fix(grainlsp): Send empty response if file cannot be formatted (#1386)

Author: marcusroberts

compiler/src/language_server/formatting.re

@@ -91,15 +91,9 @@ let process =
         )
       }
     | Error(ParseError(_)) =>
-      Protocol.error(
-        ~id,
-        {
-          code: RequestFailed,
-          message:
-            "Unable to parse the document: "
-            ++ Protocol.uri_to_filename(params.text_document.uri),
-        },
-      )
+      // If we can't parse the file we can't format it
+      // return null to signal a response
+      Protocol.empty_response(id)
     | Error(InvalidCompilationState) =>
       Protocol.error(
         ~id,

compiler/src/language_server/protocol.re

@@ -221,6 +221,26 @@ let response = (~id=?, result) => {
   flush(stdout);
 };
 
+let empty_response = id => {
+  let response_message = {
+    jsonrpc: version,
+    id: Some(id),
+    result: None,
+    error: None,
+  };
+  let content =
+    Yojson.Safe.to_string(
+      ~std=true,
+      response_message_to_yojson(response_message),
+    );
+  let length = String.length(content);
+
+  let len = string_of_int(length);
+  let msg = header_prefix ++ len ++ sep ++ content;
+  output_string(stdout, msg);
+  flush(stdout);
+};
+
 let error = (~id=?, error) => {
   let response_message = {
     jsonrpc: version,

compiler/src/language_server/protocol.rei

@@ -131,6 +131,8 @@ let request: unit => result(request_message, string);
 
 let response: (~id: message_id=?, Yojson.Safe.t) => unit;
 
+let empty_response: message_id => unit;
+
 let error: (~id: message_id=?, response_error) => unit;
 
 let notification: (~method: string, Yojson.Safe.t) => unit;