Fix #1050 by filtering out invisible AppTy arguments

This makes the `synifyType` case for `AppTy` more intelligent by
taking into consideration the visibilities of each `AppTy` argument
and filtering out any invisible arguments, as they aren't intended
to be displayed in the source code. (See #1050 for an example of what
can happen if you fail to filter these out.)

Along the way, I noticed that a special `synifyType` case for
`AppTy t1 (CoercionTy {})` could be consolidated with the case below
it, so I took the opportunity to tidy this up.

1 files changed, 11 insertions, 0 deletions

diff --git a/html-test/src/Bug1050.hs b/html-test/src/Bug1050.hs
new file mode 100644
index 00000000..ea293e6e
--- /dev/null
+++ b/html-test/src/Bug1050.hs
@@ -0,0 +1,11 @@
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE RankNTypes #-}
+module Bug1050 where
+
+import Data.Kind
+
+newtype T :: (forall k. k -> Type) -> (forall k. k -> Type) where
+  MkT :: forall (f :: forall k. k -> Type) k (a :: k). f a -> T f a
+
+mkT = MkT