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, 0 insertions, 7 deletions

diff --git a/compiler/GHC/Unit/Module/Status.hs b/compiler/GHC/Unit/Module/Status.hs
index d7fb83e582..539158fdb1 100644
--- a/compiler/GHC/Unit/Module/Status.hs
+++ b/compiler/GHC/Unit/Module/Status.hs
@@ -5,8 +5,6 @@ where
 
 import GHC.Prelude
 
-import GHC.Driver.Session
-
 import GHC.Unit
 import GHC.Unit.Module.ModGuts
 import GHC.Unit.Module.ModIface
@@ -38,9 +36,4 @@ data HscStatus
           -- exists. Pass to `hscMaybeWriteIface` when writing the interface to
           -- avoid updating the existing interface when the interface isn't
           -- changed.
-        , hscs_iface_dflags :: !DynFlags
-          -- ^ Generate final iface using this DynFlags.
-          -- 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.
         }