[project @ 2003-10-20 14:02:19 by simonpj]

Suppress renamer warnings (such as unused variables) when
renaming stuff generated by 'deriving' code.

diff --git a/ghc/compiler/typecheck/TcDeriv.lhs b/ghc/compiler/typecheck/TcDeriv.lhs
index 2f63cf7..012a5d0 100644 (file)
--- a/ghc/compiler/typecheck/TcDeriv.lhs
+++ b/ghc/compiler/typecheck/TcDeriv.lhs
@@ -248,8 +248,9 @@ deriveOrdinaryStuff eqns
        ; tcg_env <- getGblEnv
        ; let gen_binds = mkGenericBinds (typeEnvTyCons (tcg_type_env tcg_env))
 
-       -- Rename these extra bindings
-       ; (rn_binds, _fvs1) <- rnTopMonoBinds (extra_binds `AndMonoBinds` gen_binds) []
+       -- Rename these extra bindings, discarding warnings about unused bindings etc
+       ; (rn_binds, _fvs1) <- discardWarnings $
+                              rnTopMonoBinds (extra_binds `AndMonoBinds` gen_binds) []
 
        ; let all_binds = rn_binds `ThenBinds` 
                          foldr ThenBinds EmptyBinds aux_binds_s

diff --git a/ghc/compiler/typecheck/TcRnMonad.lhs b/ghc/compiler/typecheck/TcRnMonad.lhs
index 4d2e8bf..c30ead5 100644 (file)
--- a/ghc/compiler/typecheck/TcRnMonad.lhs
+++ b/ghc/compiler/typecheck/TcRnMonad.lhs
@@ -403,6 +403,18 @@ addMessages (m_warns, m_errs)
         (warns, errs) <- readMutVar errs_var ;
         writeMutVar errs_var (warns `unionBags` m_warns,
                               errs  `unionBags` m_errs) }
+
+discardWarnings :: TcRn a -> TcRn a
+-- Ignore warnings inside the thing inside;
+-- used to ignore-unused-variable warnings inside derived code
+-- With -dppr-debug, the effects is switched off, so you can still see
+-- what warnings derived code would give
+discardWarnings thing_inside
+  = do { errs_var <- newMutVar emptyMessages
+       ; result <- setErrsVar errs_var thing_inside
+       ; (_warns, errs) <- readMutVar errs_var
+       ; addMessages (emptyBag, errs)
+       ; return result }
 \end{code}