[project @ 2001-05-09 13:28:11 by simonpj]

****	MERGE WITH 5.00 BRANCH     ********

	-------------------------------
	Fix a rather obscure rule bogon
	-------------------------------

The problem was that there was

	class Foo a where
	  op :: a -> a

	{-# RULES "op" op x = x #-}

or something like that.  We attach locally defined rules, like this one,
to the local binding, in SimplCore.prepareRules.  Alas op doesn't reply
"True" to isLocalId, because it's a class selector (so it's a GlobalId
throughout).   Result: we treated the rule as an imported rule, and
therefore gave 'op' a fresh unique (becuase it looked as if it was
already in scope).  This only blew up in ghc --make or --interactive.

The handling of local vs global rules is rather unsatisfactory.
Something to muse on.

diff --git a/ghc/compiler/simplCore/SimplCore.lhs b/ghc/compiler/simplCore/SimplCore.lhs
index 7197e77..b419461 100644 (file)
--- a/ghc/compiler/simplCore/SimplCore.lhs
+++ b/ghc/compiler/simplCore/SimplCore.lhs
@@ -32,7 +32,7 @@ import SimplMonad
 import ErrUtils                ( dumpIfSet, dumpIfSet_dyn )
 import FloatIn         ( floatInwards )
 import FloatOut                ( floatOutwards )
-import Id              ( idName, isDataConWrapId, setIdNoDiscard, isLocalId, isImplicitId )
+import Id              ( idName, isDataConWrapId, setIdNoDiscard, isImplicitId )
 import VarSet
 import LiberateCase    ( liberateCase )
 import SAT             ( doStaticArgs )
@@ -210,7 +210,17 @@ prepareRules dflags pkg_rule_base hst us binds local_rules
   = do { let (better_rules,_) = initSmpl dflags sw_chkr us local_ids black_list_all 
                                          (mapSmpl simplRule local_rules)
 
-       ; let (local_rules, orphan_rules) = partition (isLocalId . fst) better_rules
+       ; let (local_rules, orphan_rules) = partition ((`elemVarSet` local_ids) . fst) better_rules
+               -- We use (`elemVarSet` local_ids) rather than isLocalId because
+               -- isLocalId isn't true of class methods.
+               -- If we miss any rules for Ids defined here, then we end up
+               -- giving the local decl a new Unique (because the in-scope-set is the
+               -- same as the rule-id set), and now the binding for the class method 
+               -- doesn't have the same Unique as the one in the Class and the tc-env
+               --      Example:        class Foo a where
+               --                        op :: a -> a
+               --                      {-# RULES "op" op x = x #-}
+
              rule_rhs_fvs                = unionVarSets (map (ruleRhsFreeVars . snd) better_rules)
              local_rule_base             = extendRuleBaseList emptyRuleBase local_rules
              local_rule_ids              = ruleBaseIds local_rule_base -- Local Ids with rules attached
@@ -235,8 +245,6 @@ prepareRules dflags pkg_rule_base hst us binds local_rules
     add_rules rule_base mds = extendRuleBaseList rule_base (md_rules mds)
 
        -- Boringly, we need to gather the in-scope set.
-       -- Typically this thunk won't even be forced, but the test in
-       -- simpVar fails if it isn't right, and it might conceiveably matter
     local_ids = foldr (unionVarSet . mkVarSet . bindersOf) emptyVarSet binds