Crash when exporting record selectors of data family instances

This fixes bug #294.

This also fixes a related but never-before-mentioned bug about the
display of GADT record selectors with non-polymorphic type signatures.

Note: Associated data type constructors fail to show up if nothing is
exported that they could be attached to. Exporting any of the data types
in the instance head, or the class + data family itself, causes them to
show up, but in the absence of either of these, exporting just the
associated data type with the constructor itself will result in it
being hidden.

The only scenario I can come up that would involve this kind of
situation involved OverlappingInstances, and even then it can be
mitigated by just exporting the class itself, so I'm not going to solve
it since the logic would most likely be very complicated.

1 files changed, 24 insertions, 10 deletions

diff --git a/src/Haddock/Interface/Create.hs b/src/Haddock/Interface/Create.hs
index f1262d9f..fb1038f2 100644
--- a/src/Haddock/Interface/Create.hs
+++ b/src/Haddock/Interface/Create.hs
@@ -767,21 +767,33 @@ extractDecl name mdl decl
   | name `elem` getMainDeclBinder (unLoc decl) = decl
   | otherwise  =
     case unLoc decl of
-      TyClD d | isClassDecl d ->
+      TyClD d@ClassDecl {} ->
         let matches = [ sig | sig <- tcdSigs d, name `elem` sigName sig,
                         isVanillaLSig sig ] -- TODO: document fixity
         in case matches of
-          [s0] -> let (n, tyvar_names) = name_and_tyvars d
+          [s0] -> let (n, tyvar_names) = (tcdName d, getTyVars d)
                       L pos sig = extractClassDecl n tyvar_names s0
                   in L pos (SigD sig)
-          _ -> error "internal: extractDecl"
-      TyClD d | isDataDecl d ->
-        let (n, tyvar_names) = name_and_tyvars d
-            L pos sig = extractRecSel name mdl n tyvar_names (dd_cons (tcdDataDefn d))
-        in L pos (SigD sig)
+          _ -> error "internal: extractDecl (ClassDecl)"
+      TyClD d@DataDecl {} ->
+        let (n, tyvar_names) = (tcdName d, map toTypeNoLoc $ getTyVars d)
+        in SigD <$> extractRecSel name mdl n tyvar_names (dd_cons (tcdDataDefn d))
+      InstD (DataFamInstD DataFamInstDecl { dfid_tycon = L _ n
+                                          , dfid_pats = HsWB { hswb_cts = tys }
+                                          , dfid_defn = defn }) ->
+        SigD <$> extractRecSel name mdl n tys (dd_cons defn)
+      InstD (ClsInstD ClsInstDecl { cid_datafam_insts = insts }) ->
+        let matches = [ d | L _ d <- insts
+                          , L _ ConDecl { con_details = RecCon rec } <- dd_cons (dfid_defn d)
+                          , ConDeclField { cd_fld_name = L _ n } <- rec
+                          , n == name
+                      ]
+        in case matches of
+          [d0] -> extractDecl name mdl (noLoc . InstD $ DataFamInstD d0)
+          _ -> error "internal: extractDecl (ClsInstD)"
       _ -> error "internal: extractDecl"
   where
-    name_and_tyvars d = (tcdName d, hsLTyVarLocNames (tyClDeclTyVars d))
+    getTyVars = hsLTyVarLocNames . tyClDeclTyVars
 
 
 toTypeNoLoc :: Located Name -> LHsType Name
@@ -799,7 +811,7 @@ extractClassDecl c tvs0 (L pos (TypeSig lname ltype)) = case ltype of
 extractClassDecl _ _ _ = error "extractClassDecl: unexpected decl"
 
 
-extractRecSel :: Name -> Module -> Name -> [Located Name] -> [LConDecl Name]
+extractRecSel :: Name -> Module -> Name -> [LHsType Name] -> [LConDecl Name]
               -> LSig Name
 extractRecSel _ _ _ _ [] = error "extractRecSel: selector not found"
 
@@ -810,7 +822,9 @@ extractRecSel nm mdl t tvs (L _ con : rest) =
     _ -> extractRecSel nm mdl t tvs rest
  where
   matching_fields flds = [ f | f@(ConDeclField n _ _) <- flds, unLoc n == nm ]
-  data_ty = foldl (\x y -> noLoc (HsAppTy x y)) (noLoc (HsTyVar t)) (map toTypeNoLoc tvs)
+  data_ty
+    | ResTyGADT ty <- con_res con = ty
+    | otherwise = foldl' (\x y -> noLoc (HsAppTy x y)) (noLoc (HsTyVar t)) tvs
 
 
 -- | Keep export items with docs.