Rework exportsMap on top of hiedb

[pepeiborra]

haskell-language-server/ghcide/src/Development/IDE/Core/Shake.hs

Line 203 in 0b3bb10

,exportsMap :: Var ExportsMap

is a mutable table of names exported by modules in the local project that is used to drive import quick fixes.

The current implementation populates the table by

1. Typechecking all the project modules at startup:
   

   haskell-language-server/ghcide/session-loader/Development/IDE/Session.hs

   Lines 400 to 410 in 861c8bf

   	-- Typecheck all files in the project on startup
   	checkProject <- getCheckProject
   	unless (null cs || not checkProject) $ do
   	cfps' <- liftIO $ filterM (IO.doesFileExist . fromNormalizedFilePath) (concatMap targetLocations cs)
   	void $ shakeEnqueue extras $ mkDelayedAction "InitialLoad" Debug $ void $ do
   	mmt <- uses GetModificationTime cfps'
   	let cs_exist = catMaybes (zipWith (<$) cfps' mmt)
   	modIfaces <- uses GetModIface cs_exist
   	-- update exports map
   	extras <- getShakeExtras
   	let !exportsMap' = createExportsMap $ mapMaybe (fmap hirModIface) modIfaces

2. Refreshing on every kick:

haskell-language-server/ghcide/src/Development/IDE/Core/OfInterest.hs

Lines 111 to 120 in 2ee2943

	ifaces <- if checkProject then return Nothing else runMaybeT $ do
	deps <- MaybeT $ sequence <$> uses GetDependencies files
	hiResults <- lift $ uses GetModIface (nubOrd $ foldMap transitiveModuleDeps deps)
	return $ map hirModIface $ catMaybes hiResults
	ShakeExtras{exportsMap} <- getShakeExtras
	let mguts = catMaybes results
	!exportsMap' = createExportsMapMg mguts
	!exportsMap'' = maybe mempty createExportsMap ifaces
	void $ liftIO $ modifyVar' exportsMap $ (exportsMap'' <>) . (exportsMap' <>)

1 could be replaced by a hiedb query, assuming that the hiedb is fully uptodate. This may not be always the case for a new project, but it will work fine on a project that has previously been loaded and type checked.

2 does a lot of work when checkProject is disabled, by scanning all the transitive dependencies. If we switch 1 to use hiedb we can also make it unconditional and then eliminate the transitive scan from 2.

[pepeiborra]

This will require adding a new table to hiedb that tracks the module exports