Jump to instance definition and explain typeclass evidence (#4392)

* Jump to instance definition and explain typeclass evidence

* improve hover rendering

* Add "Goto Implementation" LSP handler

Adds the necessary instances for handling the request type
`Method_TextDocumentImplementation`.
Further, wire up the appropriate handlers for the "gotoImplementation"
request.

* Add docs for 'Jump to Implementation' request

* Add Tests for 'Goto Implementation' feature

* Add pretty link for source location to hover

* Improve documentation for Evidence tree rendering

Also, add extensive note about skipping 'EvLetBinding' evidence nodes.

* Remove unused test code with helpful error message

---------

Co-authored-by: Zubin Duggal <[email protected]>

Author: fendor

Diff for: .hlint.yaml

@@ -110,6 +110,7 @@
     - CompletionTests #Previously part of GHCIDE Main tests
     - DiagnosticTests #Previously part of GHCIDE Main tests
     - FindDefinitionAndHoverTests #Previously part of GHCIDE Main tests
+    - FindImplementationAndHoverTests #Previously part of GHCIDE Main tests
     - TestUtils #Previously part of GHCIDE Main tests
     - CodeLensTests #Previously part of GHCIDE Main tests
 
@@ -134,6 +135,7 @@
     - Ide.Plugin.Eval.Parse.Comments
     - Ide.Plugin.Eval.CodeLens
     - FindDefinitionAndHoverTests #Previously part of GHCIDE Main tests
+    - FindImplementationAndHoverTests #Previously part of GHCIDE Main tests
 
   - name: [Prelude.init, Data.List.init]
     within:

Diff for: docs/features.md

@@ -81,6 +81,16 @@ Known limitations:
 
 - Only works for [local definitions](https://github.com/haskell/haskell-language-server/issues/708).
 
+## Jump to implementation
+
+Provided by: `ghcide`
+
+Jump to the implementation instance of a type class method.
+
+Known limitations:
+
+- Only works for [local definitions](https://github.com/haskell/haskell-language-server/issues/708).
+
 ## Jump to note definition
 
 Provided by: `hls-notes-plugin`

Diff for: ghcide/src/Development/IDE/Core/Actions.hs

@@ -3,6 +3,7 @@ module Development.IDE.Core.Actions
 ( getAtPoint
 , getDefinition
 , getTypeDefinition
+, getImplementationDefinition
 , highlightAtPoint
 , refsAtPoint
 , workspaceSymbols
@@ -98,7 +99,7 @@ getDefinition :: NormalizedFilePath -> Position -> IdeAction (Maybe [(Location,
 getDefinition file pos = runMaybeT $ do
     ide@ShakeExtras{ withHieDb, hiedbWriter } <- ask
     opts <- liftIO $ getIdeOptionsIO ide
-    (HAR _ hf _ _ _, mapping) <- useWithStaleFastMT GetHieAst file
+    (hf, mapping) <- useWithStaleFastMT GetHieAst file
     (ImportMap imports, _) <- useWithStaleFastMT GetImportMap file
     !pos' <- MaybeT (pure $ fromCurrentPosition mapping pos)
     locationsWithIdentifier <- AtPoint.gotoDefinition withHieDb (lookupMod hiedbWriter) opts imports hf pos'
@@ -120,6 +121,15 @@ getTypeDefinition file pos = runMaybeT $ do
       pure $ Just (fixedLocation, identifier)
       ) locationsWithIdentifier
 
+getImplementationDefinition :: NormalizedFilePath -> Position -> IdeAction (Maybe [Location])
+getImplementationDefinition file pos = runMaybeT $ do
+    ide@ShakeExtras{ withHieDb, hiedbWriter } <- ask
+    opts <- liftIO $ getIdeOptionsIO ide
+    (hf, mapping) <- useWithStaleFastMT GetHieAst file
+    !pos' <- MaybeT (pure $ fromCurrentPosition mapping pos)
+    locs <- AtPoint.gotoImplementation withHieDb (lookupMod hiedbWriter) opts hf pos'
+    traverse (MaybeT . toCurrentLocation mapping file) locs
+
 highlightAtPoint :: NormalizedFilePath -> Position -> IdeAction (Maybe [DocumentHighlight])
 highlightAtPoint file pos = runMaybeT $ do
     (HAR _ hf rf _ _,mapping) <- useWithStaleFastMT GetHieAst file

Diff for: ghcide/src/Development/IDE/LSP/HoverDefinition.hs

@@ -10,6 +10,7 @@ module Development.IDE.LSP.HoverDefinition
     , foundHover
     , gotoDefinition
     , gotoTypeDefinition
+    , gotoImplementation
     , documentHighlight
     , references
     , wsSymbols
@@ -47,9 +48,11 @@ instance Pretty Log where
 gotoDefinition     :: Recorder (WithPriority Log) -> IdeState -> TextDocumentPositionParams -> ExceptT PluginError (HandlerM c) (MessageResult Method_TextDocumentDefinition)
 hover              :: Recorder (WithPriority Log) -> IdeState -> TextDocumentPositionParams -> ExceptT PluginError (HandlerM c) (Hover |? Null)
 gotoTypeDefinition :: Recorder (WithPriority Log) -> IdeState -> TextDocumentPositionParams -> ExceptT PluginError (HandlerM c) (MessageResult Method_TextDocumentTypeDefinition)
+gotoImplementation :: Recorder (WithPriority Log) -> IdeState -> TextDocumentPositionParams -> ExceptT PluginError (HandlerM c) (MessageResult Method_TextDocumentImplementation)
 documentHighlight  :: Recorder (WithPriority Log) -> IdeState -> TextDocumentPositionParams -> ExceptT PluginError (HandlerM c) ([DocumentHighlight] |? Null)
-gotoDefinition = request "Definition" getDefinition (InR $ InR Null) (InL . Definition. InR . map fst)
-gotoTypeDefinition = request "TypeDefinition" getTypeDefinition (InR $ InR Null) (InL . Definition. InR . map fst)
+gotoDefinition = request "Definition" getDefinition (InR $ InR Null) (InL . Definition . InR . map fst)
+gotoTypeDefinition = request "TypeDefinition" getTypeDefinition (InR $ InR Null) (InL . Definition . InR . map fst)
+gotoImplementation = request "Implementation" getImplementationDefinition (InR $ InR Null) (InL . Definition . InR)
 hover          = request "Hover"      getAtPoint     (InR Null)     foundHover
 documentHighlight = request "DocumentHighlight" highlightAtPoint (InR Null) InL
 

Diff for: ghcide/src/Development/IDE/Plugin/HLS/GhcIde.hs

@@ -51,6 +51,8 @@ descriptor recorder plId = (defaultPluginDescriptor plId desc)
                       Hover.gotoDefinition recorder ide TextDocumentPositionParams{..})
                   <> mkPluginHandler SMethod_TextDocumentTypeDefinition (\ide _ TypeDefinitionParams{..} ->
                       Hover.gotoTypeDefinition recorder ide TextDocumentPositionParams{..})
+                  <> mkPluginHandler SMethod_TextDocumentImplementation (\ide _ ImplementationParams{..} ->
+                      Hover.gotoImplementation recorder ide TextDocumentPositionParams{..})
                   <> mkPluginHandler SMethod_TextDocumentDocumentHighlight (\ide _ DocumentHighlightParams{..} ->
                       Hover.documentHighlight recorder ide TextDocumentPositionParams{..})
                   <> mkPluginHandler SMethod_TextDocumentReferences (Hover.references recorder)