Support LSP-compliant relatedInformation field

Summary:
Include both the nuclide-specific `relatedLocations`, and the identical LSP-standard `relatedInformation`

fixes slackhq/vscode-hack#17

Reviewed By: pittsw, arxanas

Differential Revision: D8286533

fbshipit-source-id: 2b02928b875a44ee563e1999f9ba7a1f50a3bf2f

hphp/hack/src/client/clientLsp.ml

@@ -587,7 +587,7 @@ let hack_errors_to_lsp_diagnostic
       | [] -> failwith "Expected at least one error in the error list"
     in
     let ({range; _}, message) = first_message in
-    let relatedLocations = additional_messages |> List.map ~f:(fun (location, message) ->
+    let relatedInformation = additional_messages |> List.map ~f:(fun (location, message) ->
       { PublishDiagnostics.
         relatedLocation = location;
         relatedMessage = message;
@@ -598,7 +598,8 @@ let hack_errors_to_lsp_diagnostic
       code = PublishDiagnostics.IntCode (Errors.get_code error);
       source = Some "Hack";
       message;
-      relatedLocations;
+      relatedInformation;
+      relatedLocations = relatedInformation; (* legacy FB extension *)
     }
   in
   (* The caller is required to give us a non-empty filename. If it is empty,  *)

hphp/hack/src/utils/lsp.ml

@@ -421,7 +421,8 @@ module PublishDiagnostics = struct
     code: diagnosticCode;  (* the diagnostic's code. *)
     source: string option;  (* human-readable string, eg. typescript/lint *)
     message: string;  (* the diagnostic's message *)
-    relatedLocations: relatedLocation list;
+    relatedInformation: diagnosticRelatedInformation list;
+    relatedLocations: relatedLocation list; (* legacy FB extension *)
   }
 
   and diagnosticCode =
@@ -435,10 +436,13 @@ module PublishDiagnostics = struct
     | Information (* 3 *)
     | Hint (* 4 *)
 
-  and relatedLocation = {
+  and diagnosticRelatedInformation = {
     relatedLocation: Location.t;  (* wire: just "location" *)
     relatedMessage: string;  (* wire: just "message" *)
   }
+
+  (* legacy FB extension *)
+  and relatedLocation = diagnosticRelatedInformation
 end
 
 (* DidOpenTextDocument notification, method="textDocument/didOpen" *)

hphp/hack/src/utils/lsp_fmt.ml

@@ -392,6 +392,8 @@ let print_diagnostics (r: PublishDiagnostics.params) : json =
       "code", print_diagnosticCode diagnostic.code;
       "source", Option.map diagnostic.source string_;
       "message", Some (JSON_String diagnostic.message);
+      "relatedInformation",
+        Some (JSON_Array (List.map diagnostic.relatedInformation ~f:print_related));
       "relatedLocations", Some (JSON_Array (List.map diagnostic.relatedLocations ~f:print_related));
     ]
   in