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, 6 insertions, 3 deletions

diff --git a/libraries/ghc-heap/GHC/Exts/Heap/Closures.hs b/libraries/ghc-heap/GHC/Exts/Heap/Closures.hs
index 09a94a0f3f..bdfac8bf8b 100644
--- a/libraries/ghc-heap/GHC/Exts/Heap/Closures.hs
+++ b/libraries/ghc-heap/GHC/Exts/Heap/Closures.hs
@@ -4,6 +4,8 @@
 {-# LANGUAGE MagicHash #-}
 {-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE UnliftedFFITypes #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE DeriveTraversable #-}
 
 module GHC.Exts.Heap.Closures (
     -- * Closures
@@ -35,6 +37,7 @@ import Data.Bits
 import Data.Int
 import Data.Word
 import GHC.Exts
+import GHC.Generics
 import Numeric
 
 ------------------------------------------------------------------------
@@ -222,7 +225,7 @@ data GenClosure b
     -- | A @MutVar#@
   | MutVarClosure
         { info       :: !StgInfoTable
-        , var        :: !b              -- ^ Pointer to closure
+        , var        :: !b              -- ^ Pointer to contents
         }
 
     -- | An STM blocking queue.
@@ -285,7 +288,7 @@ data GenClosure b
   | UnsupportedClosure
         { info       :: !StgInfoTable
         }
-  deriving (Show)
+  deriving (Show, Generic, Functor, Foldable, Traversable)
 
 
 data PrimType
@@ -296,7 +299,7 @@ data PrimType
   | PAddr
   | PFloat
   | PDouble
-  deriving (Eq, Show)
+  deriving (Eq, Show, Generic)
 
 -- | For generic code, this function returns all referenced closures.
 allClosures :: GenClosure b -> [b]