More explicit foralls (GHC Proposal 0007)

Allow the user to explicitly bind type/kind variables in type and data
family instances (including associated instances), closed type family
equations, and RULES pragmas. Follows the specification of GHC
Proposal 0007, also fixes #2600. Advised by Richard Eisenberg.

This modifies the Template Haskell AST -- old code may break!

Other Changes:
- convert HsRule to a record
- make rnHsSigWcType more general
- add repMaybe to DsMeta

Includes submodule update for Haddock.

Test Plan: validate

Reviewers: goldfire, bgamari, alanz

Subscribers: simonpj, RyanGlScott, goldfire, rwbarton,
             thomie, mpickering, carter

GHC Trac Issues: #2600, #14268

Differential Revision: https://phabricator.haskell.org/D4894

1 files changed, 35 insertions, 0 deletions

diff --git a/testsuite/tests/th/TH_reifyExplicitForAllFams.hs b/testsuite/tests/th/TH_reifyExplicitForAllFams.hs
new file mode 100644
index 0000000000..60a6d4563f
--- /dev/null
+++ b/testsuite/tests/th/TH_reifyExplicitForAllFams.hs
@@ -0,0 +1,35 @@
+-- test reification of explicit foralls in type families
+
+{-# LANGUAGE TypeFamilies, ExplicitForAll #-}
+module TH_reifyExplicitForAllFams where
+
+import System.IO
+import Language.Haskell.TH
+import Text.PrettyPrint.HughesPJ
+
+import Data.Proxy
+import Data.Kind
+
+$([d| data family F a
+      data instance forall a. F (Maybe a) = MkF a |])
+
+$([d| class C a where
+        type G a b
+      instance forall a. C [a] where
+        type forall b. G [a] b = Proxy b |])
+
+$([d| type family H a b where
+        forall x y. H [x] (Proxy y) = Either x y
+        forall z.   H z   z         = Maybe z |])
+
+$(return [])
+
+test :: ()
+test = $(let
+      display :: Name -> Q ()
+      display q = do { i <- reify q; runIO $ hPutStrLn stderr (pprint i) }
+    in do { display ''F
+          ; display ''C
+          ; display ''G
+          ; display ''H
+          ; [| () |] })