[commit: ghc] master: Build correct substitution in instDFunType (a49228e)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/a49228e3b6e3737da750bce59ec721b3b2f18eed/ghc

>---------------------------------------------------------------

commit a49228e3b6e3737da750bce59ec721b3b2f18eed
Author: Bartosz Nitka <niteria at gmail.com>
Date:   Tue Mar 29 12:42:16 2016 +0200

    Build correct substitution in instDFunType
    
    We will use `ty` in the range of the substitution, hence
    the substitution needs `ty`'s free vars in-scope.
    They don't seem easily available by other means, so we
    just compute them.
    
    Test Plan: ./validate
    
    Reviewers: austin, goldfire, bgamari, simonpj
    
    Reviewed By: simonpj
    
    Subscribers: thomie, simonmar
    
    Differential Revision: https://phabricator.haskell.org/D2043
    
    GHC Trac Issues: #11371


>---------------------------------------------------------------

a49228e3b6e3737da750bce59ec721b3b2f18eed
 compiler/typecheck/Inst.hs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/compiler/typecheck/Inst.hs b/compiler/typecheck/Inst.hs
index ab9a4e2..49f57a5 100644
--- a/compiler/typecheck/Inst.hs
+++ b/compiler/typecheck/Inst.hs
@@ -306,14 +306,16 @@ instDFunType :: DFunId -> [DFunInstType]
 -- See Note [DFunInstType: instantiating types] in InstEnv
 instDFunType dfun_id dfun_inst_tys
   = do { (subst, inst_tys) <- go emptyTCvSubst dfun_tvs dfun_inst_tys
-       ; return (inst_tys, substThetaUnchecked subst dfun_theta) }
+       ; return (inst_tys, substTheta subst dfun_theta) }
   where
     (dfun_tvs, dfun_theta, _) = tcSplitSigmaTy (idType dfun_id)
 
     go :: TCvSubst -> [TyVar] -> [DFunInstType] -> TcM (TCvSubst, [TcType])
     go subst [] [] = return (subst, [])
     go subst (tv:tvs) (Just ty : mb_tys)
-      = do { (subst', tys) <- go (extendTvSubst subst tv ty) tvs mb_tys
+      = do { (subst', tys) <- go (extendTvSubstAndInScope subst tv ty)
+                                 tvs
+                                 mb_tys
            ; return (subst', ty : tys) }
     go subst (tv:tvs) (Nothing : mb_tys)
       = do { (subst', tv') <- newMetaTyVarX subst tv