+++ b/users/grfn/xanthous/test/Xanthous/UtilSpec.hs
@@ -40,4 +40,7 @@ test = testGroup "Xanthous.Util"
     , testProperty "the result is the right length" $ \(xs :: [Int]) p ->
         length (removeFirst p xs) `elem` [length xs, length xs - 1]
     ]
+  , testGroup "AlphaChar"
+    [ testCase "succ 'z'" $ succ (AlphaChar 'z') @?= AlphaChar 'A'
+    ]
   ]