Support the GHCi debugger with -fexternal-interpreter

* All the tests in tests/ghci.debugger now pass with
  -fexternal-interpreter. These tests are now run with the ghci-ext way
  in addition to the normal way so we won't break it in the future.

* I removed all the unsafeCoerce# calls from RtClosureInspect. Yay!

The main changes are:

* New messages: GetClosure and Seq.  GetClosure is a remote interface to
  GHC.Exts.Heap.getClosureData, which required Binary instances for
  various datatypes. Fortunately this wasn't too painful thanks to
  DeriveGeneric.

* No cheating by unsafeCoercing values when printing them. Now we have
  to turn the Closure representation back into the native representation
  when printing Int, Float, Double, Integer and Char. Of these, Integer
  was the most painful - we now have a dependency on integer-gmp due to
  needing access to the representation.

* Fixed a bug in rts/Heap.c - it was bogusly returning stack content as
  pointers for an AP_STACK closure.

Test Plan:
* `cd testsuite/tests/ghci.debugger && make`
* validate

Reviewers: bgamari, patrickdoc, nomeata, angerman, hvr, erikd, goldfire

Subscribers: alpmestan, snowleopard, rwbarton, thomie, carter

GHC Trac Issues: #13184

Differential Revision: https://phabricator.haskell.org/D4955

1 files changed, 8 insertions, 6 deletions

diff --git a/compiler/main/InteractiveEval.hs b/compiler/main/InteractiveEval.hs
index 3f2309e7f5..bec52e6001 100644
--- a/compiler/main/InteractiveEval.hs
+++ b/compiler/main/InteractiveEval.hs
@@ -990,20 +990,22 @@ moduleIsBootOrNotObjectLinkable mod_summary = withSession $ \hsc_env ->
 -- RTTI primitives
 
 obtainTermFromVal :: HscEnv -> Int -> Bool -> Type -> a -> IO Term
-obtainTermFromVal hsc_env bound force ty x =
-              cvObtainTerm hsc_env bound force ty (unsafeCoerce# x)
+obtainTermFromVal hsc_env bound force ty x
+  | gopt Opt_ExternalInterpreter (hsc_dflags hsc_env)
+  = throwIO (InstallationError
+      "this operation requires -fno-external-interpreter")
+  | otherwise
+  = cvObtainTerm hsc_env bound force ty (unsafeCoerce# x)
 
 obtainTermFromId :: HscEnv -> Int -> Bool -> Id -> IO Term
 obtainTermFromId hsc_env bound force id =  do
-  let dflags = hsc_dflags hsc_env
-  hv <- Linker.getHValue hsc_env (varName id) >>= wormhole dflags
+  hv <- Linker.getHValue hsc_env (varName id)
   cvObtainTerm hsc_env bound force (idType id) hv
 
 -- Uses RTTI to reconstruct the type of an Id, making it less polymorphic
 reconstructType :: HscEnv -> Int -> Id -> IO (Maybe Type)
 reconstructType hsc_env bound id = do
-  let dflags = hsc_dflags hsc_env
-  hv <- Linker.getHValue hsc_env (varName id) >>= wormhole dflags
+  hv <- Linker.getHValue hsc_env (varName id)
   cvReconstructType hsc_env bound (idType id) hv
 
 mkRuntimeUnkTyVar :: Name -> Kind -> TyVar