Avoid duplicate defns of 'main' in module Main

diff --git a/compiler/iface/MkIface.lhs b/compiler/iface/MkIface.lhs
index 0fc3972..a9b9f03 100644 (file)
--- a/compiler/iface/MkIface.lhs
+++ b/compiler/iface/MkIface.lhs
@@ -257,11 +257,13 @@ mkIface hsc_env maybe_old_iface
        ; let   { entities = typeEnvElts type_env ;
                   decls  = [ tyThingToIfaceDecl entity
                           | entity <- entities,
-                             not (isImplicitTyThing entity
-                                  || isWiredInName (getName entity)) ]
-                        -- Don't put implicit Ids and class tycons in
-                        -- the interface file, Nor wired-in things; the
-                        -- compiler knows about them anyhow
+                            let name = getName entity,
+                             not (isImplicitTyThing entity),
+                               -- No implicit Ids and class tycons in the interface file
+                            not (isWiredInName name),
+                               -- Nor wired-in things; the compiler knows about them anyhow
+                            nameIsLocalOrFrom this_mod name  ]
+                               -- Sigh: see Note [Root-main Id] in TcRnDriver
 
                ; fixities    = [(occ,fix) | FixItem occ fix _ <- nameEnvElts fix_env]
                ; deprecs     = mkIfaceDeprec src_deprecs

diff --git a/compiler/typecheck/TcRnDriver.lhs b/compiler/typecheck/TcRnDriver.lhs
index eabd3bc..6c4a35f 100644 (file)
--- a/compiler/typecheck/TcRnDriver.lhs
+++ b/compiler/typecheck/TcRnDriver.lhs
@@ -726,18 +726,7 @@ check_main ghc_mode tcg_env main_mod main_fn
        ; (main_expr, ty) <- setSrcSpan (srcLocSpan (getSrcLoc main_name)) $
                             tcInferRho rhs
 
-       -- The function that the RTS invokes is always :Main.main,
-       -- which we call root_main_id.  
-       -- (Because GHC allows the user to have a module not called 
-       -- Main as the main module, we can't rely on the main function
-       -- being called "Main.main".  That's why root_main_id has a fixed
-       -- module ":Main".)
-       -- We also make root_main_id an implicit Id, by making main_name
-       -- its parent (hence (Just main_name)).  That has the effect
-       -- of preventing its type and unfolding from getting out into
-       -- the interface file. Otherwise we can end up with two defns
-       -- for 'main' in the interface file!
-
+               -- See Note [Root-main Id]
        ; let { root_main_name =  mkExternalName rootMainKey rOOT_MAIN 
                                   (mkVarOccFS FSLIT("main")) 
                                   (getSrcLoc main_name)
@@ -766,6 +755,19 @@ check_main ghc_mode tcg_env main_mod main_fn
                <+> ptext SLIT("is not defined in module") <+> quotes (ppr main_mod)
 \end{code}
 
+Note [Root-main Id]
+~~~~~~~~~~~~~~~~~~~
+The function that the RTS invokes is always :Main.main, which we call
+root_main_id.  (Because GHC allows the user to have a module not
+called Main as the main module, we can't rely on the main function
+being called "Main.main".  That's why root_main_id has a fixed module
+":Main".)  
+
+This is unusual: it's a LocalId whose Name has a Module from another
+module.  Tiresomely, we must filter it out again in MkIface, les we
+get two defns for 'main' in the interface file!
+
+
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