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, 20 insertions, 0 deletions

diff --git a/testsuite/tests/backpack/should_compile/bkp01.stdout b/testsuite/tests/backpack/should_compile/bkp01.stdout
new file mode 100644
index 0000000000..e72d7bc43c
--- /dev/null
+++ b/testsuite/tests/backpack/should_compile/bkp01.stdout
@@ -0,0 +1,20 @@
+Shape for p-impls
+provides: P -> p-impls():P
+               hello
+          Q -> p-impls():Q
+               p-impls():P.hello, world
+requires:
+==== Package p-impls ====
+[1 of 2] Compiling P                ( p-impls/P.hs, nothing )
+[2 of 2] Compiling Q                ( p-impls/Q.hs, nothing )
+Shape for q
+provides: P -> p-impls():P
+               hello
+          Q -> p-impls():Q
+               p-impls():P.hello, world
+          Main -> q():Main
+                  main
+requires:
+==== Package q ====
+[1 of 2] Including p-impls
+[2 of 2] Compiling Main             ( q/Main.hs, nothing )