[commit: ghc] ghc-7.6: Invalidate the ModSummary cache in setSessionDynFlags (#7478) (16ba757)

Repository : ssh://darcs.haskell.org//srv/darcs/ghc

On branch  : ghc-7.6

http://hackage.haskell.org/trac/ghc/changeset/16ba75714cc22aeb86425679ad24b996a2b30fea

>---------------------------------------------------------------

commit 16ba75714cc22aeb86425679ad24b996a2b30fea
Author: Simon Marlow <[email protected]>
Date:   Fri Dec 7 12:05:29 2012 +0000

    Invalidate the ModSummary cache in setSessionDynFlags (#7478)

>---------------------------------------------------------------

 compiler/main/GHC.hs |   27 +++++++++++++++++++++++++++
 1 files changed, 27 insertions(+), 0 deletions(-)

diff --git a/compiler/main/GHC.hs b/compiler/main/GHC.hs
index b1cc786..82d5a8a 100644
--- a/compiler/main/GHC.hs
+++ b/compiler/main/GHC.hs
@@ -498,6 +498,7 @@ setSessionDynFlags dflags = do
   (dflags', preload) <- liftIO $ initPackages dflags
   modifySession $ \h -> h{ hsc_dflags = dflags'
                          , hsc_IC = (hsc_IC h){ ic_dflags = dflags' } }
+  invalidateModSummaryCache
   return preload
 
 -- | Sets the program 'DynFlags'.
@@ -505,8 +506,34 @@ setProgramDynFlags :: GhcMonad m => DynFlags -> m [PackageId]
 setProgramDynFlags dflags = do
   (dflags', preload) <- liftIO $ initPackages dflags
   modifySession $ \h -> h{ hsc_dflags = dflags' }
+  invalidateModSummaryCache
   return preload
 
+-- When changing the DynFlags, we want the changes to apply to future
+-- loads, but without completely discarding the program.  But the
+-- DynFlags are cached in each ModSummary in the hsc_mod_graph, so
+-- after a change to DynFlags, the changes would apply to new modules
+-- but not existing modules; this seems undesirable.
+--
+-- Furthermore, the GHC API client might expect that changing
+-- log_action would affect future compilation messages, but for those
+-- modules we have cached ModSummaries for, we'll continue to use the
+-- old log_action.  This is definitely wrong (#7478).
+--
+-- Hence, we invalidate the ModSummary cache after changing the
+-- DynFlags.  We do this by tweaking the date on each ModSummary, so
+-- that the next downsweep will think that all the files have changed
+-- and preprocess them again.  This won't necessarily cause everything
+-- to be recompiled, because by the time we check whether we need to
+-- recopmile a module, we'll have re-summarised the module and have a
+-- correct ModSummary.
+--
+invalidateModSummaryCache :: GhcMonad m => m ()
+invalidateModSummaryCache =
+  modifySession $ \h -> h { hsc_mod_graph = map inval (hsc_mod_graph h) }
+ where
+  inval ms = ms { ms_hs_date = addUTCTime (-1) (ms_hs_date ms) }
+
 -- | Returns the program 'DynFlags'.
 getProgramDynFlags :: GhcMonad m => m DynFlags
 getProgramDynFlags = getSessionDynFlags