Use exact print for suggest missing constraint code actions (#1221)

* Cache annotated AST

* instance ASTElement RdrName

* appendConstraint + Rewrite abstraction

The Rewrite abstraction is similar to D.IDE.GHC.ExactPrint.Graft but it
does fewer things more efficiently:

- It doesn't annotate things for you (so it doesn't destroy user format)
- It doesn't provide a Monoid instance (for now)
- It doesn't need a fully parsed source
- It doesn't use SYB to perform the replacement
- It doesn't diff to compute the result

The use case is code actions where you don't have the SrcSpan that you need to
edit at hand, and instead you need to traverse the AST manually to locate the declaration to edit

* Refactor suggest constraint code action to use exactprint

Tweaking the suggest constraints tests to reflect the increased precision in
whitespace preservation

* Catch missing 'Monad m' constraints too

* Suggestions for missing implicit parameters

* hlints

* compat

* Include getAnnotatedParsedSourceRule in the main rule

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: pepeiborra

ghcide/ghcide.cabal

@@ -169,6 +169,7 @@ library
         Development.IDE.Plugin
         Development.IDE.Plugin.Completions
         Development.IDE.Plugin.CodeAction
+        Development.IDE.Plugin.CodeAction.ExactPrint
         Development.IDE.Plugin.HLS
         Development.IDE.Plugin.HLS.GhcIde
         Development.IDE.Plugin.Test

ghcide/src/Development/IDE/Core/Rules.hs

@@ -79,6 +79,7 @@ import           Development.IDE.Core.FileStore        (modificationTime, getFil
 import           Development.IDE.Types.Diagnostics as Diag
 import Development.IDE.Types.Location
 import Development.IDE.GHC.Compat hiding (parseModule, typecheckModule, writeHieFile, TargetModule, TargetFile)
+import Development.IDE.GHC.ExactPrint
 import Development.IDE.GHC.Util
 import Data.Either.Extra
 import qualified Development.IDE.Types.Logger as L
@@ -1020,6 +1021,7 @@ mainRule = do
     needsCompilationRule
     generateCoreRule
     getImportMapRule
+    getAnnotatedParsedSourceRule
 
 -- | Given the path to a module src file, this rule returns True if the
 -- corresponding `.hi` file is stable, that is, if it is newer

ghcide/src/Development/IDE/GHC/ExactPrint.hs

@@ -3,21 +3,29 @@
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE TypeFamilies #-}
 
 module Development.IDE.GHC.ExactPrint
     ( Graft(..),
       graft,
       graftDecls,
       graftDeclsWithM,
+      annotate,
       hoistGraft,
       graftWithM,
       graftWithSmallestM,
       transform,
       transformM,
       useAnnotatedSource,
       annotateParsedSource,
+      getAnnotatedParsedSourceRule,
+      GetAnnotatedParsedSource(..),
       ASTElement (..),
       ExceptStringT (..),
+      Annotated(..),
+      TransformT,
+      Anns,
+      Annotate,
     )
 where
 
@@ -35,10 +43,13 @@ import Data.Functor.Classes
 import Data.Functor.Contravariant
 import qualified Data.Text as T
 import Development.IDE.Core.RuleTypes
-import Development.IDE.Core.Rules
+import Development.IDE.Core.Service (runAction)
 import Development.IDE.Core.Shake
 import Development.IDE.GHC.Compat hiding (parseExpr)
 import Development.IDE.Types.Location
+import Development.Shake (RuleResult, Rules)
+import Development.Shake.Classes
+import qualified GHC.Generics as GHC
 import Generics.SYB
 import Ide.PluginUtils
 import Language.Haskell.GHC.ExactPrint
@@ -47,26 +58,38 @@ import Language.Haskell.LSP.Types
 import Language.Haskell.LSP.Types.Capabilities (ClientCapabilities)
 import Outputable (Outputable, ppr, showSDoc)
 import Retrie.ExactPrint hiding (parseDecl, parseExpr, parsePattern, parseType)
+import Parser (parseIdentifier)
 #if __GLASGOW_HASKELL__ == 808
 import Control.Arrow
 #endif
 
 
 ------------------------------------------------------------------------------
 
+data GetAnnotatedParsedSource = GetAnnotatedParsedSource
+  deriving (Eq, Show, Typeable, GHC.Generic)
+
+instance Hashable GetAnnotatedParsedSource
+instance NFData GetAnnotatedParsedSource
+instance Binary GetAnnotatedParsedSource
+type instance RuleResult GetAnnotatedParsedSource = Annotated ParsedSource
+
 -- | Get the latest version of the annotated parse source.
-useAnnotatedSource ::
-    String ->
-    IdeState ->
-    NormalizedFilePath ->
-    IO (Maybe (Annotated ParsedSource))
-useAnnotatedSource herald state nfp =
-    fmap annotateParsedSource
-        <$> runAction herald state (use GetParsedModule nfp)
+getAnnotatedParsedSourceRule :: Rules ()
+getAnnotatedParsedSourceRule = define $ \GetAnnotatedParsedSource nfp -> do
+  pm <- use GetParsedModule nfp
+  return ([], fmap annotateParsedSource pm)
 
 annotateParsedSource :: ParsedModule -> Annotated ParsedSource
 annotateParsedSource = fixAnns
 
+useAnnotatedSource ::
+  String ->
+  IdeState ->
+  NormalizedFilePath ->
+  IO (Maybe (Annotated ParsedSource))
+useAnnotatedSource herald state nfp =
+    runAction herald state (use GetAnnotatedParsedSource nfp)
 ------------------------------------------------------------------------------
 
 {- | A transformation for grafting source trees together. Use the semigroup
@@ -291,6 +314,10 @@ instance p ~ GhcPs => ASTElement (HsDecl p) where
     parseAST = parseDecl
     maybeParensAST = id
 
+instance ASTElement RdrName where
+    parseAST df fp = parseWith df fp parseIdentifier
+    maybeParensAST = id
+
 ------------------------------------------------------------------------------
 
 -- | Dark magic I stole from retrie. No idea what it does.
@@ -302,6 +329,7 @@ fixAnns ParsedModule {..} =
 ------------------------------------------------------------------------------
 
 -- | Given an 'LHSExpr', compute its exactprint annotations.
+--   Note that this function will throw away any existing annotations (and format)
 annotate :: ASTElement ast => DynFlags -> Located ast -> TransformT (Either String) (Anns, Located ast)
 annotate dflags ast = do
     uniq <- show <$> uniqueSrcSpanT

ghcide/src/Development/IDE/GHC/Orphans.hs

@@ -21,6 +21,7 @@ import           GhcPlugins
 import qualified StringBuffer               as SB
 import Data.Text (Text)
 import Data.String (IsString(fromString))
+import Retrie.ExactPrint (Annotated)
 
 
 -- Orphan instances for types from the GHC API.
@@ -144,3 +145,9 @@ instance NFData ModGuts where
 
 instance NFData (ImportDecl GhcPs) where
     rnf = rwhnf
+
+instance Show (Annotated ParsedSource) where
+  show _ = "<Annotated ParsedSource>"
+
+instance NFData (Annotated ParsedSource) where
+  rnf = rwhnf