Add HoleFitPlugins and RawHoleFits
This patch adds a new kind of plugin, Hole Fit Plugins. These plugins can change what candidates are considered when looking for valid hole fits, and add hole fits of their own. The type of a plugin is relatively simple,
type FitPlugin = TypedHole -> [HoleFit] -> TcM [HoleFit]
type CandPlugin = TypedHole -> [HoleFitCandidate] -> TcM [HoleFitCandidate]
data HoleFitPlugin = HoleFitPlugin { candPlugin :: CandPlugin
, fitPlugin :: FitPlugin }
data TypedHole = TyH { relevantCts :: Cts -- ^ Any relevant Cts to the hole
, implics :: [Implication] -- ^ The nested implications of the hole
-- with the innermost implication first.
, holeCt :: Maybe Ct -- ^ The hole constraint itself, if available. }
This allows users and plugin writers to interact with the candidates and
fits as they wish, even going as far as to allow them to reimplement the
current functionality (since TypedHole
contains all the relevant
information).
As an example, consider the following plugin:
module HolePlugin where
import GhcPlugins
import TcHoleErrors
import Data.List (intersect, stripPrefix)
import RdrName (importSpecModule)
import TcRnTypes
import System.Process
plugin :: Plugin
plugin = defaultPlugin { holeFitPlugin = hfp, pluginRecompile = purePlugin }
hfp :: [CommandLineOption] -> Maybe HoleFitPlugin
hfp opts = Just (HoleFitPlugin (candP opts) (fp opts))
toFilter :: Maybe String -> Maybe String
toFilter = flip (>>=) (stripPrefix "_module_")
replace :: Eq a => a -> a -> [a] -> [a]
replace match repl str = replace' [] str
where
replace' sofar (x:xs) | x == match = replace' (repl:sofar) xs
replace' sofar (x:xs) = replace' (x:sofar) xs
replace' sofar [] = reverse sofar
-- | This candidate plugin filters the candidates by module,
-- using the name of the hole as module to search in
candP :: [CommandLineOption] -> CandPlugin
candP _ hole cands =
do let he = case holeCt hole of
Just (CHoleCan _ h) -> Just (occNameString $ holeOcc h)
_ -> Nothing
case toFilter he of
Just undscModName -> do let replaced = replace '_' '.' undscModName
let res = filter (greNotInOpts [replaced]) cands
return $ res
_ -> return cands
where greNotInOpts opts (GreHFCand gre) = not $ null $ intersect (inScopeVia gre) opts
greNotInOpts _ _ = True
inScopeVia = map (moduleNameString . importSpecModule) . gre_imp
-- Yes, it's pretty hacky, but it is just an example :)
searchHoogle :: String -> IO [String]
searchHoogle ty = lines <$> (readProcess "hoogle" [(show ty)] [])
fp :: [CommandLineOption] -> FitPlugin
fp ("hoogle":[]) hole hfs =
do dflags <- getDynFlags
let tyString = showSDoc dflags . ppr . ctPred <$> holeCt hole
res <- case tyString of
Just ty -> liftIO $ searchHoogle ty
_ -> return []
return $ (take 2 $ map (RawHoleFit . text .("Hoogle says: " ++)) res) ++ hfs
fp _ _ hfs = return hfs
with this plugin available, you can compile the following file
{-# OPTIONS -fplugin=HolePlugin -fplugin-opt=HolePlugin:hoogle #-}
module Main where
import Prelude hiding (head, last)
import Data.List (head, last)
t :: [Int] -> Int
t = _module_Prelude
g :: [Int] -> Int
g = _module_Data_List
main :: IO ()
main = print $ t [1,2,3]
and get the following output:
Main.hs:14:5: error:
• Found hole: _module_Prelude :: [Int] -> Int
Or perhaps ‘_module_Prelude’ is mis-spelled, or not in scope
• In the expression: _module_Prelude
In an equation for ‘t’: t = _module_Prelude
• Relevant bindings include
t :: [Int] -> Int (bound at Main.hs:14:1)
Valid hole fits include
Hoogle says: GHC.List length :: [a] -> Int
Hoogle says: GHC.OldList length :: [a] -> Int
t :: [Int] -> Int (bound at Main.hs:14:1)
g :: [Int] -> Int (bound at Main.hs:17:1)
length :: forall (t :: * -> *) a. Foldable t => t a -> Int
with length @[] @Int
(imported from ‘Prelude’ at Main.hs:5:1-34
(and originally defined in ‘Data.Foldable’))
maximum :: forall (t :: * -> *) a. (Foldable t, Ord a) => t a -> a
with maximum @[] @Int
(imported from ‘Prelude’ at Main.hs:5:1-34
(and originally defined in ‘Data.Foldable’))
(Some hole fits suppressed; use -fmax-valid-hole-fits=N or -fno-max-valid-hole-fits)
|
14 | t = _module_Prelude
| ^^^^^^^^^^^^^^^
Main.hs:17:5: error:
• Found hole: _module_Data_List :: [Int] -> Int
Or perhaps ‘_module_Data_List’ is mis-spelled, or not in scope
• In the expression: _module_Data_List
In an equation for ‘g’: g = _module_Data_List
• Relevant bindings include
g :: [Int] -> Int (bound at Main.hs:17:1)
Valid hole fits include
Hoogle says: GHC.List length :: [a] -> Int
Hoogle says: GHC.OldList length :: [a] -> Int
g :: [Int] -> Int (bound at Main.hs:17:1)
head :: forall a. [a] -> a
with head @Int
(imported from ‘Data.List’ at Main.hs:7:19-22
(and originally defined in ‘GHC.List’))
last :: forall a. [a] -> a
with last @Int
(imported from ‘Data.List’ at Main.hs:7:25-28
(and originally defined in ‘GHC.List’))
|
17 | g = _module_Data_List
This relatively simple plugin has two functions, as an example of what
is possible to do with hole fit plugins. The candidate plugin starts by
filtering the candidates considered by module, indicated by the name of
the hole (_module_Data_List
). The second function is in the fit
plugin, where the plugin invokes a local hoogle instance to search by
the type of the hole.
By adding the RawHoleFit
type, we can also allow these completely free
suggestions, used in the plugin above to display fits found by Hoogle.
Of course, the syntax here is up for debate, but hole fit plugins allow us to experiment relatively easily with ways to interact with typed-holes without having to dig deep into GHC.
Previously Differential Revision https://phabricator.haskell.org/D5373