Some small changes to isolate handling in ddbg.

tools/ddbg.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Simple interactive debugger shell that connects to the Dart VM's debugger
 // connection port.
 
 import "dart:convert";
 import "dart:io";
 import "dart:async";
@@ skipping 60 matching lines @@
   outstandingCommands[id] = completer;
   if (verbose) {
     print("sending: '${JSON.encode(cmd)}'");
   }
   vmSock.write(JSON.encode(cmd));
   return completer.future;
 }
 
 
 bool checkCurrentIsolate() {
-  if (currentIsolate != null) {
-    return true;
+  if (vmSock == null) {
+    print("There is no active script.  Try 'help run'.");
+    return false;
   }
-  print("Need valid current isolate");
-  return false;
+  if (currentIsolate == null) {
+    print('There is no current isolate.');
+    return false;
+  }
+  return true;
+}
+
+
+void setCurrentIsolate(TargetIsolate isolate) {
+  if (isolate != currentIsolate) {
+    currentIsolate = isolate;
+    if (mainIsolate == null) {
+      print("Main isolate is ${isolate.id}");
+      mainIsolate = isolate;
+    }
+    print("Current isolate is now ${isolate.id}");
+  }
 }
 
 
 bool checkPaused() {
   if (!checkCurrentIsolate()) return false;
   if (currentIsolate.isPaused) return true;
   print("Current isolate must be paused");
   return false;
 }
 
@@ skipping 423 matching lines @@
   cmdLine = cmdLine.trim();
   var args = cmdLine.split(' ');
   if (args.length == 0) {
     return;
   }
   var command = args[0];
 
   var resume_commands =
       { 'r':'resume', 's':'stepOver', 'si':'stepInto', 'so':'stepOut'};
   if (resume_commands[command] != null) {
-    if (!checkPaused()) return;
+    if (!checkPaused()) {
+      cmdo.show();
+      return;
+    }
     var cmd = { "id": seqNum,
                 "command": resume_commands[command],
                 "params": { "isolateId" : currentIsolate.id } };
     sendCmd(cmd).then(showPromptAfter(handleResumedResponse));
   } else if (command == "bt") {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var cmd = { "id": seqNum,
                 "command": "getStackTrace",
                 "params": { "isolateId" : currentIsolate.id } };
     sendCmd(cmd).then(showPromptAfter(handleStackTraceResponse));
   } else if (command == "ll") {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var cmd = { "id": seqNum,
                 "command": "getLibraries",
                 "params": { "isolateId" : currentIsolate.id } };
     sendCmd(cmd).then(showPromptAfter(handleGetLibraryResponse));
   } else if (command == "sbp" && args.length >= 2) {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var url, line;
     if (args.length == 2 && currentIsolate.pausedLocation != null) {
       url = currentIsolate.pausedLocation["url"];
       assert(url != null);
       line = int.parse(args[1]);
     } else {
       url = args[1];
       line = int.parse(args[2]);
     }
     var cmd = { "id": seqNum,
                 "command": "setBreakpoint",
                 "params": { "isolateId" : currentIsolate.id,
                             "url": url,
                             "line": line }};
     sendCmd(cmd).then(showPromptAfter(handleSetBpResponse));
   } else if (command == "rbp" && args.length == 2) {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var cmd = { "id": seqNum,
                 "command": "removeBreakpoint",
                 "params": { "isolateId" : currentIsolate.id,
                             "breakpointId": int.parse(args[1]) } };
     sendCmd(cmd).then(showPromptAfter(handleGenericResponse));
   } else if (command == "ls" && args.length == 2) {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var cmd = { "id": seqNum,
                 "command": "getScriptURLs",
                 "params": { "isolateId" : currentIsolate.id,
                             "libraryId": int.parse(args[1]) } };
     sendCmd(cmd).then(showPromptAfter(handleGetScriptsResponse));
   } else if (command == "eval" && args.length > 3) {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var expr = args.getRange(3, args.length).join(" ");
     var target = args[1];
     if (target == "obj") {
       target = "objectId";
     } else if (target == "cls") {
       target = "classId";
     } else if (target == "lib") {
       target = "libraryId";
     } else {
       huh();
       return;
     }
     var cmd = { "id": seqNum,
                 "command": "evaluateExpr",
                 "params": { "isolateId": currentIsolate.id,
                             target: int.parse(args[2]),
                             "expression": expr } };
     sendCmd(cmd).then(showPromptAfter(handleEvalResponse));
   } else if (command == "po" && args.length == 2) {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var cmd = { "id": seqNum,
                 "command": "getObjectProperties",
                 "params": { "isolateId" : currentIsolate.id,
                             "objectId": int.parse(args[1]) } };
     sendCmd(cmd).then(showPromptAfter(handleGetObjPropsResponse));
   } else if (command == "pl" && args.length >= 3) {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var cmd;
     if (args.length == 3) {
       cmd = { "id": seqNum,
               "command": "getListElements",
               "params": { "isolateId" : currentIsolate.id,
                           "objectId": int.parse(args[1]),
                           "index": int.parse(args[2]) } };
     } else {
       cmd = { "id": seqNum,
               "command": "getListElements",
               "params": { "isolateId" : currentIsolate.id,
                           "objectId": int.parse(args[1]),
                           "index": int.parse(args[2]),
                           "length": int.parse(args[3]) } };
     }
     sendCmd(cmd).then(showPromptAfter(handleGetListResponse));
   } else if (command == "pc" && args.length == 2) {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var cmd = { "id": seqNum,
                 "command": "getClassProperties",
                 "params": { "isolateId" : currentIsolate.id,
                             "classId": int.parse(args[1]) } };
     sendCmd(cmd).then(showPromptAfter(handleGetClassPropsResponse));
   } else if (command == "plib" && args.length == 2) {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var cmd = { "id": seqNum,
                 "command": "getLibraryProperties",
                 "params": {"isolateId" : currentIsolate.id,
                            "libraryId": int.parse(args[1]) } };
     sendCmd(cmd).then(showPromptAfter(handleGetLibraryPropsResponse));
   } else if (command == "slib" && args.length == 3) {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var cmd = { "id": seqNum,
                 "command": "setLibraryProperties",
                 "params": {"isolateId" : currentIsolate.id,
                            "libraryId": int.parse(args[1]),
                            "debuggingEnabled": args[2] } };
     sendCmd(cmd).then(showPromptAfter(handleSetLibraryPropsResponse));
   } else if (command == "pg" && args.length == 2) {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var cmd = { "id": seqNum,
                 "command": "getGlobalVariables",
                 "params": { "isolateId" : currentIsolate.id,
                             "libraryId": int.parse(args[1]) } };
     sendCmd(cmd).then(showPromptAfter(handleGetGlobalVarsResponse));
   } else if (command == "gs" && args.length == 3) {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var cmd = { "id": seqNum,
                 "command":  "getScriptSource",
                 "params": { "isolateId" : currentIsolate.id,
                             "libraryId": int.parse(args[1]),
                             "url": args[2] } };
     sendCmd(cmd).then(showPromptAfter(handleGetSourceResponse));
   } else if (command == "tok" && args.length == 3) {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var cmd = { "id": seqNum,
                 "command":  "getLineNumberTable",
                 "params": { "isolateId" : currentIsolate.id,
                             "libraryId": int.parse(args[1]),
                             "url": args[2] } };
     sendCmd(cmd).then(showPromptAfter(handleGetLineTableResponse));
   } else if (command == "epi" && args.length == 2) {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var cmd = { "id": seqNum,
                 "command":  "setPauseOnException",
                 "params": { "isolateId" : currentIsolate.id,
                             "exceptions": args[1] } };
     sendCmd(cmd).then(showPromptAfter(handleGenericResponse));
   } else if (command == "li") {
+    if (!checkCurrentIsolate()) {
+      cmdo.show();
+      return;
+    }
     var cmd = { "id": seqNum, "command": "getIsolateIds" };
     sendCmd(cmd).then(showPromptAfter(handleGetIsolatesResponse));
   } else if (command == "sci" && args.length == 2) {
     var id = int.parse(args[1]);
     if (targetIsolates[id] != null) {
-      currentIsolate = targetIsolates[id];
-      print("Setting current target isolate to $id");
+      setCurrentIsolate(targetIsolates[id]);
     } else {
       print("$id is not a valid isolate id");
     }
     cmdo.show();
   } else if (command == "i" && args.length == 2) {
     var cmd = { "id": seqNum,
                 "command": "interrupt",
                 "params": { "isolateId": int.parse(args[1]) } };
     sendCmd(cmd).then(showPromptAfter(handleGenericResponse));
   } else if (command.length == 0) {
@@ skipping 343 matching lines @@
 Future handlePausedEvent(msg) {
   assert(msg["params"] != null);
   var reason = msg["params"]["reason"];
   int isolateId = msg["params"]["isolateId"];
   assert(isolateId != null);
   var isolate = targetIsolates[isolateId];
   assert(isolate != null);
   assert(!isolate.isPaused);
   var location = msg["params"]["location"];;
   assert(location != null);
+  setCurrentIsolate(isolate);
   isolate.pausedLocation = location;
   if (reason == "breakpoint") {
     var bpId = (msg["params"]["breakpointId"]);
     var label = (bpId != null) ? "Breakpoint $bpId" : null;
     return printLocation(label, location);
   } else if (reason == "interrupted") {
     return printLocation("Interrupted", location);
   } else {
     assert(reason == "exception");
     var excObj = msg["params"]["exception"];
     print("Isolate $isolateId paused on exception");
     print(remoteObject(excObj));
     return new Future.value();
   }
 }
 
 void handleIsolateEvent(msg) {
   Map params = msg["params"];
   assert(params != null);
   var isolateId = params["id"];
   var reason = params["reason"];
   if (reason == "created") {
     print("Isolate $isolateId has been created.");
     assert(targetIsolates[isolateId] == null);
     targetIsolates[isolateId] = new TargetIsolate(isolateId);
-    if (mainIsolate == null) {
-      mainIsolate = targetIsolates[isolateId];
-      currentIsolate = mainIsolate;
-      print("Current isolate set to ${currentIsolate.id}.");
-    }
   } else {
     assert(reason == "shutdown");
     var isolate = targetIsolates.remove(isolateId);
     assert(isolate != null);
     if (isolate == mainIsolate) {
       mainIsolate = null;
       print("Main isolate ${isolate.id} has terminated.");
     } else {
       print("Isolate ${isolate.id} has terminated.");
     }
@@ skipping 334 matching lines @@
       handleUncaughtError: debuggerError));
 
   zone.run(() {
       parseArgs(args);
       cmdo = new Commando(completer: debuggerCommandCompleter);
       cmdSubscription = cmdo.commands.listen(processCommand,
                                              onError: processError,
                                              onDone: processDone);
     });
 }