Improve error message when debugging fails to start (intersystems-community#908)

Author: isc-bsaviano

docs/RunDebug.md

@@ -110,4 +110,6 @@ Clicking on the green arrow runs the currently selected debug configuration.
 
 When starting **objectscript launch** debug session, make sure that the file containing the **program** that you are debugging is open in your editor and is the active tab. VS Code will start a debug session with the server of the file in the active editor (the tab that the user is focused on).
 
-Debugging commands and items on the **Run** menu function much as they do for other languages supported by VS Code. For information on VS Code debugging, see the documentation resources listed at the start of this section. 
+This extension uses WebSockets to communicate with the InterSystems server during debugging. If you are experiencing issues when trying to start a debugging session, check that the InterSystems server's web server allows WebSocket connections.
+
+Debugging commands and items on the **Run** menu function much as they do for other languages supported by VS Code. For information on VS Code debugging, see the documentation resources listed at the start of this section. 

src/debug/debugSession.ts

@@ -128,8 +128,6 @@ export class ObjectScriptDebugSession extends LoggingDebugSession {
       this._namespace = api.ns;
       this._url = api.xdebugUrl();
 
-      await api.serverInfo();
-
       const socket = new WebSocket(this._url, {
         headers: {
           cookie: this.cookies,
@@ -164,8 +162,14 @@ export class ObjectScriptDebugSession extends LoggingDebugSession {
 
       this.sendEvent(new InitializedEvent());
     } catch (error) {
+      let message = "Failed to start the debug session. ";
+      if (error instanceof Error && error.message == "Connection not active") {
+        message += "Server connection is inactive.";
+      } else {
+        message += "Check that the InterSystems server's web server supports WebSockets.";
+      }
       response.success = false;
-      response.message = "Debugger can not start";
+      response.message = message;
       this.sendResponse(response);
     }
   }