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!

7 files changed, 69 insertions, 148 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]
diff --git a/testsuite/tests/roles/should_compile/Roles14.stderr b/testsuite/tests/roles/should_compile/Roles14.stderr
index 13231931e3..e0f26a14d3 100644
--- a/testsuite/tests/roles/should_compile/Roles14.stderr
+++ b/testsuite/tests/roles/should_compile/Roles14.stderr
@@ -1,9 +1,7 @@
 TYPE SIGNATURES
 TYPE CONSTRUCTORS
-  C2 :: * -> Constraint
-  class C2 a
-    Roles: [representational]
-    RecFlag NonRecursive
+  type role C2 representational
+  class C2 a where
     meth2 :: a -> a
 COERCION AXIOMS
   axiom Roles12.NTCo:C2 :: C2 a = a -> a
diff --git a/testsuite/tests/roles/should_compile/Roles2.stderr b/testsuite/tests/roles/should_compile/Roles2.stderr
index f5bcbe6829..e6f9bcd8d0 100644
--- a/testsuite/tests/roles/should_compile/Roles2.stderr
+++ b/testsuite/tests/roles/should_compile/Roles2.stderr
@@ -1,19 +1,7 @@
 TYPE SIGNATURES
 TYPE CONSTRUCTORS
-  T1 :: * -> *
-  data T1 a
-    No C type associated
-    Roles: [representational]
-    RecFlag NonRecursive, Not promotable
-    = K1 :: forall a. (IO a) -> T1 a Stricts: _
-    FamilyInstance: none
-  T2 :: * -> *
-  data T2 a
-    No C type associated
-    Roles: [representational]
-    RecFlag NonRecursive, Not promotable
-    = K2 :: forall a. (FunPtr a) -> T2 a Stricts: _
-    FamilyInstance: none
+  data T1 a = K1 (IO a)
+  data T2 a = K2 (FunPtr a)
 COERCION AXIOMS
 Dependent modules: []
 Dependent packages: [base, ghc-prim, integer-gmp]
diff --git a/testsuite/tests/roles/should_compile/Roles3.stderr b/testsuite/tests/roles/should_compile/Roles3.stderr
index 62eb2a9474..270afca9cd 100644
--- a/testsuite/tests/roles/should_compile/Roles3.stderr
+++ b/testsuite/tests/roles/should_compile/Roles3.stderr
@@ -1,31 +1,16 @@
 TYPE SIGNATURES
 TYPE CONSTRUCTORS
-  C1 :: * -> Constraint
-  class C1 a
-    Roles: [nominal]
-    RecFlag NonRecursive
+  class C1 a where
     meth1 :: a -> a
-  C2 :: * -> * -> Constraint
-  class C2 a b
-    Roles: [nominal, nominal]
-    RecFlag NonRecursive
-    meth2 :: (~) * a b -> a -> b
-  C3 :: * -> * -> Constraint
-  class C3 a b
-    Roles: [nominal, nominal]
-    RecFlag NonRecursive
-    type family F3 b :: * (open)
+  class C2 a b where
+    meth2 :: a ~ b => a -> b
+  class C3 a b where
+    type family F3 b :: * open
     meth3 :: a -> F3 b -> F3 b
-  C4 :: * -> * -> Constraint
-  class C4 a b
-    Roles: [nominal, nominal]
-    RecFlag NonRecursive
+  class C4 a b where
     meth4 :: a -> F4 b -> F4 b
-  F4 :: * -> *
-  type family F4 a :: * (open)
-  Syn1 :: * -> *
+  type family F4 a :: * open
   type Syn1 a = F4 a
-  Syn2 :: * -> *
   type Syn2 a = [a]
 COERCION AXIOMS
   axiom Roles3.NTCo:C1 :: C1 a = a -> a
diff --git a/testsuite/tests/roles/should_compile/Roles4.stderr b/testsuite/tests/roles/should_compile/Roles4.stderr
index 32862ea073..f2b590fadd 100644
--- a/testsuite/tests/roles/should_compile/Roles4.stderr
+++ b/testsuite/tests/roles/should_compile/Roles4.stderr
@@ -1,16 +1,9 @@
 TYPE SIGNATURES
 TYPE CONSTRUCTORS
-  C1 :: * -> Constraint
-  class C1 a
-    Roles: [nominal]
-    RecFlag NonRecursive
+  class C1 a where
     meth1 :: a -> a
-  C3 :: * -> Constraint
-  class C3 a
-    Roles: [nominal]
-    RecFlag NonRecursive
+  class C3 a where
     meth3 :: a -> Syn1 a
-  Syn1 :: * -> *
   type Syn1 a = [a]
 COERCION AXIOMS
   axiom Roles4.NTCo:C1 :: C1 a = a -> a
diff --git a/testsuite/tests/roles/should_compile/T8958.stderr b/testsuite/tests/roles/should_compile/T8958.stderr
index 919530bb03..d400b9190c 100644
--- a/testsuite/tests/roles/should_compile/T8958.stderr
+++ b/testsuite/tests/roles/should_compile/T8958.stderr
@@ -1,49 +1,40 @@
-

-T8958.hs:1:31: Warning:

-    -XDatatypeContexts is deprecated: It was widely considered a misfeature, and has been removed from the Haskell language.

-TYPE SIGNATURES

-TYPE CONSTRUCTORS

-  Map :: * -> * -> *

-  newtype (Nominal k, Representational v) => Map k v

-    No C type associated

-    Roles: [nominal, representational]

-    RecFlag NonRecursive, Promotable

-    = MkMap :: [(k, v)] -> Map k v Stricts: _

-    FamilyInstance: none

-  Nominal :: * -> Constraint

-  class Nominal a

-    Roles: [nominal]

-    RecFlag NonRecursive

-  Representational :: * -> Constraint

-  class Representational a

-    Roles: [representational]

-    RecFlag NonRecursive

-COERCION AXIOMS

-  axiom T8958.NTCo:Map :: Map k v = [(k, v)]

-INSTANCES

-  instance [incoherent] Representational a

-    -- Defined at T8958.hs:10:10

-  instance [incoherent] Nominal a -- Defined at T8958.hs:7:10

-Dependent modules: []

-Dependent packages: [base, ghc-prim, integer-gmp]

-

-==================== Typechecker ====================

-AbsBinds [a] []

-  {Exports: [T8958.$fRepresentationala <= $dRepresentational

-               <>]

-   Exported types: T8958.$fRepresentationala [InlPrag=[ALWAYS] CONLIKE]

-                     :: forall a. Representational a

-                   [LclIdX[DFunId],

-                    Str=DmdType,

-                    Unf=DFun: \ (@ a) -> T8958.D:Representational TYPE a]

-   Binds: $dRepresentational = T8958.D:Representational}

-AbsBinds [a] []

-  {Exports: [T8958.$fNominala <= $dNominal

-               <>]

-   Exported types: T8958.$fNominala [InlPrag=[ALWAYS] CONLIKE]

-                     :: forall a. Nominal a

-                   [LclIdX[DFunId],

-                    Str=DmdType,

-                    Unf=DFun: \ (@ a) -> T8958.D:Nominal TYPE a]

-   Binds: $dNominal = T8958.D:Nominal}

-

+
+T8958.hs:1:31: Warning:
+    -XDatatypeContexts is deprecated: It was widely considered a misfeature, and has been removed from the Haskell language.
+TYPE SIGNATURES
+TYPE CONSTRUCTORS
+  type role Map nominal representational
+  newtype (Nominal k, Representational v) => Map k v = MkMap [(k, v)]
+    Promotable
+  class Nominal a
+  type role Representational representational
+  class Representational a
+COERCION AXIOMS
+  axiom T8958.NTCo:Map :: Map k v = [(k, v)]
+INSTANCES
+  instance [incoherent] Representational a
+    -- Defined at T8958.hs:10:10
+  instance [incoherent] Nominal a -- Defined at T8958.hs:7:10
+Dependent modules: []
+Dependent packages: [base, ghc-prim, integer-gmp]
+
+==================== Typechecker ====================
+AbsBinds [a] []
+  {Exports: [T8958.$fRepresentationala <= $dRepresentational
+               <>]
+   Exported types: T8958.$fRepresentationala [InlPrag=[ALWAYS] CONLIKE]
+                     :: forall a. Representational a
+                   [LclIdX[DFunId],
+                    Str=DmdType,
+                    Unf=DFun: \ (@ a) -> T8958.D:Representational TYPE a]
+   Binds: $dRepresentational = T8958.D:Representational}
+AbsBinds [a] []
+  {Exports: [T8958.$fNominala <= $dNominal
+               <>]
+   Exported types: T8958.$fNominala [InlPrag=[ALWAYS] CONLIKE]
+                     :: forall a. Nominal a
+                   [LclIdX[DFunId],
+                    Str=DmdType,
+                    Unf=DFun: \ (@ a) -> T8958.D:Nominal TYPE a]
+   Binds: $dNominal = T8958.D:Nominal}
+
diff --git a/testsuite/tests/roles/should_fail/Roles12.stderr b/testsuite/tests/roles/should_fail/Roles12.stderr
index bb830beae3..9b0f2cfdb5 100644
--- a/testsuite/tests/roles/should_fail/Roles12.stderr
+++ b/testsuite/tests/roles/should_fail/Roles12.stderr
@@ -4,4 +4,4 @@ Roles12.hs:5:1:
     and its hs-boot file
     Main module: type role T phantom
                  data T a
-    Boot file:   data T a
+    Boot file:   abstract T a