Do pretty-printing of TyThings via IfaceDecl (Trac #7730)

All the initial work on this was done fy 'archblob' (fcsernik@gmail.com);
thank you!

I reviewed the patch, started some tidying, up and then ended up in a huge
swamp of changes, not all of which I can remember now.  But:

* To suppress kind arguments when we have -fno-print-explicit-kinds,
    - IfaceTyConApp argument types are in a tagged list IfaceTcArgs

* To allow overloaded types to be printed with =>, add IfaceDFunTy to IfaceType.

* When printing data/type family instances for the user, I've made them
  print out an informative RHS, which is a new feature. Thus
        ghci> info T
        data family T a
        data instance T Int = T1 Int Int
        data instance T Bool = T2

* In implementation terms, pprIfaceDecl has just one "context" argument,
  of type IfaceSyn.ShowSub, which says
       - How to print the binders of the decl
         see note [Printing IfaceDecl binders] in IfaceSyn
       - Which sub-comoponents (eg constructors) to print

* Moved FastStringEnv from RnEnv to OccName

It all took a ridiculously long time to do.  But it's done!

1 files changed, 15 insertions, 49 deletions

diff --git a/testsuite/tests/roles/should_compile/Roles1.stderr b/testsuite/tests/roles/should_compile/Roles1.stderr
index de4ecf36e2..96d5603bbf 100644
--- a/testsuite/tests/roles/should_compile/Roles1.stderr
+++ b/testsuite/tests/roles/should_compile/Roles1.stderr
@@ -1,54 +1,20 @@
 TYPE SIGNATURES
 TYPE CONSTRUCTORS
-  T1 :: * -> *
-  data T1 a
-    No C type associated
-    Roles: [nominal]
-    RecFlag NonRecursive, Promotable
-    = K1 :: forall a. a -> T1 a Stricts: _
-    FamilyInstance: none
-  T2 :: * -> *
-  data T2 a
-    No C type associated
-    Roles: [representational]
-    RecFlag NonRecursive, Promotable
-    = K2 :: forall a. a -> T2 a Stricts: _
-    FamilyInstance: none
-  T3 :: forall (k :: BOX). k -> *
-  data T3 (k::BOX) (a::k)
-    No C type associated
-    Roles: [nominal, phantom]
-    RecFlag NonRecursive, Not promotable
-    = K3 :: forall (k::BOX) (a::k). T3 k a
-    FamilyInstance: none
-  T4 :: (* -> *) -> * -> *
-  data T4 (a::* -> *) b
-    No C type associated
-    Roles: [nominal, nominal]
-    RecFlag NonRecursive, Not promotable
-    = K4 :: forall (a::* -> *) b. (a b) -> T4 a b Stricts: _
-    FamilyInstance: none
-  T5 :: * -> *
-  data T5 a
-    No C type associated
-    Roles: [representational]
-    RecFlag NonRecursive, Promotable
-    = K5 :: forall a. a -> T5 a Stricts: _
-    FamilyInstance: none
-  T6 :: forall (k :: BOX). k -> *
-  data T6 (k::BOX) (a::k)
-    No C type associated
-    Roles: [nominal, phantom]
-    RecFlag NonRecursive, Not promotable
-    = K6 :: forall (k::BOX) (a::k). T6 k a
-    FamilyInstance: none
-  T7 :: forall (k :: BOX). k -> * -> *
-  data T7 (k::BOX) (a::k) b
-    No C type associated
-    Roles: [nominal, phantom, representational]
-    RecFlag NonRecursive, Not promotable
-    = K7 :: forall (k::BOX) (a::k) b. b -> T7 k a b Stricts: _
-    FamilyInstance: none
+  type role T1 nominal
+  data T1 a = K1 a
+    Promotable
+  data T2 a = K2 a
+    Promotable
+  type role T3 phantom
+  data T3 (a :: k) = K3
+  type role T4 nominal nominal
+  data T4 (a :: * -> *) b = K4 (a b)
+  data T5 a = K5 a
+    Promotable
+  type role T6 phantom
+  data T6 (a :: k) = K6
+  type role T7 phantom representational
+  data T7 (a :: k) b = K7 b
 COERCION AXIOMS
 Dependent modules: []
 Dependent packages: [base, ghc-prim, integer-gmp]