Rework renaming of children in export lists.

The target of this patch is exports such as:

```
module Foo ( T(A, B, C) ) where
```

Essentially this patch makes sure that we use the correct lookup functions in order
to lookup the names in parent-children export lists. This change
highlighted the complexity of this small part of GHC which accounts for
the scale.

This change was motivated by wanting to
remove the `PatternSynonym` constructor from `Parent`. As with all these
things, it quickly spiraled out of control into a much larger refactor.

Reviewers: simonpj, goldfire, bgamari, austin

Subscribers: adamgundry, thomie

Differential Revision: https://phabricator.haskell.org/D2179

GHC Trac Issues: #11970

1 files changed, 19 insertions, 0 deletions

diff --git a/testsuite/tests/module/T11970.hs b/testsuite/tests/module/T11970.hs
new file mode 100644
index 0000000000..3c90c6913d
--- /dev/null
+++ b/testsuite/tests/module/T11970.hs
@@ -0,0 +1,19 @@
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE PatternSynonyms #-}
+
+module T11970(B(recSel), Foo((--.->)), C(C,P,x,Q, B, recSel)) where
+
+pattern D = Nothing
+
+newtype B = B { recSel :: Int }
+
+class Foo a where
+  type (--.->) a
+
+newtype C = C Int
+
+pattern P x = C x
+
+pattern Q{x} = C x