Return Diagnostic.category from the server

Author: mhegazy

src/server/protocol.ts

@@ -1828,6 +1828,11 @@ namespace ts.server.protocol {
          * The error code of the diagnostic message.
          */
         code?: number;
+
+        /**
+         * The category of the diagnostic message, e.g. "error" vs. "warning"
+         */
+        category: string;
     }
 
     export interface DiagnosticEventBody {

src/server/session.ts

@@ -67,15 +67,17 @@ namespace ts.server {
             start: scriptInfo.positionToLineOffset(diag.start),
             end: scriptInfo.positionToLineOffset(diag.start + diag.length),
             text: ts.flattenDiagnosticMessageText(diag.messageText, "\n"),
-            code: diag.code
+            code: diag.code,
+            category: DiagnosticCategory[diag.category].toLowerCase()
         };
     }
 
     function formatConfigFileDiag(diag: ts.Diagnostic): protocol.Diagnostic {
         return {
             start: undefined,
             end: undefined,
-            text: ts.flattenDiagnosticMessageText(diag.messageText, "\n")
+            text: ts.flattenDiagnosticMessageText(diag.messageText, "\n"),
+            category: DiagnosticCategory[diag.category].toLowerCase()
         };
     }