The Backpack patch.

Summary:
This patch implements Backpack for GHC.  It's a big patch but I've tried quite
hard to keep things, by-in-large, self-contained.

The user facing specification for Backpack can be found at:

    https://github.com/ezyang/ghc-proposals/blob/backpack/proposals/0000-backpack.rst

A guide to the implementation can be found at:

    https://github.com/ezyang/ghc-proposals/blob/backpack-impl/proposals/0000-backpack-impl.rst

Has a submodule update for Cabal, as well as a submodule update
for filepath to handle more strict checking of cabal-version.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Test Plan: validate

Reviewers: simonpj, austin, simonmar, bgamari, goldfire

Subscribers: thomie, mpickering

Differential Revision: https://phabricator.haskell.org/D1482

1 files changed, 28 insertions, 0 deletions

diff --git a/testsuite/tests/backpack/reexport/bkpreex05.bkp b/testsuite/tests/backpack/reexport/bkpreex05.bkp
new file mode 100644
index 0000000000..e496ed76fa
--- /dev/null
+++ b/testsuite/tests/backpack/reexport/bkpreex05.bkp
@@ -0,0 +1,28 @@
+unit bar where
+    signature A(bar) where
+        data A = A { foo :: Int, bar :: Bool }
+
+unit foo where
+    signature A(foo) where
+        data A = A { foo :: Int, bar :: Bool }
+
+unit impl where
+    module A1 where
+        data A = A { foo :: Int, bar :: Bool }
+    module A2 where
+        data A = A { foo :: Int, bar :: Bool }
+    module A(foo, bar) where
+        import A1(foo)
+        import A2(bar)
+
+-- Kind of boring test now haha
+
+unit barimpl where
+    dependency bar[A=impl:A]
+
+unit fooimpl where
+    dependency foo[A=impl:A]
+
+unit foobarimpl where
+    dependency foo[A=impl:A]
+    dependency bar[A=impl:A]