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, 8 insertions, 2 deletions

diff --git a/compiler/utils/Util.hs b/compiler/utils/Util.hs
index 687ced2f47..5f66b53171 100644
--- a/compiler/utils/Util.hs
+++ b/compiler/utils/Util.hs
@@ -56,7 +56,7 @@ module Util (
 
         -- * List operations controlled by another list
         takeList, dropList, splitAtList, split,
-        dropTail,
+        dropTail, capitalise,
 
         -- * For loop
         nTimes,
@@ -147,7 +147,7 @@ import System.IO.Error as IO ( isDoesNotExistError )
 import System.Directory ( doesDirectoryExist, getModificationTime )
 import System.FilePath
 
-import Data.Char        ( isUpper, isAlphaNum, isSpace, chr, ord, isDigit )
+import Data.Char        ( isUpper, isAlphaNum, isSpace, chr, ord, isDigit, toUpper)
 import Data.Int
 import Data.Ratio       ( (%) )
 import Data.Ord         ( comparing )
@@ -720,6 +720,12 @@ split c s = case rest of
                 _:rest -> chunk : split c rest
   where (chunk, rest) = break (==c) s
 
+-- | Convert a word to title case by capitalising the first letter
+capitalise :: String -> String
+capitalise [] = []
+capitalise (c:cs) = toUpper c : cs
+
+
 {-
 ************************************************************************
 *                                                                      *