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, 7 insertions, 14 deletions

diff --git a/testsuite/tests/indexed-types/should_compile/T3017.stderr b/testsuite/tests/indexed-types/should_compile/T3017.stderr
index 20190471ae..a6c744a177 100644
--- a/testsuite/tests/indexed-types/should_compile/T3017.stderr
+++ b/testsuite/tests/indexed-types/should_compile/T3017.stderr
@@ -3,24 +3,17 @@ TYPE SIGNATURES
   test2 ::
     forall c t t1. (Coll c, Num t1, Num t, Elem c ~ (t, t1)) => c -> c
 TYPE CONSTRUCTORS
-  Coll :: * -> Constraint
-  class Coll c
-    Roles: [nominal]
-    RecFlag NonRecursive
-    type family Elem c :: * (open)
-    empty :: c insert :: Elem c -> c -> c
-  ListColl :: * -> *
-  data ListColl a
-    No C type associated
-    Roles: [representational]
-    RecFlag NonRecursive, Promotable
-    = L :: [a] -> ListColl a Stricts: _
-    FamilyInstance: none
+  class Coll c where
+    type family Elem c :: * open
+    empty :: c
+    insert :: Elem c -> c -> c
+  data ListColl a = L [a]
+    Promotable
 COERCION AXIOMS
   axiom Foo.TFCo:R:ElemListColl :: Elem (ListColl a) = a
 INSTANCES
   instance Coll (ListColl a) -- Defined at T3017.hs:12:11
 FAMILY INSTANCES
-  type Elem (ListColl a) -- Defined at T3017.hs:13:4
+  type Elem (ListColl a)
 Dependent modules: []
 Dependent packages: [base, ghc-prim, integer-gmp]