Improve recovery in hptRules

diff --git a/compiler/main/HscTypes.lhs b/compiler/main/HscTypes.lhs
index a0e4857..e6e8e4c 100644 (file)
--- a/compiler/main/HscTypes.lhs
+++ b/compiler/main/HscTypes.lhs
@@ -295,12 +295,15 @@ hptRules hsc_env deps
     , mod /= moduleName gHC_PRIM
 
        -- Look it up in the HPT
-    , let mod_info = case lookupUFM hpt mod of
-                       Nothing -> pprPanic "hptRules" (ppr mod <+> ppr deps)
-                       Just x  -> x
+    , let rules = case lookupUFM hpt mod of
+                   Just info -> md_rules (hm_details info)
+                   Nothing -> pprTrace "WARNING in hptRules" msg [] 
+         msg = vcat [ptext SLIT("missing module") <+> ppr mod,
+                     ptext SLIT("Probable cause: out-of-date interface files")]
+                       -- This really shouldn't happen, but see Trac #962
 
        -- And get its dfuns
-    , rule <- md_rules (hm_details mod_info) ]
+    , rule <- rules ]
 \end{code}
 
 %************************************************************************