auto-derivation of Enum is disallowed with recursive imports

A data type with one single-parameter constructor can normally be declared deriving(Enum) when compiling with -fglasgow-exts. However, when the data type is also declared in a hs-boot file, this is not accepted. The following test case demonstrates the problem. The same thing happens if the 'deriving' clause is also present in the hs-boot file.

{- file X.hs-boot -}
module X where
newtype X = X Int

{- file X.hs -}
module X where
import {-# SOURCE #-} X
newtype X = X Int deriving(Enum)

ghc -c -fglasgow-exts X.hs-boot X.hs

The error occurs in X.hs: Can't make a derived instance of Enum X' (X' has non-nullary constructors)

Trac metadata

Trac field	Value
Version	6.6
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
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Blocking
CC
Operating system	Unknown
Architecture	Unknown