Fix checkHiBootIface for instances declared in hs-boot files

Hs-boot files can contain instance declarations, but Duncan used this feature
for the first time today, and it didn't quite work.  I'm not sure whether
it worked before; anyway it does now.

The point is that the hs-boot file advertises an instance for, say, Num Int,
with the arbitrary name $fx1.  The main module declares Num Int, and gives
it the name, say, $f3.  So we need to generate a declaration
	$fx1 = $f3
to make it all line up.  And (this is the bit that was wrong) we need
to make that new binding visible to imported unfoldings that mention
$fx1.

diff --git a/compiler/typecheck/TcRnDriver.lhs b/compiler/typecheck/TcRnDriver.lhs
index d8446be..4e0f283 100644 (file)
--- a/compiler/typecheck/TcRnDriver.lhs
+++ b/compiler/typecheck/TcRnDriver.lhs
@@ -169,6 +169,11 @@ tcRnModule hsc_env hsc_src save_rn_syntax
        -- Must be done after processing the exports
        tcg_env <- checkHiBootIface tcg_env boot_iface ;
 
+       -- Make the new type env available to stuff slurped from interface files
+       -- Must do this after checkHiBootIface, because the latter might add new
+       -- bindings for boot_dfuns, which may be mentioned in imported unfoldings
+       writeMutVar (tcg_type_env_var tcg_env) (tcg_type_env tcg_env) ;
+
                -- Rename the Haddock documentation 
        tcg_env <- rnHaddock module_info maybe_doc tcg_env ;
 
@@ -373,9 +378,6 @@ tcRnSrcDecls boot_iface decls
                                   tcg_rules = rules', 
                                   tcg_fords = fords' } } ;
 
-       -- Make the new type env available to stuff slurped from interface files
-       writeMutVar (tcg_type_env_var tcg_env) final_type_env ;
-
        return (tcg_env' { tcg_binds = tcg_binds tcg_env' }) 
    }
 
@@ -508,7 +510,13 @@ checkHiBootIface
        ; mapM_ check_export boot_exports
 
                -- Check instance declarations
-       ; dfun_binds <- mapM check_inst boot_insts
+       ; mb_dfun_prs <- mapM check_inst boot_insts
+       ; let tcg_env' = tcg_env { tcg_binds    = binds `unionBags` dfun_binds,
+                                  tcg_type_env = extendTypeEnvWithIds local_type_env boot_dfuns }
+             dfun_prs   = catMaybes mb_dfun_prs
+             boot_dfuns = map fst dfun_prs
+             dfun_binds = listToBag [ noLoc $ VarBind boot_dfun (nlHsVar dfun)
+                                    | (boot_dfun, dfun) <- dfun_prs ]
 
                -- Check for no family instances
        ; unless (null boot_fam_insts) $
@@ -518,7 +526,7 @@ checkHiBootIface
             --       be the equivalent to the dfun bindings returned for class
             --       instances?  We can't easily equate tycons...
 
-       ; return (tcg_env { tcg_binds = binds `unionBags` unionManyBags dfun_binds }) }
+       ; return tcg_env' }
   where
     check_export boot_avail    -- boot_avail is exported by the boot iface
       | name `elem` dfun_names = return ()     
@@ -558,12 +566,14 @@ checkHiBootIface
     local_export_env :: NameEnv AvailInfo
     local_export_env = availsToNameEnv local_exports
 
+    check_inst :: Instance -> TcM (Maybe (Id, Id))
+       -- Returns a pair of the boot dfun in terms of the equivalent real dfun
     check_inst boot_inst
        = case [dfun | inst <- local_insts, 
                       let dfun = instanceDFunId inst,
                       idType dfun `tcEqType` boot_inst_ty ] of
-           [] -> do { addErrTc (instMisMatch boot_inst); return emptyBag }
-           (dfun:_) -> return (unitBag $ noLoc $ VarBind local_boot_dfun (nlHsVar dfun))
+           [] -> do { addErrTc (instMisMatch boot_inst); return Nothing }
+           (dfun:_) -> return (Just (local_boot_dfun, dfun))
        where
          boot_dfun = instanceDFunId boot_inst
          boot_inst_ty = idType boot_dfun