GHC 7.10 rejects nullary type class with associated data

In GHC 7.8.4, the following code is legal:

{-# LANGUAGE NullaryTypeClasses, TypeFamilies #-}
module NullaryData where

class NullaryClass where
    data NullaryData

In GHC 7.10, NullaryTypeClasses was deprecated in favor of MultiParamTypeClasses. However, running this code on GHC 7.10-rc1:

{-# LANGUAGE MultiParamTypeClasses, TypeFamilies #-}
module NullaryData where

class NullaryClass where
    data NullaryData

results in this error:

NullaryData.hs:4:1:
    The associated type ‘NullaryData’
    mentions none of the type or kind variables of the class ‘NullaryClass’
    In the class declaration for ‘NullaryClass’

It's probably related to this earlier bugfix.

Trac metadata

Trac field	Value
Version	7.10.1-rc1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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changed weight to 5

added Tbug Trac import labels

mentioned in commit dda65282

Thanks for reporting this.

Trac metadata

Trac field	Value
Test case	→ indexed-types/should_compile/T10020

added 1 deleted label

closed

changed milestone to %7.10.1

Merged to ghc-7.10 (via 4c8b6521).

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

removed 1 deleted label

mentioned in issue #10300 (closed)

added Pnormal label