Fix Trac #959: a long-standing bug in instantiating otherwise-unbound type variables

[ghc-hetmet.git] / compiler / basicTypes / OccName.lhs

diff --git a/compiler/basicTypes/OccName.lhs b/compiler/basicTypes/OccName.lhs
index 6f5267d..3a2338e 100644 (file)
--- a/compiler/basicTypes/OccName.lhs
+++ b/compiler/basicTypes/OccName.lhs
@@ -9,7 +9,7 @@
 -- GHC uses several kinds of name internally:
 --
 -- * 'OccName.OccName' represents names as strings with just a little more information:
---   the "namespace" that the name came from, e.g. the namespace of value, type constructors or
+--   the \"namespace\" that the name came from, e.g. the namespace of value, type constructors or
 --   data constructors
 --
 -- * 'RdrName.RdrName': see "RdrName#name_types"
@@ -95,11 +95,9 @@ module OccName (
 import Util
 import Unique
 import BasicTypes
-import StaticFlags
 import UniqFM
 import UniqSet
 import FastString
-import FastTypes
 import Outputable
 import Binary
 import Data.Char
@@ -305,22 +303,24 @@ mkClsOccFS = mkOccNameFS clsName
 
 OccEnvs are used mainly for the envts in ModIfaces.
 
+Note [The Unique of an OccName]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 They are efficient, because FastStrings have unique Int# keys.  We assume
-this key is less than 2^24, so we can make a Unique using
+this key is less than 2^24, and indeed FastStrings are allocated keys 
+sequentially starting at 0.
+
+So we can make a Unique using
        mkUnique ns key  :: Unique
 where 'ns' is a Char reprsenting the name space.  This in turn makes it
 easy to build an OccEnv.
 
 \begin{code}
 instance Uniquable OccName where
-  getUnique (OccName ns fs)
-      = mkUnique char (iBox (uniqueOfFS fs))
-      where    -- See notes above about this getUnique function
-        char = case ns of
-               VarName   -> 'i'
-               DataName  -> 'd'
-               TvName    -> 'v'
-               TcClsName -> 't'
+      -- See Note [The Unique of an OccName]
+  getUnique (OccName VarName   fs) = mkVarOccUnique  fs
+  getUnique (OccName DataName  fs) = mkDataOccUnique fs
+  getUnique (OccName TvName    fs) = mkTvOccUnique   fs
+  getUnique (OccName TcClsName fs) = mkTcOccUnique   fs
 
 newtype OccEnv a = A (UniqFM a)
 
@@ -601,31 +601,41 @@ mkLocalOcc uniq occ
 \begin{code}
 -- | Derive a name for the representation type constructor of a
 -- @data@\/@newtype@ instance.
-mkInstTyTcOcc :: Int                   -- ^ DFun Index
-             -> OccName                -- ^ Family name, e.g. @Map@
-             -> OccName                -- ^ Nice unique version, e.g. @:R23Map@
-mkInstTyTcOcc index occ
-   = mk_deriv tcName ("R" ++ show index ++ ":") (occNameString occ)
+mkInstTyTcOcc :: String                -- ^ Family name, e.g. @Map@
+              -> OccSet                 -- ^ avoid these Occs
+             -> OccName                -- ^ @R:Map@
+mkInstTyTcOcc str set =
+  chooseUniqueOcc tcName ('R' : ':' : str) set
 \end{code}
 
 \begin{code}
 mkDFunOcc :: String            -- ^ Typically the class and type glommed together e.g. @OrdMaybe@.
                                -- Only used in debug mode, for extra clarity
          -> Bool               -- ^ Is this a hs-boot instance DFun?
-         -> Int                -- ^ Unique index
+          -> OccSet             -- ^ avoid these Occs
          -> OccName            -- ^ E.g. @$f3OrdMaybe@
 
 -- In hs-boot files we make dict funs like $fx7ClsTy, which get bound to the real
 -- thing when we compile the mother module. Reason: we don't know exactly
 -- what the  mother module will call it.
 
-mkDFunOcc info_str is_boot index 
-  = mk_deriv VarName prefix string
+mkDFunOcc info_str is_boot set
+  = chooseUniqueOcc VarName (prefix ++ info_str) set
   where
     prefix | is_boot   = "$fx"
           | otherwise = "$f"
-    string | opt_PprStyle_Debug = show index ++ info_str
-          | otherwise          = show index
+\end{code}
+
+Sometimes we need to pick an OccName that has not already been used,
+given a set of in-use OccNames.
+
+\begin{code}
+chooseUniqueOcc :: NameSpace -> String -> OccSet -> OccName
+chooseUniqueOcc ns str set = loop (mkOccName ns str) (0::Int)
+  where
+  loop occ n
+   | occ `elemOccSet` set = loop (mkOccName ns (str ++ show n)) (n+1)
+   | otherwise            = occ
 \end{code}
 
 We used to add a '$m' to indicate a method, but that gives rise to bad