[project @ 2004-03-11 14:31:35 by simonpj]

Sanity checking

diff --git a/ghc/compiler/iface/TcIface.lhs b/ghc/compiler/iface/TcIface.lhs
index 57c40de..244c919 100644 (file)
--- a/ghc/compiler/iface/TcIface.lhs
+++ b/ghc/compiler/iface/TcIface.lhs
@@ -59,7 +59,7 @@ import Outputable
 import SrcLoc          ( noSrcLoc )
 import Util            ( zipWithEqual, dropList, equalLength, zipLazy )
 import Maybes          ( expectJust )
-import CmdLineOpts     ( DynFlag(..) )
+import CmdLineOpts     ( DynFlag(..), dopt )
 \end{code}
 
 This module takes
@@ -487,11 +487,22 @@ loadImportedInsts cls tys
        ; eps_var <- getEpsVar
        ; eps <- readMutVar eps_var
 
+       -- For interest: report the no-type-constructor case.
+       -- Don't report when -fallow-undecidable-instances is on, because then
+       -- we call loadImportedInsts when looking up even predicates like (C a)
+       -- But without undecidable instances it's rare to see C (a b) and 
+       -- somethat interesting
+#ifdef DEBUG
+       ; dflags  <- getDOpts
+       ; WARN( not (dopt Opt_AllowUndecidableInstances dflags) && null tc_gates, 
+               ptext SLIT("Interesting! No tycons in Inst:") 
+                       <+> pprClassPred cls tys )
+         return ()
+#endif
+
        -- Suck in the instances
        ; let { (inst_pool', iface_insts) 
-                   = WARN( null tc_gates, ptext SLIT("Interesting! No tycons in Inst:") 
-                                               <+> pprClassPred cls tys )
-                     selectInsts (eps_insts eps) cls_gate tc_gates }
+                   = selectInsts (eps_insts eps) cls_gate tc_gates }
 
        -- Empty => finish up rapidly, without writing to eps
        ; if null iface_insts then