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

12 files changed, 70 insertions, 6 deletions

diff --git a/testsuite/tests/backpack/cabal/bkpcabal02/bkpcabal02.stderr b/testsuite/tests/backpack/cabal/bkpcabal02/bkpcabal02.stderr
index c1aa54d95e..681c541e21 100644
--- a/testsuite/tests/backpack/cabal/bkpcabal02/bkpcabal02.stderr
+++ b/testsuite/tests/backpack/cabal/bkpcabal02/bkpcabal02.stderr
@@ -2,8 +2,8 @@
 q/H.hsig:2:1: error:
     • Identifier ‘x’ has conflicting definitions in the module
       and its hsig file
-      Main module: x :: ghc-prim-0.5.0.0:GHC.Types.Int
-      Hsig file:  x :: ghc-prim-0.5.0.0:GHC.Types.Bool
+      Main module: x :: Int
+      Hsig file:  x :: Bool
       The two types are different
     • while merging the signatures from:
         • z-bkpcabal01-z-p-0.1.0.0[H=<H>]:H
diff --git a/testsuite/tests/backpack/reexport/all.T b/testsuite/tests/backpack/reexport/all.T
index 55a5004571..5619707e5d 100644
--- a/testsuite/tests/backpack/reexport/all.T
+++ b/testsuite/tests/backpack/reexport/all.T
@@ -5,3 +5,7 @@ test('bkpreex04', normal, backpack_typecheck, [''])
 # These signatures are behaving badly and the renamer gets confused
 test('bkpreex05', expect_broken(0), backpack_typecheck, [''])
 test('bkpreex06', normal, backpack_typecheck, [''])
+test('bkpreex07', normal, backpack_typecheck, [''])
+test('bkpreex08', normal, backpack_typecheck, [''])
+test('bkpreex09', normal, backpack_typecheck, [''])
+test('bkpreex10', normal, backpack_typecheck, [''])
diff --git a/testsuite/tests/backpack/reexport/bkpreex07.bkp b/testsuite/tests/backpack/reexport/bkpreex07.bkp
new file mode 100644
index 0000000000..9cfb539152
--- /dev/null
+++ b/testsuite/tests/backpack/reexport/bkpreex07.bkp
@@ -0,0 +1,3 @@
+unit p where
+    signature A(module Prelude) where
+        import Prelude
diff --git a/testsuite/tests/backpack/reexport/bkpreex07.stderr b/testsuite/tests/backpack/reexport/bkpreex07.stderr
new file mode 100644
index 0000000000..4852528959
--- /dev/null
+++ b/testsuite/tests/backpack/reexport/bkpreex07.stderr
@@ -0,0 +1,2 @@
+[1 of 1] Processing p
+  [1 of 1] Compiling A[sig]           ( p/A.hsig, nothing )
diff --git a/testsuite/tests/backpack/reexport/bkpreex08.bkp b/testsuite/tests/backpack/reexport/bkpreex08.bkp
new file mode 100644
index 0000000000..596e5ea034
--- /dev/null
+++ b/testsuite/tests/backpack/reexport/bkpreex08.bkp
@@ -0,0 +1,17 @@
+unit q where
+    module B where
+        f = 2 :: Int
+unit p2 where
+    dependency q
+    signature A(f) where
+        import B
+unit p where
+    dependency q
+    dependency p2[A=<A>]
+    signature A(module A, module Prelude) where
+        import Prelude
+        f :: Int
+    module M where
+        import B
+        import A
+        g = f
diff --git a/testsuite/tests/backpack/reexport/bkpreex08.stderr b/testsuite/tests/backpack/reexport/bkpreex08.stderr
new file mode 100644
index 0000000000..41983efaed
--- /dev/null
+++ b/testsuite/tests/backpack/reexport/bkpreex08.stderr
@@ -0,0 +1,8 @@
+[1 of 3] Processing q
+  Instantiating q
+  [1 of 1] Compiling B                ( q/B.hs, nothing )
+[2 of 3] Processing p2
+  [1 of 1] Compiling A[sig]           ( p2/A.hsig, nothing )
+[3 of 3] Processing p
+  [1 of 2] Compiling A[sig]           ( p/A.hsig, nothing )
+  [2 of 2] Compiling M                ( p/M.hs, nothing )
diff --git a/testsuite/tests/backpack/reexport/bkpreex09.bkp b/testsuite/tests/backpack/reexport/bkpreex09.bkp
new file mode 100644
index 0000000000..5b16c44875
--- /dev/null
+++ b/testsuite/tests/backpack/reexport/bkpreex09.bkp
@@ -0,0 +1,10 @@
+unit p where
+    signature A where
+        f :: Bool
+unit q where
+    dependency p[A=<A>]
+    signature A(module A) where
+        h :: Bool
+    module M where
+        import A
+        g = f && h
diff --git a/testsuite/tests/backpack/reexport/bkpreex09.stderr b/testsuite/tests/backpack/reexport/bkpreex09.stderr
new file mode 100644
index 0000000000..d4bedc39f5
--- /dev/null
+++ b/testsuite/tests/backpack/reexport/bkpreex09.stderr
@@ -0,0 +1,5 @@
+[1 of 2] Processing p
+  [1 of 1] Compiling A[sig]           ( p/A.hsig, nothing )
+[2 of 2] Processing q
+  [1 of 2] Compiling A[sig]           ( q/A.hsig, nothing )
+  [2 of 2] Compiling M                ( q/M.hs, nothing )
diff --git a/testsuite/tests/backpack/reexport/bkpreex10.bkp b/testsuite/tests/backpack/reexport/bkpreex10.bkp
new file mode 100644
index 0000000000..4b00e57b5e
--- /dev/null
+++ b/testsuite/tests/backpack/reexport/bkpreex10.bkp
@@ -0,0 +1,10 @@
+{-# LANGUAGE ConstraintKinds #-}
+unit p where
+    signature A(module Data.Typeable) where
+        import Data.Typeable
+unit q where
+    dependency p[A=<A>]
+    signature A(module A) where
+    module M where
+        import A
+        type X = Typeable
diff --git a/testsuite/tests/backpack/reexport/bkpreex10.stderr b/testsuite/tests/backpack/reexport/bkpreex10.stderr
new file mode 100644
index 0000000000..d4bedc39f5
--- /dev/null
+++ b/testsuite/tests/backpack/reexport/bkpreex10.stderr
@@ -0,0 +1,5 @@
+[1 of 2] Processing p
+  [1 of 1] Compiling A[sig]           ( p/A.hsig, nothing )
+[2 of 2] Processing q
+  [1 of 2] Compiling A[sig]           ( q/A.hsig, nothing )
+  [2 of 2] Compiling M                ( q/M.hs, nothing )
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