- = do { ctxt_msgs <- do_ctxt tidy_env ctxt ;
- addLongErrAt loc err_msg (vcat (ctxt_to_use ctxt_msgs)) }
-
-do_ctxt :: TidyEnv -> [TidyEnv -> TcM (TidyEnv, SDoc)] -> TcM [SDoc]
-do_ctxt _ []
- = return []
-do_ctxt tidy_env (c:cs)
- = do { (tidy_env', m) <- c tidy_env ;
- ms <- do_ctxt tidy_env' cs ;
- return (m:ms) }
-
-ctxt_to_use :: [SDoc] -> [SDoc]
-ctxt_to_use ctxt | opt_PprStyle_Debug = ctxt
- | otherwise = take 3 ctxt
+ = do { err_info <- mkErrInfo tidy_env ctxt ;
+ addLongErrAt loc err_msg err_info }
+
+mkErrInfo :: TidyEnv -> [ErrCtxt] -> TcM SDoc
+-- Tidy the error info, trimming excessive contexts
+mkErrInfo env ctxts
+ = go 0 env ctxts
+ where
+ go :: Int -> TidyEnv -> [ErrCtxt] -> TcM SDoc
+ go _ _ [] = return empty
+ go n env ((is_landmark, ctxt) : ctxts)
+ | is_landmark || opt_PprStyle_Debug || n < mAX_CONTEXTS
+ = do { (env', msg) <- ctxt env
+ ; let n' = if is_landmark then n else n+1
+ ; rest <- go n' env' ctxts
+ ; return (msg $$ rest) }
+ | otherwise
+ = go n env ctxts
+
+mAX_CONTEXTS :: Int -- No more than this number of non-landmark contexts
+mAX_CONTEXTS = 3