feat: handle hovers with null replies

src/Lean/Data/JsonRpc.lean

@@ -149,6 +149,8 @@ message ← err.getObjValAs? String "message";
 let data? := err.getObjVal? "data";
 pure (Message.responseError id code message data?)
 
+-- HACK: The implementation must be made up of several `auxN`s instead
+-- of one large block because of a bug in the compiler.
 instance messageFromJson : HasFromJson Message :=
 ⟨fun j => do
   "2.0" ← j.getObjVal? "jsonrpc" | none;

src/Lean/Data/Lsp.lean

@@ -5,9 +5,10 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Gabriel Ebner, Marc Huisinga
 -/
 import Lean.Data.Lsp.GeneralMessage
-import Lean.Data.Lsp.Structure 
-import Lean.Data.Lsp.TextSync 
+import Lean.Data.Lsp.Structure
+import Lean.Data.Lsp.TextSync
 import Lean.Data.Lsp.Communication
 import Lean.Data.Lsp.Capabilities
 import Lean.Data.Lsp.Diagnostics
+import Lean.Data.Lsp.Hover
 import Lean.Data.Lsp.Utf16

src/Lean/Data/Lsp/Capabilities.lean

@@ -16,14 +16,17 @@ instance clientCapabilitiesHasFromJson : HasFromJson ClientCapabilities :=
 -- TODO largely unimplemented
 structure ServerCapabilities :=
 (textDocumentSync? : Option TextDocumentSyncOptions := none)
+(hoverProvider : Bool := false)
 
 instance serverCapabilitiesHasToJson : HasToJson ServerCapabilities :=
 ⟨fun o => mkObj $
-  opt "textDocumentSync" o.textDocumentSync? ++ []⟩
+  opt "textDocumentSync" o.textDocumentSync? ++
+  [⟨"hoverProvider", o.hoverProvider⟩]⟩
 
 def mkLeanServerCapabilities : ServerCapabilities :=
 { textDocumentSync? := some
   { openClose := true
-  , change? := TextDocumentSyncKind.incremental }}
+  , change? := TextDocumentSyncKind.incremental }
+, hoverProvider := true }
 
 end Lean.Lsp

src/Lean/Data/Lsp/Hover.lean

@@ -0,0 +1,25 @@
+import Lean.Data.Json
+import Lean.Data.Lsp.Structure
+
+namespace Lean.Lsp
+
+open Lean
+open Lean.Json
+
+/- The result of a hover request. -/
+structure Hover :=
+/- The hover's content -/
+--(contents: MarkedString | MarkedString[] | MarkupContent)
+/- An optional range is a range inside a text document
+that is used to visualize a hover, e.g. by changing the background color. -/
+(range? : Range)
+
+structure HoverParams extends TextDocumentPositionParams
+
+instance hoverParamsHasFromJson : HasFromJson HoverParams :=
+⟨fun j => do
+  tdpp : TextDocumentPositionParams ← fromJson? j;
+  pure ⟨tdpp⟩⟩
+
+end Lean.Lsp
+

src/Lean/Data/Lsp/Structure.lean

@@ -13,6 +13,12 @@ abbrev DocumentUri := String
 -- character is accepted liberally: actual character := min(line length, character)
 structure Position := (line : Nat) (character : Nat)
 
+instance positionHasFromJson : HasFromJson Position :=
+⟨fun j => do
+  line ← j.getObjValAs? Nat "line";
+  character ← j.getObjValAs? Nat "character";
+  pure ⟨line, character⟩⟩
+
 -- [start, end)
 structure Range := (start : Position) («end» : Position)
 
@@ -117,6 +123,11 @@ def TextEditBatch := Array TextEdit
 
 structure TextDocumentIdentifier := (uri : DocumentUri)
 
+instance textDocumentIdentifierHasFromJson : HasFromJson TextDocumentIdentifier :=
+⟨fun j => do
+  uri ← j.getObjValAs? DocumentUri "uri";
+  pure ⟨uri⟩⟩
+
 structure VersionedTextDocumentIdentifier :=
 (uri : DocumentUri)
 -- increases after each change, undo and redo
@@ -147,6 +158,12 @@ structure TextDocumentPositionParams :=
 (textDocument : TextDocumentIdentifier)
 (position : Position)
 
+instance textDocumentPositionParamsHasFromJson : HasFromJson TextDocumentPositionParams :=
+⟨fun j => do
+  textDocument ← j.getObjValAs? TextDocumentIdentifier "textDocument";
+  position ← j.getObjValAs? Position "position";
+  pure ⟨textDocument, position⟩⟩
+
 structure DocumentFilter :=
 (language? : Option String := none) -- language id
 -- uri scheme like 'file' or 'untitled'
@@ -176,12 +193,6 @@ structure TextDocumentRegistrationOptions := (documentSelector? : Option Documen
 instance documentUriHasFromJson : HasFromJson DocumentUri :=
 ⟨fun j => j.getStr?⟩
 
-instance positionHasFromJson : HasFromJson Position :=
-⟨fun j => do
-  line ← j.getObjValAs? Nat "line";
-  character ← j.getObjValAs? Nat "character";
-  pure ⟨line, character⟩⟩
-
 instance rangeHasFromJson : HasFromJson Range :=
 ⟨fun j => do
   start ← j.getObjValAs? Position "start";
@@ -223,11 +234,6 @@ instance diagnosticHasFromJson : HasFromJson Diagnostic :=
   let relatedInformation? := j.getObjValAs? (Array DiagnosticRelatedInformation) "relatedInformation";
   pure ⟨range, severity?, code?, source?, message, tags?, relatedInformation?⟩⟩
 
-instance textDocumentIdentifierHasFromJson : HasFromJson TextDocumentIdentifier :=
-⟨fun j => do
-  uri ← j.getObjValAs? DocumentUri "uri";
-  pure ⟨uri⟩⟩
-
 instance versionedTextDocumentIdentifierHasFromJson : HasFromJson VersionedTextDocumentIdentifier :=
 ⟨fun j => do
   uri ← j.getObjValAs? DocumentUri "uri";

src/Lean/Server/Server.lean

@@ -1,5 +1,6 @@
 import Init.System.IO
 import Std.Data.RBMap
+
 import Lean.Environment
 import Lean.Elab.Frontend
 import Lean.Data.Lsp
@@ -147,6 +148,10 @@ match method with
 def handleRequest (s : ServerState) (id : RequestID) (method : String) (params : Json)
   : IO Unit := do
   match method with
+  | "textDocument/hover" => do
+    p ← parseParams HoverParams params;
+    writeLspResponse s.o id Json.null;
+    pure ()
   | _ => throw (userError "Not supporting requests for now!")
 
 partial def mainLoop : ServerState → IO Unit
@@ -184,5 +189,6 @@ def main (n : List String) : IO UInt32 := do
 i ← IO.stdin;
 o ← IO.stdout;
 Lean.initSearchPath;
+env ← Lean.mkEmptyEnvironment;
 catch (Lean.Server.initialize i o) (fun err => o.putStrLn (toString err));
 pure 0