diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
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diff --git a/hls-haddock-comments-plugin.cabal b/hls-haddock-comments-plugin.cabal
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--- /dev/null
+++ b/hls-haddock-comments-plugin.cabal
@@ -0,0 +1,30 @@
+cabal-version: 2.2
+name:          hls-haddock-comments-plugin
+version:       0.1.0.0
+synopsis:      Haddock comments plugin for Haskell Language Server
+description:
+  Please see Haskell Language Server Readme (https://github.com/haskell/haskell-language-server#readme)
+
+license:       Apache-2.0
+license-file:  LICENSE
+author:        Potato Hatsue
+maintainer:    berberman@yandex.com
+category:      Development
+build-type:    Simple
+
+library
+  exposed-modules:  Ide.Plugin.HaddockComments
+  hs-source-dirs:   src
+  ghc-options:      -Wall -Wno-name-shadowing -Wredundant-constraints
+  build-depends:
+    , base                  >=4.12 && <5
+    , containers
+    , ghc
+    , ghc-exactprint
+    , ghcide
+    , haskell-lsp-types
+    , hls-plugin-api
+    , text
+    , unordered-containers
+
+  default-language: Haskell2010
diff --git a/src/Ide/Plugin/HaddockComments.hs b/src/Ide/Plugin/HaddockComments.hs
new file mode 100644
--- /dev/null
+++ b/src/Ide/Plugin/HaddockComments.hs
@@ -0,0 +1,147 @@
+{-# LANGUAGE ExistentialQuantification #-}
+{-# LANGUAGE NamedFieldPuns #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE ViewPatterns #-}
+
+module Ide.Plugin.HaddockComments where
+
+import Control.Monad (join)
+import qualified Data.HashMap.Strict as HashMap
+import qualified Data.Map as Map
+import qualified Data.Text as T
+import Development.IDE
+import Development.IDE.GHC.Compat
+import Ide.Types
+import Language.Haskell.GHC.ExactPrint
+import Language.Haskell.GHC.ExactPrint.Types hiding (GhcPs)
+import Language.Haskell.GHC.ExactPrint.Utils
+import Language.Haskell.LSP.Types
+
+-----------------------------------------------------------------------------
+descriptor :: PluginId -> PluginDescriptor IdeState
+descriptor plId =
+  (defaultPluginDescriptor plId)
+    { pluginCodeActionProvider = Just codeActionProvider
+    }
+
+haddockCommentsId :: CommandId
+haddockCommentsId = "HaddockCommentsCommand"
+
+codeActionProvider :: CodeActionProvider IdeState
+codeActionProvider _lspFuncs ideState _pId (TextDocumentIdentifier uri) range CodeActionContext {_diagnostics = List diags} =
+  do
+    let noErr = and $ (/= Just DsError) . _severity <$> diags
+        nfp = uriToNormalizedFilePath $ toNormalizedUri uri
+    (join -> pm) <- runAction "HaddockComments.GetParsedModule" ideState $ use GetParsedModule `traverse` nfp
+    let locDecls = hsmodDecls . unLoc . pm_parsed_source <$> pm
+        anns = relativiseApiAnns <$> (pm_parsed_source <$> pm) <*> (pm_annotations <$> pm)
+        edits = [runGenComments gen locDecls anns range | noErr, gen <- genList]
+    return $ Right $ List [CACodeAction $ toAction title uri edit | (Just (title, edit)) <- edits]
+
+genList :: [GenComments]
+genList =
+  [ genForSig,
+    genForRecord
+  ]
+
+-----------------------------------------------------------------------------
+data GenComments = forall a.
+  GenComments
+  { title :: T.Text,
+    fromDecl :: HsDecl GhcPs -> Maybe a,
+    collectKeys :: a -> [AnnKey],
+    isFresh :: Annotation -> Bool,
+    updateAnn :: Annotation -> Annotation
+  }
+
+runGenComments :: GenComments -> Maybe [LHsDecl GhcPs] -> Maybe Anns -> Range -> Maybe (T.Text, TextEdit)
+runGenComments GenComments {..} mLocDecls mAnns range
+  | Just locDecls <- mLocDecls,
+    Just anns <- mAnns,
+    [(locDecl, src, x)] <- [(locDecl, l, x) | locDecl@(L l (fromDecl -> Just x)) <- locDecls, range `isIntersectWith` l],
+    annKeys <- collectKeys x,
+    not $ null annKeys,
+    and $ maybe False isFresh . flip Map.lookup anns <$> annKeys,
+    anns' <- foldr (Map.adjust updateAnn) anns annKeys,
+    Just range' <- toRange src,
+    result <- T.strip . T.pack $ exactPrint locDecl anns' =
+    Just (title, TextEdit range' result)
+  | otherwise = Nothing
+
+-----------------------------------------------------------------------------
+
+genForSig :: GenComments
+genForSig = GenComments {..}
+  where
+    title = "Generate signature comments"
+
+    fromDecl (SigD _ (TypeSig _ _ (HsWC _ (HsIB _ x)))) = Just x
+    fromDecl _ = Nothing
+
+    updateAnn x = x {annEntryDelta = DP (0, 1), annsDP = dp}
+
+    isFresh Ann {annsDP} = null [() | (AnnComment _, _) <- annsDP]
+
+    collectKeys = keyFromTyVar 0
+
+    comment = mkComment "-- ^ " noSrcSpan
+    dp = [(AnnComment comment, DP (0, 1)), (G AnnRarrow, DP (1, 2))]
+
+genForRecord :: GenComments
+genForRecord = GenComments {..}
+  where
+    title = "Generate fields comments"
+
+    fromDecl (TyClD _ DataDecl {tcdDataDefn = HsDataDefn {dd_cons = cons}}) =
+      Just [x | (L _ ConDeclH98 {con_args = x}) <- cons]
+    fromDecl _ = Nothing
+
+    updateAnn x = x {annEntryDelta = DP (1, 2), annPriorComments = [(comment, DP (1, 2))]}
+
+    isFresh Ann {annPriorComments} = null annPriorComments
+
+    collectKeys = keyFromCon
+
+    comment = mkComment "-- | " noSrcSpan
+
+-----------------------------------------------------------------------------
+
+toAction :: T.Text -> Uri -> TextEdit -> CodeAction
+toAction title uri edit = CodeAction {..}
+  where
+    _title = title
+    _kind = Just CodeActionQuickFix
+    _diagnostics = Nothing
+    _command = Nothing
+    _changes = Just $ HashMap.singleton uri $ List [edit]
+    _documentChanges = Nothing
+    _edit = Just WorkspaceEdit {..}
+
+toRange :: SrcSpan -> Maybe Range
+toRange src
+  | (RealSrcSpan span) <- src,
+    range' <- realSrcSpanToRange span =
+    Just range'
+  | otherwise = Nothing
+
+isIntersectWith :: Range -> SrcSpan -> Bool
+isIntersectWith Range {_start, _end} x = isInsideSrcSpan _start x || isInsideSrcSpan _end x
+
+-----------------------------------------------------------------------------
+
+keyFromTyVar :: Int -> LHsType GhcPs -> [AnnKey]
+keyFromTyVar dep c@(L _ (HsFunTy _ x y))
+  | dep < 1 = mkAnnKey c : keyFromTyVar dep x ++ keyFromTyVar dep y
+  | otherwise = []
+keyFromTyVar dep (L _ t@HsForAllTy {}) = keyFromTyVar dep (hst_body t)
+keyFromTyVar dep (L _ t@HsQualTy {}) = keyFromTyVar dep (hst_body t)
+keyFromTyVar dep (L _ (HsKindSig _ x _)) = keyFromTyVar dep x
+keyFromTyVar dep (L _ (HsParTy _ x)) = keyFromTyVar (succ dep) x
+keyFromTyVar dep (L _ (HsBangTy _ _ x)) = keyFromTyVar dep x
+keyFromTyVar _ _ = []
+
+keyFromCon :: [HsConDeclDetails GhcPs] -> [AnnKey]
+keyFromCon cons = mconcat [mkAnnKey <$> xs | (RecCon (L _ xs)) <- cons]
+
+-----------------------------------------------------------------------------
