[GHC] #14045: Data family instances must list all patterns of family, despite documentation's claims to the contrary

[GHC]

#14045: Data family instances must list all patterns of family, despite
documentation's claims to the contrary
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.3
  checker)                           |
      Resolution:                    |             Keywords:  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  GHC rejects       |            Test Case:  indexed-
  valid program                      |  types/should_compile/T14045,
                                     |  indexed-types/should_fail/T14045a
      Blocked By:                    |             Blocking:
 Related Tickets:  #12369            |  Differential Rev(s):  Phab:D3804
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 I ran out of time, got stuck upgrading to GHC 8 which is now required...

 Here is the patch: Ryan, would you like to validate and commit?
 {{{
 simonpj at cam-05-unx:~/code/HEAD$ git show 143f08a3
 commit 143f08a32b80f7f80d77b518ce207a1051368b9e
 Author: Simon Peyton Jones <simonpj at microsoft.com>
 Date:   Wed Aug 2 15:57:21 2017 +0100

     Get the roles right for newtype instances

     This was a simple slip, that gave rise to the bug reported in
     comment:13 of Trac #14045.  We were supplying roles to mkAlgTyCon
     that didn't match the tyvars.

 diff --git a/compiler/typecheck/TcInstDcls.hs
 b/compiler/typecheck/TcInstDcls.hs
 index fe513f4..58d4506 100644
 --- a/compiler/typecheck/TcInstDcls.hs
 +++ b/compiler/typecheck/TcInstDcls.hs
 @@ -695,7 +695,7 @@ tcDataFamInstDecl mb_clsinfo
                        -- the end of Note [Data type families] in TyCon
                      rep_tc   = mkAlgTyCon rep_tc_name
                                            ty_binders liftedTypeKind
 -                                          (map (const Nominal) full_tvs)
 +                                          (map (const Nominal)
 ty_binders)
                                            (fmap unLoc cType) stupid_theta
                                            tc_rhs parent
                                            gadt_syntax
 diff --git a/compiler/types/Type.hs b/compiler/types/Type.hs
 index b81192f..dcc134c 100644
 --- a/compiler/types/Type.hs
 +++ b/compiler/types/Type.hs
 @@ -1315,8 +1315,12 @@ mkLamType v ty

  mkLamTypes vs ty = foldr mkLamType ty vs

 --- | Given a list of type-level vars and a result type, makes TyBinders,
 preferring
 --- anonymous binders if the variable is, in fact, not dependent.
 +-- | Given a list of type-level vars and a result kind,
 +-- makes TyBinders, preferring anonymous binders
 +-- if the variable is, in fact, not dependent.
 +-- e.g.    mkTyConBindersPreferAnon [(k:*),(b:k),(c:k)] (k->k)
 +-- We want (k:*) Named, (a;k) Anon, (c:k) Anon
 +--
  -- All binders are /visible/.
  mkTyConBindersPreferAnon :: [TyVar] -> Type -> [TyConBinder]
  mkTyConBindersPreferAnon vars inner_ty = fst (go vars)
 diff --git a/testsuite/tests/deriving/should_compile/T14045.hs
 b/testsuite/tests/deriving/should_compile/T14045.hs
 new file mode 100644
 index 0000000..d721a3d
 --- /dev/null
 +++ b/testsuite/tests/deriving/should_compile/T14045.hs
 @@ -0,0 +1,13 @@
 +{-# LANGUAGE TypeFamilies, KindSignatures, GADTs,
 GeneralizedNewtypeDeriving #-}
 +
 +module T14045 where
 +
 +import Data.Kind ( Type )
 +
 +data family T a b :: Type
 +
 +-- newtype instance T Int d = MkT (IO d)
 +
 +newtype instance T Int :: Type -> Type where
 +   MkT :: IO d -> T Int d
 +  deriving( Monad, Applicative, Functor )
 diff --git a/testsuite/tests/deriving/should_compile/all.T
 b/testsuite/tests/deriving/should_compile/all.T
 index 0025d25..10e2e60 100644
 --- a/testsuite/tests/deriving/should_compile/all.T
 +++ b/testsuite/tests/deriving/should_compile/all.T
 @@ -94,3 +94,4 @@ test('drv-phantom',
 [normalise_errmsg_fun(just_the_deriving)],compile, ['-ddump-
  test('T13813', normal, compile, [''])
  test('T13919', normal, compile, [''])
  test('T13998', normal, compile, [''])
 +test('T14045', normal, compile, [''])
 }}}
 Thanks!

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14045#comment:16>
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