Use IfaceAppArgs to store an IfaceAppTy's arguments

Summary:
Currently, an `IfaceAppTy` has no way to tell whether its
argument is visible or not, so it simply treats all arguments as
visible, leading to #15330. We already have a solution for this
problem in the form of the `IfaceTcArgs` data structure, used by
`IfaceTyConApp` to represent the arguments to a type constructor.
Therefore, it makes sense to reuse this machinery for `IfaceAppTy`,
so this patch does just that.

This patch:

1. Renames `IfaceTcArgs` to `IfaceAppArgs` to reflect its more
   general purpose.
2. Changes the second field of `IfaceAppTy` from `IfaceType` to
   `IfaceAppArgs`, and propagates the necessary changes through. In
   particular, pretty-printing an `IfaceAppTy` now goes through the
   `IfaceAppArgs` pretty-printer, which correctly displays arguments
   as visible or not for free, fixing #15330.
3. Changes `toIfaceTypeX` and related functions so that when
   converting an `AppTy` to an `IfaceAppTy`, it flattens as many
   argument `AppTy`s as possible, and then converts those arguments
   into an `IfaceAppArgs` list, using the kind of the function
   `Type` as a guide. (Doing so minimizes the number of times we need
   to call `typeKind`, which is more expensive that finding the kind
   of a `TyCon`.)

Test Plan: make test TEST=T15330

Reviewers: goldfire, simonpj, bgamari

Reviewed By: simonpj

Subscribers: rwbarton, thomie, carter

GHC Trac Issues: #15330

Differential Revision: https://phabricator.haskell.org/D4938

1 files changed, 9 insertions, 9 deletions

diff --git a/compiler/backpack/RnModIface.hs b/compiler/backpack/RnModIface.hs
index 6b958df760..51f312f975 100644
--- a/compiler/backpack/RnModIface.hs
+++ b/compiler/backpack/RnModIface.hs
@@ -512,7 +512,7 @@ rnIfaceTyConParent :: Rename IfaceTyConParent
 rnIfaceTyConParent (IfDataInstance n tc args)
     = IfDataInstance <$> rnIfaceGlobal n
                      <*> rnIfaceTyCon tc
-                     <*> rnIfaceTcArgs args
+                     <*> rnIfaceAppArgs args
 rnIfaceTyConParent IfNoParent = pure IfNoParent
 
 rnIfaceConDecls :: Rename IfaceConDecls
@@ -557,7 +557,7 @@ rnMaybeDefMethSpec mb = return mb
 rnIfaceAxBranch :: Rename IfaceAxBranch
 rnIfaceAxBranch d = do
     ty_vars <- mapM rnIfaceTvBndr (ifaxbTyVars d)
-    lhs <- rnIfaceTcArgs (ifaxbLHS d)
+    lhs <- rnIfaceAppArgs (ifaxbLHS d)
     rhs <- rnIfaceType (ifaxbRHS d)
     return d { ifaxbTyVars = ty_vars
              , ifaxbLHS = lhs
@@ -693,16 +693,16 @@ rnIfaceType :: Rename IfaceType
 rnIfaceType (IfaceFreeTyVar n) = pure (IfaceFreeTyVar n)
 rnIfaceType (IfaceTyVar   n)   = pure (IfaceTyVar n)
 rnIfaceType (IfaceAppTy t1 t2)
-    = IfaceAppTy <$> rnIfaceType t1 <*> rnIfaceType t2
+    = IfaceAppTy <$> rnIfaceType t1 <*> rnIfaceAppArgs t2
 rnIfaceType (IfaceLitTy l)         = return (IfaceLitTy l)
 rnIfaceType (IfaceFunTy t1 t2)
     = IfaceFunTy <$> rnIfaceType t1 <*> rnIfaceType t2
 rnIfaceType (IfaceDFunTy t1 t2)
     = IfaceDFunTy <$> rnIfaceType t1 <*> rnIfaceType t2
 rnIfaceType (IfaceTupleTy s i tks)
-    = IfaceTupleTy s i <$> rnIfaceTcArgs tks
+    = IfaceTupleTy s i <$> rnIfaceAppArgs tks
 rnIfaceType (IfaceTyConApp tc tks)
-    = IfaceTyConApp <$> rnIfaceTyCon tc <*> rnIfaceTcArgs tks
+    = IfaceTyConApp <$> rnIfaceTyCon tc <*> rnIfaceAppArgs tks
 rnIfaceType (IfaceForAllTy tv t)
     = IfaceForAllTy <$> rnIfaceForAllBndr tv <*> rnIfaceType t
 rnIfaceType (IfaceCoercionTy co)
@@ -713,7 +713,7 @@ rnIfaceType (IfaceCastTy ty co)
 rnIfaceForAllBndr :: Rename IfaceForAllBndr
 rnIfaceForAllBndr (TvBndr tv vis) = TvBndr <$> rnIfaceTvBndr tv <*> pure vis
 
-rnIfaceTcArgs :: Rename IfaceTcArgs
-rnIfaceTcArgs (ITC_Invis t ts) = ITC_Invis <$> rnIfaceType t <*> rnIfaceTcArgs ts
-rnIfaceTcArgs (ITC_Vis t ts) = ITC_Vis <$> rnIfaceType t <*> rnIfaceTcArgs ts
-rnIfaceTcArgs ITC_Nil = pure ITC_Nil
+rnIfaceAppArgs :: Rename IfaceAppArgs
+rnIfaceAppArgs (IA_Invis t ts) = IA_Invis <$> rnIfaceType t <*> rnIfaceAppArgs ts
+rnIfaceAppArgs (IA_Vis t ts) = IA_Vis <$> rnIfaceType t <*> rnIfaceAppArgs ts
+rnIfaceAppArgs IA_Nil = pure IA_Nil