FIX #1385: make sure tuple instances are loaded

Typechecking of explicit tuples is done "by hand" (rather than using
boxySplitTyConApp) so that rigidity is maintained.  In making that change
I'd forgotten to retain the call to checkWiredInTyCon, which is important
to make sure instances are brought into scope.

Test is tc227.

diff --git a/compiler/typecheck/TcExpr.lhs b/compiler/typecheck/TcExpr.lhs
index c3bc64b..39e8a5c 100644 (file)
--- a/compiler/typecheck/TcExpr.lhs
+++ b/compiler/typecheck/TcExpr.lhs
@@ -29,6 +29,7 @@ import TcHsType
 import TcPat
 import TcMType
 import TcType
+import TcIface ( checkWiredInTyCon )
 import Id
 import DataCon
 import Name
@@ -302,10 +303,11 @@ tcExpr (ExplicitTuple exprs boxity) res_ty
   = do { tvs <- newBoxyTyVars [argTypeKind | e <- exprs]
        ; let tup_tc     = tupleTyCon boxity (length exprs)
              tup_res_ty = mkTyConApp tup_tc (mkTyVarTys tvs)
-       ; arg_tys   <- preSubType tvs (mkVarSet tvs) tup_res_ty res_ty
-       ; exprs'    <-  tcPolyExprs exprs arg_tys
+       ; checkWiredInTyCon tup_tc      -- Ensure instances are available
+       ; arg_tys  <- preSubType tvs (mkVarSet tvs) tup_res_ty res_ty
+       ; exprs'   <- tcPolyExprs exprs arg_tys
        ; arg_tys' <- mapM refineBox arg_tys
-       ; co_fn <- tcFunResTy (tyConName tup_tc) (mkTyConApp tup_tc arg_tys') res_ty
+       ; co_fn    <- tcFunResTy (tyConName tup_tc) (mkTyConApp tup_tc arg_tys') res_ty
        ; return (mkHsWrap co_fn (ExplicitTuple exprs' boxity)) }
 
 tcExpr (HsProc pat cmd) res_ty