Improvements/bugfixes to signature reexport handling.

Summary:
A number of changes:

- Keep the TcGblEnv from typechecking the local signature
  around when we do merging.  In particular, we setup
  tcg_imports and tcg_rdr_env according to the local
  signature.  This improves our error output (for example,
  see bkpfail04) and also fixes a bug with reexporting
  modules in signatures (see bkpreex07)

- Fix a bug in thinning, where if we had signature A(module A),
  this previously would have *thinned out* all of the inherited
  signatures.  Now we treat every inherited signature as having
  come from an import like "import A", so a module A reexport
  will pick them up.

- Recompilation checking now keeps track of dependent source files
  of the source signature; previously we forgot to retain this
  info.

There's a manual update too.

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

Test Plan: validate

Reviewers: bgamari, austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D3133

2 files changed, 4 insertions, 4 deletions

diff --git a/testsuite/tests/backpack/should_fail/bkpfail04.stderr b/testsuite/tests/backpack/should_fail/bkpfail04.stderr
index f445c57f8e..07159cf277 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail04.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail04.stderr
@@ -8,8 +8,8 @@
 bkpfail04.bkp:7:9: error:
     • Type constructor ‘A’ has conflicting definitions in the module
       and its hsig file
-      Main module: data A = A {foo :: GHC.Types.Int}
-      Hsig file:  data A = A {bar :: GHC.Types.Bool}
+      Main module: data A = A {foo :: Int}
+      Hsig file:  data A = A {bar :: Bool}
       The constructors do not match:
         The record label lists for ‘A’ differ
         The types for ‘A’ differ
diff --git a/testsuite/tests/backpack/should_fail/bkpfail42.stderr b/testsuite/tests/backpack/should_fail/bkpfail42.stderr
index 30b43d829e..5a9e1aa9c3 100644
--- a/testsuite/tests/backpack/should_fail/bkpfail42.stderr
+++ b/testsuite/tests/backpack/should_fail/bkpfail42.stderr
@@ -7,9 +7,9 @@ bkpfail42.bkp:9:9: error:
     • Type constructor ‘F’ has conflicting definitions in the module
       and its hsig file
       Main module: type family F a :: *
-                     where [a] F a = GHC.Types.Int
+                     where [a] F a = Int
       Hsig file:  type family F a :: *
-                    where [a] F a = GHC.Types.Bool
+                    where [a] F a = Bool
     • while merging the signatures from:
         • p[A=<A>]:A
         • ...and the local signature for A