[project @ 2003-02-21 14:52:31 by simonpj]

Fix buglets in new unused-binding story

diff --git a/ghc/compiler/rename/RnBinds.lhs b/ghc/compiler/rename/RnBinds.lhs
index cd3d575..461016a 100644 (file)
--- a/ghc/compiler/rename/RnBinds.lhs
+++ b/ghc/compiler/rename/RnBinds.lhs
@@ -197,13 +197,21 @@ rnMonoBindsAndThen mbinds sigs thing_inside -- Non-empty monobinds
 
        -- Final error checking
     let
+       all_uses     = duUses bind_dus `plusFV` result_fvs
        bndrs        = duDefs bind_dus
-       all_uses     = findUses bind_dus result_fvs
+       real_uses    = findUses bind_dus result_fvs
        unused_bndrs = nameSetToList (bndrs `minusNameSet` all_uses)
     in
     warnUnusedLocalBinds unused_bndrs  `thenM_`
 
     returnM (result, all_uses `minusNameSet` bndrs)
+       -- It's important to return all the uses, not the 'real uses' used for
+       -- warning about unused bindings.  Otherwise consider:
+       --      x = 3
+       --      y = let p = x in 'x'
+       -- If we don't "see" the dependency of 'y' on 'x', we may put the
+       -- bindings in the wrong order, and the type checker will complain
+       -- that x isn't in scope
   where
     mbinders_w_srclocs = collectLocatedMonoBinders mbinds
     doc = text "In the binding group for:"
@@ -246,7 +254,6 @@ rnMonoBinds top_lvl mbinds sigs
        final_binds = foldr ThenBinds EmptyBinds binds_s
        binders     = duDefs bind_dus
     in
-
        -- Check for duplicate or mis-placed signatures
     checkSigs (okBindSig binders) siglist      `thenM_`