Refactoring of where tcSimplifyTop happens

We want to do tcSimplifyTop after checkMain, because checkMain can add
useful type information that eliminates ambiguity.  E.g.
	main = return undefined

This is the way it used to be in 6.6, and I think I mistakenly moved it
when doing implication constraints. This patch effectively puts it back
the way it was.

Cures the cg053 failure.

diff --git a/compiler/typecheck/TcRnDriver.lhs b/compiler/typecheck/TcRnDriver.lhs
index af9a03d..f20de55 100644 (file)
--- a/compiler/typecheck/TcRnDriver.lhs
+++ b/compiler/typecheck/TcRnDriver.lhs
@@ -337,15 +337,34 @@ tcRnSrcDecls decls
        boot_iface <- tcHiBootIface mod ;
 
                -- Do all the declarations
-       tcg_env <- tc_rn_src_decls boot_iface decls ;
+       (tc_envs, lie) <- getLIE $ tc_rn_src_decls boot_iface decls ;
+
+            --         Finish simplifying class constraints
+            -- 
+            -- tcSimplifyTop deals with constant or ambiguous InstIds.  
+            -- How could there be ambiguous ones?  They can only arise if a
+            -- top-level decl falls under the monomorphism restriction
+            -- and no subsequent decl instantiates its type.
+            --
+            -- We do this after checkMain, so that we use the type info 
+            -- thaat checkMain adds
+            -- 
+            -- We do it with both global and local env in scope:
+            --  * the global env exposes the instances to tcSimplifyTop
+            --  * the local env exposes the local Ids to tcSimplifyTop, 
+            --    so that we get better error messages (monomorphism restriction)
+        traceTc (text "Tc8") ;
+       inst_binds <- setEnvs tc_envs (tcSimplifyTop lie) ;
 
            -- Backsubstitution.  This must be done last.
            -- Even tcSimplifyTop may do some unification.
         traceTc (text "Tc9") ;
-       let { TcGblEnv { tcg_type_env = type_env, tcg_binds = binds, 
-                        tcg_rules = rules, tcg_fords = fords } = tcg_env } ;
+       let { (tcg_env, _) = tc_envs
+           ; TcGblEnv { tcg_type_env = type_env, tcg_binds = binds, 
+                        tcg_rules = rules, tcg_fords = fords } = tcg_env
+           ; all_binds = binds `unionBags` inst_binds } ;
 
-       (bind_ids, binds', fords', rules') <- zonkTopDecls binds rules fords ;
+       (bind_ids, binds', fords', rules') <- zonkTopDecls all_binds rules fords ;
 
        let { final_type_env = extendTypeEnvWithIds type_env bind_ids
            ; tcg_env' = tcg_env { tcg_type_env = final_type_env,
@@ -362,7 +381,7 @@ tcRnSrcDecls decls
        return (tcg_env' { tcg_binds = tcg_binds tcg_env' `unionBags` dfun_binds }) 
    }
 
-tc_rn_src_decls :: ModDetails -> [LHsDecl RdrName] -> TcM TcGblEnv
+tc_rn_src_decls :: ModDetails -> [LHsDecl RdrName] -> TcM (TcGblEnv, TcLclEnv)
 -- Loops around dealing with each top level inter-splice group 
 -- in turn, until it's dealt with the entire module
 tc_rn_src_decls boot_details ds
@@ -370,39 +389,27 @@ tc_rn_src_decls boot_details ds
                -- If ds is [] we get ([], Nothing)
 
        -- Deal with decls up to, but not including, the first splice
-       (tcg_env, rn_decls) <- rnTopSrcDecls first_group ;
-       ((tcg_env, tcl_env), lie) <- getLIE $ setGblEnv tcg_env $ 
-                                    tcTopSrcDecls boot_details rn_decls ;
-
-            -- tcSimplifyTop deals with constant or ambiguous InstIds.  
-            -- How could there be ambiguous ones?  They can only arise if a
-            -- top-level decl falls under the monomorphism restriction
-            -- and no subsequent decl instantiates its type.
-        traceTc (text "Tc8") ;
-       inst_binds <- setEnvs (tcg_env, tcl_env) (tcSimplifyTop lie) ;
-               -- Setting the global env exposes the instances to tcSimplifyTop
-               -- Setting the local env exposes the local Ids to tcSimplifyTop, 
-               -- so that we get better error messages (monomorphism restriction)
-
-       let { tcg_env' = tcg_env { tcg_binds = tcg_binds tcg_env `unionBags` inst_binds } } ;
-
-       setEnvs (tcg_env', tcl_env) $ 
+       (tcg_env, rn_decls) <- checkNoErrs $ rnTopSrcDecls first_group ;
+               -- checkNoErrs: don't typecheck if renaming failed
+       tc_envs <- setGblEnv tcg_env $ 
+                  tcTopSrcDecls boot_details rn_decls ;
 
        -- If there is no splice, we're nearly done
+       setEnvs tc_envs $ 
        case group_tail of {
-          Nothing ->   -- Last thing: check for `main'
-                       checkMain ;
+          Nothing -> do { tcg_env <- checkMain ;       -- Check for `main'
+                          return (tcg_env, snd tc_envs) 
+                     } ;
 
        -- If there's a splice, we must carry on
-          Just (SpliceDecl splice_expr, rest_ds) -> 
-   do {
+          Just (SpliceDecl splice_expr, rest_ds) -> do {
 #ifndef GHCI
        failWithTc (text "Can't do a top-level splice; need a bootstrapped compiler")
 #else
 
        -- Rename the splice expression, and get its supporting decls
-       (rn_splice_expr, splice_fvs) <- rnLExpr splice_expr ;
-       failIfErrsM ;   -- Don't typecheck if renaming failed
+       (rn_splice_expr, splice_fvs) <- checkNoErrs (rnLExpr splice_expr) ;
+               -- checkNoErrs: don't typecheck if renaming failed
        rnDump (ppr rn_splice_expr) ;
 
        -- Execute the splice
@@ -412,7 +419,7 @@ tc_rn_src_decls boot_details ds
        setGblEnv (tcg_env `addTcgDUs` usesOnly splice_fvs) $
        tc_rn_src_decls boot_details (spliced_decls ++ rest_ds)
 #endif /* GHCI */
-    }}}
+    } } }
 \end{code}
 
 %************************************************************************