From 46c673a70fe14fe05d7160b456925b8591b5f779 Mon Sep 17 00:00:00 2001
From: Simon Marlow <marlowsd@gmail.com>
Date: Mon, 30 Nov 2009 11:23:27 +0000
Subject: [PATCH 1/1] Check whether the main function is actually exported
 (#414)

---
 compiler/typecheck/TcRnDriver.lhs |   28 ++++++++++++++++++++++++----
 compiler/typecheck/TcRnMonad.lhs  |    3 ++-
 compiler/typecheck/TcRnTypes.lhs  |    8 ++++++--
 3 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/compiler/typecheck/TcRnDriver.lhs b/compiler/typecheck/TcRnDriver.lhs
index 5cfb612..511fcbf 100644
--- a/compiler/typecheck/TcRnDriver.lhs
+++ b/compiler/typecheck/TcRnDriver.lhs
@@ -178,6 +178,9 @@ tcRnModule hsc_env hsc_src save_rn_syntax
 	tcg_env <- rnExports (isJust maybe_mod) export_ies tcg_env ;
 	traceRn (text "rn4b: after exportss") ;
 
+                -- Check that main is exported (must be after rnExports)
+        checkMainExported tcg_env ;
+
 	-- Compare the hi-boot iface (if any) with the real thing
 	-- Must be done after processing the exports
  	tcg_env <- checkHiBootIface tcg_env boot_iface ;
@@ -942,13 +945,14 @@ check_main dflags tcg_env
 	      ; rhs = nlHsApp (mkLHsWrap co (nlHsVar run_main_id)) main_expr
 	      ; main_bind = mkVarBind root_main_id rhs }
 
-	; return (tcg_env { tcg_binds = tcg_binds tcg_env 
+	; return (tcg_env { tcg_main  = Just main_name,
+                            tcg_binds = tcg_binds tcg_env
 					`snocBag` main_bind,
 			    tcg_dus   = tcg_dus tcg_env
 				        `plusDU` usesOnly (unitFV main_name)
 			-- Record the use of 'main', so that we don't 
 			-- complain about it being defined but not used
-		 }) 
+		 })
     }}}
   where
     mod 	 = tcg_mod tcg_env
@@ -964,8 +968,13 @@ check_main dflags tcg_env
     mainCtxt  = ptext (sLit "When checking the type of the") <+> pp_main_fn
     noMainMsg = ptext (sLit "The") <+> pp_main_fn
 		<+> ptext (sLit "is not defined in module") <+> quotes (ppr main_mod)
-    pp_main_fn | main_fn == main_RDR_Unqual = ptext (sLit "function") <+> quotes (ppr main_fn)
-	       | otherwise                  = ptext (sLit "main function") <+> quotes (ppr main_fn)
+    pp_main_fn = ppMainFn main_fn
+
+ppMainFn main_fn
+  | main_fn == main_RDR_Unqual
+  = ptext (sLit "function") <+> quotes (ppr main_fn)
+  | otherwise
+  = ptext (sLit "main function") <+> quotes (ppr main_fn)
 	       
 -- | Get the unqualified name of the function to use as the \"main\" for the main module.
 -- Either returns the default name or the one configured on the command line with -main-is
@@ -973,6 +982,17 @@ getMainFun :: DynFlags -> RdrName
 getMainFun dflags = case (mainFunIs dflags) of
     Just fn -> mkRdrUnqual (mkVarOccFS (mkFastString fn))
     Nothing -> main_RDR_Unqual
+
+checkMainExported :: TcGblEnv -> TcM ()
+checkMainExported tcg_env = do
+  dflags    <- getDOpts
+  case tcg_main tcg_env of
+    Nothing -> return () -- not the main module
+    Just main_name -> do
+      let main_mod = mainModIs dflags
+      checkTc (main_name `elem` concatMap availNames (tcg_exports tcg_env)) $
+              ptext (sLit "The") <+> ppMainFn (nameRdrName main_name) <+>
+              ptext (sLit "is not exported by module") <+> quotes (ppr main_mod)
 \end{code}
 
 Note [Root-main Id]
diff --git a/compiler/typecheck/TcRnMonad.lhs b/compiler/typecheck/TcRnMonad.lhs
index 90028bd..f4b9131 100644
--- a/compiler/typecheck/TcRnMonad.lhs
+++ b/compiler/typecheck/TcRnMonad.lhs
@@ -115,7 +115,8 @@ initTc hsc_env hsc_src keep_rn_syntax mod do_this
 		tcg_dfun_n   = dfun_n_var,
 		tcg_keep     = keep_var,
 		tcg_doc_hdr  = Nothing,
-                tcg_hpc      = False
+                tcg_hpc      = False,
+                tcg_main     = Nothing
 	     } ;
 	     lcl_env = TcLclEnv {
 		tcl_errs       = errs_var,
diff --git a/compiler/typecheck/TcRnTypes.lhs b/compiler/typecheck/TcRnTypes.lhs
index c011d20..a91e95e 100644
--- a/compiler/typecheck/TcRnTypes.lhs
+++ b/compiler/typecheck/TcRnTypes.lhs
@@ -247,8 +247,12 @@ data TcGblEnv
 	tcg_fords     :: [LForeignDecl Id], -- ...Foreign import & exports
 
 	tcg_doc_hdr   :: Maybe LHsDocString, -- ^ Maybe Haddock header docs
-        tcg_hpc :: AnyHpcUsage -- ^ @True@ if any part of the prog uses hpc
-                               -- instrumentation.
+        tcg_hpc       :: AnyHpcUsage,        -- ^ @True@ if any part of the
+                                             --  prog uses hpc instrumentation.
+
+        tcg_main      :: Maybe Name          -- ^ The Name of the main
+                                             -- function, if this module is
+                                             -- the main module.
     }
 
 data RecFieldEnv 
-- 
1.7.10.4