GHC thinks pattern match is exhaustive

{-# OPTIONS_GHC -Werror #-}

module Lib where

data Value = Finite Integer | Infinity
  deriving (Eq)

instance Num Value where
  (+)         = undefined
  (*)         = undefined
  abs         = undefined
  signum      = undefined
  negate      = undefined
  fromInteger = Finite

isSpecial :: Value -> Bool
isSpecial Infinity = True
isSpecial 0        = True
isSpecial 1        = True
isSpecial _        = False

> ghc Lib.hs
[1 of 1] Compiling Lib              ( Lib.hs, Lib.o )

Lib.hs:19:1: error: [-Woverlapping-patterns, -Werror=overlapping-patterns]
    Pattern match is redundant
    In an equation for ‘isSpecial’: isSpecial 1 = ...
   |
19 | isSpecial 1        = True
   | ^^^^^^^^^^^^^^^^^^^^^^^^^

Lib.hs:20:1: error: [-Woverlapping-patterns, -Werror=overlapping-patterns]
    Pattern match is redundant
    In an equation for ‘isSpecial’: isSpecial _ = ...
   |
20 | isSpecial _        = False
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^

Trac metadata

Trac field	Value
Version	8.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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