Preserve docs on type family instances (#867)

* Preserve docs on type family instances

The only problem was that the instance location was slightly off
for type family instances.

* Accept output

2 files changed, 8 insertions, 2 deletions

diff --git a/haddock-api/src/Haddock/Interface/Create.hs b/haddock-api/src/Haddock/Interface/Create.hs
index a35e2053..ced7cae5 100644
--- a/haddock-api/src/Haddock/Interface/Create.hs
+++ b/haddock-api/src/Haddock/Interface/Create.hs
@@ -419,9 +419,12 @@ mkMaps dflags pkgName gre instances decls = do
     instanceMap = M.fromList [ (getSrcSpan n, n) | n <- instances ]
 
     names :: SrcSpan -> HsDecl GhcRn -> [Name]
-    names l (InstD d) = maybeToList (M.lookup loc instanceMap) -- See note [2].
+    names _ (InstD d) = maybeToList (M.lookup loc instanceMap) -- See note [2].
       where loc = case d of
-              TyFamInstD _ -> l -- The CoAx's loc is the whole line, but only for TFs
+              -- The CoAx's loc is the whole line, but only for TFs. The
+              -- workaround is to dig into the family instance declaration and
+              -- get the identifier with the right location.
+              TyFamInstD (TyFamInstDecl d') -> getLoc (feqn_tycon (hsib_body d'))
               _ -> getInstLoc d
     names l (DerivD {}) = maybeToList (M.lookup l instanceMap) -- See note [2].
     names _ decl = getMainDeclBinder decl
diff --git a/haddock-api/src/Haddock/Types.hs b/haddock-api/src/Haddock/Types.hs
index 36ed7baf..5ef5a7b9 100644
--- a/haddock-api/src/Haddock/Types.hs
+++ b/haddock-api/src/Haddock/Types.hs
@@ -28,6 +28,7 @@ module Haddock.Types (
 import Control.Exception
 import Control.Arrow hiding ((<+>))
 import Control.DeepSeq
+import Control.Monad.IO.Class (MonadIO(..))
 import Data.Typeable
 import Data.Map (Map)
 import Data.Data (Data)
@@ -661,6 +662,8 @@ instance Monad ErrMsgGhc where
   m >>= k = WriterGhc $ runWriterGhc m >>= \ (a, msgs1) ->
                fmap (second (msgs1 ++)) (runWriterGhc (k a))
 
+instance MonadIO ErrMsgGhc where
+  liftIO m = WriterGhc (fmap (\x -> (x, [])) (liftIO m))
 
 -----------------------------------------------------------------------------
 -- * Pass sensitive types