Merge branch 'type-constraints' of https://github.com/atom-haskell/ghc-mod into release-5.6.0.0

Language/Haskell/GhcMod/Gap.hs

@@ -44,6 +44,7 @@ module Language.Haskell.GhcMod.Gap (
   , Language.Haskell.GhcMod.Gap.isSynTyCon
   , parseModuleHeader
   , mkErrStyle'
+  , everythingStagedWithContext
   ) where
 
 import Control.Applicative hiding (empty)
@@ -115,6 +116,8 @@ import Lexer as L
 import Parser
 import SrcLoc
 import Packages
+import Data.Generics (GenericQ, extQ, gmapQ)
+import GHC.SYB.Utils (Stage(..))
 
 import Language.Haskell.GhcMod.Types (Expression(..))
 import Prelude
@@ -595,3 +598,20 @@ instance NFData ByteString where
   rnf Empty       = ()
   rnf (Chunk _ b) = rnf b
 #endif
+
+-- | Like 'everything', but avoid known potholes, based on the 'Stage' that
+--   generated the Ast.
+everythingStagedWithContext :: Stage -> s -> (r -> r -> r) -> r -> GenericQ (s -> (r, s)) -> GenericQ r
+everythingStagedWithContext stage s0 f z q x
+  | (const False
+#if __GLASGOW_HASKELL__ <= 708
+      `extQ` postTcType
+#endif
+      `extQ` fixity `extQ` nameSet) x = z
+  | otherwise = foldl f r (gmapQ (everythingStagedWithContext stage s' f z q) x)
+  where nameSet    = const (stage `elem` [Parser,TypeChecker]) :: NameSet -> Bool
+#if __GLASGOW_HASKELL__ <= 708
+        postTcType = const (stage<TypeChecker)                 :: PostTcType -> Bool
+#endif
+        fixity     = const (stage<Renamer)                     :: GHC.Fixity -> Bool
+        (r, s') = q x s0

Language/Haskell/GhcMod/Info.hs

@@ -5,10 +5,9 @@ module Language.Haskell.GhcMod.Info (
 
 import Data.Function (on)
 import Data.List (sortBy)
-import Data.Maybe (catMaybes)
 import System.FilePath
 import Exception (ghandle, SomeException(..))
-import GHC (GhcMonad, LHsBind, LHsExpr, LPat, Id, TypecheckedModule(..), SrcSpan, Type)
+import GHC (GhcMonad, SrcSpan)
 import Prelude
 import qualified GHC as G
 import qualified Language.Haskell.GhcMod.Gap as Gap
@@ -53,17 +52,18 @@ info file expr =
 
 -- | Obtaining type of a target expression. (GHCi's type:)
 types :: IOish m
-      => FilePath     -- ^ A target file.
+      => Bool         -- ^ Include constraints into type signature
+      -> FilePath     -- ^ A target file.
       -> Int          -- ^ Line number.
       -> Int          -- ^ Column number.
       -> GhcModT m String
-types file lineNo colNo =
+types withConstraints file lineNo colNo =
   ghandle handler $
     runGmlT' [Left file] deferErrors $
       withInteractiveContext $ do
         crdl         <- cradle
         modSum       <- fileModSummaryWithMapping (cradleCurrentDir crdl </> file)
-        srcSpanTypes <- getSrcSpanType modSum lineNo colNo
+        srcSpanTypes <- getSrcSpanType withConstraints modSum lineNo colNo
         dflag        <- G.getSessionDynFlags
         st           <- getStyle
         convert' $ map (toTup dflag st) $ sortBy (cmp `on` fst) srcSpanTypes
@@ -72,14 +72,8 @@ types file lineNo colNo =
      gmLog GmException "types" $ showDoc ex
      return []
 
-getSrcSpanType :: GhcMonad m => G.ModSummary -> Int -> Int -> m [(SrcSpan, Type)]
-getSrcSpanType modSum lineNo colNo = do
-  p <- G.parseModule modSum
-  tcm@TypecheckedModule{tm_typechecked_source = tcs} <- G.typecheckModule p
-  let bs = listifySpans tcs (lineNo, colNo) :: [LHsBind Id]
-      es = listifySpans tcs (lineNo, colNo) :: [LHsExpr Id]
-      ps = listifySpans tcs (lineNo, colNo) :: [LPat Id]
-  bts <- mapM (getType tcm) bs
-  ets <- mapM (getType tcm) es
-  pts <- mapM (getType tcm) ps
-  return $ catMaybes $ concat [ets, bts, pts]
+getSrcSpanType :: (GhcMonad m) => Bool -> G.ModSummary -> Int -> Int -> m [(SrcSpan, G.Type)]
+getSrcSpanType withConstraints modSum lineNo colNo =
+  G.parseModule modSum
+  >>= G.typecheckModule
+  >>= flip (collectSpansTypes withConstraints) (lineNo, colNo)

Language/Haskell/GhcMod/SrcUtils.hs

@@ -1,4 +1,4 @@
-{-# LANGUAGE TupleSections, FlexibleInstances, Rank2Types #-}
+{-# LANGUAGE TupleSections, FlexibleInstances, Rank2Types, ImpredicativeTypes #-}
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 
 module Language.Haskell.GhcMod.SrcUtils where
@@ -6,11 +6,14 @@ module Language.Haskell.GhcMod.SrcUtils where
 import Control.Applicative
 import CoreUtils (exprType)
 import Data.Generics
-import Data.Maybe (fromMaybe)
+import Data.Maybe
 import Data.Ord as O
 import GHC (LHsExpr, LPat, Id, DynFlags, SrcSpan, Type, Located, ParsedSource, RenamedSource, TypecheckedSource, GenLocated(L))
+import Var (Var)
 import qualified GHC as G
-import GHC.SYB.Utils (Stage(..), everythingStaged)
+import qualified Var as G
+import qualified Type as G
+import GHC.SYB.Utils
 import GhcMonad
 import qualified Language.Haskell.Exts.Annotated as HE
 import Language.Haskell.GhcMod.Doc
@@ -20,6 +23,10 @@ import OccName (OccName)
 import Outputable (PprStyle)
 import TcHsSyn (hsPatType)
 import Prelude
+import Control.Monad
+import Data.List (nub)
+import Control.Arrow
+import qualified Data.Map as M
 
 ----------------------------------------------------------------
 
@@ -34,6 +41,82 @@ instance HasType (LPat Id) where
 
 ----------------------------------------------------------------
 
+-- | Stores mapping from monomorphic to polymorphic types
+type CstGenQS = M.Map Var Type
+-- | Generic type to simplify SYB definition
+type CstGenQT a = forall m. GhcMonad m => a Id -> CstGenQS -> (m [(SrcSpan, Type)], CstGenQS)
+
+collectSpansTypes :: (GhcMonad m) => Bool -> G.TypecheckedModule -> (Int, Int) -> m [(SrcSpan, Type)]
+collectSpansTypes withConstraints tcs lc =
+  -- This walks AST top-down, left-to-right, while carrying CstGenQS down the tree
+  -- (but not left-to-right)
+  everythingStagedWithContext TypeChecker M.empty (liftM2 (++))
+    (return [])
+    ((return [],)
+      `mkQ`  (hsBind    :: CstGenQT G.LHsBind) -- matches on binds
+      `extQ` (genericCT :: CstGenQT G.LHsExpr) -- matches on expressions
+      `extQ` (genericCT :: CstGenQT G.LPat) -- matches on patterns
+      )
+    (G.tm_typechecked_source tcs)
+  where
+    -- Helper function to insert mapping into CstGenQS
+    insExp x = M.insert (G.abe_mono x) (G.varType $ G.abe_poly x)
+    -- If there is AbsBinds here, insert mapping into CstGenQS if needed
+    hsBind (L _ G.AbsBinds{abs_exports = es'}) s
+      | withConstraints = (return [], foldr insExp s es')
+      | otherwise       = (return [], s)
+    -- Otherwise, it's the same as other cases
+    hsBind x s = genericCT x s
+    -- Generic SYB function to get type
+    genericCT x s
+      | withConstraints
+      = (maybe [] (uncurry $ constrainedType (collectBinders x) s) <$> getType' x, s)
+      | otherwise = (maybeToList <$> getType' x, s)
+    -- Collects everything with Id from LHsBind, LHsExpr, or LPat
+    collectBinders :: Data a => a -> [Id]
+    collectBinders = listifyStaged TypeChecker (const True)
+    -- Gets monomorphic type with location
+    getType' x@(L spn _)
+      | G.isGoodSrcSpan spn && spn `G.spans` lc
+      = getType tcs x
+      | otherwise = return Nothing
+    -- Gets constrained type
+    constrainedType :: [Var] -- ^ Binders in expression, i.e. anything with Id
+                    -> CstGenQS -- ^ Map from Id to polymorphic type
+                    -> SrcSpan -- ^ extent of expression, copied to result
+                    -> Type -- ^ monomorphic type
+                    -> [(SrcSpan, Type)] -- ^ result
+    constrainedType pids s spn genTyp =
+      let
+        -- runs build on every binder.
+        ctys  = mapMaybe build (nub pids)
+        -- Computes constrained type for x. Returns (constraints, substitutions)
+        -- Substitutions are needed because type variables don't match
+        -- between polymorphic and monomorphic types.
+        -- E.g. poly type might be `Monad m => m ()`, while monomorphic might be `f ()`
+        build x | Just cti <- x `M.lookup` s
+                = let
+                    (preds', ctt) = getPreds cti
+                    -- list of type variables in monomorphic type
+                    vts = listifyStaged TypeChecker G.isTyVar $ G.varType x
+                    -- list of type variables in polymorphic type
+                    tvm = listifyStaged TypeChecker G.isTyVarTy ctt
+                  in Just (preds', zip vts tvm)
+                | otherwise = Nothing
+        -- list of constraints
+        preds = concatMap fst ctys
+        -- Type variable substitutions
+        subs  = G.mkTopTvSubst $ concatMap snd ctys
+        -- Constrained type
+        ty    = G.substTy subs $ G.mkFunTys preds genTyp
+      in [(spn, ty)]
+    -- Splits a given type into list of constraints and simple type. Drops foralls.
+    getPreds :: Type -> ([Type], Type)
+    getPreds x | G.isForAllTy x = getPreds $ G.dropForAlls x
+               | Just (c, t) <- G.splitFunTy_maybe x
+               , G.isPredTy c = first (c:) $ getPreds t
+               | otherwise = ([], x)
+
 listifySpans :: Typeable a => TypecheckedSource -> (Int, Int) -> [Located a]
 listifySpans tcs lc = listifyStaged TypeChecker p tcs
   where