Made sure that warnings are shown along with errors in the parser

The solution is a bit hacky, but this was an important problem.  If your PRAGMA failed to parse, that was worthy of a warning.  But if that then caused the parse to fail, all you would get is the parser error (could not find name), and you would never see the warnings about the pragmas not being recognised.  So now the pragmas are shoved into the error (using a basic encoding) and pulled out and issued if the parser dies.

frontends/ParseOccam.hs

@@ -26,6 +26,7 @@ import qualified Data.Map as Map
 import Data.Maybe
 import qualified Data.Set as Set
 import Text.ParserCombinators.Parsec
+import Text.ParserCombinators.Parsec.Error
 import Text.Regex
 
 import qualified AST as A
@@ -61,9 +62,31 @@ instance Warn (GenParser tok CompState) where
         else csWarnings cs }
 
 
-instance Die (GenParser tok st) where
-  dieReport (Just m, err) = fail $ packMeta m err
-  dieReport (Nothing, err) = fail err
+instance Die (GenParser tok CompState) where
+  dieReport (Just m, err) = do st <- getCompState
+                               fail $ packWarnings (csWarnings st) $ packMeta m $ err
+  dieReport (Nothing, err) = do st <- getCompState
+                                fail $ packWarnings (csWarnings st) err
+
+packWarnings :: [WarningReport] -> String -> String
+packWarnings ws = (("\0\1\2\3" ++ show ws ++ "\0") ++)
+
+unpackWarnings :: String -> ([WarningReport], String)
+unpackWarnings ws = if "\0\1\2\3" `isInfixOf` ws then (nub w, s) else ([], ws)
+  where
+    (w, s) = findAllWarnings ws
+    findAllWarnings :: String -> ([WarningReport], String)
+    findAllWarnings s
+      = case b of
+          [] -> ([], s)
+          '\0':'\1':'\2':'\3':rest ->
+            let (warningText, _:otherText) = span (/='\0') rest
+                (furtherWarnings, remainingText) = findAllWarnings otherText
+            in (read warningText ++ furtherWarnings, a ++ remainingText)
+          (_:bs) -> let (furtherWarnings, remainingText) = findAllWarnings bs
+                    in (furtherWarnings, a ++ "\0" ++ remainingText)
+      where
+        (a, b) = span (/= '\0') s
 --}}}
 
 --{{{ matching rules for raw tokens
@@ -1877,10 +1900,12 @@ runTockParser toks prod cs
             Left err ->
               -- If a position was encoded into the message, use that;
               -- else use the parser position.
-              let errMeta = sourcePosToMeta $ errorPos err
-                  (msgMeta, msg) = unpackMeta $ show err
-                  m = Just errMeta >> msgMeta
-                in dieReport (m, "Parse error: " ++ msg)
+                let errMeta = sourcePosToMeta $ errorPos err
+                    (msgWs, msg') = unpackWarnings $ show err
+                    (msgMeta, msg) = unpackMeta msg'
+                    m = fromMaybe errMeta msgMeta
+                in do mapM_ warnReport msgWs
+                      dieReport (Just m, "Parse error: " ++ msg)
             Right r -> return r
 
 -- | Parse an occam program.