Rule binders shouldn't have DFun pragmas

When DsBinds deals with a SPECIALISE pragma, it makes up the binders
for a RULE. These binders should be very vanilla: no IdInfo of any sort.
But the way it was before they could have DFun pragmas, which led to
Bad Joss downstream.  (Actually to cause a downstream *error* was itself
a bug, which I've fixed, but it's clearly wrong for them to be DFuns!)

diff --git a/compiler/deSugar/DsBinds.lhs b/compiler/deSugar/DsBinds.lhs
index 31cb75d..cc7ecfd 100644 (file)
--- a/compiler/deSugar/DsBinds.lhs
+++ b/compiler/deSugar/DsBinds.lhs
@@ -38,6 +38,7 @@ import TysPrim  ( anyTypeOfKind )
 import CostCentre
 import Module
 import Id
 import CostCentre
 import Module
 import Id

+import Name    ( localiseName )

 import MkId    ( seqId )
 import Var     ( Var, TyVar, tyVarKind )
 import IdInfo  ( vanillaIdInfo )
 import MkId    ( seqId )
 import Var     ( Var, TyVar, tyVarKind )
 import IdInfo  ( vanillaIdInfo )

@@ -482,10 +483,10 @@ dsSpecs poly_id poly_rhs prags
                      -- Get the INLINE pragma from SPECIALISE declaration, or,
                       -- failing that, from the original Id
 
                      -- Get the INLINE pragma from SPECIALISE declaration, or,
                       -- failing that, from the original Id
 

-                extra_dict_bndrs = [ localiseId d  -- See Note [Constant rule dicts]
+                extra_dict_bndrs = [ mkLocalId (localiseName (idName d)) (idType d)
+                                            -- See Note [Constant rule dicts]

                                    | d <- varSetElems (exprFreeVars ds_spec_expr)
                                    , isDictId d]
                                    | d <- varSetElems (exprFreeVars ds_spec_expr)
                                    , isDictId d]

-                               -- Note [Const rule dicts]

 
                 rule =  mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr poly_name)))
                                AlwaysActive poly_name
 
                 rule =  mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr poly_name)))
                                AlwaysActive poly_name

@@ -552,7 +553,7 @@ the constraint is unused.  We could bind 'd' to (error "unused")
 but it seems better to reject the program because it's almost certainly
 a mistake.  That's what the isDeadBinder call detects.
 
 but it seems better to reject the program because it's almost certainly
 a mistake.  That's what the isDeadBinder call detects.
 

-Note [Const rule dicts]
+Note [Constant rule dicts]

 ~~~~~~~~~~~~~~~~~~~~~~~
 When the LHS of a specialisation rule, (/\as\ds. f es) has a free dict, 
 which is presumably in scope at the function definition site, we can quantify 
 ~~~~~~~~~~~~~~~~~~~~~~~
 When the LHS of a specialisation rule, (/\as\ds. f es) has a free dict, 
 which is presumably in scope at the function definition site, we can quantify 

@@ -573,8 +574,9 @@ And from that we want the rule
 
 But be careful!  That dInt might be GHC.Base.$fOrdInt, which is an External
 Name, and you can't bind them in a lambda or forall without getting things
 
 But be careful!  That dInt might be GHC.Base.$fOrdInt, which is an External
 Name, and you can't bind them in a lambda or forall without getting things

-confused. Hence the use of 'localiseId' to make it Internal.
-
+confused.   Likewise it might have an InlineRule or something, which would be
+utterly bogus. So we really make a fresh Id, with the same unique and type
+as the old one, but with an Internal name and no IdInfo.

 
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