Clarify error message (Trac #3805)

[ghc-hetmet.git] / compiler / parser / RdrHsSyn.lhs

diff --git a/compiler/parser/RdrHsSyn.lhs b/compiler/parser/RdrHsSyn.lhs
index d18b8d8..b86068c 100644 (file)
--- a/compiler/parser/RdrHsSyn.lhs
+++ b/compiler/parser/RdrHsSyn.lhs
@@ -549,12 +549,14 @@ checkInstType (L l t)
 checkDictTy :: LHsType RdrName -> P (LHsType RdrName)
 checkDictTy (L spn ty) = check ty []
   where
-  check (HsTyVar t) args | not (isRdrTyVar t) 
-       = return (L spn (HsPredTy (HsClassP t args)))
+  check (HsTyVar tc)            args | isRdrTc tc = done tc args
+  check (HsOpTy t1 (L _ tc) t2) args | isRdrTc tc = done tc (t1:t2:args)
   check (HsAppTy l r) args = check (unLoc l) (r:args)
   check (HsParTy t)   args = check (unLoc t) args
   check _ _ = parseError spn "Malformed instance header"
 
+  done tc args = return (L spn (HsPredTy (HsClassP tc args)))
+
 checkTParams :: Bool     -- Type/data family
             -> [LHsType RdrName]
             -> P ([LHsTyVarBndr RdrName], Maybe [LHsType RdrName])
@@ -865,8 +867,20 @@ checkValSig
 checkValSig (L l (HsVar v)) ty 
   | isUnqual v && not (isDataOcc (rdrNameOcc v))
   = return (TypeSig (L l v) ty)
-checkValSig (L l _)         _
-  = parseError l "Invalid type signature"
+checkValSig lhs@(L l _)         _
+  | looks_like_foreign lhs
+  = parseError l "Invalid type signature; perhaps you meant to use -XForeignFunctionInterface?"
+  | otherwise
+  = parseError l "Invalid type signature: should be of form <variable> :: <type>"
+  where
+    -- A common error is to forget the ForeignFunctionInterface flag
+    -- so check for that, and suggest.  cf Trac #3805
+    -- Sadly 'foreign import' still barfs 'parse error' because 'import' is a keyword
+    looks_like_foreign (L _ (HsVar v))     = v == foreign_RDR
+    looks_like_foreign (L _ (HsApp lhs _)) = looks_like_foreign lhs
+    looks_like_foreign _                   = False
+
+    foreign_RDR = mkUnqual varName (fsLit "foreign")
 \end{code}
 
 
@@ -963,6 +977,7 @@ mkInlinePragma :: Maybe Activation -> RuleMatchInfo -> Bool -> InlinePragma
 -- The Maybe is because the user can omit the activation spec (and usually does)
 mkInlinePragma mb_act match_info inl 
   = InlinePragma { inl_inline = inl
+                 , inl_sat    = Nothing
                  , inl_act    = act
                  , inl_rule   = match_info }
   where