Display minimal complete definitions for type classes

This corresponds to the new {-# MINIMAL #-} pragma present in GHC 7.8+.
I also cleaned up some of the places in which ExportDecl is used to make
adding fields easier in the future.

Lots of test cases have been updated since they now render with
minimality information.

9 files changed, 78 insertions, 30 deletions

diff --git a/src/Haddock/Backends/Hoogle.hs b/src/Haddock/Backends/Hoogle.hs
index 6405861d..628e1cd0 100644
--- a/src/Haddock/Backends/Hoogle.hs
+++ b/src/Haddock/Backends/Hoogle.hs
@@ -110,7 +110,10 @@ operator x = x
 -- How to print each export
 
 ppExport :: DynFlags -> ExportItem Name -> [String]
-ppExport dflags (ExportDecl decl dc subdocs _ _ _) = ppDocumentation dflags (fst dc) ++ f (unL decl)
+ppExport dflags ExportDecl { expItemDecl    = L _ decl
+                           , expItemMbDoc   = (dc, _)
+                           , expItemSubDocs = subdocs
+                           } = ppDocumentation dflags dc ++ f decl
     where
         f (TyClD d@DataDecl{})  = ppData dflags d subdocs
         f (TyClD d@SynDecl{})   = ppSynonym dflags d
@@ -139,6 +142,7 @@ ppClass dflags x = out dflags x{tcdSigs=[]} :
             concatMap (ppSig dflags . addContext . unL) (tcdSigs x)
     where
         addContext (TypeSig name (L l sig)) = TypeSig name (L l $ f sig)
+        addContext (MinimalSig sig) = MinimalSig sig
         addContext _ = error "expected TypeSig"
 
         f (HsForAllTy a b con d) = HsForAllTy a b (reL (context : unLoc con)) d
diff --git a/src/Haddock/Backends/LaTeX.hs b/src/Haddock/Backends/LaTeX.hs
index 44b3fc35..7b72c030 100644
--- a/src/Haddock/Backends/LaTeX.hs
+++ b/src/Haddock/Backends/LaTeX.hs
@@ -177,7 +177,7 @@ string_txt (LStr s1 _) s2 = unpackLitString s1 ++ s2
 
 
 exportListItem :: ExportItem DocName -> LaTeX
-exportListItem (ExportDecl decl _doc subdocs _insts _fixities _splice)
+exportListItem ExportDecl { expItemDecl = decl, expItemSubDocs = subdocs }
   = sep (punctuate comma . map ppDocBinder $ declNames decl) <>
      case subdocs of
        [] -> empty
@@ -211,8 +211,8 @@ processExports (e : es) =
 
 
 isSimpleSig :: ExportItem DocName -> Maybe ([DocName], HsType DocName)
-isSimpleSig (ExportDecl (L _ (SigD (TypeSig lnames (L _ t))))
-                        (Documentation Nothing Nothing, argDocs) _ _ _ _)
+isSimpleSig ExportDecl { expItemDecl = L _ (SigD (TypeSig lnames (L _ t)))
+                       , expItemMbDoc = (Documentation Nothing Nothing, argDocs) }
   | Map.null argDocs = Just (map unLoc lnames, t)
 isSimpleSig _ = Nothing
 
diff --git a/src/Haddock/Backends/Xhtml.hs b/src/Haddock/Backends/Xhtml.hs
index 5e728108..9628a33d 100644
--- a/src/Haddock/Backends/Xhtml.hs
+++ b/src/Haddock/Backends/Xhtml.hs
@@ -533,7 +533,7 @@ ifaceToHtml maybe_source_url maybe_wiki_url iface unicode qual
 
     -- todo: if something has only sub-docs, or fn-args-docs, should
     -- it be measured here and thus prevent omitting the synopsis?
-    has_doc (ExportDecl _ (Documentation mDoc mWarning, _) _ _ _ _) = isJust mDoc || isJust mWarning
+    has_doc ExportDecl { expItemMbDoc = (Documentation mDoc mWarning, _) } = isJust mDoc || isJust mWarning
     has_doc (ExportNoDecl _ _) = False
     has_doc (ExportModule _) = False
     has_doc _ = True
@@ -578,7 +578,7 @@ miniSynopsis mdl iface unicode qual =
 
 processForMiniSynopsis :: Module -> Bool -> Qualification -> ExportItem DocName
                        -> [Html]
-processForMiniSynopsis mdl unicode qual (ExportDecl (L _loc decl0) _doc _ _insts _fixities _splice) =
+processForMiniSynopsis mdl unicode qual ExportDecl { expItemDecl = L _loc decl0 } =
   ((divTopDecl <<).(declElem <<)) <$> case decl0 of
     TyClD d -> let b = ppTyClBinderWithVarsMini mdl d in case d of
         (FamDecl decl)    -> [ppTyFamHeader True False decl unicode qual]
@@ -648,7 +648,7 @@ numberSectionHeadings = go 1
 
 processExport :: Bool -> LinksInfo -> Bool -> Qualification
               -> ExportItem DocName -> Maybe Html
-processExport _ _ _ _ (ExportDecl (L _ (InstD _)) _ _ _ _ _) = Nothing -- Hide empty instances
+processExport _ _ _ _ ExportDecl { expItemDecl = L _ (InstD _) } = Nothing -- Hide empty instances
 processExport summary _ _ qual (ExportGroup lev id0 doc)
   = nothingIf summary $ groupHeading lev id0 << docToHtml qual doc
 processExport summary links unicode qual (ExportDecl decl doc subdocs insts fixities splice)
diff --git a/src/Haddock/Backends/Xhtml/Decl.hs b/src/Haddock/Backends/Xhtml/Decl.hs
index cd504d8e..39276441 100644
--- a/src/Haddock/Backends/Xhtml/Decl.hs
+++ b/src/Haddock/Backends/Xhtml/Decl.hs
@@ -28,7 +28,7 @@ import Haddock.GhcUtils
 import Haddock.Types
 import Haddock.Doc (combineDocumentation)
 
-import           Data.List             ( intersperse )
+import           Data.List             ( intersperse, sort )
 import qualified Data.Map as Map
 import           Data.Maybe
 import           Data.Monoid           ( mempty )
@@ -37,6 +37,7 @@ import           Text.XHtml hiding     ( name, title, p, quote )
 import GHC
 import GHC.Exts
 import Name
+import BooleanFormula
 
 
 ppDecl :: Bool -> LinksInfo -> LHsDecl DocName
@@ -406,7 +407,7 @@ ppShortClassDecl :: Bool -> LinksInfo -> TyClDecl DocName -> SrcSpan
 ppShortClassDecl summary links (ClassDecl { tcdCtxt = lctxt, tcdLName = lname, tcdTyVars = tvs
                                           , tcdFDs = fds, tcdSigs = sigs, tcdATs = ats }) loc
     subdocs splice unicode qual =
-  if null sigs && null ats
+  if not (any isVanillaLSig sigs) && null ats
     then (if summary then id else topDeclElem links loc splice [nm]) hdr
     else (if summary then id else topDeclElem links loc splice [nm]) (hdr <+> keyword "where")
       +++ shortSubDecls
@@ -441,11 +442,11 @@ ppClassDecl summary links instances fixities loc d subdocs
             splice unicode qual
   | summary = ppShortClassDecl summary links decl loc subdocs splice unicode qual
   | otherwise = classheader +++ docSection qual d
-                  +++ atBit +++ methodBit  +++ instancesBit
+                  +++ minimalBit +++ atBit +++ methodBit +++ instancesBit
   where
     classheader
-      | null lsigs = topDeclElem links loc splice [nm] (hdr unicode qual <+> fixs)
-      | otherwise  = topDeclElem links loc splice [nm] (hdr unicode qual <+> keyword "where" <+> fixs)
+      | any isVanillaLSig lsigs = topDeclElem links loc splice [nm] (hdr unicode qual <+> keyword "where" <+> fixs)
+      | otherwise = topDeclElem links loc splice [nm] (hdr unicode qual <+> fixs)
 
     -- Only the fixity relevant to the class header
     fixs = ppFixities [ f | f@(n,_) <- fixities, n == unLoc lname ] qual
@@ -472,6 +473,23 @@ ppClassDecl summary links instances fixities loc d subdocs
                            -- there are different subdocs for different names in a single
                            -- type signature?
 
+    minimalBit = case [ s | L _ (MinimalSig s) <- lsigs ] of
+      -- Miminal complete definition = every method
+      And xs : _ | sort [getName n | Var (L _ n) <- xs] ==
+                   sort [getName n | L _ (TypeSig ns _) <- lsigs, L _ n <- ns]
+        -> noHtml
+
+      -- Minimal complete definition = nothing
+      And [] : _ -> subMinimal $ toHtml "Nothing"
+
+      m : _  -> subMinimal $ ppMinimal False m
+      _ -> noHtml
+
+    ppMinimal _ (Var (L _ n)) = ppDocName qual Prefix True n
+    ppMinimal _ (And fs) = foldr1 (\a b -> a+++", "+++b) $ map (ppMinimal True) fs
+    ppMinimal p (Or fs) = wrap $ foldr1 (\a b -> a+++" | "+++b) $ map (ppMinimal False) fs
+      where wrap | p = parens | otherwise = id
+
     instancesBit = ppInstances instances nm unicode qual
 
 ppClassDecl _ _ _ _ _ _ _ _ _ _ _ = error "declaration type not supported by ppShortClassDecl"
diff --git a/src/Haddock/Backends/Xhtml/Layout.hs b/src/Haddock/Backends/Xhtml/Layout.hs
index 6784fb30..d3d94424 100644
--- a/src/Haddock/Backends/Xhtml/Layout.hs
+++ b/src/Haddock/Backends/Xhtml/Layout.hs
@@ -33,6 +33,7 @@ module Haddock.Backends.Xhtml.Layout (
   subFields,
   subInstances,
   subMethods,
+  subMinimal,
 
   topDeclElem, declElem,
 ) where
@@ -182,6 +183,9 @@ subInstances qual nm = maybe noHtml wrap . instTable
 subMethods :: [Html] -> Html
 subMethods = divSubDecls "methods" "Methods" . subBlock
 
+subMinimal :: Html -> Html
+subMinimal = divSubDecls "minimal" "Minimal complete definition" . Just . declElem
+
 
 -- a box for displaying code
 declElem :: Html -> Html
diff --git a/src/Haddock/Convert.hs b/src/Haddock/Convert.hs
index 1245b2b9..1bf02e3c 100644
--- a/src/Haddock/Convert.hs
+++ b/src/Haddock/Convert.hs
@@ -73,8 +73,9 @@ tyThingToLHsDecl t = noLoc $ case t of
          , tcdFDs = map (\ (l,r) -> noLoc
                         (map getName l, map getName r) ) $
                          snd $ classTvsFds cl
-         , tcdSigs = map (noLoc . synifyIdSig DeleteTopLevelQuantification)
-                         (classMethods cl)
+         , tcdSigs = noLoc (MinimalSig . fmap noLoc $ classMinimalDef cl) :
+                      map (noLoc . synifyIdSig DeleteTopLevelQuantification)
+                        (classMethods cl)
          , tcdMeths = emptyBag --ignore default method definitions, they don't affect signature
          -- class associated-types are a subset of TyCon:
          , tcdATs = atFamDecls
diff --git a/src/Haddock/GhcUtils.hs b/src/Haddock/GhcUtils.hs
index bf6436d1..c06b34a6 100644
--- a/src/Haddock/GhcUtils.hs
+++ b/src/Haddock/GhcUtils.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE FlexibleInstances, ViewPatterns #-}
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 {-# OPTIONS_HADDOCK hide #-}
 -----------------------------------------------------------------------------
@@ -35,6 +35,7 @@ import GhcMonad (withSession)
 import HscTypes
 import UniqFM
 import GHC
+import Class
 
 
 moduleString :: Module -> String
@@ -114,6 +115,7 @@ filterSigNames :: (name -> Bool) -> Sig name -> Maybe (Sig name)
 filterSigNames p orig@(SpecSig n _ _)          = ifTrueJust (p $ unLoc n) orig
 filterSigNames p orig@(InlineSig n _)          = ifTrueJust (p $ unLoc n) orig
 filterSigNames p orig@(FixSig (FixitySig n _)) = ifTrueJust (p $ unLoc n) orig
+filterSigNames _ orig@(MinimalSig _)           = Just orig
 filterSigNames p (TypeSig ns ty)               =
   case filter (p . unLoc) ns of
     []       -> Nothing
@@ -279,6 +281,13 @@ modifySessionDynFlags f = do
 gbracket_ :: ExceptionMonad m => m a -> m b -> m c -> m c
 gbracket_ before_ after thing = gbracket before_ (const after) (const thing)
 
+-- Extract the minimal complete definition of a Name, if one exists
+minimalDef :: GhcMonad m => Name -> m (Maybe ClassMinimalDef)
+minimalDef n = do
+  mty <- lookupGlobalName n
+  case mty of
+    Just (ATyCon (tyConClass_maybe -> Just c)) -> return . Just $ classMinimalDef c
+    _ -> return Nothing
 
 -------------------------------------------------------------------------------
 -- * DynFlags
diff --git a/src/Haddock/Interface/Create.hs b/src/Haddock/Interface/Create.hs
index aef2cd8f..f1262d9f 100644
--- a/src/Haddock/Interface/Create.hs
+++ b/src/Haddock/Interface/Create.hs
@@ -437,7 +437,7 @@ filterClasses decls = [ if isClassD d then (L loc (filterClass d), doc) else x
                       | x@(L loc d, doc) <- decls ]
   where
     filterClass (TyClD c) =
-      TyClD $ c { tcdSigs = filter isVanillaLSig $ tcdSigs c }
+      TyClD $ c { tcdSigs = filter (liftA2 (||) isVanillaLSig isMinimalLSig) $ tcdSigs c }
     filterClass _ = error "expected TyClD"
 
 
@@ -547,17 +547,23 @@ mkExportItems
                    return []
 
               -- normal case
-              | otherwise -> return [ mkExportDecl t newDecl docs_ ]
-                  where
-                    -- A single signature might refer to many names, but we
-                    -- create an export item for a single name only.  So we
-                    -- modify the signature to contain only that single name.
-                    newDecl = case decl of
-                      (L loc (SigD sig)) ->
-                        L loc . SigD . fromJust $ filterSigNames (== t) sig
-                        -- fromJust is safe since we already checked in guards
-                        -- that 't' is a name declared in this declaration.
-                      _                  -> decl
+              | otherwise -> case decl of
+                  -- A single signature might refer to many names, but we
+                  -- create an export item for a single name only.  So we
+                  -- modify the signature to contain only that single name.
+                  L loc (SigD sig) ->
+                    -- fromJust is safe since we already checked in guards
+                    -- that 't' is a name declared in this declaration.
+                    let newDecl = L loc . SigD . fromJust $ filterSigNames (== t) sig
+                    in return [ mkExportDecl t newDecl docs_ ]
+
+                  L loc (TyClD cl@ClassDecl{}) -> do
+                    mdef <- liftGhcToErrMsgGhc $ minimalDef t
+                    let sig = maybeToList $ fmap (noLoc . MinimalSig . fmap noLoc) mdef
+                    return [ mkExportDecl t
+                      (L loc $ TyClD cl { tcdSigs = sig ++ tcdSigs cl }) docs_ ]
+
+                  _ -> return [ mkExportDecl t decl docs_ ]
 
         -- Declaration from another package
         ([], _) -> do
@@ -737,15 +743,20 @@ fullModuleContents dflags warnings gre (docMap, argMap, subMap, declMap, instMap
       | Just name <- M.lookup (getInstLoc d) instMap =
         let (doc, subs) = lookupDocs name warnings docMap argMap subMap in
         return $ Just (ExportDecl decl doc subs [] (fixities name subs) (l `elem` splices))
+    mkExportItem (L l (TyClD cl@ClassDecl{ tcdLName = L _ name, tcdSigs = sigs })) = do
+      mdef <- liftGhcToErrMsgGhc $ minimalDef name
+      let sig = maybeToList $ fmap (noLoc . MinimalSig . fmap noLoc) mdef
+      expDecl (L l (TyClD cl { tcdSigs = sig ++ sigs })) l name
     mkExportItem decl@(L l d)
-      | name:_ <- getMainDeclBinder d =
-        let (doc, subs) = lookupDocs name warnings docMap argMap subMap in
-        return $ Just (ExportDecl decl doc subs [] (fixities name subs) (l `elem` splices))
+      | name:_ <- getMainDeclBinder d = expDecl decl l name
       | otherwise = return Nothing
 
     fixities name subs = [ (n,f) | n <- name : map fst subs
                                  , Just f <- [M.lookup n fixMap] ]
 
+    expDecl decl l name = return $ Just (ExportDecl decl doc subs [] (fixities name subs) (l `elem` splices))
+      where (doc, subs) = lookupDocs name warnings docMap argMap subMap
+
 
 -- | Sometimes the declaration we want to export is not the "main" declaration:
 -- it might be an individual record selector or a class method.  In these
diff --git a/src/Haddock/Interface/Rename.hs b/src/Haddock/Interface/Rename.hs
index 4160f4f7..748e0210 100644
--- a/src/Haddock/Interface/Rename.hs
+++ b/src/Haddock/Interface/Rename.hs
@@ -414,6 +414,7 @@ renameSig sig = case sig of
   FixSig (FixitySig lname fixity) -> do
     lname' <- renameL lname
     return $ FixSig (FixitySig lname' fixity)
+  MinimalSig s -> MinimalSig <$> traverse renameL s
   -- we have filtered out all other kinds of signatures in Interface.Create
   _ -> error "expected TypeSig"