Show Instance for IOException discards error code

The Show instance for IOException currently looks like this:

instance Show IOException where
    showsPrec p (IOError hdl iot loc s _ fn) =
      (case fn of
         Nothing -> case hdl of
                        Nothing -> id
                        Just h  -> showsPrec p h . showString ": "
         Just name -> showString name . showString ": ") .
      (case loc of
         "" -> id
         _  -> showString loc . showString ": ") .
      showsPrec p iot .
      (case s of
         "" -> id
         _  -> showString " (" . showString s . showString ")")

Notice that it discards the error code (the fifth field in the data constructor). This means that when we call ioError to raise an IOException, we end up missing out on useful information. For example, in a project I'm working on now, I get this:

*** Exception: Network.Icmp.Ping: ping: permission denied (Permission denied)

But I expected to see the original error code in there as well, which would help me diagnose issues.

Trac metadata

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