Comments on instances

Implementing this was a little trickier than I thought, since we need to match
up instances from the renamed syntax with instances represented by
InstEnv.Instance. This is due to the current design of Haddock, which matches
comments with declarations from the renamed syntax, while getting the list of
instances of a class/family directly using the GHC API.

- Works for class instances only (Haddock has no support for type family
  instances yet)
- The comments are rendered to the right of the instance head in the HTML output
- No change to the .haddock file format
- Works for normal user-written instances only. No comments are added on
  derived or TH-generated instances

1 files changed, 12 insertions, 3 deletions

diff --git a/src/Haddock/Interface/Rename.hs b/src/Haddock/Interface/Rename.hs
index 5eac9e67..308c86c5 100644
--- a/src/Haddock/Interface/Rename.hs
+++ b/src/Haddock/Interface/Rename.hs
@@ -37,8 +37,13 @@ renameInterface renamingEnv warnings iface =
   let localEnv = foldl fn renamingEnv (ifaceVisibleExports iface)
         where fn env name = Map.insert name (ifaceMod iface) env
 
-      docMap = Map.map (\(_,x,_) -> x) (ifaceDeclMap iface)
-      docs   = Map.toList docMap
+      docMap   = Map.map (\(_,x,_) -> x) (ifaceDeclMap iface)
+
+      -- make instance docs into 'docForDecls'
+      instDocs = [ (name, (Just doc, Map.empty))
+                 | (name, doc) <- Map.toList (ifaceInstanceDocMap iface) ]
+
+      docs     = Map.toList docMap ++ instDocs
       renameMapElem (k,d) = do d' <- renameDocForDecl d; return (k, d')
 
       -- rename names in the exported declarations to point to things that
@@ -448,7 +453,11 @@ renameExportItem item = case item of
     decl' <- renameLDecl decl
     doc'  <- renameDocForDecl doc
     subs' <- mapM renameSub subs
-    instances' <- mapM renameInstHead instances
+    instances' <- forM instances $ \(name, inst, idoc) -> do
+      name' <- rename name
+      inst' <- renameInstHead inst
+      idoc' <- mapM renameDoc idoc
+      return (name', inst', idoc')
     return (ExportDecl decl' doc' subs' instances')
   ExportNoDecl x subs -> do
     x'    <- lookupRn id x