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, 13 insertions, 0 deletions

diff --git a/testsuite/tests/backpack/should_fail/bkpfail21.bkp b/testsuite/tests/backpack/should_fail/bkpfail21.bkp
new file mode 100644
index 0000000000..322fe5172c
--- /dev/null
+++ b/testsuite/tests/backpack/should_fail/bkpfail21.bkp
@@ -0,0 +1,13 @@
+unit p where
+    signature A where
+        data T
+    signature C(T) where
+        import A
+unit q where
+    signature B where
+        data T
+    signature C(T) where
+        import B
+unit r where
+    dependency p[A=<H1>,C=<H3>]
+    dependency q[B=<H2>,C=<H3>]