Refactor -dynamic-too handling

1) Don't modify DynFlags (too much) for -dynamic-too: now when we
   generate dynamic outputs for "-dynamic-too", we only set "dynamicNow"
   boolean field in DynFlags instead of modifying several other fields.
   These fields now have accessors that take dynamicNow into account.

2) Use DynamicTooState ADT to represent -dynamic-too state. It's much
   clearer than the undocumented "DynamicTooConditional" that was used
   before.

As a result, we can finally remove the hscs_iface_dflags field in
HscRecomp. There was a comment on this field saying:

   "FIXME (osa): I don't understand why this is necessary, but I spent
   almost two days trying to figure this out and I couldn't .. perhaps
   someone who understands this code better will remove this later."

I don't fully understand the details, but it was needed because of the
changes made to the DynFlags for -dynamic-too.

There is still something very dubious in GHC.Iface.Recomp: we have to
disable the "dynamicNow" flag at some point for some Backpack's "heinous
hack" to continue to work. It may be because interfaces for indefinite
units are always non-dynamic, or because we mix and match dynamic and
non-dynamic interfaces (#9176), or something else, who knows?

1 files changed, 5 insertions, 5 deletions

diff --git a/compiler/GHC/Driver/MakeFile.hs b/compiler/GHC/Driver/MakeFile.hs
index 81408ab7c9..c8c4c07d0d 100644
--- a/compiler/GHC/Driver/MakeFile.hs
+++ b/compiler/GHC/Driver/MakeFile.hs
@@ -67,11 +67,11 @@ doMkDependHS srcs = do
     -- We therefore do the initial dependency generation with an empty
     -- way and .o/.hi extensions, regardless of any flags that might
     -- be specified.
-    let dflags = dflags0 {
-                     ways = Set.empty,
-                     hiSuf = "hi",
-                     objectSuf = "o"
-                 }
+    let dflags = dflags0
+            { targetWays_ = Set.empty
+            , hiSuf_      = "hi"
+            , objectSuf_  = "o"
+            }
     GHC.setSessionDynFlags dflags
 
     when (null (depSuffixes dflags)) $ liftIO $